Spring点滴六：Spring中定义bean的继承

在基于XML配置元数据中，bean标签可以包含很多配置信息，可以包含构造函数的参数，属性值以及其他一些初始化方法。子bean的定义可以继承父bean定义元数据，子bean定义可以根据需要重写父bean属性值或者添加一些其他属性。

Spring bean中的继承和Java中继承无关，只是继承的思想一致。可以把父bean作为一个定义模板，供其他子bean使用。

示例：

spring-beans.xml

<?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="parent" class="com.test.spring.Parent">
          <property name="message1" value="This is parent message1"></property>
          <property name="message2" value="This is parent message2"></property>
    </bean>
    <!-- 使用parent属性来引用父bean -->
    <bean id="children" class="com.test.spring.Children" parent="parent">
          <!-- 直接引用父bean中message1属性-->
          <property name="message1" value="This is parent message1"></property>
          <!-- 重写父bean中message2属性-->
          <property name="message2" value="This is children message2"></property>
          <!-- 子bean中添加了message3属性-->
          <property name="message3" value="This is children message3"></property>
    </bean>
</beans>

Java 类：

package com.test.spring;

public class Parent {
    private String message1;
    private String message2;

    public String getMessage1() {
        return message1;
    }

    public void setMessage1(String message1) {
        this.message1 = message1;
    }

    public String getMessage2() {
        return message2;
    }

    public void setMessage2(String message2) {
        this.message2 = message2;
    }

    @Override
    public String toString() {
        return "Parent [message1=" + message1 + ", message2=" + message2 + "]";
    }

}
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package com.test.spring;

public class Children {
    private String message1;
    private String message2;
    private String message3;

    public String getMessage1() {
        return message1;
    }

    public void setMessage1(String message1) {
        this.message1 = message1;
    }

    public String getMessage2() {
        return message2;
    }

    public void setMessage2(String message2) {
        this.message2 = message2;
    }

    public String getMessage3() {
        return message3;
    }

    public void setMessage3(String message3) {
        this.message3 = message3;
    }

    @Override
    public String toString() {
        return "Children [message1=" + message1 + ", message2=" + message2
                + ", message3=" + message3 + "]";
    }
}

测试：

package com.test.spring;

import org.junit.Before;
import org.junit.Test;
import org.springframework.context.support.AbstractApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class T {
    AbstractApplicationContext applicationcontext=null;
    @Before
    public void before() {
        System.out.println("》》》Spring ApplicationContext容器开始初始化了......");
        applicationcontext= new ClassPathXmlApplicationContext(new String[]{"test1-service.xml"});
        System.out.println("》》》Spring ApplicationContext容器初始化完毕了......");
    }
    @Test
    public void  test() {
        //BeanLifecycle beanLifecycle =applicationcontext.getBean("beanLifecycle",BeanLifecycle.class);
        //applicationcontext.close();
        //applicationcontext.registerShutdownHook();
        Parent parent=applicationcontext.getBean(Parent.class);
        System.out.println(parent);
        Children children=applicationcontext.getBean("children", Children.class);
        System.out.println(children);
    }
}

测试结果：

》》》Spring ApplicationContext容器开始初始化了......
2017-03-19 12:54:55  INFO:ClassPathXmlApplicationContext-Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@5facc36f: startup date [Sun Mar 19 12:54:55 CST 2017]; root of context hierarchy
2017-03-19 12:54:55  INFO:XmlBeanDefinitionReader-Loading XML bean definitions from class path resource [test1-service.xml]
》》》Spring ApplicationContext容器初始化完毕了......
Parent [message1=This is parent message1, message2=This is parent message2]
Children [message1=This is parent message1, message2=This is children message2, message3=This is children message3