深入理解SpringCloud之配置刷新

　　我们知道在SpringCloud中，当配置变更时，我们通过访问http://xxxx/refresh，可以在不启动服务的情况下获取最新的配置，那么它是如何做到的呢，当我们更改数据库配置并刷新后，如何能获取最新的数据源对象呢？下面我们看SpringCloud如何做到的。

一、环境变化

1.1、关于ContextRefresher

　　当我们访问/refresh时，会被RefreshEndpoint类所处理。我们来看源代码：

/*
 * Copyright 2013-2014 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.cloud.endpoint;

import java.util.Arrays;
import java.util.Collection;
import java.util.Set;

import org.springframework.boot.actuate.endpoint.AbstractEndpoint;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.cloud.context.refresh.ContextRefresher;
import org.springframework.jmx.export.annotation.ManagedOperation;
import org.springframework.jmx.export.annotation.ManagedResource;

/**
 * @author Dave Syer
 * @author Venil Noronha
 */
@ConfigurationProperties(prefix = "endpoints.refresh", ignoreUnknownFields = false)
@ManagedResource
public class RefreshEndpoint extends AbstractEndpoint<Collection<String>> {

    private ContextRefresher contextRefresher;

    public RefreshEndpoint(ContextRefresher contextRefresher) {
        super("refresh");
        this.contextRefresher = contextRefresher;
    }

    @ManagedOperation
    public String[] refresh() {
        Set<String> keys = contextRefresher.refresh();
        return keys.toArray(new String[keys.size()]);
    }

    @Override
    public Collection<String> invoke() {
        return Arrays.asList(refresh());
    }

}

　　通过源代码我们了解到：当访问refresh端点时，实际上执行的是ContextRefresher的refresh方法，那么我们继续追踪源代码，找到其refresh方法：

public synchronized Set<String> refresh() {
        Map<String, Object> before = extract(
                this.context.getEnvironment().getPropertySources());
        addConfigFilesToEnvironment();
        Set<String> keys = changes(before,
                extract(this.context.getEnvironment().getPropertySources())).keySet();
        this.context.publishEvent(new EnvironmentChangeEvent(context, keys));
        this.scope.refreshAll();
        return keys;
    }

　　我们可以看到refresh方法做了如下几件事情：

　　1）获取刷新之前的所有PropertySource

　　2) 调用addConfigFilesToEnvironment方法获取最新的配置

　　3) 调用changes方法更新配置信息

　　4) 发布EnvironmentChangeEnvent事件

　　5）调用refreshScope的refreshAll方法刷新范围

　　我们重点关注一下2，3，4步骤

1.2、addConfigFilesToEnvironment方法

　　我们先来看看这个方法是怎么实现的：

/* for testing */ ConfigurableApplicationContext addConfigFilesToEnvironment() {
        ConfigurableApplicationContext capture = null;
        try {
            StandardEnvironment environment = copyEnvironment(
                    this.context.getEnvironment());
            SpringApplicationBuilder builder = new SpringApplicationBuilder(Empty.class)
                    .bannerMode(Mode.OFF).web(false).environment(environment);
            // Just the listeners that affect the environment (e.g. excluding logging
            // listener because it has side effects)
            builder.application()
                    .setListeners(Arrays.asList(new BootstrapApplicationListener(),
                            new ConfigFileApplicationListener()));
            capture = builder.run();
            if (environment.getPropertySources().contains(REFRESH_ARGS_PROPERTY_SOURCE)) {
                environment.getPropertySources().remove(REFRESH_ARGS_PROPERTY_SOURCE);
            }
            MutablePropertySources target = this.context.getEnvironment()
                    .getPropertySources();
            String targetName = null;
            for (PropertySource<?> source : environment.getPropertySources()) {
                String name = source.getName();
                if (target.contains(name)) {
                    targetName = name;
                }
                if (!this.standardSources.contains(name)) {
                    if (target.contains(name)) {
                        target.replace(name, source);
                    }
                    else {
                        if (targetName != null) {
                            target.addAfter(targetName, source);
                        }
                        else {
                            // targetName was null so we are at the start of the list
                            target.addFirst(source);
                            targetName = name;
                        }
                    }
                }
            }
        }
        finally {
            ConfigurableApplicationContext closeable = capture;
            while (closeable != null) {
                try {
                    closeable.close();
                }
                catch (Exception e) {
                    // Ignore;
                }
                if (closeable.getParent() instanceof ConfigurableApplicationContext) {
                    closeable = (ConfigurableApplicationContext) closeable.getParent();
                }
                else {
                    break;
                }
            }
        }
        return capture;
    }

　　1) 该方法首先拷贝当前的Environment

　　2) 通过SpringApplicationBuilder构建了一个简单的SpringBoot启动程序并启动

builder.application().setListeners(Arrays.asList(new BootstrapApplicationListener(),
                            new ConfigFileApplicationListener()));

　　这里面会添加两个监听器分别为：BootstrapApplicationListener与ConfigFileApplicationListener，通过先前的学习，我们知道BootstrapApplicationListener是引导程序的核心监听器，而ConfigFileApplicationListener也是非常重要的类：

/*
 * Copyright 2012-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.boot.context.config;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;
import java.util.Set;

import org.apache.commons.logging.Log;

import org.springframework.beans.BeansException;
import org.springframework.beans.CachedIntrospectionResults;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.bind.PropertiesConfigurationFactory;
import org.springframework.boot.bind.PropertySourcesPropertyValues;
import org.springframework.boot.bind.RelaxedDataBinder;
import org.springframework.boot.bind.RelaxedPropertyResolver;
import org.springframework.boot.context.event.ApplicationEnvironmentPreparedEvent;
import org.springframework.boot.context.event.ApplicationPreparedEvent;
import org.springframework.boot.env.EnumerableCompositePropertySource;
import org.springframework.boot.env.EnvironmentPostProcessor;
import org.springframework.boot.env.PropertySourcesLoader;
import org.springframework.boot.logging.DeferredLog;
import org.springframework.context.ApplicationEvent;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.ConfigurationClassPostProcessor;
import org.springframework.context.event.SmartApplicationListener;
import org.springframework.core.Ordered;
import org.springframework.core.annotation.AnnotationAwareOrderComparator;
import org.springframework.core.convert.ConversionService;
import org.springframework.core.convert.support.DefaultConversionService;
import org.springframework.core.env.ConfigurableEnvironment;
import org.springframework.core.env.EnumerablePropertySource;
import org.springframework.core.env.MutablePropertySources;
import org.springframework.core.env.PropertySource;
import org.springframework.core.env.PropertySources;
import org.springframework.core.io.DefaultResourceLoader;
import org.springframework.core.io.Resource;
import org.springframework.core.io.ResourceLoader;
import org.springframework.core.io.support.SpringFactoriesLoader;
import org.springframework.util.Assert;
import org.springframework.util.ResourceUtils;
import org.springframework.util.StringUtils;
import org.springframework.validation.BindException;

/**
 * {@link EnvironmentPostProcessor} that configures the context environment by loading
 * properties from well known file locations. By default properties will be loaded from
 * 'application.properties' and/or 'application.yml' files in the following locations:
 * <ul>
 * <li>classpath:</li>
 * <li>file:./</li>
 * <li>classpath:config/</li>
 * <li>file:./config/:</li>
 * </ul>
 * <p>
 * Alternative search locations and names can be specified using
 * {@link #setSearchLocations(String)} and {@link #setSearchNames(String)}.
 * <p>
 * Additional files will also be loaded based on active profiles. For example if a 'web'
 * profile is active 'application-web.properties' and 'application-web.yml' will be
 * considered.
 * <p>
 * The 'spring.config.name' property can be used to specify an alternative name to load
 * and the 'spring.config.location' property can be used to specify alternative search
 * locations or specific files.
 * <p>
 * Configuration properties are also bound to the {@link SpringApplication}. This makes it
 * possible to set {@link SpringApplication} properties dynamically, like the sources
 * ("spring.main.sources" - a CSV list) the flag to indicate a web environment
 * ("spring.main.web_environment=true") or the flag to switch off the banner
 * ("spring.main.show_banner=false").
 *
 * @author Dave Syer
 * @author Phillip Webb
 * @author Stephane Nicoll
 * @author Andy Wilkinson
 * @author Eddú Meléndez
 */
public class ConfigFileApplicationListener
        implements EnvironmentPostProcessor, SmartApplicationListener, Ordered {

    private static final String DEFAULT_PROPERTIES = "defaultProperties";

