Spring入门学习笔记(2)——基于Java的配置

基于Java的配置

@Configuration & @Bean Annotations

使用@Configuration注释类表示,Spring IoC容器可以将该类用作bean定义的源。@Bean注释告诉Spring,用@Bean注释的方法将返回一个应该在Spring应用程序上下文中注册为bean的对象。最简单的@Configuration类如下所示:

package com.tutorialspoint;
import org.springframework.context.annotation.*;

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

它和以下的XML方式定义的是等价的:

<beans>
   <bean id = "helloWorld" class = "com.tutorialspoint.HelloWorld" />
</beans>

带@Bean的方法名作为bean id注释,他创建并返回实际的bean。一个配置类可以拥有多个Bean的声明。一旦定义了配置类,你可以通过 AnnotationConfigApplicationContex加载并获取
他们。

public static void main(String[] args) {
   ApplicationContext ctx = new AnnotationConfigApplicationContext(HelloWorldConfig.class);
   
   HelloWorld helloWorld = ctx.getBean(HelloWorld.class);
   helloWorld.setMessage("Hello World!");
   helloWorld.getMessage();
}

也可以获取加载不同的configuration

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();
}

Example

HelloWorldConfig.java

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

HelloWorld.java

public class HelloWorld {
   private String message;

   public void setMessage(String message){
      this.message  = message;
   }
   public void getMessage(){
      System.out.println("Your Message : " + message);
   }
}

MainApp.java

public class MainApp {
   public static void main(String[] args) {
      ApplicationContext ctx = 
         new AnnotationConfigApplicationContext(HelloWorldConfig.class);
   
      HelloWorld helloWorld = ctx.getBean(HelloWorld.class);
      helloWorld.setMessage("Hello World!");
      helloWorld.getMessage();
   }
}

输出:

Your Message : Hello World!

注入Bean依赖

当@ bean相互依赖时,表示依赖关系就像让一个bean方法调用另一个bean一样简单,如下所示

@Configuration
public class AppConfig {
    @Bean
    public Foo foo() {
        return new Foo(bar());
    }
    
    @Bean
    public Bar bar() {
        return new Bar();
    }
}

foo bean通过构造函数注入接收到bar的引用

Example

TextEditorConfig.java

@Configuration
public class TextEditorConfig {
   @Bean 
   public TextEditor textEditor(){
      return new TextEditor( spellChecker() );
   }

   @Bean 
   public SpellChecker spellChecker(){
      return new SpellChecker( );
   }
}

TextEditor.java

public class TextEditor {
   private SpellChecker spellChecker;

   public TextEditor(SpellChecker spellChecker){
      System.out.println("Inside TextEditor constructor." );
      this.spellChecker = spellChecker;
   }
   public void spellCheck(){
      spellChecker.checkSpelling();
   }
}

SpellChecker.java

public class SpellChecker {
   public SpellChecker(){
      System.out.println("Inside SpellChecker constructor." );
   }
   public void checkSpelling(){
      System.out.println("Inside checkSpelling." );
   }
}

MainApp.java

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

      TextEditor te = ctx.getBean(TextEditor.class);
      te.spellCheck();
   }
}

输出:

Inside SpellChecker constructor.
Inside TextEditor constructor.
Inside checkSpelling.

@Import注解

@Import注解允许在一个Configuration中导入另外一个配置类。

@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(); 
   }
}

这样,只需要加载ConfigB,则可以加载A,B两个配置文件,而不需要一样加载两次.

Lifecycle Callbacks(声明周期回调)

@bean注释支持指定任意的初始化和销毁回调方法,就像Spring XML的init方法和销毁方法。

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();
   }
}

指定Bean的作用域

默认作用域是singleton,可以通过以下方法重写:

@Configuration
public class AppConfig {
   @Bean
   @Scope("prototype")
   public Foo foo() {
      return new Foo();
   }
}
posted @ 2018-10-13 22:32  NinWoo  阅读(...)  评论(... 编辑 收藏