Spring bean之间的关系：继承；依赖

继承Bean配置

Spring允许继承bean的配置，被继承的bean称为父bean，继承这个父Bean的Bean称为子Bean
子Bean从父Bean中继承配置，包括Bean的属性配置
子Bean也可以覆盖从父Bean继承过来的配置
父Bean可以作为配置模版，也可以作为Bean实例，若只想把父Bean作为模版，可以配置<bean>的abstract属性为true ，这样Spring将不会实例化这个Bean
并不是<bean>元素里的所有属性都会被继承。比如：autowire，abstract等。
也可以忽略父Bean的class属性，让子Bean指定自己的类，而共享相同的属性配置，但此时 abstract必须设为true

依赖Bean配置

Spring允许用户通过depends-on属性设定Bean前置依赖的Bean ，前置依赖的Bean会在本Bean实例化之前创建好
如果前置依赖于多个Bean，则可以通过逗号，空格或的方式配置Bean的名称

实例代码详解

package com.spring.auto.wire;

public class Department {
	private String name;

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}


	@Override
	public String toString() {
		return "Department [name=" + name + "]";
	}

}

package com.spring.auto.wire;


public class Company {

	private String name;
	private Department  department;
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public Department getDepartment() {
		return department;
	}
	public void setDepartment(Department department) {
		this.department = department;
	}
	
	@Override
	public String toString() {
		return "Company [name=" + name + ", department=" + department + "]";
	}

	
}

package com.spring.auto.wire;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Main_relation {

	public static void main(String[] args) {
		ApplicationContext ctx = new ClassPathXmlApplicationContext("beans-relation.xml");
		
		Department department = (Department) ctx.getBean("department2");
		System.out.println(department);
		
		Company company = (Company) ctx.getBean("company");
		System.out.println(company);

		Company company1 = (Company) ctx.getBean("company1");
		System.out.println(company1);
		
		Company company2 = (Company) ctx.getBean("company2");
		System.out.println(company2);
	}

}

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"
	xmlns:p="http://www.springframework.org/schema/p"
	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">

<!-- 抽象bean：bean的abstract属性为true的bean。这样bean不能被IOC容器实例化，只能用来被继承继承 
    若某一个bean的class属性没有指定，则该bean必须是一个抽象bean-->
<bean id="department1" p:name="JKY" abstract="true"></bean>

<!-- bean 配置的继承：使用bean 的parent 属性指定继承哪个baen的配置 -->
<bean id="department2" class="com.spring.auto.wire.Department" parent="department1"></bean>

<bean id="company" class="com.spring.auto.wire.Company" p:name="TT" p:department-ref="department2"></bean>

   <!-- 
    要求在配置company1时，必须有一个关联的department2！换句话说company这个bean依赖于department2这个bean. 
    注： 这里的依赖是指在实例化这个bean之前，必须实例化依赖的bean. 注意与ref的区别
   -->
<bean id="company1" class="com.spring.auto.wire.Company" p:name="TT1" depends-on="department2" p:department-ref="department2"></bean>

<bean id="company2" class="com.spring.auto.wire.Company" p:name="TT1" depends-on="company"></bean>

</beans>

运行结果：

Department [name=JKY]

Company [name=TT, department=Department [name=JKY]]

Company [name=TT1, department=Department [name=JKY]]

Company [name=TT1, department=null]

注意： depends-on 与 ref的区别，见：

http://stackoverflow.com/questions/12663491/ref-vs-depends-on-attributes-in-spring

Spring bean之间的关系：继承；依赖

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