    // Note the order is from least to most specific (last one wins)
    private static final String DEFAULT_SEARCH_LOCATIONS = "classpath:/,classpath:/config/,file:./,file:./config/";

    private static final String DEFAULT_NAMES = "application";

    /**
     * The "active profiles" property name.
     */
    public static final String ACTIVE_PROFILES_PROPERTY = "spring.profiles.active";

    /**
     * The "includes profiles" property name.
     */
    public static final String INCLUDE_PROFILES_PROPERTY = "spring.profiles.include";

    /**
     * The "config name" property name.
     */
    public static final String CONFIG_NAME_PROPERTY = "spring.config.name";

    /**
     * The "config location" property name.
     */
    public static final String CONFIG_LOCATION_PROPERTY = "spring.config.location";

    /**
     * The default order for the processor.
     */
    public static final int DEFAULT_ORDER = Ordered.HIGHEST_PRECEDENCE + 10;

    /**
     * Name of the application configuration {@link PropertySource}.
     */
    public static final String APPLICATION_CONFIGURATION_PROPERTY_SOURCE_NAME = "applicationConfigurationProperties";

    private final DeferredLog logger = new DeferredLog();

    private String searchLocations;

    private String names;

    private int order = DEFAULT_ORDER;

    private final ConversionService conversionService = new DefaultConversionService();

    @Override
    public boolean supportsEventType(Class<? extends ApplicationEvent> eventType) {
        return ApplicationEnvironmentPreparedEvent.class.isAssignableFrom(eventType)
                || ApplicationPreparedEvent.class.isAssignableFrom(eventType);
    }

    @Override
    public boolean supportsSourceType(Class<?> aClass) {
        return true;
    }

    @Override
    public void onApplicationEvent(ApplicationEvent event) {
        if (event instanceof ApplicationEnvironmentPreparedEvent) {
            onApplicationEnvironmentPreparedEvent(
                    (ApplicationEnvironmentPreparedEvent) event);
        }
        if (event instanceof ApplicationPreparedEvent) {
            onApplicationPreparedEvent(event);
        }
    }

    private void onApplicationEnvironmentPreparedEvent(
            ApplicationEnvironmentPreparedEvent event) {
        List<EnvironmentPostProcessor> postProcessors = loadPostProcessors();
        postProcessors.add(this);
        AnnotationAwareOrderComparator.sort(postProcessors);
        for (EnvironmentPostProcessor postProcessor : postProcessors) {
            postProcessor.postProcessEnvironment(event.getEnvironment(),
                    event.getSpringApplication());
        }
    }

    List<EnvironmentPostProcessor> loadPostProcessors() {
        return SpringFactoriesLoader.loadFactories(EnvironmentPostProcessor.class,
                getClass().getClassLoader());
    }

    @Override
    public void postProcessEnvironment(ConfigurableEnvironment environment,
            SpringApplication application) {
        addPropertySources(environment, application.getResourceLoader());
        configureIgnoreBeanInfo(environment);
        bindToSpringApplication(environment, application);
    }

    private void configureIgnoreBeanInfo(ConfigurableEnvironment environment) {
        if (System.getProperty(
                CachedIntrospectionResults.IGNORE_BEANINFO_PROPERTY_NAME) == null) {
            RelaxedPropertyResolver resolver = new RelaxedPropertyResolver(environment,
                    "spring.beaninfo.");
            Boolean ignore = resolver.getProperty("ignore", Boolean.class, Boolean.TRUE);
            System.setProperty(CachedIntrospectionResults.IGNORE_BEANINFO_PROPERTY_NAME,
                    ignore.toString());
        }
    }

    private void onApplicationPreparedEvent(ApplicationEvent event) {
        this.logger.replayTo(ConfigFileApplicationListener.class);
        addPostProcessors(((ApplicationPreparedEvent) event).getApplicationContext());
    }

    /**
     * Add config file property sources to the specified environment.
     * @param environment the environment to add source to
     * @param resourceLoader the resource loader
     * @see #addPostProcessors(ConfigurableApplicationContext)
     */
    protected void addPropertySources(ConfigurableEnvironment environment,
            ResourceLoader resourceLoader) {
        RandomValuePropertySource.addToEnvironment(environment);
        new Loader(environment, resourceLoader).load();
    }

    /**
     * Bind the environment to the {@link SpringApplication}.
     * @param environment the environment to bind
     * @param application the application to bind to
     */
    protected void bindToSpringApplication(ConfigurableEnvironment environment,
            SpringApplication application) {
        PropertiesConfigurationFactory<SpringApplication> binder = new PropertiesConfigurationFactory<SpringApplication>(
                application);
        binder.setTargetName("spring.main");
        binder.setConversionService(this.conversionService);
        binder.setPropertySources(environment.getPropertySources());
        try {
            binder.bindPropertiesToTarget();
        }
        catch (BindException ex) {
            throw new IllegalStateException("Cannot bind to SpringApplication", ex);
        }
    }

    /**
     * Add appropriate post-processors to post-configure the property-sources.
     * @param context the context to configure
     */
    protected void addPostProcessors(ConfigurableApplicationContext context) {
        context.addBeanFactoryPostProcessor(
                new PropertySourceOrderingPostProcessor(context));
    }

    public void setOrder(int order) {
        this.order = order;
    }

    @Override
    public int getOrder() {
        return this.order;
    }

    /**
     * Set the search locations that will be considered as a comma-separated list. Each
     * search location should be a directory path (ending in "/") and it will be prefixed
     * by the file names constructed from {@link #setSearchNames(String) search names} and
     * profiles (if any) plus file extensions supported by the properties loaders.
     * Locations are considered in the order specified, with later items taking precedence
     * (like a map merge).
     * @param locations the search locations
     */
    public void setSearchLocations(String locations) {
        Assert.hasLength(locations, "Locations must not be empty");
        this.searchLocations = locations;
    }

    /**
     * Sets the names of the files that should be loaded (excluding file extension) as a
     * comma-separated list.
     * @param names the names to load
     */
    public void setSearchNames(String names) {
        Assert.hasLength(names, "Names must not be empty");
        this.names = names;
    }

    /**
     * {@link BeanFactoryPostProcessor} to re-order our property sources below any
     * {@code @PropertySource} items added by the {@link ConfigurationClassPostProcessor}.
     */
    private class PropertySourceOrderingPostProcessor
            implements BeanFactoryPostProcessor, Ordered {

        private ConfigurableApplicationContext context;

        PropertySourceOrderingPostProcessor(ConfigurableApplicationContext context) {
            this.context = context;
        }

        @Override
        public int getOrder() {
            return Ordered.HIGHEST_PRECEDENCE;
        }

        @Override
        public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory)
                throws BeansException {
            reorderSources(this.context.getEnvironment());
        }

        private void reorderSources(ConfigurableEnvironment environment) {
            ConfigurationPropertySources
                    .finishAndRelocate(environment.getPropertySources());
            PropertySource<?> defaultProperties = environment.getPropertySources()
                    .remove(DEFAULT_PROPERTIES);
            if (defaultProperties != null) {
                environment.getPropertySources().addLast(defaultProperties);
            }
        }

    }

    /**
     * Loads candidate property sources and configures the active profiles.
     */
    private class Loader {

        private final Log logger = ConfigFileApplicationListener.this.logger;

        private final ConfigurableEnvironment environment;

        private final ResourceLoader resourceLoader;

        private PropertySourcesLoader propertiesLoader;

        private Queue<Profile> profiles;

        private List<Profile> processedProfiles;

        private boolean activatedProfiles;

        Loader(ConfigurableEnvironment environment, ResourceLoader resourceLoader) {
            this.environment = environment;
            this.resourceLoader = resourceLoader == null ? new DefaultResourceLoader()
                    : resourceLoader;
        }

        public void load() {
            this.propertiesLoader = new PropertySourcesLoader();
            this.activatedProfiles = false;
            this.profiles = Collections.asLifoQueue(new LinkedList<Profile>());
            this.processedProfiles = new LinkedList<Profile>();

            // Pre-existing active profiles set via Environment.setActiveProfiles()
            // are additional profiles and config files are allowed to add more if
            // they want to, so don't call addActiveProfiles() here.
            Set<Profile> initialActiveProfiles = initializeActiveProfiles();
            this.profiles.addAll(getUnprocessedActiveProfiles(initialActiveProfiles));
            if (this.profiles.isEmpty()) {
                for (String defaultProfileName : this.environment.getDefaultProfiles()) {
                    Profile defaultProfile = new Profile(defaultProfileName, true);
                    if (!this.profiles.contains(defaultProfile)) {
                        this.profiles.add(defaultProfile);
                    }
                }
            }

