spingboot自动装配

spingboot自动装配

从Application类的@SpringBootApplication注解开始：

@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 {

  @AliasFor(annotation = EnableAutoConfiguration.class)
  Class<?>[] exclude() default {};

  @AliasFor(annotation = EnableAutoConfiguration.class)
  String[] excludeName() default {};

  @AliasFor(annotation = ComponentScan.class, attribute = "basePackages")
  String[] scanBasePackages() default {};
  
  @AliasFor(annotation = ComponentScan.class, attribute = "basePackageClasses")
  Class<?>[] scanBasePackageClasses() default {};
}

从上面可以看出该注解里面包含了@EnableAutoConfiguration注解。

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {
  String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";

  Class<?>[] exclude() default {};
  String[] excludeName() default {};
}

@EnableAutoConfiguration注解会引入AutoConfigurationImportSelector类。

该类的selectImports方法一个关键方法：

@Override
  public String[] selectImports(AnnotationMetadata annotationMetadata) {
    //配置有没有配置spring.boot.enableautoconfiguration开关，默认为true
    //如果为false，则不执行自动配置的功能，直接返回
    if (!isEnabled(annotationMetadata)) {
      return NO_IMPORTS;
    }
    //找spring-autoconfigure-metadata.properties中的元素
    AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader
        .loadMetadata(this.beanClassLoader);
    //获取EnableAutoConfiguration注解中的属性 
    AnnotationAttributes attributes = getAttributes(annotationMetadata);
    //获取工程下所有配置key为EnableAutoConfiguration的值，即IdGenerateConfiguration等类。
    List<String> configurations = getCandidateConfigurations(annotationMetadata,
        attributes);
    //删除重复的值    
    configurations = removeDuplicates(configurations);
    //获取需要排除的规则列表
    Set<String> exclusions = getExclusions(annotationMetadata, attributes);
    //检查
    checkExcludedClasses(configurations, exclusions);
    //删除需要排除的值
    configurations.removeAll(exclusions);
    //根据配置文件中配置的开关，过滤一部分不满足条件的值
    configurations = filter(configurations, autoConfigurationMetadata);
    fireAutoConfigurationImportEvents(configurations, exclusions);
    return StringUtils.toStringArray(configurations);
  }

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