spring装配

Spring装配Bean

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Spring容器配置的三种主要的装配机制：

• 在XML中进行显示配置
• 在Java中进行显式配置
• 隐式的bean发现机制和自动装配

1-自动装配

Spring从两个角度实现自动化装配：

• 组件扫描（component scanning） 自动发现应用上下文中所创建的bean
• 自动装配（autowiring） Spring自动满足bean之间的依赖

使用@Component注解来告诉Spring为这个类创建bean

@Component
public class CDPlayer implements MediaPlayer {
  private CompactDisc cd;

  @Autowired
  public CDPlayer(CompactDisc cd) {
    this.cd = cd;
  }

  public void play() {
    cd.play();
  }

}

通过设置组件扫描可以不用显示配置bean。但是组件扫描默认是不启用的。所以要通过配置来启用。

• 在java配置类中开启组件扫描@ComponentScan

  @Configuration
  @ComponentScan
  public class CDPlayerConfig { 
  }
  

因为@ComponentScan会扫描与配置类相同的包。可以通过下面两个配置来设置扫描的包：

• @ComponentScan(basePackages={“soundsystem,”sdd”})

  扫描包的名字

• @ComponentScan(basePackageClasses={CDplayer.class,DVDPlayer.class})

  扫描类所在的包

• 在XML中开启组件扫描

  <context:component-scan base-package="soundsystem" />
  

• 为组件扫描的bean命名

  • 通过@Component注解

@Component("sgtPerr")
public class SgtPeppers implements CompactDisc {

  private String title = "Sgt. Pepper's Lonely Hearts Club Band";  
  private String artist = "The Beatles";

  public void play() {
    System.out.println("Playing " + title + " by " + artist);
  }

}

• 通过@Named注解

@Named("sgtPerr")
public class SgtPeppers implements CompactDisc {

}

2- JAVA代码装配Bean

通过配置类来实现装配Bean

@Configuration //表明这是一个配置类
public class CDPlayerConfig {

  @Bean //声明这是一个bean
  public CompactDisc compactDisc() {
    return new SgtPeppers();
  }

  @Bean
    //通过构造器注入
  public CDPlayer cdPlayer(CompactDisc compactDisc) {
    return new CDPlayer(compactDisc);
  }

  @Bean 
    //通过setter方法注入
  public CDPlayer cdPlayer(CompactDisc compactDisc) {
    CDPlayer cdPlayer = new CDPlayer(compactDisc);
    cdPlayer.setCompactDisc(compactDisc);
    return cdPlayer
  }

}

3- 通过XML装配bean

• 通过构造器注入

<bean id="compactDisc" class="soundsystem.collections.BlankDisc">
    <constructor-arg value="Sgt. Pepper's Lonely Hearts Club Band" />
    <constructor-arg value="The Beatles" />
    <constructor-arg>
      <list>
        <value>Sgt. Pepper's Lonely Hearts Club Band</value>
        <value>With a Little Help from My Friends</value>
        <value>Lucy in the Sky with Diamonds</value>
        <value>Getting Better</value>
        <value>Fixing a Hole</value>
        <value>She's Leaving Home</value>
        <value>Being for the Benefit of Mr. Kite!</value>
        <value>Within You Without You</value>
        <value>When I'm Sixty-Four</value>
        <value>Lovely Rita</value>
        <value>Good Morning Good Morning</value>
        <value>Sgt. Pepper's Lonely Hearts Club Band (Reprise)</value>
        <value>A Day in the Life</value>
      </list>
    </constructor-arg>
  </bean>

• 通过setter注入

<bean id="compactDisc"
   class="soundsystem.properties.BlankDisc">
   <property name="title" value="Sgt. Pepper's Lonely Hearts Club Band" />
   <property name="artist" value="The Beatles" />
   <property name="tracks">
     <list>
       <value>Sgt. Pepper's Lonely Hearts Club Band</value>
       <value>With a Little Help from My Friends</value>
       <value>Lucy in the Sky with Diamonds</value>
       <value>Getting Better</value>
       <value>Fixing a Hole</value>
       <value>She's Leaving Home</value>
       <value>Being for the Benefit of Mr. Kite!</value>
       <value>Within You Without You</value>
       <value>When I'm Sixty-Four</value>
       <value>Lovely Rita</value>
       <value>Good Morning Good Morning</value>
       <value>Sgt. Pepper's Lonely Hearts Club Band (Reprise)</value>
       <value>A Day in the Life</value>
     </list>
   </property>
 </bean>

4-混合配置

• 在javaConfig引用xml配置

  @Configuration
  @Import(CDPlayerConfig.class) //导入其他的java配置
  @ImportResource("classpath:cd-config.xml") // 导入xml配置
  public class SoundSystemConfig {
  
  }
  

• 在xml配置中引用javaconfig

  <bean class="soundsystem.CDConfig" /> 导入config配置类
  <import resource="cd-player-config.xml"/> 导入xml配置
  

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##高级装配

1- 环境与profile