            // The default profile for these purposes is represented as null. We add it
            // last so that it is first out of the queue (active profiles will then
            // override any settings in the defaults when the list is reversed later).
            this.profiles.add(null);

            while (!this.profiles.isEmpty()) {
                Profile profile = this.profiles.poll();
                for (String location : getSearchLocations()) {
                    if (!location.endsWith("/")) {
                        // location is a filename already, so don't search for more
                        // filenames
                        load(location, null, profile);
                    }
                    else {
                        for (String name : getSearchNames()) {
                            load(location, name, profile);
                        }
                    }
                }
                this.processedProfiles.add(profile);
            }

            addConfigurationProperties(this.propertiesLoader.getPropertySources());
        }

        private Set<Profile> initializeActiveProfiles() {
            if (!this.environment.containsProperty(ACTIVE_PROFILES_PROPERTY)
                    && !this.environment.containsProperty(INCLUDE_PROFILES_PROPERTY)) {
                return Collections.emptySet();
            }
            // Any pre-existing active profiles set via property sources (e.g. System
            // properties) take precedence over those added in config files.
            SpringProfiles springProfiles = bindSpringProfiles(
                    this.environment.getPropertySources());
            Set<Profile> activeProfiles = new LinkedHashSet<Profile>(
                    springProfiles.getActiveProfiles());
            activeProfiles.addAll(springProfiles.getIncludeProfiles());
            maybeActivateProfiles(activeProfiles);
            return activeProfiles;
        }

        /**
         * Return the active profiles that have not been processed yet. If a profile is
         * enabled via both {@link #ACTIVE_PROFILES_PROPERTY} and
         * {@link ConfigurableEnvironment#addActiveProfile(String)} it needs to be
         * filtered so that the {@link #ACTIVE_PROFILES_PROPERTY} value takes precedence.
         * <p>
         * Concretely, if the "cloud" profile is enabled via the environment, it will take
         * less precedence that any profile set via the {@link #ACTIVE_PROFILES_PROPERTY}.
         * @param initialActiveProfiles the profiles that have been enabled via
         * {@link #ACTIVE_PROFILES_PROPERTY}
         * @return the unprocessed active profiles from the environment to enable
         */
        private List<Profile> getUnprocessedActiveProfiles(
                Set<Profile> initialActiveProfiles) {
            List<Profile> unprocessedActiveProfiles = new ArrayList<Profile>();
            for (String profileName : this.environment.getActiveProfiles()) {
                Profile profile = new Profile(profileName);
                if (!initialActiveProfiles.contains(profile)) {
                    unprocessedActiveProfiles.add(profile);
                }
            }
            // Reverse them so the order is the same as from getProfilesForValue()
            // (last one wins when properties are eventually resolved)
            Collections.reverse(unprocessedActiveProfiles);
            return unprocessedActiveProfiles;
        }

        private void load(String location, String name, Profile profile) {
            String group = "profile=" + (profile == null ? "" : profile);
            if (!StringUtils.hasText(name)) {
                // Try to load directly from the location
                loadIntoGroup(group, location, profile);
            }
            else {
                // Search for a file with the given name
                for (String ext : this.propertiesLoader.getAllFileExtensions()) {
                    if (profile != null) {
                        // Try the profile-specific file
                        loadIntoGroup(group, location + name + "-" + profile + "." + ext,
                                null);
                        for (Profile processedProfile : this.processedProfiles) {
                            if (processedProfile != null) {
                                loadIntoGroup(group, location + name + "-"
                                        + processedProfile + "." + ext, profile);
                            }
                        }
                        // Sometimes people put "spring.profiles: dev" in
                        // application-dev.yml (gh-340). Arguably we should try and error
                        // out on that, but we can be kind and load it anyway.
                        loadIntoGroup(group, location + name + "-" + profile + "." + ext,
                                profile);
                    }
                    // Also try the profile-specific section (if any) of the normal file
                    loadIntoGroup(group, location + name + "." + ext, profile);
                }
            }
        }

        private PropertySource<?> loadIntoGroup(String identifier, String location,
                Profile profile) {
            try {
                return doLoadIntoGroup(identifier, location, profile);
            }
            catch (Exception ex) {
                throw new IllegalStateException(
                        "Failed to load property source from location '" + location + "'",
                        ex);
            }
        }

        private PropertySource<?> doLoadIntoGroup(String identifier, String location,
                Profile profile) throws IOException {
            Resource resource = this.resourceLoader.getResource(location);
            PropertySource<?> propertySource = null;
            StringBuilder msg = new StringBuilder();
            if (resource != null && resource.exists()) {
                String name = "applicationConfig: [" + location + "]";
                String group = "applicationConfig: [" + identifier + "]";
                propertySource = this.propertiesLoader.load(resource, group, name,
                        (profile == null ? null : profile.getName()));
                if (propertySource != null) {
                    msg.append("Loaded ");
                    handleProfileProperties(propertySource);
                }
                else {
                    msg.append("Skipped (empty) ");
                }
            }
            else {
                msg.append("Skipped ");
            }
            msg.append("config file ");
            msg.append(getResourceDescription(location, resource));
            if (profile != null) {
                msg.append(" for profile ").append(profile);
            }
            if (resource == null || !resource.exists()) {
                msg.append(" resource not found");
                this.logger.trace(msg);
            }
            else {
                this.logger.debug(msg);
            }
            return propertySource;
        }

        private String getResourceDescription(String location, Resource resource) {
            String resourceDescription = "'" + location + "'";
            if (resource != null) {
                try {
                    resourceDescription = String.format("'%s' (%s)",
                            resource.getURI().toASCIIString(), location);
                }
                catch (IOException ex) {
                    // Use the location as the description
                }
            }
            return resourceDescription;
        }

        private void handleProfileProperties(PropertySource<?> propertySource) {
            SpringProfiles springProfiles = bindSpringProfiles(propertySource);
            maybeActivateProfiles(springProfiles.getActiveProfiles());
            addProfiles(springProfiles.getIncludeProfiles());
        }

        private SpringProfiles bindSpringProfiles(PropertySource<?> propertySource) {
            MutablePropertySources propertySources = new MutablePropertySources();
            propertySources.addFirst(propertySource);
            return bindSpringProfiles(propertySources);
        }

        private SpringProfiles bindSpringProfiles(PropertySources propertySources) {
            SpringProfiles springProfiles = new SpringProfiles();
            RelaxedDataBinder dataBinder = new RelaxedDataBinder(springProfiles,
                    "spring.profiles");
            dataBinder.bind(new PropertySourcesPropertyValues(propertySources, false));
            springProfiles.setActive(resolvePlaceholders(springProfiles.getActive()));
            springProfiles.setInclude(resolvePlaceholders(springProfiles.getInclude()));
            return springProfiles;
        }

        private List<String> resolvePlaceholders(List<String> values) {
            List<String> resolved = new ArrayList<String>();
            for (String value : values) {
                resolved.add(this.environment.resolvePlaceholders(value));
            }
            return resolved;
        }

        private void maybeActivateProfiles(Set<Profile> profiles) {
            if (this.activatedProfiles) {
                if (!profiles.isEmpty()) {
                    this.logger.debug("Profiles already activated, '" + profiles
                            + "' will not be applied");
                }
                return;
            }
            if (!profiles.isEmpty()) {
                addProfiles(profiles);
                this.logger.debug("Activated profiles "
                        + StringUtils.collectionToCommaDelimitedString(profiles));
                this.activatedProfiles = true;
                removeUnprocessedDefaultProfiles();
            }
        }

        private void removeUnprocessedDefaultProfiles() {
            for (Iterator<Profile> iterator = this.profiles.iterator(); iterator
                    .hasNext();) {
                if (iterator.next().isDefaultProfile()) {
                    iterator.remove();
                }
            }
        }

        private void addProfiles(Set<Profile> profiles) {
            for (Profile profile : profiles) {
                this.profiles.add(profile);
                if (!environmentHasActiveProfile(profile.getName())) {
                    // If it's already accepted we assume the order was set
                    // intentionally
                    prependProfile(this.environment, profile);
                }
            }
        }

