Spring bean之间的关系：继承，依赖

--Spring允许继承bean的配置，被继承的bean成为父bean，继承这个父bean的称为子bean；

--子bean从父bean中继承配置，包括bean的属性配置；

--父bean可以做为配置模版，也可以作为Bean实例，若只想把父bean作为模版，可以设置<bean>的abstract属性为true，这样spring将不会实例化这个bean。

--并不是<bean>元素中的所以属性都会被继承，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，而共享相同的配置，单此时abstract必须设为true。

例子：

Address类：

 

package com.xia.entity;

public class Address {
    private String city;
    private String street;
    
    public Address() {
        super();
        // TODO Auto-generated constructor stub
    }

    public String getCity() {
        return city;
    }

    public void setCity(String city) {
        this.city = city;
    }

    public String getStreet() {
        return street;
    }

    public void setStreet(String street) {
        this.street = street;
    }

    @Override
    public String toString() {
        return "Address [city=" + city + ", street=" + street + "]";
    }
    
    
}

 

配置文件：

<!-- 抽象bean：bean的abstract 属性为true时，这样的bean不能被IOC容器实例化，只用于被继承配置，
          若某一个bean的class属性没有被指定，那么bean必须是一个抽象bean-->
    <bean id="address" abstract="true">
        <property name="city" value="BeiJing"></property>
        <property name="street" value="wuDaoKou"></property>
    </bean>
    
       <bean id="address1" parent="address" class="com.xia.entity.Address">
        <property name="street" value="daZhangSi"></property>
       </bean>

测试：

        ApplicationContext ac = new ClassPathXmlApplicationContext("ApplicationContext.xml");
//        Address address = (Address) ac.getBean("address");
//        System.out.println(address);
        Address address1 = (Address) ac.getBean("address1");
        
        System.out.println(address1);
    }

输出：

Address [city=BeiJing, street=daZhangSi]

 --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。

例子：

添加两个类：

car：

 

package com.xia.entity;

public class Car {
    private String cname;
    private double price;
    public Car(String cname, double price) {
        super();
        this.cname = cname;
        this.price = price;
    }
    
    
    @Override
    public String toString() {
        return "Car [cname=" + cname + ", price=" + price + "]";
    }


    public Car() {
        super();
    }
    
    public String getCname() {
        return cname;
    }
    public void setCname(String cname) {
        this.cname = cname;
    }
    public double getPrice() {
        return price;
    }
    public void setPrice(double price) {
        this.price = price;
    }
    
    
    
}    

 

person：

package com.xia.entity;

public class Person {
    private String name;
    private int age;
    private Car car;
    private Address address;

    @Override
    public String toString() {
        return "Person [name=" + name + ", age=" + age + ", car=" + car + ", address=" + address + "]";
    }
    
    public Car getCar() {
        return car;
    }
    public Address getAddress() {
        return address;
    }

    public void setAddress(Address address) {
        this.address = address;
    }

    public void setCar(Car car) {
        this.car = car;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    
    
}

配置文件：

<?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">   
  
  <!-- 抽象bean：bean的abstract 属性为true时，这样的bean不能被IOC容器实例化，只用于被继承配置，
          若某一个bean的class属性没有被指定，那么bean必须是一个抽象bean-->
    <bean id="address" abstract="true">
        <property name="city" value="BeiJing"></property>
        <property name="street" value="wuDaoKou"></property>
    </bean>
    
       <bean id="address1" parent="address" class="com.xia.entity.Address">
        <property name="street" value="daZhangSi"></property>
       </bean>
       
       <bean id="car" class="com.xia.entity.Car">
           <property name="cname" value="auto"></property>
           <property name="price">
               <value>1000000</value>
           </property>
       </bean>
       <!-- 要求配置Person时，必须要有一个关联的car！  换句话说person这个Bean依赖于car这个Bean-->
       <bean id="person" class="com.xia.entity.Person" depends-on="car">
           <property name="name" value="Tom"></property>
           <property name="age">
               <value>18</value>
           </property>
           <property name="address">
               <ref bean="address1"/>
           </property>
       </bean>
   
</beans> 

测试类：

package com.xia.test;

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

import com.xia.entity.Address;
import com.xia.entity.Person;

public class Test {
    public static void main(String[] args) {
        ApplicationContext ac = new ClassPathXmlApplicationContext("ApplicationContext.xml");
        Person p = (Person) ac.getBean("person");
        System.out.println(p);
    }
}

如果配置文件中没有配置car，将会抛出异常：

 org.springframework.beans.factory.NoSuchBeanDefinitionException: No bean named 'car' is defined

正常输出：

Person [name=Tom, age=18, car=null, address=Address [city=BeiJing, street=daZhangSi]]