Bean的繼承

• **Spring允許繼承bean的配置,**被繼承的bean稱為父bean。繼承這個父Bean的Bean稱為子Bean.
• 子Bean從父Bean中繼承配置，包括Bean的屬性配置.
• 子Bean也可以覆蓋從父Bean繼承過來的配置.
• 父Bean可以作為配置模板，也可以作為Bean例項.若只想把父Bean作為模板,可以設定的abstracts屬性為true,這樣Spring將不會例項化這個Bean.
• 並不是元素裡的所有屬性都會被繼承.比如:autowire,abstract等.
• 也可以忽略父Bean的class屬性,讓子Bean指定自己的類,而共享相同的屬性配置.但此時 !! abstract必須設為true.
  !!

依賴Bean配置

• Spring允許使用者通過depends-on屬性設定Bean前置依賴的Bean,前置依賴的Bean會在本Bean例項化之前建立好
• 如果前置依賴於多個Bean,則可以通過逗號,空格或的方式配置Bean的名稱

例子程式

基本結構

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 屬性為true的bean.這樣的bean不能被IOC例項化，只用來被繼承配置.
    若某一個bean的class屬性沒有指定，則該bean必須是一個抽象bean-->
    <bean id="address" class="com.spring.beans.autowire.Address"
        p:city="BeiJing^" p:street="WuDaoKou" abstract="true"></bean>

    <!--
        原來的配置方法，但是如何用bean的繼承實現呢？
        <bean id="address2" class="com.spring.beans.autowire.Address"
          p:city="BeiJing" p:street="DaZhongSi"></bean>
    -->

    <!--bean 配置的繼承: 使用bean的parent 屬性指定繼承哪個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時，必須有一個關聯的car! 換句話說person這個bean 依賴於Car這個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);

    }
}

執行結果