SpringBoot自动配置源码探究

  1. @SpringBootApplication

    • @SpringBootApplication表示SpringBoot应用，标注在某个类上说明这个类是SpringBoot的主配置类，SpringBoot就运行这个类的main方法来启动应用；
    • @SpringBootApplication是组合注解 
      @Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = {
        @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
        @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
public @interface SpringBootApplication {
        ........    
}
      • @SpringBootConfiguration：表示是一个SpringBoot的配置类 
        @Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Configuration
public @interface SpringBootConfiguration {
}
        • @Configuration：Spring定义的注解，标注在类上表示这是个配置类，使用注解定义配置类来取代配置文件；配置类也是容器中的一个组件 
          @Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
public @interface Configuration {
    @AliasFor(
        annotation = Component.class
    )
    String value() default "";
}
      • @EnableAutoConfiguration：开启自动配置功能 
        @AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {
      .......
}
        • @AutoConfigurationPackage：自动配置包；Spring的底层注解@Import，表示给容器导入一个组件 
          @Import(AutoConfigurationPackages.Registrar.class)
public @interface AutoConfigurationPackage {}
          • Registrar.class：new PackageImports(metadata).getPackageNames().toArray(new String[0])获得注解类@SpringBootApplication所在的包名，把包下面的所有类都注册到Spring容器中供后续进行实例化 
                    @Override
        public void registerBeanDefinitions(AnnotationMetadata metadata, BeanDefinitionRegistry registry) {
            register(registry, new PackageImports(metadata).getPackageNames().toArray(new String[0]));
        }
        • AutoConfigurationImportSelector.class：给容器导入组件的自动配置类，并配置好这些组件，有了自动配置类，就免去了手动编写配置注入功能组件等操作； 
              @Override
    public String[] selectImports(AnnotationMetadata annotationMetadata) {
        if (!isEnabled(annotationMetadata)) {
            return NO_IMPORTS;
        }
        AutoConfigurationEntry autoConfigurationEntry = getAutoConfigurationEntry(annotationMetadata);
        return StringUtils.toStringArray(autoConfigurationEntry.getConfigurations());
    }
    protected AutoConfigurationEntry getAutoConfigurationEntry(AnnotationMetadata annotationMetadata) {
        if (!isEnabled(annotationMetadata)) {
            return EMPTY_ENTRY;
        }
        AnnotationAttributes attributes = getAttributes(annotationMetadata);
        //获得所有组件的自动配置类，包括mq的RabbitAutoConfiguration、redis的RedisAutoConfiguration等等
        List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes);
        configurations = removeDuplicates(configurations);
        Set<String> exclusions = getExclusions(annotationMetadata, attributes);
        checkExcludedClasses(configurations, exclusions);
        configurations.removeAll(exclusions);
        configurations = getConfigurationClassFilter().filter(configurations);
        fireAutoConfigurationImportEvents(configurations, exclusions);
        return new AutoConfigurationEntry(configurations, exclusions);
    }
    protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {
        List<String> configurations = SpringFactoriesLoader.loadFactoryNames(getSpringFactoriesLoaderFactoryClass(),
                getBeanClassLoader());
        Assert.notEmpty(configurations, "No auto configuration classes found in META-INF/spring.factories. If you "
                + "are using a custom packaging, make sure that file is correct.");
        return configurations;
    }
    public static final String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories";
    //spi:loadFactoryNames调用了loadSpringFactories(),它加载了spring.factories配置的信息，根据Map键值对获取信息，然后导入到容器中，在spring-boot-autoconfigure-2.3.0.RELEASE.jar中定义了文件
    public static List<String> loadFactoryNames(Class<?> factoryType, @Nullable ClassLoader classLoader) {
        String factoryTypeName = factoryType.getName();
        return loadSpringFactories(classLoader).getOrDefault(factoryTypeName, Collections.emptyList());
    }

           

          • 比如MVC的自动配置，就使用了WebMvcAutoConfiguration类，下面的代码就是给容器添加了视图解析器 
            @Configuration
@ConditionalOnWebApplication
@ConditionalOnClass({ Servlet.class, DispatcherServlet.class,
        WebMvcConfigurerAdapter.class })
@ConditionalOnMissingBean(WebMvcConfigurationSupport.class)
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE + 10)
@AutoConfigureAfter({ DispatcherServletAutoConfiguration.class,
        ValidationAutoConfiguration.class })
public class WebMvcAutoConfiguration {
        @Bean
        @ConditionalOnBean(View.class)
        @ConditionalOnMissingBean
        public BeanNameViewResolver beanNameViewResolver() {
            BeanNameViewResolver resolver = new BeanNameViewResolver();
            resolver.setOrder(Ordered.LOWEST_PRECEDENCE - 10);
            return resolver;
        }
}

