- 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 可以作为配置模板 也可以作为 Bean 实例. 若只想把父Bean 作为模板,可以设置bean的abstract 属性为 true, 这样 Spring 将不会实例化这个 Bean,只可以用来被继承配置
- 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
- 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
代码演示
Address.java
package com.atguigu.spring.bean;
public class Address {
private String address;
private String location;
public void setAddress(String address) {
this.address = address;
}
public void setLocation(String location) {
this.location = location;
}
@Override
public String toString() {
return "Address [address=" + address + ", location=" + location + "]";
}
}
Car.java
package com.atguigu.spring.bean;
public class Car {
private String name;
private String number;
public Car(String name, String number) {
super();
this.name = name;
this.number = number;
}
@Override
public String toString() {
return "Car [name=" + name + ", number=" + number + "]";
}
}
Person.java
package com.atguigu.spring.bean;
public class Person {
private Address address;
private Car car;
public void setAddress(Address address) {
this.address = address;
}
public void setCar(Car car) {
this.car = car;
}
@Override
public String toString() {
return "Person [address=" + address + ", car=" + car + "]";
}
}
application.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="car1" class="com.atguigu.spring.bean.Car">
<constructor-arg value="baoma"></constructor-arg>
<constructor-arg value="闽A7878"></constructor-arg>
</bean>
<bean id="address1" class="com.atguigu.spring.bean.Address">
<property name="address" value="mq"></property>
<property name="location" value="fj"></property>
</bean>
<!-- bean的配置继承:使用bean的parent属性指定继承那个bean的值 -->
<bean id="address2" class="com.atguigu.spring.bean.Address" parent="address1">
<property name="address" value="fz"></property>
<property name="location" value="fj"></property>
</bean>
<!-- 抽象bean:bean的abstract属性为true的bean,这样的bean不可以被ioc实例化,只可以用来被继承配置
若某一个bean的class属性没有指定值,则该bean必须是一个抽象bean -->
<bean id="address3" abstract="true">
<property name="address" value="mq"></property>
<property name="location" value="zz"></property>
</bean>
<bean id="address4" class="com.atguigu.spring.bean.Address" parent="address3">
</bean>
<!--测试要求配置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="person1" class="com.atguigu.spring.bean.Person" depends-on="car1">
<property name="address" ref="address1"></property>
</bean>
</beans>
Main.java
package com.atguigu.spring.bean;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class Main {
public static void main(String[] args) {
ApplicationContext applicationContext = new ClassPathXmlApplicationContext("application.xml");
Person person1 = (Person) applicationContext.getBean("person1");
Address address4 = (Address) applicationContext.getBean("address4");
Address address2 = (Address) applicationContext.getBean("address2");
System.out.println(person1);
System.out.println(address4);
System.out.println(address2);
}
}