带有AnnotationConfigApplicationContext的Java @Component类和@Configuration类 [英] Java @Component class and @Configuration class with AnnotationConfigApplicationContext

问题描述

我知道弹簧 AnnotationConfigApplicationContext 不仅可以接受 @Configuration 类作为输入，还可以接受普通的 @Component 类和带有JSR-330元数据注释的类。

I know springs AnnotationConfigApplicationContext is capable of accepting not only @Configuration classes as input but also plain @Component classes and classes annotated with JSR-330 metadata.

我在下面创建了没有@Configuration注释的AppConfig.java。 / p>

I have created AppConfig.java below without @Configuration annotation.

public class AppConfig {

   @Bean(name="sampleService")
   public SampleService getSampleService(){
       return new SampleService();
   }

}

将该类作为我的java配置传递 AnnotationConfigApplicationContext 类，它接受并注册了我的服务bean。

Passed this class as my java config class to AnnotationConfigApplicationContext, it accepted and registered my service beans.

我对同一个AppConfig进行了如下修改

I did some modification on above same AppConfig like below.

  @Component
  public class AppConfig {

     @Bean(name="sampleService")
     public SampleService getSampleService(){
          return new SampleService();
     }
  }

将AppConfig传递给AnnotationConfigApplicationContext，它接受并注册了我的服务

passed AppConfig to AnnotationConfigApplicationContext, it accepted and registered my service beans.

问题：

1. AnnotationConfigApplicationContext 类接受带有 @Configuration ，不带有 @Configuration 和带有@Component批注， @Component 和 @Configuration 有什么区别？

1. AnnotationConfigApplicationContext class is accepting the java config class with @Configuration, without @Configuration and with @Component annotations, what is the difference between @Component and @Configuration?

为什么没有 @Configuration 批注也能接受？

Why is it Accepting even without @Configuration annotation?

何时使用 @Configuration ，何时使用@Component作为Java配置类？

When to use @Configuration, and when to use @Component as java config class?

推荐答案

@Component

表示带注释的类是

Indicates that an annotated class is a "component".

也就是说，在启用了组件扫描的上下文中，Spring为 @Component 带注释的类型。这些bean定义最终变成了bean。

That is, in a context where component scanning is enabled, Spring generates bean definitions for @Component annotated types. These bean definitions end up being turned into beans.

@Configuration ，其本身带有

@Configuration, which is itself annotated with

表示一个类声明了一个或多个 @Bean 方法，并可能由
处理Spring容器在运行时为这些bean生成bean定义和
服务请求，[...]

Indicates that a class declares one or more @Bean methods and may be processed by the Spring container to generate bean definitions and service requests for those beans at runtime, [...]

@Configuration 类型（Spring会为此生成一个bean）充当bean的工厂。

So any @Configuration type, for which Spring generates a bean, acts as a factory for beans.

的javadoc @Bean 状态

@Bean 方法也可以在不是
的类中声明用 @Configuration 注释。例如，bean方法可以是在 @Component 类中甚至在普通的旧类中声明的
。在这种
情况下， @Bean 方法将以所谓的精简模式进行处理。

@Bean methods may also be declared within classes that are not annotated with @Configuration. For example, bean methods may be declared in a @Component class or even in a plain old class. In such cases, a @Bean method will get processed in a so-called 'lite' mode.

Bean方法将被
容器视为普通工厂方法（类似于XML中的工厂方法声明），并正确应用
作用域和生命周期回调。在这种情况下，包含类
保持不变，并且包含类或工厂方法没有
异常约束。

Bean methods in lite mode will be treated as plain factory methods by the container (similar to factory-method declarations in XML), with scoping and lifecycle callbacks properly applied. The containing class remains unmodified in this case, and there are no unusual constraints for the containing class or the factory methods.

在 @Configuration
类中的bean方法的语义中，精简模式不支持 bean间引用。
相反，当一个 @Bean 方法调用精简版
中的另一个 @Bean 方法时模式，该调用是标准的Java方法调用； Spring不会
不会通过CGLIB代理拦截调用。这类似于
inter- @Transactional 方法调用，其中在代理模式下，Spring不会
拦截调用— Spring仅在AspectJ模式下会如此

In contrast to the semantics for bean methods in @Configuration classes, 'inter-bean references' are not supported in lite mode. Instead, when one @Bean-method invokes another @Bean-method in lite mode, the invocation is a standard Java method invocation; Spring does not intercept the invocation via a CGLIB proxy. This is analogous to inter-@Transactional method calls where in proxy mode, Spring does not intercept the invocation — Spring does so only in AspectJ mode.

所以 @Bean 方法在 @Configuration 带注释的类和 @Component 带注释的类中的功能受限。

So @Bean methods have full functionality in @Configuration annotated classes and limited functionality in @Component annotated classes.

为什么即使没有@Configuration注释也可以接受？

why it is Accepting even without @Configuration annotation?

这就是设计类的方式。 ApplicationContext 是 BeanFactory 。 AnnotationConfigApplicationContext 只是提供了一种额外的方法来注册bean定义。

That's how the class is designed. An ApplicationContext is a BeanFactory. AnnotationConfigApplicationContext simply offers an extra way to register a bean definition.

何时使用@Configuration，以及何时使用@Component作为java config类？

When to use @Configuration, and when to use @Component as java config class?

这些确实是完全独立的目标。遵循javadoc。当您需要设置 ApplicationContext 时，可以将 AnnotationConfigApplicationContext 与 @Configuration 带注释的类。如果您只需要一个bean，请使用 @Component 注释其类型。

These really completely separate goals. Follow the javadoc. When you need to setup an ApplicationContext, you can use an AnnotationConfigApplicationContext with a @Configuration annotated class. If you simply need a bean, annotate its type with @Component.

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