             

            @Configuration：表示这是一个配置类，IOC会进行CGLIB代理；
            @ConditionalOnWebApplication：Spring底层@Conditional注解（Spring注解版），根据不同的条件，如果满足指定的条件，整个配置类里面的配置就会生效； 判断当前应用是否是web应用，如果是，当前配置类生效； 
            @Target({ ElementType.TYPE, ElementType.METHOD })
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Conditional(OnWebApplicationCondition.class)
public @interface ConditionalOnWebApplication {

}

            @ConditionalOnClass：判断当前项目有没有类Servlet（服务器），类DispatcherServlet（前端控制器），WebMvcConfigurerAdapter（MVC配置适配器）；

            @ConditionalOnMissingBean：保证IOC容器中只有一个WebMvcConfigurationSupport类型的bean；

            @AutoConfigureOrder：加载的优先级别

            @AutoConfigureAfter：在DispatcherServletAutoConfiguration, ValidationAutoConfiguration 类加载后进行装配。

            WebMvcAutoConfiguration中有3个内部类：WebMvcAutoConfigurationAdapter、EnableWebMvcConfiguration、ResourceChainCustomizerConfiguration；

            其中
            WebMvcAutoConfigurationAdapter：声明在WebMvcAutoConfiguration中,是为了确保当该类不在类路径下时不会被读取到，其中@EabaleConfigurationProperties是将配置文件中的值和对应的Bean类进行绑定，并将对应的Bean类加载到IOC容器中；
            EnableWebMvcConfiguration：配置类，相当于@EnableWebMvc的功能，对 spring mvc 进行自动化配置；

             

            比如@EnableConfigurationProperties往IOC容器加载了 WebMvcProperties类，该类通过@ConfigurationProperties注解将配置文件和自身属性进行绑定到WebMvcProperties类中，如下图application.propertis声明的spring.mvc.view.suffix就是通过@ConfigurationProperties和setPrefix进行绑定到WebMvcProperties类的；

             

              

    • 总结：

          @SpringBootApplication注解导入了两个类，@SpringBootConfiguration和@EnableAutoConfiguration，前者表示一个配置类，后者进行自动装配；
          其中@EnableAutoConfiguration注解有两个功能：
          @AutoConfigurationPackage：自动导入包，将@SpringBootApplication所在的包名下的所有类都注册到Spring容器中供后续进行实例化；
          AutoConfigurationImportSelector：给容器导入组件的自动配置类，并配置好这些组件；
          最终每个自动配置类通过@EnableConfigurationProperties({xxx.class})导入配置类，并把配置类加入到IOC容器中，其中配置类的属性值配置是通过@ConfigurationProperties(prefix = "xxx")和setXX方法将配置文件的值进行绑定；

  2. @ConfigurationProperties

    • 批量注入配置文件中的属性值，默认从全局配置文件中获取：在配置文件yml或properties定义值，使用该注解给配置类赋值 
      //application.properties
//可使用$占位符定义值，比如person.name=张三${random.int},person.maps.k2=${person.name}_v2；${person.name:hello}表示person_name没有定义，则使用默认值hello
//结果name为张三12afa124,k2为张三12afa124_v2
person.name=张三
person.age=11
person.maps.k1=v1
person.maps.k2=v2
person.list=a,b
//定义配置类并加入容器中，将上面的值按照键值对一一赋值
@Component
@ConfigurationProperties(prefix = "person")
public class Person {
    private String name;
    private Integer age;
    private Map<String,Object> maps;
    private List<String> list;
}
    • @ConfigurationProperties和@Value对比
      • @ConfigurationProperties批量注入文件的属性值；@Value一个个指定；
      • @ConfigurationProperties支持松散绑定(person.lastName；person.last_name；person.last-name；PERSON_LAST_NAME)；@Value不支持；
      • @ConfigurationProperties不支持SpEL；@Value支持，比如@Value("#{10}")；
      • @ConfigurationProperties支持JSR303数据校验，比如在配置类上添加@Validated，然后在属性上添加@Email，它表示属性值必须符合Email格式；@Value不支持，同时也不支持复杂类型封装，比如Map；
      • 如果需要JavaBean和配置文件值进行映射，使用@ConfigurationProperties；如果是单个值使用@Value；
    • @PropertySource：表示加载指定路径的配置文件 
      @PropertySource(value = {"classpath:person.properties"})
    • @ImportResource：导入Spring的配置文件，让配置文件里面的内容生效，比如我们写了bean.xml，里面使用<bean>创建了一个实例，但没有加入容器中 
      @ImportResource(locations = {"classpath:bean.xml"})
      • 使用@Configuration和@Bean来给容器添加组件，代替上面的xml文件中方式 
        @Configuration
public class MyConfiguration {
    @Bean
    public HelloService helloService(){
        return new HelloService();
    }
}