        private boolean environmentHasActiveProfile(String profile) {
            for (String activeProfile : this.environment.getActiveProfiles()) {
                if (activeProfile.equals(profile)) {
                    return true;
                }
            }
            return false;
        }

        private void prependProfile(ConfigurableEnvironment environment,
                Profile profile) {
            Set<String> profiles = new LinkedHashSet<String>();
            environment.getActiveProfiles(); // ensure they are initialized
            // But this one should go first (last wins in a property key clash)
            profiles.add(profile.getName());
            profiles.addAll(Arrays.asList(environment.getActiveProfiles()));
            environment.setActiveProfiles(profiles.toArray(new String[profiles.size()]));
        }

        private Set<String> getSearchLocations() {
            Set<String> locations = new LinkedHashSet<String>();
            // User-configured settings take precedence, so we do them first
            if (this.environment.containsProperty(CONFIG_LOCATION_PROPERTY)) {
                for (String path : asResolvedSet(
                        this.environment.getProperty(CONFIG_LOCATION_PROPERTY), null)) {
                    if (!path.contains("$")) {
                        path = StringUtils.cleanPath(path);
                        if (!ResourceUtils.isUrl(path)) {
                            path = ResourceUtils.FILE_URL_PREFIX + path;
                        }
                    }
                    locations.add(path);
                }
            }
            locations.addAll(
                    asResolvedSet(ConfigFileApplicationListener.this.searchLocations,
                            DEFAULT_SEARCH_LOCATIONS));
            return locations;
        }

        private Set<String> getSearchNames() {
            if (this.environment.containsProperty(CONFIG_NAME_PROPERTY)) {
                return asResolvedSet(this.environment.getProperty(CONFIG_NAME_PROPERTY),
                        null);
            }
            return asResolvedSet(ConfigFileApplicationListener.this.names, DEFAULT_NAMES);
        }

        private Set<String> asResolvedSet(String value, String fallback) {
            List<String> list = Arrays.asList(StringUtils.trimArrayElements(
                    StringUtils.commaDelimitedListToStringArray(value != null
                            ? this.environment.resolvePlaceholders(value) : fallback)));
            Collections.reverse(list);
            return new LinkedHashSet<String>(list);
        }

        private void addConfigurationProperties(MutablePropertySources sources) {
            List<PropertySource<?>> reorderedSources = new ArrayList<PropertySource<?>>();
            for (PropertySource<?> item : sources) {
                reorderedSources.add(item);
            }
            addConfigurationProperties(
                    new ConfigurationPropertySources(reorderedSources));
        }

        private void addConfigurationProperties(
                ConfigurationPropertySources configurationSources) {
            MutablePropertySources existingSources = this.environment
                    .getPropertySources();
            if (existingSources.contains(DEFAULT_PROPERTIES)) {
                existingSources.addBefore(DEFAULT_PROPERTIES, configurationSources);
            }
            else {
                existingSources.addLast(configurationSources);
            }
        }

    }

    private static class Profile {

        private final String name;

        private final boolean defaultProfile;

        Profile(String name) {
            this(name, false);
        }

        Profile(String name, boolean defaultProfile) {
            Assert.notNull(name, "Name must not be null");
            this.name = name;
            this.defaultProfile = defaultProfile;
        }

        public String getName() {
            return this.name;
        }

        public boolean isDefaultProfile() {
            return this.defaultProfile;
        }

        @Override
        public String toString() {
            return this.name;
        }

        @Override
        public int hashCode() {
            return this.name.hashCode();
        }

        @Override
        public boolean equals(Object obj) {
            if (obj == this) {
                return true;
            }
            if (obj == null || obj.getClass() != getClass()) {
                return false;
            }
            return ((Profile) obj).name.equals(this.name);
        }

    }

    /**
     * Holds the configuration {@link PropertySource}s as they are loaded can relocate
     * them once configuration classes have been processed.
     */
    static class ConfigurationPropertySources
            extends EnumerablePropertySource<Collection<PropertySource<?>>> {

        private final Collection<PropertySource<?>> sources;

        private final String[] names;

        ConfigurationPropertySources(Collection<PropertySource<?>> sources) {
            super(APPLICATION_CONFIGURATION_PROPERTY_SOURCE_NAME, sources);
            this.sources = sources;
            List<String> names = new ArrayList<String>();
            for (PropertySource<?> source : sources) {
                if (source instanceof EnumerablePropertySource) {
                    names.addAll(Arrays.asList(
                            ((EnumerablePropertySource<?>) source).getPropertyNames()));
                }
            }
            this.names = names.toArray(new String[names.size()]);
        }

        @Override
        public Object getProperty(String name) {
            for (PropertySource<?> propertySource : this.sources) {
                Object value = propertySource.getProperty(name);
                if (value != null) {
                    return value;
                }
            }
            return null;
        }

        public static void finishAndRelocate(MutablePropertySources propertySources) {
            String name = APPLICATION_CONFIGURATION_PROPERTY_SOURCE_NAME;
            ConfigurationPropertySources removed = (ConfigurationPropertySources) propertySources
                    .get(name);
            if (removed != null) {
                for (PropertySource<?> propertySource : removed.sources) {
                    if (propertySource instanceof EnumerableCompositePropertySource) {
                        EnumerableCompositePropertySource composite = (EnumerableCompositePropertySource) propertySource;
                        for (PropertySource<?> nested : composite.getSource()) {
                            propertySources.addAfter(name, nested);
                            name = nested.getName();
                        }
                    }
                    else {
                        propertySources.addAfter(name, propertySource);
                    }
                }
                propertySources.remove(APPLICATION_CONFIGURATION_PROPERTY_SOURCE_NAME);
            }
        }

        @Override
        public String[] getPropertyNames() {
            return this.names;
        }

    }

    /**
     * Holder for {@code spring.profiles} properties.
     */
    static final class SpringProfiles {

        private List<String> active = new ArrayList<String>();

        private List<String> include = new ArrayList<String>();

        public List<String> getActive() {
            return this.active;
        }

        public void setActive(List<String> active) {
            this.active = active;
        }

        public List<String> getInclude() {
            return this.include;
        }

        public void setInclude(List<String> include) {
            this.include = include;
        }

        Set<Profile> getActiveProfiles() {
            return asProfileSet(this.active);
        }

        Set<Profile> getIncludeProfiles() {
            return asProfileSet(this.include);
        }

        private Set<Profile> asProfileSet(List<String> profileNames) {
            List<Profile> profiles = new ArrayList<Profile>();
            for (String profileName : profileNames) {
                profiles.add(new Profile(profileName));
            }
            Collections.reverse(profiles);
            return new LinkedHashSet<Profile>(profiles);
        }

    }

}

　　根据javadoc注释的说明，这个类会从指定的位置加载application.properties或者application.yml并将它们的属性读到Envrionment当中，其中这几个方法大家关注下：

    @Override
    public void onApplicationEvent(ApplicationEvent event) {
        if (event instanceof ApplicationEnvironmentPreparedEvent) {
            onApplicationEnvironmentPreparedEvent(
                    (ApplicationEnvironmentPreparedEvent) event);
        }
        if (event instanceof ApplicationPreparedEvent) {
            onApplicationPreparedEvent(event);
        }
    }

　　当springboot程序启动时一定会触发该事件监听，如果当前是 ApplicationEnvironmentPreparedEvent事件就会调用 onApplicationEnvironmentPreparedEvent方法，最终该方法会执行：

    @Override
    public void postProcessEnvironment(ConfigurableEnvironment environment,
            SpringApplication application) {
        addPropertySources(environment, application.getResourceLoader());
        configureIgnoreBeanInfo(environment);
        bindToSpringApplication(environment, application);
    }

　  其中 bindToSpringApplication方法为：

/**
     * Bind the environment to the {@link SpringApplication}.
     * @param environment the environment to bind
     * @param application the application to bind to
     */
    protected void bindToSpringApplication(ConfigurableEnvironment environment,
            SpringApplication application) {
        PropertiesConfigurationFactory<SpringApplication> binder = new PropertiesConfigurationFactory<SpringApplication>(
                application);
        binder.setTargetName("spring.main");
        binder.setConversionService(this.conversionService);
        binder.setPropertySources(environment.getPropertySources());
        try {
            binder.bindPropertiesToTarget();
        }
        catch (BindException ex) {
            throw new IllegalStateException("Cannot bind to SpringApplication", ex);
        }
    }

