Spring的依賴註入可以是我們不需要去管理bean，網上看到一個回答很精辟：

現在你需要買一把錘子:

1、自己做一把，解釋成java就是，調用者創建被調用著，也就是自己去創造一個造錘子的方法，然後自己調用；

2、自己找到生產錘子的工廠，然後問工廠買。就是工廠模式；

3、可以打電話給商店，讓商店給自己送一把錘子過來，這就是sping的依賴註入;

第一種方法調用者創建被調用者，兩者之前無法實現松耦合；

第二種方法調用者無須關心被調用者具體實現過程，只需要找到符合某種標準(接口)的實例，即可使用；

第三種調用者無須自己定位工廠，程序運行到需要被調用者時，系統自動提供被調用者實例。調用者和被調用者通過spring管理。他們的關系由spring維護

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">

    <!--屬性註入  -->
    <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>
    
    <!-- 構造方法類型註入 -->
    <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>
    
    <!-- 構造方法順序註入 -->
    <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>
    <!-- 工廠註入 -->
    <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>

執行類

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");
        //屬性註入
        People people1 = (People)ca.getBean("people1");
        System.out.println(people1);
        
        //構造方法type註入
        People people2 = (People)ca.getBean("people2");
        System.out.println(people2);
        
        //構造方法順序註入
        People people3 = (People)ca.getBean("people3");
        System.out.println(people3);
        
        //非靜態工廠
        People people4 = (People)ca.getBean("people4");
        System.out.println(people4);
        
        //靜態工廠註入
        People people5 = (People)ca.getBean("people5");
        System.out.println(people5);
    }
}

工廠

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;
        
    }
}

Sping4之依賴註入