  3. 自动配置原理

    1. SpringBoot启动加载主配置类(@SpringBootApplication)，开启了自动配置功能(@EnableAutoConfiguration)；
    2. 自动配置使用了@Import(AutoConfigurationImportSelector.class)导入了组件，可查看getAutoConfigurationEntry()的getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes)返回的集合，即候选的配置；
    3. SpringFactoriesLoader.loadFactoryNames()扫描所有jar包路径下的META-INF/spring.factories，把扫描到的文件的内容包装成properties对象，从properties中获取到EnableAutoConfiguration.class类对应的值，然后把它们添加到容器中； 
      #spring-boot-autoconfigure-2.3.0.RELEASE.jar中spring.factories的信息，EnableAutoConfiguration后面每个xxxAutoConfiguration都是一个组件，都加入到容器中
# Auto Configure
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,\
org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,\
org.springframework.boot.autoconfigure.amqp.RabbitAutoConfiguration,\
org.springframework.boot.autoconfigure.batch.BatchAutoConfiguration,\
org.springframework.boot.autoconfigure.cache.CacheAutoConfiguration,\
org.springframework.boot.autoconfigure.cassandra.CassandraAutoConfiguration,\
org.springframework.boot.autoconfigure.context.ConfigurationPropertiesAutoConfiguration,\
org.springframework.boot.autoconfigure.context.LifecycleAutoConfiguration,\
org.springframework.boot.autoconfigure.context.MessageSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.context.PropertyPlaceholderAutoConfiguration,\
org.springframework.boot.autoconfigure.couchbase.CouchbaseAutoConfiguration,\
org.springframework.boot.autoconfigure.dao.PersistenceExceptionTranslationAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraReactiveDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraReactiveRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ReactiveElasticsearchRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ReactiveElasticsearchRestClientAutoConfiguration,\
org.springframework.boot.autoconfigure.data.jdbc.JdbcRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.jpa.JpaRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.ldap.LdapRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoReactiveDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoReactiveRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.neo4j.Neo4jDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.neo4j.Neo4jRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.solr.SolrRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.r2dbc.R2dbcDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.r2dbc.R2dbcRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.r2dbc.R2dbcTransactionManagerAutoConfiguration,\
org.springframework.boot.autoconfigure.data.redis.RedisAutoConfiguration,\
org.springframework.boot.autoconfigure.data.redis.RedisReactiveAutoConfiguration,\
org.springframework.boot.autoconfigure.data.redis.RedisRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.rest.RepositoryRestMvcAutoConfiguration,\
org.springframework.boot.autoconfigure.data.web.SpringDataWebAutoConfiguration,\
org.springframework.boot.autoconfigure.elasticsearch.ElasticsearchRestClientAutoConfiguration,\
org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration,\
org.springframework.boot.autoconfigure.freemarker.FreeMarkerAutoConfiguration,\
org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAutoConfiguration,\
org.springframework.boot.autoconfigure.gson.GsonAutoConfiguration,\
org.springframework.boot.autoconfigure.h2.H2ConsoleAutoConfiguration,\
org.springframework.boot.autoconfigure.hateoas.HypermediaAutoConfiguration,\
org.springframework.boot.autoconfigure.hazelcast.HazelcastAutoConfiguration,\
org.springframework.boot.autoconfigure.hazelcast.HazelcastJpaDependencyAutoConfiguration,\
org.springframework.boot.autoconfigure.http.HttpMessageConvertersAutoConfiguration,\
org.springframework.boot.autoconfigure.http.codec.CodecsAutoConfiguration,\
org.springframework.boot.autoconfigure.influx.InfluxDbAutoConfiguration,\
org.springframework.boot.autoconfigure.info.ProjectInfoAutoConfiguration,\
org.springframework.boot.autoconfigure.integration.IntegrationAutoConfiguration,\
org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.JdbcTemplateAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.JndiDataSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.XADataSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.DataSourceTransactionManagerAutoConfiguration,\
org.springframework.boot.autoconfigure.jms.JmsAutoConfiguration,\
org.springframework.boot.autoconfigure.jmx.JmxAutoConfiguration,\
org.springframework.boot.autoconfigure.jms.JndiConnectionFactoryAutoConfiguration,\
org.springframework.boot.autoconfigure.jms.activemq.ActiveMQAutoConfiguration,\
org.springframework.boot.autoconfigure.jms.artemis.ArtemisAutoConfiguration,\
org.springframework.boot.autoconfigure.jersey.JerseyAutoConfiguration,\
org.springframework.boot.autoconfigure.jooq.JooqAutoConfiguration,\
org.springframework.boot.autoconfigure.jsonb.JsonbAutoConfiguration,\
org.springframework.boot.autoconfigure.kafka.KafkaAutoConfiguration,\
org.springframework.boot.autoconfigure.availability.ApplicationAvailabilityAutoConfiguration,\
