15分钟读懂Spring之IOC和DI

基本概念
IOC （Inversion of Control：控制反转 ）将创建UserService对象的控制权交给Spring管理
DI（Dependency Injection）依赖注入，在Spring创建Bean对象时动态将以来对象注入到Bean对象中的方法。
两者区别：Ioc是指对象的创建权反转给Spring，DI是创建对象的时候将对象依赖的属性以配置方式注入。

例子：

• User.class:

    public class User {
    private String username;
    private String password;
    public User(String username, String password) {
        super();
        this.username = username;
        this.password = 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;
    }
    @Override
    public String toString() {
        return "User [username is: " + username + ", password is: " + password + "]";
    }
}

• UserDAO.class:

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

• UserDAOImpl.class:

public class UserDAOImpl implements UserDAO {
    public void save(User user){
    // todo 
    };
    public void delete(User user){
    // todo ;
    }
}

• UserFactory.class:

public class UserFactory {
    public User CreatUser () {
        User user=new User();
        user.setUsername("Toto");
        user.setPassword("123456");
        return user;
    }
}

• UserService:

public class UserService {
    
    private UserDAO userDAO;  
        public void init() {
        //todo
        System.out.println("init");
    }   
    public void save(User user) {
        userDAO.save(user);
    }
    public UserDAO getUserDAO() {
        return userDAO;
    }
    public void setUserDAO(UserDAO userDAO) {
        this.userDAO = userDAO;
    }
    
    public UserService(UserDAO userDAO) {
        super();
        this.userDAO = userDAO;
    }
    
    public void destroy() {
        //todo
        System.out.println("destroy");
    }
}

• 测试：
• UserServiceTest.class

public class UserServiceTest {
    @Test
    public void test() {
        //Ioc
        ApplicationContext applicationContext=new ClassPathXmlApplicationContext("beans.xml");
        UserService userService=(UserService) applicationContext.getBean("userService");
        //DI构造方法注入
        User userFac=(User) applicationContext.getBean("user");
        //DI属性注入
        User user1=(User) applicationContext.getBean("user1");
        //DI工厂注入
        User user2=(User) applicationContext.getBean("user2");
           
        System.out.println(userFac);
        System.out.println(user1);
        System.out.println(user2);
       
        userService.save(userFac);
        userService.destroy();
    }

• 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-2.5.xsd">
    <!-- 构造方法DI -->
    <bean id="user" class="com.bjsxt.model.User" >
    <constructor-arg index="0" type="String" value="userCon"></constructor-arg>
    <constructor-arg index="1" type="String" value="123"></constructor-arg>
    </bean>
    
    <!-- 属性DI -->
    <bean id="user1" class="com.bjsxt.model.User" >
    <property name="username" value="u1"></property>
    <property name="password" value="000000"></property>
    </bean>

    <!-- 工厂DI -->
    <bean  id= "userFactory" class="com.bjsxt.factory.UserFactory" > </bean>
    <bean id="user2" factory-bean="userFactory" factory-method="CreatUser"></bean>
   
    <bean id="userDao" class="com.bjsxt.dao.impl.UserDAOImpl"></bean> 
    <bean id="userService" class="com.bjsxt.service.UserService" init-method="init" destroy-method="destroy" scope="prototype">      
    <property name="userDAO" ref="userDao" />
    </beans>