　　很明显该方法是将Environment绑定到对应SpringApplication上，通过这个类就可以获取到我们更改过后的配置了

1.3、changes方法

private Map<String, Object> changes(Map<String, Object> before,
            Map<String, Object> after) {
        Map<String, Object> result = new HashMap<String, Object>();
        for (String key : before.keySet()) {
            if (!after.containsKey(key)) {
                result.put(key, null);
            }
            else if (!equal(before.get(key), after.get(key))) {
                result.put(key, after.get(key));
            }
        }
        for (String key : after.keySet()) {
            if (!before.containsKey(key)) {
                result.put(key, after.get(key));
            }
        }
        return result;
    }

　　changes方法其实就是处理配置变更信息的，分以下几种情况：

　　1）如果刷新过后配置文件新增配置就添加到Map里

　　2)  如果有配置变更就添加变更后的配置

　　3) 如果删除了原先的配置，就把原先的key对应的值设置为null

 

　　至此经过changes方法后，上下文环境已经拥有最新的配置了。

1.4、发布事件

　　当上述步骤都执行完毕后，紧接着会发布EnvrionmentChangeEvent事件，可是这个事件谁来监听呢？在这里我贴出官网的一段描述：

　　　应用程序将收听EnvironmentChangeEvent，并以几种标准方式进行更改（用户可以以常规方式添加ApplicationListeners附加ApplicationListeners）。当观察到EnvironmentChangeEvent时，它将有一个已更改的键值列表，应用程序将使用以下内容：

1.重新绑定上下文中的任何@ConfigurationProperties bean

2.为logging.level.*中的任何属性设置记录器级别

　　根据官网描述我们知道将变更一下操作行为@ConfigurationProperties的bean与更改日志level，那么如何做到的呢？结合官网文档我们来关注以下两个类：

　　ConfigurationPropertiesRebinder:

/*
 * Copyright 2013-2014 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.springframework.cloud.context.properties;

import java.util.HashSet;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;

import org.springframework.aop.framework.Advised;
import org.springframework.aop.support.AopUtils;
import org.springframework.beans.BeansException;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.cloud.context.config.annotation.RefreshScope;
import org.springframework.cloud.context.environment.EnvironmentChangeEvent;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.context.ApplicationListener;
import org.springframework.core.env.Environment;
import org.springframework.jmx.export.annotation.ManagedAttribute;
import org.springframework.jmx.export.annotation.ManagedOperation;
import org.springframework.jmx.export.annotation.ManagedResource;
import org.springframework.stereotype.Component;

/**
 * Listens for {@link EnvironmentChangeEvent} and rebinds beans that were bound to the
 * {@link Environment} using {@link ConfigurationProperties
 * <code>@ConfigurationProperties</code>}. When these beans are re-bound and
 * re-initialized the changes are available immediately to any component that is using the
 * <code>@ConfigurationProperties</code> bean.
 *
 * @see RefreshScope for a deeper and optionally more focused refresh of bean components
 *
 * @author Dave Syer
 *
 */
@Component
@ManagedResource
public class ConfigurationPropertiesRebinder
        implements ApplicationContextAware, ApplicationListener<EnvironmentChangeEvent> {

    private ConfigurationPropertiesBeans beans;

    private ApplicationContext applicationContext;

    private Map<String, Exception> errors = new ConcurrentHashMap<>();

    public ConfigurationPropertiesRebinder(ConfigurationPropertiesBeans beans) {
        this.beans = beans;
    }

    @Override
    public void setApplicationContext(ApplicationContext applicationContext)
            throws BeansException {
        this.applicationContext = applicationContext;
    }

    /**
     * A map of bean name to errors when instantiating the bean.
     *
     * @return the errors accumulated since the latest destroy
     */
    public Map<String, Exception> getErrors() {
        return this.errors;
    }

    @ManagedOperation
    public void rebind() {
        this.errors.clear();
        for (String name : this.beans.getBeanNames()) {
            rebind(name);
        }
    }

    @ManagedOperation
    public boolean rebind(String name) {
        if (!this.beans.getBeanNames().contains(name)) {
            return false;
        }
        if (this.applicationContext != null) {
            try {
                Object bean = this.applicationContext.getBean(name);
                if (AopUtils.isAopProxy(bean)) {
                    bean = getTargetObject(bean);
                }
                this.applicationContext.getAutowireCapableBeanFactory().destroyBean(bean);
                this.applicationContext.getAutowireCapableBeanFactory()
                        .initializeBean(bean, name);
                return true;
            }
            catch (RuntimeException e) {
                this.errors.put(name, e);
                throw e;
            }
        }
        return false;
    }

    @SuppressWarnings("unchecked")
    private static <T> T getTargetObject(Object candidate) {
        try {
            if (AopUtils.isAopProxy(candidate) && (candidate instanceof Advised)) {
                return (T) ((Advised) candidate).getTargetSource().getTarget();
            }
        }
        catch (Exception ex) {
            throw new IllegalStateException("Failed to unwrap proxied object", ex);
        }
        return (T) candidate;
    }

    @ManagedAttribute
    public Set<String> getBeanNames() {
        return new HashSet<String>(this.beans.getBeanNames());
    }

    @Override
    public void onApplicationEvent(EnvironmentChangeEvent event) {
        if (this.applicationContext.equals(event.getSource())
                // Backwards compatible
                || event.getKeys().equals(event.getSource())) {
            rebind();
        }
    }

}

　　我们可以看到该类监听了ChangeEnvrionmentEvent事件，它最主要作用是拿到更新的配置以后，重新绑定@ConfigurationProperties标记的类使之能够读取最新的属性

　　LoggingRebinder:

/*
 * Copyright 2013-2014 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.springframework.cloud.logging;

import java.util.Map;
import java.util.Map.Entry;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.boot.bind.RelaxedPropertyResolver;
import org.springframework.boot.logging.LogLevel;
import org.springframework.boot.logging.LoggingSystem;
import org.springframework.cloud.context.environment.EnvironmentChangeEvent;
import org.springframework.context.ApplicationListener;
import org.springframework.context.EnvironmentAware;
import org.springframework.core.env.Environment;

/**
 * Listener that looks for {@link EnvironmentChangeEvent} and rebinds logger levels if any
 * changed.
 *
 * @author Dave Syer
 *
 */
public class LoggingRebinder
        implements ApplicationListener<EnvironmentChangeEvent>, EnvironmentAware {

    private final Log logger = LogFactory.getLog(getClass());

    private Environment environment;

    @Override
    public void setEnvironment(Environment environment) {
        this.environment = environment;
    }

    @Override
    public void onApplicationEvent(EnvironmentChangeEvent event) {
        if (this.environment == null) {
            return;
        }
        LoggingSystem system = LoggingSystem.get(LoggingSystem.class.getClassLoader());
        setLogLevels(system, this.environment);
    }

    protected void setLogLevels(LoggingSystem system, Environment environment) {
        Map<String, Object> levels = new RelaxedPropertyResolver(environment)
                .getSubProperties("logging.level.");
        for (Entry<String, Object> entry : levels.entrySet()) {
            setLogLevel(system, environment, entry.getKey(), entry.getValue().toString());
        }
    }

    private void setLogLevel(LoggingSystem system, Environment environment, String name,
            String level) {
        try {
            if (name.equalsIgnoreCase("root")) {
                name = null;
            }
            level = environment.resolvePlaceholders(level);
            system.setLogLevel(name, LogLevel.valueOf(level.toUpperCase()));
        }
        catch (RuntimeException ex) {
            this.logger.error("Cannot set level: " + level + " for '" + name + "'");
        }
    }

}

　　该类也是监听了ChangeEnvrionmentEvent事件，用于重新绑定日志级别

 

二、刷新范围

　　我们考虑如下场景，当我们变更数据库配置后，通过refresh刷新，虽然能获取到最新的配置，可是我们的DataSource对象早就被初始化好了，换句话说即便配置刷新了我们拿到的依然是配置刷新前的对象。怎么解决这个问题呢？

　　我们继续看ContextRefresher的refresh方法，最后有一处代码值得我们关注一下this.scope.refreshAll()，此处scope对象是RefreshScope类型，那么这个类有什么作用呢？那么我们先要关注一下@RefreshScope注解。在这里我在贴出官网一段解释：

　　当配置更改时，标有@RefreshScope的Spring @Bean将得到特殊处理。这解决了状态bean在初始化时只注入配置的问题。例如，如果通过Environment更改数据库URL时DataSource有开放连接，那么我们可能希望这些连接的持有人能够完成他们正在做的工作。然后下一次有人从游泳池借用一个连接，他得到一个新的URL
　　

