Sping4之依赖注入

Posted 2020-10-08 wo卜配

Spring的依赖注入可以是我们不需要去管理bean，网上看到一个回答很精辟：

现在你需要买一把锤子:

1、自己做一把，解释成java就是，调用者创建被调用着，也就是自己去创造一个造锤子的方法，然后自己调用；

2、自己找到生产锤子的工厂，然后问工厂买。就是工厂模式；

3、可以打电话给商店，让商店给自己送一把锤子过来，这就是sping的依赖注入;

第一种方法调用者创建被调用者，两者之前无法实现松耦合；

第二种方法调用者无须关心被调用者具体实现过程，只需要找到符合某种标准(接口)的实例，即可使用；

第三种调用者无须自己定位工厂，程序运行到需要被调用者时，系统自动提供被调用者实例。调用者和被调用者通过spring管理。他们的关系由spring维护

 

model

package com.hongcong.model;

public class People {
    private int id;
    private String name;
    private int age;
    
    
    public People() {
        super();
        // TODO Auto-generated constructor stub
    }
    public People(int id, String name, int age) {
        super();
        this.id = id;
        this.name = name;
        this.age = age;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    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;
    }
    
    
    @Override
    public String toString() {
        return "People [id=" + id + ", name=" + name + ", age=" + age + "]";
    }
    
}

beans.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">

    <!--属性注入  -->
    <bean id="people1" class="com.hongcong.model.People">
        <property name="id" value="1"/>
        <property name="name" value="小一"/>
        <property name="age" value="11"/>
    </bean>
    
    <!-- 构造方法类型注入 -->
    <bean id="people2" class="com.hongcong.model.People">
        <constructor-arg type="int" value="2"></constructor-arg>
        <constructor-arg type="String" value="小二"></constructor-arg>
        <constructor-arg type="int" value="22"></constructor-arg>
    </bean>
    
    <!-- 构造方法顺序注入 -->
    <bean id="people3" class="com.hongcong.model.People">
        <constructor-arg index="0" value="3"></constructor-arg>
        <constructor-arg index="1" value="小三"></constructor-arg>
        <constructor-arg index="2" value="33"></constructor-arg>
    </bean>
    <!-- 工厂注入 -->
    <bean id="peopleFactory" class="com.hongcong.factory.PeopleFactory"></bean>
    <bean id="people4" factory-bean="peopleFactory" factory-method="CreatePeople"></bean>
      <bean id="people5" class="com.hongcong.factory.PeopleFactory" factory-method="CreatePeopleByStatic"></bean>
</beans>

执行类

package com.hongcong.test;

import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.hongcong.model.People;

public class test {
    public static void main(String[] args) {
        ClassPathXmlApplicationContext ca = new  ClassPathXmlApplicationContext("beans.xml");
        //属性注入
        People people1 = (People)ca.getBean("people1");
        System.out.println(people1);
        
        //构造方法type注入
        People people2 = (People)ca.getBean("people2");
        System.out.println(people2);
        
        //构造方法顺序注入
        People people3 = (People)ca.getBean("people3");
        System.out.println(people3);
        
        //非静态工厂
        People people4 = (People)ca.getBean("people4");
        System.out.println(people4);
        
        //静态工厂注入
        People people5 = (People)ca.getBean("people5");
        System.out.println(people5);
    }
}

工厂

package com.hongcong.factory;


import com.hongcong.model.People;

public class PeopleFactory {
    public People CreatePeople(){
        People people = new People();
        people.setId(4);
        people.setName("小四");
        people.setAge(44);
        return people;
    }
    
    public static People CreatePeopleByStatic(){
        People people = new People();
        people.setId(5);
        people.setName("小五");
        people.setAge(55);
        return people;
        
    }
}