spring_(6)bean之间的关系之继承和依赖

Bean的继承

• **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,可以设置的abstracts属性为true,这样Spring将不会实例化这个Bean.
• 并不是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

例子程序

基本结构

Address.java

package com.spring.beans.autowire;

public class Address {

    private String city;

    private String street;

    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 + '\'' +
                '}';
    }
}

Car.java

package com.spring.beans.autowire;

public class Car {

    private String brand;
    private double price;

    public String getBrand() {
        return brand;
    }

    public void setBrand(String brand) {
        this.brand = brand;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }

    @Override
    public String toString() {
        return "Car{" +
                "brand='" + brand + '\'' +
                ", price=" + price +
                '}';
    }
}

Person.java

package com.spring.beans.autowire;

public class Person {

    private String name;

    private Address address;

    private Car car;

    public String getName() {
        return name;
    }

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

    public Address getAddress() {
        return address;
    }

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

    public Car getCar() {
        return car;
    }

    public void setCar(Car car) {
        this.car = car;
    }

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", address=" + address +
                ", car=" + car +
                '}';
    }
}

beans-relation.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.这样的bean不能被IOC实例化，只用来被继承配置.
    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="address" class="com.spring.beans.autowire.Address"
        p:city="BeiJing^" p:street="WuDaoKou" abstract="true"></bean>

    <!--
        原来的配置方法，但是如何用bean的继承实现呢？
        <bean id="address2" class="com.spring.beans.autowire.Address"
          p:city="BeiJing" p:street="DaZhongSi"></bean>
    -->

    <!--bean 配置的继承: 使用bean的parent 属性指定继承哪个bean 的配置-->
    <bean id="address2" p:city="BeiJing" p:street="DaZhongSi" parent="address"></bean>
    <bean id="address3" p:city="BeiJing" p:street="WuDaoKou" parent="address"></bean>


    <bean id="car" class="com.spring.beans.autowire.Car"
    p:brand="Audi" p:price="300000"></bean>

    <!--要求在配置Person时，必须有一个关联的car! 换句话说person这个bean 依赖于Car这个bean-->
    <bean id="person" class="com.spring.beans.autowire.Person"
          p:name="Tom" p:address-ref="address2" depends-on="car"></bean>

</beans>

Main.java

package com.spring.beans.relation;

import com.spring.beans.autowire.Address;
import com.spring.beans.autowire.Person;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Main {
    public static void main(String[] args){

        ApplicationContext ctx = new ClassPathXmlApplicationContext("beans-relation.xml");

        Address address = (Address) ctx.getBean("address2");
        System.out.println(address );

        address = (Address) ctx.getBean("address3");
        System.out.println(address);

        Person person = (Person) ctx.getBean("person");
        System.out.println(person);

    }
}

运行结果