本文來探討一下依賴注入的三種實現方式是哪三種，Spring的支援又怎麼樣。

首先，依賴注入（DI）的實現方式有三種：設值注入、構造方法注入、介面注入，下面來看看這三種注入方式在Spring中的支援怎麼樣。

1、設值注入。

   ①、新建一個專案

   ②、新建一個User類，實現setter、getter方法

package com.bean;

public class User {
    String username;
    String password;
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    
}
 

   ③、新建一個介面，名字為UserDAO，裡面包含一個save方法，將資訊存入資料庫

package com.dao;

import com.bean.User;

public interface UserDAO {
    public void save(User user);
}

    ④、新建一個UserDAO的實現類UserDAOImpl，實現save方法，模擬資料庫存入

package com.dao;

import com.bean.User;

public class UserDAOImpl implements UserDAO {

    @Override
    public void save(User user) {
        // TODO Auto-generated method stub
        System.out.println(user.getUsername()+"被儲存");
    }
    
}
 

    ⑤、為了不將直接操作資料庫的物件UserDAO暴露給使用者，需新增service層，在資料庫操作前後新增業務邏輯。
先實現業務邏輯介面UserService:

package com.bean;

public interface UserService {
    public void add(User user);
}

然後再寫這個介面的實現類UserServiceImpl:

package com.bean;

import com.dao.UserDAO;

public class UserServiceImpl implements UserService {

    private UserDAO userDAO;
    
    public UserDAO getUserDAO() {
        return userDAO;
    }
    
    //設值注入 為UserDAO的注入做準備
    public void setUserDAO(UserDAO userDAO) {
        this.userDAO = userDAO;
    }
    //實現負責業務邏輯的add方法
    @Override
    public void add(User user) {
        // TODO Auto-generated method stub
        userDAO.save(user);
    }
    
}
 

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:context="http://www.springframework.org/schema/context" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop"
    xmlns:tx="http://www.springframework.org/schema/tx" xmlns:p="http://www.springframework.org/schema/p" xmlns:util="http://www.springframework.org/schema/util" xmlns:jdbc="http://www.springframework.org/schema/jdbc"
    xmlns:cache="http://www.springframework.org/schema/cache"
    xsi:schemaLocation="
    http://www.springframework.org/schema/context
    http://www.springframework.org/schema/context/spring-context.xsd
    http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans.xsd
    http://www.springframework.org/schema/tx
    http://www.springframework.org/schema/tx/spring-tx.xsd
    http://www.springframework.org/schema/jdbc
    http://www.springframework.org/schema/jdbc/spring-jdbc-3.1.xsd
    http://www.springframework.org/schema/cache
    http://www.springframework.org/schema/cache/spring-cache-3.1.xsd
    http://www.springframework.org/schema/aop
    http://www.springframework.org/schema/aop/spring-aop.xsd
    http://www.springframework.org/schema/util
    http://www.springframework.org/schema/util/spring-util.xsd">
<!-- 配置資料訪問類，例項名稱為u -->
    <bean id="u" class="com.dao.UserDAOImpl">
    </bean>
    <bean id="user" class="com.bean.User">
    </bean>
    
    <!-- 設值注入 配置業務邏輯實現類，例項名稱為userService-->
    <bean id="userService" class="com.bean.UserServiceImpl">
        <!-- 在這裡實現注入，注入例項名稱為u的例項到該例項的userDAO屬性 -->
        <property name="userDAO">
            <ref bean="u" />
        </property>
    </bean>
</beans>

 //設值注入測試
    public static void setValDI(){
        //初始化容器
        ApplicationContext ctx = new ClassPathXmlApplicationContext("applicationContext.xml");
        UserServiceImpl service = (UserServiceImpl)ctx.getBean("userService");
        User u=(User)ctx.getBean("user");
        u.setPassword("123456");
        u.setUsername("test");
        service.add(u);
    }

package com.bean;

import com.dao.UserDAO;

public class UserServiceImpl implements UserService {

    private UserDAO userDAO;
    
    public UserDAO getUserDAO() {
        return userDAO;
    }
    
    public void setUserDAO(UserDAO userDAO) {
        this.userDAO = userDAO;
    }
    
    //如果需要構造方法注入 則這裡必須寫上構造方法
    public UserServiceImpl(UserDAO userDAO) {
        super();
        this.userDAO = userDAO;
    }

    @Override
    public void add(User user) {
        // TODO Auto-generated method stub
        userDAO.save(user);
    }
    
}

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:context="http://www.springframework.org/schema/context" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop"
    xmlns:tx="http://www.springframework.org/schema/tx" xmlns:p="http://www.springframework.org/schema/p" xmlns:util="http://www.springframework.org/schema/util" xmlns:jdbc="http://www.springframework.org/schema/jdbc"
    xmlns:cache="http://www.springframework.org/schema/cache"
    xsi:schemaLocation="
    http://www.springframework.org/schema/context
    http://www.springframework.org/schema/context/spring-context.xsd
    http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans.xsd
    http://www.springframework.org/schema/tx
    http://www.springframework.org/schema/tx/spring-tx.xsd
    http://www.springframework.org/schema/jdbc
    http://www.springframework.org/schema/jdbc/spring-jdbc-3.1.xsd
    http://www.springframework.org/schema/cache
    http://www.springframework.org/schema/cache/spring-cache-3.1.xsd
    http://www.springframework.org/schema/aop
    http://www.springframework.org/schema/aop/spring-aop.xsd
    http://www.springframework.org/schema/util
    http://www.springframework.org/schema/util/spring-util.xsd">
    <bean id="u" class="com.dao.UserDAOImpl">
    </bean>
    <bean id="userService" class="user.bean.UserServiceImpl">
        <!-- 構造注入 -->
        <constructor-arg>
            <ref bean="u"/>
        </constructor-arg>
    </bean>
</beans>