通过实例解析spring bean之间的关系

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这篇文章主要介绍了通过实例解析spring bean之间的关系,文中通过示例代码介绍的非常详细，对大家的学习或者工作具有一定的参考学习价值,需要的朋友可以参考下

两种关系：继承、依赖

一、继承关系

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="武汉" p:street="络南街道"></bean>
  <!-- 使用parent指定指定哪个bean的配置，子bean可以覆盖父bean的配置 -->
  <bean id="address2" class="com.gong.spring.beans.autowire.Address" parent="address" 
  p:street="珞狮街道"></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.创建spring的IOC容器对象
    ApplicationContext ctx = new ClassPathXmlApplicationContext("beans-relation.xml");
    //2.从容器中获取Bean实例
    Address address = (Address) ctx.getBean("address"); 
    System.out.println(address.toString());
    Address address2 = (Address) ctx.getBean("address2"); 
    System.out.println(address2.toString());
  }
}

输出：

address2继承了address的city配置，因此city=武汉。

当然，我们也可以使用abstract来表明一个Bean是一个抽象bean。抽象bean可以作为一个模板，且不能被实例化。同时，如果一个bean没有声明class，那么该bean也是一个抽象bean，且必须指定abstract="true"。

<bean id="address" class="com.gong.spring.beans.autowire.Address" abstract="true"
  p:city="武汉" p:street="络南街道"></bean>

此时，在进行实例化就会报错

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

将抽象bean作为父bean，可以实例化它的子bean：

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

二、依赖关系

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="武汉" p:street="络南街道"></bean>
  <!-- 要求配置Student时，要依赖于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允许用户通过depends-on属性设定bean前置依赖bean，前置依赖bean会在本Bean实例化之前就创建好。如果前置依赖于多个Bean，则可以通过逗号，空格的方式来配置bean的名称。

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.创建spring的IOC容器对象
    ApplicationContext ctx = new ClassPathXmlApplicationContext("beans-relation.xml");
    //2.从容器中获取Bean实例
    Student student = (Student) ctx.getBean("student"); 
    System.out.println(student.toString());
  }
}

输出：