SPRING IN ACTION 第4版笔记-第二章Wiring Beans-005-<constructor-arg>和c-namespace

1.

package soundsystem;

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);
  }

}

2.

package soundsystem;
import org.springframework.beans.factory.annotation.Autowired;

public class CDPlayer implements MediaPlayer {
  private CompactDisc cd;

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

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

}

一、-<constructor-arg>

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">

  <bean id="compactDisc" class="soundsystem.SgtPeppers" />
        
  <bean id="cdPlayer" class="soundsystem.CDPlayer">
    <constructor-arg ref="compactDisc" />
  </bean>

</beans>

二、c-namespace(3.0开始有)

(1)指定参数名称

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns:c="http://www.springframework.org/schema/c"
  xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">

  <bean id="compactDisc" class="soundsystem.SgtPeppers" />
        
  <bean id="cdPlayer" class="soundsystem.CDPlayer"
        c:cd-ref="compactDisc" />

</beans>

(2)指定参数顺序

<bean id="cdPlayer" class="soundsystem.CDPlayer"
c:_0-ref="compactDisc" />

(3)如查构造函数只有一个参数，则可以连顺序都不用指定

<bean id="cdPlayer" class="soundsystem.CDPlayer"
c:_-ref="compactDisc" />