org.springframework.boot.autoconfigure.ldap.embedded.EmbeddedLdapAutoConfiguration,\
org.springframework.boot.autoconfigure.ldap.LdapAutoConfiguration,\
org.springframework.boot.autoconfigure.liquibase.LiquibaseAutoConfiguration,\
org.springframework.boot.autoconfigure.mail.MailSenderAutoConfiguration,\
org.springframework.boot.autoconfigure.mail.MailSenderValidatorAutoConfiguration,\
org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongoAutoConfiguration,\
org.springframework.boot.autoconfigure.mongo.MongoAutoConfiguration,\
org.springframework.boot.autoconfigure.mongo.MongoReactiveAutoConfiguration,\
org.springframework.boot.autoconfigure.mustache.MustacheAutoConfiguration,\
org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration,\
org.springframework.boot.autoconfigure.quartz.QuartzAutoConfiguration,\
org.springframework.boot.autoconfigure.r2dbc.R2dbcAutoConfiguration,\
org.springframework.boot.autoconfigure.rsocket.RSocketMessagingAutoConfiguration,\
org.springframework.boot.autoconfigure.rsocket.RSocketRequesterAutoConfiguration,\
org.springframework.boot.autoconfigure.rsocket.RSocketServerAutoConfiguration,\
org.springframework.boot.autoconfigure.rsocket.RSocketStrategiesAutoConfiguration,\
org.springframework.boot.autoconfigure.security.servlet.SecurityAutoConfiguration,\
org.springframework.boot.autoconfigure.security.servlet.UserDetailsServiceAutoConfiguration,\
org.springframework.boot.autoconfigure.security.servlet.SecurityFilterAutoConfiguration,\
org.springframework.boot.autoconfigure.security.reactive.ReactiveSecurityAutoConfiguration,\
org.springframework.boot.autoconfigure.security.reactive.ReactiveUserDetailsServiceAutoConfiguration,\
org.springframework.boot.autoconfigure.security.rsocket.RSocketSecurityAutoConfiguration,\
org.springframework.boot.autoconfigure.security.saml2.Saml2RelyingPartyAutoConfiguration,\
org.springframework.boot.autoconfigure.sendgrid.SendGridAutoConfiguration,\
org.springframework.boot.autoconfigure.session.SessionAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.client.servlet.OAuth2ClientAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.client.reactive.ReactiveOAuth2ClientAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.resource.servlet.OAuth2ResourceServerAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.resource.reactive.ReactiveOAuth2ResourceServerAutoConfiguration,\
org.springframework.boot.autoconfigure.solr.SolrAutoConfiguration,\
org.springframework.boot.autoconfigure.task.TaskExecutionAutoConfiguration,\
org.springframework.boot.autoconfigure.task.TaskSchedulingAutoConfiguration,\
org.springframework.boot.autoconfigure.thymeleaf.ThymeleafAutoConfiguration,\
org.springframework.boot.autoconfigure.transaction.TransactionAutoConfiguration,\
org.springframework.boot.autoconfigure.transaction.jta.JtaAutoConfiguration,\
org.springframework.boot.autoconfigure.validation.ValidationAutoConfiguration,\
org.springframework.boot.autoconfigure.web.client.RestTemplateAutoConfiguration,\
org.springframework.boot.autoconfigure.web.embedded.EmbeddedWebServerFactoryCustomizerAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.HttpHandlerAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.ReactiveWebServerFactoryAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.WebFluxAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.error.ErrorWebFluxAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.function.client.ClientHttpConnectorAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.function.client.WebClientAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.error.ErrorMvcAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.HttpEncodingAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.MultipartAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration,\
org.springframework.boot.autoconfigure.websocket.reactive.WebSocketReactiveAutoConfiguration,\
org.springframework.boot.autoconfigure.websocket.servlet.WebSocketServletAutoConfiguration,\
org.springframework.boot.autoconfigure.websocket.servlet.WebSocketMessagingAutoConfiguration,\
org.springframework.boot.autoconfigure.webservices.WebServicesAutoConfiguration,\
org.springframework.boot.autoconfigure.webservices.client.WebServiceTemplateAutoConfiguration
    4. 每一个自动配置类进行自动配置，以HttpEncodingAutoConfiguration为例： 
      @Configuration(proxyBeanMethods = false)//表示这是一个配置类
@EnableConfigurationProperties(ServerProperties.class)//启动指定类的ConfigurationProperties功能，将配置文件中对应的值和ServerProperties绑定起来，然后加入到IOC容器中
@ConditionalOnWebApplication(type = ConditionalOnWebApplication.Type.SERVLET)//Spring底层@Conditional注解，根据不同的条件，如果满足指定的条件，整个配置类里面的配置就会生效；判断当前应用是否是web应用，如果是，当前配置类生效
@ConditionalOnClass(CharacterEncodingFilter.class)//判断当前项目有没有这个CharacterEncodingFilter类；SpringMVC中进行乱码解决的过滤器
@ConditionalOnProperty(prefix = "server.servlet.encoding", value = "enabled", matchIfMissing = true)//判断配置文件中是否存在某个配置，server.servlet.encoding，如果不存在，判断也是成立的
public class HttpEncodingAutoConfiguration {

