【Spring实战】—— 6 内部Bean

本篇文章讲解了Spring的通过内部Bean设置Bean的属性。

　　类似内部类，内部Bean与普通的Bean关联不同的是：

　　1 普通的Bean，在其他的Bean实例引用时，都引用同一个实例。

　　2 内部Bean，每次引用时都是新创建的实例。

　　鉴于上述的场景，内部Bean是一个很常用的编程模式。

　　下面先通过前文所述的表演者的例子，描述一下主要的类：

package com.spring.test.setter;

import com.spring.test.action1.PerformanceException;
import com.spring.test.action1.Performer;

public class Instrumentalist implements Performer{
    private String song;
    private int age;
    private Instrument instrument;
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public String getSong() {
        return song;
    }
    public void setSong(String song) {
        this.song = song;
    }
    public Instrument getInstrument() {
        return instrument;
    }
    public void setInstrument(Instrument instrument) {
        this.instrument = instrument;
    }
    public Instrumentalist(){}
    public Instrumentalist(String song,int age,Instrument instrument){
        this.song = song;
        this.age = age;
        this.instrument = instrument;
    }
    public void perform() throws PerformanceException {
        System.out.println("Instrumentalist age:"+age);
        System.out.print("Playing "+song+":");
        instrument.play();
    }
}

　　其他代码，如下：

package com.spring.test.setter;

public interface Instrument {
    public void play();
}

package com.spring.test.setter;

public class Saxophone implements Instrument {
    public Saxophone(){}
    public void play() {
        System.out.println("TOOT TOOT TOOT");
    }
}

package com.spring.test.action1;

public interface Performer {
    void perform() throws PerformanceException;
}

　　如果使用 设值注入 需要设定属性和相应的setter getter方法。

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://www.springframework.org/schema/beans"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">
     <bean id="kenny" class="com.spring.test.setter.Instrumentalist">
         <property name="song" value="Jingle Bells" />
         <property name="age" value="25" />
         <property name="instrument">
             <bean class="com.spring.test.setter.Saxophone"/>
         </property>
     </bean>
</beans>

　　如果使用 构造注入 需要构造函数。

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://www.springframework.org/schema/beans"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">
     <bean id="kenny-constructor" class="com.spring.test.setter.Instrumentalist">
         <constructor-arg value="Happy New Year"/>
         <constructor-arg value="30"/>
         <constructor-arg>
             <bean class="com.spring.test.setter.Saxophone"/>
         </constructor-arg>
     </bean>
</beans>

　　应用上下文使用方法：

public class test {
    public static void main(String[] args) throws PerformanceException {
        ApplicationContext ctx = new ClassPathXmlApplicationContext("bean.xml");
        
        Instrumentalist performer = (Instrumentalist)ctx.getBean("kenny");
        performer.perform();
        
        Instrumentalist performer2 = (Instrumentalist)ctx.getBean("kenny-constructor");
        performer2.perform();
    }
}