Springboot 自動裝配源碼分析

點擊去之後可以看到 核心註解springbootApplication 包含了三個註解

@SpringBootConfiguration ：實現配置功能
@EnableAutoConfiguration ：實現自動配置功能
@ComponentScan：spring組件掃描

再看一下最最主要的註解@EnableAutoConfiguration，點進去

 分析一下AutoConfigurationImportSelector內部實現

 @Override
public String[] selectImports(AnnotationMetadata annotationMetadata) {
    if (!isEnabled(annotationMetadata)) {
        return NO_IMPORTS;
    }
    try {
          AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader
                    .loadMetadata(this.beanClassLoader);
          AnnotationAttributes attributes = getAttributes(annotationMetadata);
          //掃描具有META-INF/spring.factories文件的jar包
          List<String> configurations = getCandidateConfigurations(annotationMetadata,
                    attributes);
          //去重
          configurations = removeDuplicates(configurations);
          //排序
          configurations = sort(configurations, autoConfigurationMetadata);
           //刪除需要排除的類
         Set<String> exclusions = getExclusions(annotationMetadata, attributes);
         checkExcludedClasses(configurations, exclusions);
         configurations.removeAll(exclusions);
         configurations = filter(configurations, autoConfigurationMetadata);
         fireAutoConfigurationImportEvents(configurations, exclusions);
         return configurations.toArray(new String[configurations.size()]);
    }
    catch (IOException ex) {
        throw new IllegalStateException(ex);
    }
}

//加載spring.factories實現
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;
}

 任何一個springboot應用，都會引入spring-boot-autoconfigure，而spring.factories文件就在該包下面。spring.factories文件是Key=Value形式，多個Value時使用,隔開，該文件中定義了關於初始化，監聽器等信息，而真正使自動配置生效的key是org.springframework.boot.autoconfigure.EnableAutoConfiguration，如下所示

# 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,\
//省略