通過實(shí)例解析spring bean之間的關(guān)系

更新時(shí)間：2020年01月07日 10:03:34 作者：西西嘛呦

這篇文章主要介紹了通過實(shí)例解析spring bean之間的關(guān)系,文中通過示例代碼介紹的非常詳細(xì)，對(duì)大家的學(xué)習(xí)或者工作具有一定的參考學(xué)習(xí)價(jià)值,需要的朋友可以參考下

兩種關(guān)系：繼承、依賴

一、繼承關(guān)系

Address.java

package com.gong.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 + "]";
  }
}

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">
  <bean id="address" class="com.gong.spring.beans.autowire.Address" 
  p:city="武漢" p:street="絡(luò)南街道"></bean>
  <!-- 使用parent指定指定哪個(gè)bean的配置，子bean可以覆蓋父bean的配置 -->
  <bean id="address2" class="com.gong.spring.beans.autowire.Address" parent="address" 
  p:street="珞獅街道"></bean>
</beans>

Main.java

package com.gong.spring.beans.autowire;

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

public class Main {
  public static void main(String[] args) {
    //1.創(chuàng)建spring的IOC容器對(duì)象
    ApplicationContext ctx = new ClassPathXmlApplicationContext("beans-relation.xml");
    //2.從容器中獲取Bean實(shí)例
    Address address = (Address) ctx.getBean("address"); 
    System.out.println(address.toString());
    Address address2 = (Address) ctx.getBean("address2"); 
    System.out.println(address2.toString());
  }
}

輸出：

address2繼承了address的city配置，因此city=武漢。

當(dāng)然，我們也可以使用abstract來表明一個(gè)Bean是一個(gè)抽象bean。抽象bean可以作為一個(gè)模板，且不能被實(shí)例化。同時(shí)，如果一個(gè)bean沒有聲明class，那么該bean也是一個(gè)抽象bean，且必須指定abstract="true"。

<bean id="address" class="com.gong.spring.beans.autowire.Address" abstract="true"
  p:city="武漢" p:street="絡(luò)南街道"></bean>

此時(shí)，在進(jìn)行實(shí)例化就會(huì)報(bào)錯(cuò)

Address address = (Address) ctx.getBean("address");

將抽象bean作為父bean，可以實(shí)例化它的子bean：

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

二、依賴關(guān)系

Car.java

package com.gong.spring.beans.autowire;

public class Car {
  
  public Car() {
  }

  public Car(String name) {
    this.name = name;
  }
  private String name;

  public String getName() {
    return name;
  }

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

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

Student.java

package com.gong.spring.beans.autowire;
import java.util.List;
import java.util.Map;

public class Student {
  
  private String name;
  private int age;
  private double score;
  private Car car;
  private Address address;
  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;
  }
  public double getScore() {
    return score;
  }
  public void setScore(double score) {
    this.score = score;
  }
  public Car getCar() {
    return car;
  }
  public void setCar(Car car) {
    this.car = car;
  }
  public Address getAddress() {
    return address;
  }
  public void setAddress(Address address) {
    this.address = address;
  }
  @Override
  public String toString() {
    return "Student [name=" + name + ", age=" + age + ", score=" + score + ", car=" + car + ", address=" + address
        + "]";
  }
  
  
}

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">
  
  <bean id="car" class="com.gong.spring.beans.autowire.Car" p:name="baoma"></bean>
  <bean id="address" class="com.gong.spring.beans.autowire.Address" 
  p:city="武漢" p:street="絡(luò)南街道"></bean>
  <!-- 要求配置Student時(shí)，要依賴于Car-->
  <bean id="student" class="com.gong.spring.beans.autowire.Student" p:name="tom"
  p:age="12" p:score="99.00" autowire="byName" depends-on="car"></bean>
</beans>

spring允許用戶通過depends-on屬性設(shè)定bean前置依賴bean，前置依賴bean會(huì)在本Bean實(shí)例化之前就創(chuàng)建好。如果前置依賴于多個(gè)Bean，則可以通過逗號(hào)，空格的方式來配置bean的名稱。

Main.java

package com.gong.spring.beans.autowire;

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

public class Main {
  public static void main(String[] args) {
    //1.創(chuàng)建spring的IOC容器對(duì)象
    ApplicationContext ctx = new ClassPathXmlApplicationContext("beans-relation.xml");
    //2.從容器中獲取Bean實(shí)例
    Student student = (Student) ctx.getBean("student"); 
    System.out.println(student.toString());
  }
}

輸出：