　　　刷新范围bean是在使用时初始化的懒惰代理（即当调用一个方法时），并且作用域作为初始值的缓存。要强制bean重新初始化下一个方法调用，您只需要使其缓存条目无效。RefreshScope是上下文中的一个bean，它有一个公共方法refreshAll()来清除目标缓存中的范围内的所有bean。还有一个refresh(String)方法可以按名称刷新单个bean。此功能在/refresh端点（通过HTTP或JMX）中公开。

 　　这里我贴出@RefreshScope源码：

/*
 * Copyright 2013-2014 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.springframework.cloud.context.config.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import org.springframework.context.annotation.Scope;
import org.springframework.context.annotation.ScopedProxyMode;

/**
 * Convenience annotation to put a <code>@Bean</code> definition in
 * {@link org.springframework.cloud.context.scope.refresh.RefreshScope refresh scope}.
 * Beans annotated this way can be refreshed at runtime and any components that are using
 * them will get a new instance on the next method call, fully initialized and injected
 * with all dependencies.
 * 
 * @author Dave Syer
 *
 */
@Target({ ElementType.TYPE, ElementType.METHOD })
@Retention(RetentionPolicy.RUNTIME)
@Scope("refresh")
@Documented
public @interface RefreshScope {
    /**
     * @see Scope#proxyMode()
     */
    ScopedProxyMode proxyMode() default ScopedProxyMode.TARGET_CLASS;

}

　　在这个注解上我们关注一下此处标记了@Scope("refresh")，我们知道Spring的Bean属性有个叫scope的，它定义了bean的作用范围，常见的有singleon,prototype,session等。此处新定义了一个范围叫做refresh，在此我贴出RefreshScope的源代码来分析一下：

/*
 * Copyright 2002-2009 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
 * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
 * specific language governing permissions and limitations under the License.
 */

package org.springframework.cloud.context.scope.refresh;

import java.io.Serializable;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.cloud.context.scope.GenericScope;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.context.event.ContextRefreshedEvent;
import org.springframework.context.event.EventListener;
import org.springframework.core.Ordered;
import org.springframework.jmx.export.annotation.ManagedOperation;
import org.springframework.jmx.export.annotation.ManagedResource;

/**
 * <p>
 * A Scope implementation that allows for beans to be refreshed dynamically at runtime
 * (see {@link #refresh(String)} and {@link #refreshAll()}). If a bean is refreshed then
 * the next time the bean is accessed (i.e. a method is executed) a new instance is
 * created. All lifecycle methods are applied to the bean instances, so any destruction
 * callbacks that were registered in the bean factory are called when it is refreshed, and
 * then the initialization callbacks are invoked as normal when the new instance is
 * created. A new bean instance is created from the original bean definition, so any
 * externalized content (property placeholders or expressions in string literals) is
 * re-evaluated when it is created.
 * </p>
 *
 * <p>
 * Note that all beans in this scope are <em>only</em> initialized when first accessed, so
 * the scope forces lazy initialization semantics. The implementation involves creating a
 * proxy for every bean in the scope, so there is a flag
 * {@link #setProxyTargetClass(boolean) proxyTargetClass} which controls the proxy
 * creation, defaulting to JDK dynamic proxies and therefore only exposing the interfaces
 * implemented by a bean. If callers need access to other methods then the flag needs to
 * be set (and CGLib present on the classpath). Because this scope automatically proxies
 * all its beans, there is no need to add <code>&lt;aop:auto-proxy/&gt;</code> to any bean
 * definitions.
 * </p>
 *
 * <p>
 * The scoped proxy approach adopted here has a side benefit that bean instances are
 * automatically {@link Serializable}, and can be sent across the wire as long as the
 * receiver has an identical application context on the other side. To ensure that the two
 * contexts agree that they are identical they have to have the same serialization id. One
 * will be generated automatically by default from the bean names, so two contexts with
 * the same bean names are by default able to exchange beans by name. If you need to
 * override the default id then provide an explicit {@link #setId(String) id} when the
 * Scope is declared.
 * </p>
 *
 * @author Dave Syer
 *
 * @since 3.1
 *
 */
@ManagedResource
public class RefreshScope extends GenericScope
        implements ApplicationContextAware, Ordered {

    private ApplicationContext context;
    private BeanDefinitionRegistry registry;
    private boolean eager = true;
    private int order = Ordered.LOWEST_PRECEDENCE - 100;

    /**
     * Create a scope instance and give it the default name: "refresh".
     */
    public RefreshScope() {
        super.setName("refresh");
    }

    @Override
    public int getOrder() {
        return this.order;
    }

    public void setOrder(int order) {
        this.order = order;
    }

    /**
     * Flag to determine whether all beans in refresh scope should be instantiated eagerly
     * on startup. Default true.
     *
     * @param eager the flag to set
     */
    public void setEager(boolean eager) {
        this.eager = eager;
    }

    @Override
    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry)
            throws BeansException {
        this.registry = registry;
        super.postProcessBeanDefinitionRegistry(registry);
    }

    @EventListener
    public void start(ContextRefreshedEvent event) {
        if (event.getApplicationContext() == this.context && this.eager
                && this.registry != null) {
            eagerlyInitialize();
        }
    }

    private void eagerlyInitialize() {
        for (String name : this.context.getBeanDefinitionNames()) {
            BeanDefinition definition = this.registry.getBeanDefinition(name);
            if (this.getName().equals(definition.getScope()) && !definition.isLazyInit()) {
                Object bean = this.context.getBean(name);
                if (bean != null) {
                    bean.getClass();
                }
            }
        }
    }

    @ManagedOperation(description = "Dispose of the current instance of bean name provided and force a refresh on next method execution.")
    public boolean refresh(String name) {
        if (!name.startsWith(SCOPED_TARGET_PREFIX)) {
            // User wants to refresh the bean with this name but that isn't the one in the
            // cache...
            name = SCOPED_TARGET_PREFIX + name;
        }
        // Ensure lifecycle is finished if bean was disposable
        if (super.destroy(name)) {
            this.context.publishEvent(new RefreshScopeRefreshedEvent(name));
            return true;
        }
        return false;
    }

    @ManagedOperation(description = "Dispose of the current instance of all beans in this scope and force a refresh on next method execution.")
    public void refreshAll() {
        super.destroy();
        this.context.publishEvent(new RefreshScopeRefreshedEvent());
    }

    @Override
    public void setApplicationContext(ApplicationContext context) throws BeansException {
        this.context = context;
    }

}

　　该类继承了GenericScope：

/*
 * Copyright 2002-2009 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
 * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
 * specific language governing permissions and limitations under the License.
 */

package org.springframework.cloud.context.scope;

import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.UUID;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

import org.aopalliance.intercept.MethodInterceptor;
import org.aopalliance.intercept.MethodInvocation;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.aop.framework.Advised;
import org.springframework.aop.scope.ScopedObject;
import org.springframework.aop.scope.ScopedProxyFactoryBean;
import org.springframework.aop.support.AopUtils;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.DisposableBean;
import org.springframework.beans.factory.ObjectFactory;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.config.Scope;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.BeanDefinitionRegistryPostProcessor;
import org.springframework.beans.factory.support.DefaultListableBeanFactory;
import org.springframework.beans.factory.support.RootBeanDefinition;
import org.springframework.expression.Expression;
import org.springframework.expression.ExpressionParser;
import org.springframework.expression.ParseException;
import org.springframework.expression.spel.standard.SpelExpressionParser;
import org.springframework.expression.spel.support.StandardEvaluationContext;
import org.springframework.util.ReflectionUtils;
import org.springframework.util.StringUtils;

/**
 * <p>
 * A generic Scope implementation.
 * </p>
 *
 * @author Dave Syer
 *
 * @since 3.1
 *
 */
public class GenericScope implements Scope, BeanFactoryPostProcessor,
        BeanDefinitionRegistryPostProcessor, DisposableBean {

    private static final Log logger = LogFactory.getLog(GenericScope.class);

    public static final String SCOPED_TARGET_PREFIX = "scopedTarget.";

    private BeanLifecycleWrapperCache cache = new BeanLifecycleWrapperCache(
            new StandardScopeCache());

    private String name = "generic";

    private ConfigurableListableBeanFactory beanFactory;

    private StandardEvaluationContext evaluationContext;

    private String id;

    private Map<String, Exception> errors = new ConcurrentHashMap<>();

    private ConcurrentMap<String, ReadWriteLock> locks = new ConcurrentHashMap<>();

