Spring - 基於Java配置的註解

一、@Configuration & @Bean 註解

@Configuration
public class HelloWorldConfig {
   @Bean 
   public HelloWorld helloWorld(){
      return new HelloWorld();
   }
}

...
//使用舉例
public static void main(String[] args) {
   ApplicationContext ctx = new AnnotationConfigApplicationContext(HelloWorldConfig.class);

   HelloWorld helloWorld = ctx.getBean(HelloWorld.class);
   helloWorld.setMessage("Hello World!");
   helloWorld.getMessage();
}

• 像下面這樣加載多個配置類：

public static void main(String[] args) {
   AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();

   ctx.register(AppConfig.class, OtherConfig.class);
   ctx.register(AdditionalConfig.class);
   ctx.refresh();

   MyService myService = ctx.getBean(MyService.class);
   myService.doStuff();
}

二、@Import註解能夠容許從其餘配置類中加載@Bean的定義

@Configuration
public class ConfigA {
   @Bean
   public A a() {
      return new A(); 
   }
}

...

@Configuration
@Import(ConfigA.class)
public class ConfigB {
   @Bean
   public B a() {
      return new A(); 
   }
}

• 客戶端調用

public static void main(String[] args) {
   ApplicationContext ctx = new AnnotationConfigApplicationContext(ConfigB.class);

   // now both beans A and B will be available...
   A a = ctx.getBean(A.class);
   B b = ctx.getBean(B.class);
}

三、@Bean支持指定任意的初始化和銷燬的回調方法

public class Foo {
   public void init() {
      // initialization logic
   }
   public void cleanup() {
      // destruction logic
   }
}
@Configuration
public class AppConfig {
   @Bean(initMethod = "init", destroyMethod = "cleanup" )
   public Foo foo() {
      return new Foo();
   }
}

四、默認的scope是單例（Singleton），可是你能夠像下面這樣使用@Scope註解：

@Configuration
public class AppConfig {
   @Bean
   @Scope("prototype")
   public Foo foo() {
      return new Foo();
   }
}