重写spring cloud config 本地bootstrap

在spring-cloud中使用了config-server之后，需要在client端加入bootstrap作为配置文件，其中通常包含如下：

spring.application.name=ms-asset
spring.cloud.config.label=master
spring.cloud.config.profile=test
spring.cloud.config.uri=http://ms-config-server-srv:8001/

但是这样的配置存在问题，因其固定了使用的配置环境和label，如采用Docker部署，则无法通过环境变量更改，通过阅读源码可知，Spring-cloud 通过两个JVM参数控制加载的配置文件。

-Dspring.cloud.config.label=master
-Dspring.cloud.config.profile=test

其中label表示分支，profile表示加载的配置环境。

其源码非常简单，在ConfigClientProperties中，如下所示：

public ConfigClientProperties override(
            org.springframework.core.env.Environment environment) {
        ConfigClientProperties override = new ConfigClientProperties();
        BeanUtils.copyProperties(this, override);
        override.setName(
                environment.resolvePlaceholders("${" + ConfigClientProperties.PREFIX
                        + ".name:${spring.application.name:application}}"));
        if (environment.containsProperty(ConfigClientProperties.PREFIX + ".profile")) {
            override.setProfile(
                    environment.getProperty(ConfigClientProperties.PREFIX + ".profile"));
        }
        if (environment.containsProperty(ConfigClientProperties.PREFIX + ".label")) {
            override.setLabel(
                    environment.getProperty(ConfigClientProperties.PREFIX + ".label"));
        }
        return override;
    }

可以看出，spring cloud仅支持profile和label这两个配置注入，在一般情况下足够用了。

另外存在一种修改spring-boot配置文件的方式，原理是监测spring初始化完成的事件，然后将环境变量注入配置中，可用于覆盖spring cloud config server的统一配置，但由于bootstrap处在加载链的最前端，在初始化之前即以完成的远程配置文件的加载，因此该方法无效，一并贴出，有缘人自取。

package com.example;

import org.springframework.boot.context.event.ApplicationPreparedEvent;
import org.springframework.context.ApplicationListener;
import org.springframework.core.Ordered;
import org.springframework.core.annotation.Order;
import org.springframework.core.env.CompositePropertySource;
import org.springframework.core.env.ConfigurableEnvironment;
import org.springframework.core.env.MutablePropertySources;
import org.springframework.core.env.PropertySource;

@Component
@Order(Ordered.HIGHEST_PRECEDENCE)
public class ConfigServicePropertyDeprioritizer
        implements ApplicationListener<ApplicationPreparedEvent>
{
    private static final String CONFIG_SOURCE = "bootstrap";

    private static final String PRIORITY_SOURCE = "systemEnvironment";

    @Override
    public void onApplicationEvent(ApplicationPreparedEvent event)
    {
        ConfigurableEnvironment environment = event.getApplicationContext()
                .getEnvironment();
        MutablePropertySources sources = environment.getPropertySources();
        PropertySource<?> bootstrap = findSourceToMove(sources);

        if (bootstrap != null)
        {
            sources.addAfter(PRIORITY_SOURCE, bootstrap);
        }
    }

    private PropertySource<?> findSourceToMove(MutablePropertySources sources)
    {
        boolean foundPrioritySource = false;

        for (PropertySource<?> source : sources)
        {
            if (PRIORITY_SOURCE.equals(source.getName()))
            {
                foundPrioritySource = true;
                continue;
            }

            if (CONFIG_SOURCE.equals(source.getName()))
            {
                // during bootstrapping, the "bootstrap" PropertySource
                // is a simple MapPropertySource, which we don't want to
                // use, as it's eventually removed. The real values will 
                // be in a CompositePropertySource
                if (source instanceof CompositePropertySource)
                {
                    return foundPrioritySource ? null : source;
                }
            }
        }

        return null;
    }
}

转自：https://stackoverflow.com/questions/31551039/override-spring-cloud-config-values-with-environment