    /**
     * Manual override for the serialization id that will be used to identify the bean
     * factory. The default is a unique key based on the bean names in the bean factory.
     *
     * @param id the id to set
     */
    public void setId(String id) {
        this.id = id;
    }

    /**
     * The name of this scope. Default "generic".
     *
     * @param name the name value to set
     */
    public void setName(String name) {
        this.name = name;
    }

    /**
     * The cache implementation to use for bean instances in this scope.
     *
     * @param cache the cache to use
     */
    public void setScopeCache(ScopeCache cache) {
        this.cache = new BeanLifecycleWrapperCache(cache);
    }

    /**
     * A map of bean name to errors when instantiating the bean.
     *
     * @return the errors accumulated since the latest destroy
     */
    public Map<String, Exception> getErrors() {
        return this.errors;
    }

    @Override
    public void destroy() {
        List<Throwable> errors = new ArrayList<Throwable>();
        Collection<BeanLifecycleWrapper> wrappers = this.cache.clear();
        for (BeanLifecycleWrapper wrapper : wrappers) {
            try {
                Lock lock = locks.get(wrapper.getName()).writeLock();
                lock.lock();
                try {
                    wrapper.destroy();
                }
                finally {
                    lock.unlock();
                }
            }
            catch (RuntimeException e) {
                errors.add(e);
            }
        }
        if (!errors.isEmpty()) {
            throw wrapIfNecessary(errors.get(0));
        }
        this.errors.clear();
    }

    /**
     * Destroy the named bean (i.e. flush it from the cache by default).
     *
     * @param name the bean name to flush
     * @return true if the bean was already cached, false otherwise
     */
    protected boolean destroy(String name) {
        BeanLifecycleWrapper wrapper = this.cache.remove(name);
        if (wrapper != null) {
            Lock lock = locks.get(wrapper.getName()).writeLock();
            lock.lock();
            try {
                wrapper.destroy();
            }
            finally {
                lock.unlock();
            }
            this.errors.remove(name);
            return true;
        }
        return false;
    }

    @Override
    public Object get(String name, ObjectFactory<?> objectFactory) {
        BeanLifecycleWrapper value = this.cache.put(name,
                new BeanLifecycleWrapper(name, objectFactory));
        locks.putIfAbsent(name, new ReentrantReadWriteLock());
        try {
            return value.getBean();
        }
        catch (RuntimeException e) {
            this.errors.put(name, e);
            throw e;
        }
    }

    @Override
    public String getConversationId() {
        return this.name;
    }

    @Override
    public void registerDestructionCallback(String name, Runnable callback) {
        BeanLifecycleWrapper value = this.cache.get(name);
        if (value == null) {
            return;
        }
        value.setDestroyCallback(callback);
    }

    @Override
    public Object remove(String name) {
        BeanLifecycleWrapper value = this.cache.remove(name);
        if (value == null) {
            return null;
        }
        // Someone might have added another object with the same key, but we
        // keep the method contract by removing the
        // value we found anyway
        return value.getBean();
    }

    @Override
    public Object resolveContextualObject(String key) {
        Expression expression = parseExpression(key);
        return expression.getValue(this.evaluationContext, this.beanFactory);
    }

    private Expression parseExpression(String input) {
        if (StringUtils.hasText(input)) {
            ExpressionParser parser = new SpelExpressionParser();
            try {
                return parser.parseExpression(input);
            }
            catch (ParseException e) {
                throw new IllegalArgumentException("Cannot parse expression: " + input,
                        e);
            }

        }
        else {
            return null;
        }
    }

    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory)
            throws BeansException {
        this.beanFactory = beanFactory;
        beanFactory.registerScope(this.name, this);
        setSerializationId(beanFactory);
    }

    @Override
    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry)
            throws BeansException {
        for (String name : registry.getBeanDefinitionNames()) {
            BeanDefinition definition = registry.getBeanDefinition(name);
            if (definition instanceof RootBeanDefinition) {
                RootBeanDefinition root = (RootBeanDefinition) definition;
                if (root.getDecoratedDefinition() != null && root.hasBeanClass()
                        && root.getBeanClass() == ScopedProxyFactoryBean.class) {
                    if (getName().equals(root.getDecoratedDefinition().getBeanDefinition()
                            .getScope())) {
                        root.setBeanClass(LockedScopedProxyFactoryBean.class);
                    }
                }
            }
        }
    }

    /**
     * If the bean factory is a DefaultListableBeanFactory then it can serialize scoped
     * beans and deserialize them in another context (even in another JVM), as long as the
     * ids of the bean factories match. This method sets up the serialization id to be
     * either the id provided to the scope instance, or if that is null, a hash of all the
     * bean names.
     *
     * @param beanFactory the bean factory to configure
     */
    private void setSerializationId(ConfigurableListableBeanFactory beanFactory) {

        if (beanFactory instanceof DefaultListableBeanFactory) {

            String id = this.id;
            if (id == null) {
                List<String> list = new ArrayList<>(
                        Arrays.asList(beanFactory.getBeanDefinitionNames()));
                Collections.sort(list);
                String names = list.toString();
                logger.debug("Generating bean factory id from names: " + names);
                id = UUID.nameUUIDFromBytes(names.getBytes()).toString();
            }

            logger.info("BeanFactory id=" + id);
            ((DefaultListableBeanFactory) beanFactory).setSerializationId(id);

        }
        else {
            logger.warn(
                    "BeanFactory was not a DefaultListableBeanFactory, scoped proxy beans "
                            + "cannot be serialized.");
        }

    }

    static RuntimeException wrapIfNecessary(Throwable throwable) {
        if (throwable instanceof RuntimeException) {
            return (RuntimeException) throwable;
        }
        if (throwable instanceof Error) {
            throw (Error) throwable;
        }
        return new IllegalStateException(throwable);
    }

    protected String getName() {
        return this.name;
    }

    private static class BeanLifecycleWrapperCache {

        private final ScopeCache cache;

        public BeanLifecycleWrapperCache(ScopeCache cache) {
            this.cache = cache;
        }

        public BeanLifecycleWrapper remove(String name) {
            return (BeanLifecycleWrapper) this.cache.remove(name);
        }

        public Collection<BeanLifecycleWrapper> clear() {
            Collection<Object> values = this.cache.clear();
            Collection<BeanLifecycleWrapper> wrappers = new LinkedHashSet<BeanLifecycleWrapper>();
            for (Object object : values) {
                wrappers.add((BeanLifecycleWrapper) object);
            }
            return wrappers;
        }

        public BeanLifecycleWrapper get(String name) {
            return (BeanLifecycleWrapper) this.cache.get(name);
        }

        public BeanLifecycleWrapper put(String name, BeanLifecycleWrapper value) {
            return (BeanLifecycleWrapper) this.cache.put(name, value);
        }

    }

    /**
     * Wrapper for a bean instance and any destruction callback (DisposableBean etc.) that
     * is registered for it. Also decorates the bean to optionally guard it from
     * concurrent access (for instance).
     *
     * @author Dave Syer
     *
     */
    private static class BeanLifecycleWrapper {

        private Object bean;

        private Runnable callback;

        private final String name;

        private final ObjectFactory<?> objectFactory;

        public BeanLifecycleWrapper(String name, ObjectFactory<?> objectFactory) {
            this.name = name;
            this.objectFactory = objectFactory;
        }

        public String getName() {
            return this.name;
        }

        public void setDestroyCallback(Runnable callback) {
            this.callback = callback;
        }

        public Object getBean() {
            if (this.bean == null) {
                synchronized (this.name) {
                    if (this.bean == null) {
                        this.bean = this.objectFactory.getObject();
                    }
                }
            }
            return this.bean;
        }

        public void destroy() {
            if (this.callback == null) {
                return;
            }
            synchronized (this.name) {
                Runnable callback = this.callback;
                if (callback != null) {
                    callback.run();
                }
                this.callback = null;
                this.bean = null;
            }
        }

        @Override
        public int hashCode() {
            final int prime = 31;
            int result = 1;
            result = prime * result + ((this.name == null) ? 0 : this.name.hashCode());
            return result;
        }