    private final Encoding properties;//已经和SpringBoot的配置文件映射了，即ServerProperties中的Encoding对象
    //只有一个有参构造器的情况下，参数的值从容器中拿，即@EnableConfigurationProperties(ServerProperties.class)
    public HttpEncodingAutoConfiguration(ServerProperties properties) {
        this.properties = properties.getServlet().getEncoding();//从ServerProperties中获取Encoding对象并进行实例化
    }
    @Bean //给容器中添加一个组件CharacterEncodingFilter
    @ConditionalOnMissingBean
    public CharacterEncodingFilter characterEncodingFilter() {
        CharacterEncodingFilter filter = new OrderedCharacterEncodingFilter();
        filter.setEncoding(this.properties.getCharset().name());//从properties中获取值并赋值
        filter.setForceRequestEncoding(this.properties.shouldForce(Encoding.Type.REQUEST));
        filter.setForceResponseEncoding(this.properties.shouldForce(Encoding.Type.RESPONSE));
        return filter;
    }
}
//从配置文件中获取指定的值和bean的属性进行绑定（所有在配置文件中能配置的属性都是在xxxProperties类中封装着；配置文件能配置什么参数就参照该功能对应的属性类）
@ConfigurationProperties(prefix = "server", ignoreUnknownFields = true)
public class ServerProperties {}
    5. 一旦这个自动配置类生效，就会给容器添加各种组件@Bean，这些组件的属性是从对应的properties类中获取的，每个properties类里面的每一个属性又是和配置文件绑定的；

  4. @Conditional派生注解

    • 作用在某个类上，表示必须是@Condition指定的条件成立才会给容器中添加组件，配置类里面的内容才生效；
    • 通过配置文件里面的debug=true在控制台打印出自动配置的启动和没有启用的报告进行查看： 
      ============================
CONDITIONS EVALUATION REPORT条件评估报告
============================


Positive matches:(自动配置类启用的)
-----------------

   AopAutoConfiguration matched:
      - @ConditionalOnProperty (spring.aop.auto=true) matched (OnPropertyCondition)
   ...........
Negative matches:(自动配置类没有启用的)
-----------------

   ActiveMQAutoConfiguration:
      Did not match:
         - @ConditionalOnClass did not find required class 'javax.jms.ConnectionFactory' (OnClassCondition)
   ...........
posted @ 2021-03-15 22:22  码猿手  阅读(173)  评论(0)  编辑  收藏  举报
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