        @Override
        public boolean equals(Object obj) {
            if (this == obj) {
                return true;
            }
            if (obj == null) {
                return false;
            }
            if (getClass() != obj.getClass()) {
                return false;
            }
            BeanLifecycleWrapper other = (BeanLifecycleWrapper) obj;
            if (this.name == null) {
                if (other.name != null) {
                    return false;
                }
            }
            else if (!this.name.equals(other.name)) {
                return false;
            }
            return true;
        }

    }

    @SuppressWarnings("serial")
    public class LockedScopedProxyFactoryBean extends ScopedProxyFactoryBean
            implements MethodInterceptor {

        private String targetBeanName;

        @Override
        public void setBeanFactory(BeanFactory beanFactory) {
            super.setBeanFactory(beanFactory);
            Object proxy = getObject();
            if (proxy instanceof Advised) {
                Advised advised = (Advised) proxy;
                advised.addAdvice(0, this);
            }
        }

        @Override
        public void setTargetBeanName(String targetBeanName) {
            super.setTargetBeanName(targetBeanName);
            this.targetBeanName = targetBeanName;
        }

        @Override
        public Object invoke(MethodInvocation invocation) throws Throwable {
            Method method = invocation.getMethod();
            if (AopUtils.isEqualsMethod(method)
                    || AopUtils.isToStringMethod(method)
                    || AopUtils.isHashCodeMethod(method)
                    || isScopedObjectGetTargetObject(method)) {
                return invocation.proceed();
            }
            Object proxy = getObject();
            Lock lock = locks.get(this.targetBeanName).readLock();
            lock.lock();
            try {
                if (proxy instanceof Advised) {
                    Advised advised = (Advised) proxy;
                    ReflectionUtils.makeAccessible(method);
                    return ReflectionUtils.invokeMethod(method,
                            advised.getTargetSource().getTarget(),
                            invocation.getArguments());
                }
                return invocation.proceed();
            }
            finally {
                lock.unlock();
            }
        }

        private boolean isScopedObjectGetTargetObject(Method method) {
            return method.getDeclaringClass().equals(ScopedObject.class)
                    && method.getName().equals("getTargetObject")
                    && method.getParameterTypes().length == 0;
        }
    }

}

 

     这里面我们先看一下RefreshScope的构造函数：

/**
     * Create a scope instance and give it the default name: "refresh".
     */
    public RefreshScope() {
        super.setName("refresh");
    }

　　这里面创建了一个名字为refresh的scope。

　　紧接着在它的父类里我们可以看一下这个方法：

　　 @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory)
            throws BeansException {
        this.beanFactory = beanFactory;
        beanFactory.registerScope(this.name, this);
        setSerializationId(beanFactory);
    }

　　此方法中使用BeanFactory注册了一个refresh的范围，使得scope为refresh的bean生效。@RefreshScope标注的类还有一个特点：会使用代理对象并进行延迟加载。我们来看一下postProcessBeanDefinitionRegistry方法

@Override
    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry)
            throws BeansException {
        for (String name : registry.getBeanDefinitionNames()) {
            BeanDefinition definition = registry.getBeanDefinition(name);
            if (definition instanceof RootBeanDefinition) {
                RootBeanDefinition root = (RootBeanDefinition) definition;
                if (root.getDecoratedDefinition() != null && root.hasBeanClass()
                        && root.getBeanClass() == ScopedProxyFactoryBean.class) {
                    if (getName().equals(root.getDecoratedDefinition().getBeanDefinition()
                            .getScope())) {
                        root.setBeanClass(LockedScopedProxyFactoryBean.class);
                    }
                }
            }
        }
    }

　　该方法遍历所有的bean定义 如果当前的bean的scope为refresh,那么就把当前的bean设置为 LockedScopedProxyFactoryBean的代理对象。

　　RefreshScope还会监听一个ContextRefreshedEvent，该事件会在ApplicationContext初始化或者refreshed时触发，我们来看一下代码：

　　

　　 @EventListener
    public void start(ContextRefreshedEvent event) {
        if (event.getApplicationContext() == this.context && this.eager
                && this.registry != null) {
            eagerlyInitialize();
        }
    }

    private void eagerlyInitialize() {
        for (String name : this.context.getBeanDefinitionNames()) {
            BeanDefinition definition = this.registry.getBeanDefinition(name);
            if (this.getName().equals(definition.getScope()) && !definition.isLazyInit()) {
                Object bean = this.context.getBean(name);
                if (bean != null) {
                    bean.getClass();
                }
            }
        }
    }

　　注意此处获取refreshscope的bean，其中getBean是一个复杂而又繁琐的过程，此处我们先不在这里讨论，只不过经过这个方法以后，其通过代理机制会在GernericScope的BeanLifecycleWrapperCache缓存里把这个@RefreshScope标记的bean添加进去。

　　最后我们回过头来看一看RefreshScope的refreshAll方法：

    @ManagedOperation(description = "Dispose of the current instance of all beans in this scope and force a refresh on next method execution.")
    public void refreshAll() {
        super.destroy();
        this.context.publishEvent(new RefreshScopeRefreshedEvent());
    }

//.......GernericScope的destroy方法

    @Override
    public void destroy() {
        List<Throwable> errors = new ArrayList<Throwable>();
        Collection<BeanLifecycleWrapper> wrappers = this.cache.clear();
        for (BeanLifecycleWrapper wrapper : wrappers) {
            try {
                Lock lock = locks.get(wrapper.getName()).writeLock();
                lock.lock();
                try {
                    wrapper.destroy();
                }
                finally {
                    lock.unlock();
                }
            }
            catch (RuntimeException e) {
                errors.add(e);
            }
        }
        if (!errors.isEmpty()) {
            throw wrapIfNecessary(errors.get(0));
        }
        this.errors.clear();
    }

　　这里的代码逻辑很简单清除与释放缓存里被@RefreshScope标记的bean 。

　　当我们要获取对象时，我们可以关注如下方法：

    @Override
    public Object get(String name, ObjectFactory<?> objectFactory) {
        BeanLifecycleWrapper value = this.cache.put(name,
                new BeanLifecycleWrapper(name, objectFactory));
        locks.putIfAbsent(name, new ReentrantReadWriteLock());
        try {
            return value.getBean();
        }
        catch (RuntimeException e) {
            this.errors.put(name, e);
            throw e;
        }
    }     

//.....  BeanLifecycleWrapper的方法

        public Object getBean() {
            if (this.bean == null) {
                synchronized (this.name) {
                    if (this.bean == null) {
                        this.bean = this.objectFactory.getObject();
                    }
                }
            }
            return this.bean;
        }            

BeanLifecycleWrapper这个是@RefreshScope标记bean的一个包装类，会被存储到缓存里，在这里取不到值的话就会从objectFactory里去拿

三、示例与总结

3.1、示例

　　创建AppConfig类代码如下：

package com.bdqn.lyrk.refresh.scope.server;

import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.cloud.context.config.annotation.RefreshScope;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
@EnableConfigurationProperties(StudentConfig.class)
public class AppConfig {

    @RefreshScope
    @Bean
    public Student student(StudentConfig config) {
        Student student = new Student();
        student.setName(config.getName());
        return student;
    }
}

　　在这里，将Student设置为@RefreshScope 那么刷新以后会获取最新的Bean

　　启动类：

package com.bdqn.lyrk.refresh.scope.server;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@SpringBootApplication
@RestController
public class RefreshScopeApplication {

    @Autowired
    private Student student;

    @GetMapping
    public String student() {
        return student.getName();
    }

    public static void main(String[] args) throws InterruptedException {

        SpringApplication.run(RefreshScopeApplication.class, args);
    }
}

　　application.yml文件：

spring:
  application:
    name: refresh-scope-server
endpoints:
  refresh:
    sensitive: false
server:
  port: 8089
student:
  name: admin

 　　这里把refresh端点开放出来，然后变更配置后就可以获取最新的对象了

 

3.2、总结

　　1) 当配置更新并通过refresh端点刷新后，会执行ContextRefresher的refresh方法，该方法会记录当前的Environment，而后构建一个简易的SpringApplicationBuilder并执行其run方法，此时ConfigFileApplicationListener会读取我们修改过后的配置并绑定到SpringApplication对象上，最后进行changes操作来变更已有的PropertySource

　　2) @RefreshScope最好配合@Bean使用，当且仅当变更配置后，需要重新获取最新的bean时使用。加上该注解的Bean会被代理并且延迟加载，所有的scope属性为Refresh的bean会被包装成BeanLifecycleWrapper存入缓存(ConcurrentHashMap)中,所有的读取，修改，删除都是基于该缓存的