依赖注⼊（DI）的三种实现⽅式
本⽂来探讨⼀下依赖注⼊的三种实现⽅式是哪三种，Spring的⽀持⼜怎么样。
⾸先，依赖注⼊（DI）的实现⽅式有三种：设值注⼊、构造⽅法注⼊、接⼝注⼊，下⾯来看看这三种注⼊⽅式在Spring中的⽀持怎么样。
1、设值注⼊。
①、新建⼀个项⽬
②、新建⼀个User类，实现setter、getter⽅法
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package com.bean;
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public class User {
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String username;
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String password;
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public String getUsername() {
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return username;
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}
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public void setUsername(String username) {
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this.username = username;
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}
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public String getPassword() {
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return password;
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}
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public void setPassword(String password) {
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this.password = password;
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}
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}
③、新建⼀个接⼝，名字为UserDAO，⾥⾯包含⼀个save⽅法，将信息存⼊数据库
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import com.bean.User;
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public interface UserDAO {
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public void save(User user);
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}
④、新建⼀个UserDAO的实现类UserDAOImpl，实现save⽅法，模拟数据库存⼊
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package com.dao;
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import com.bean.User;
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public class UserDAOImpl implements UserDAO {
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@Override
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public void save(User user) {
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// TODO Auto-generated method stub
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System.out.Username()+"被存储");
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}
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}
⑤、为了不将直接操作数据库的对象UserDAO暴露给⽤户，需添加service层，在数据库操作前后添加业务逻辑。先实现业务逻辑接⼝UserService:
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package com.bean;
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public interface UserService {
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public void add(User user);
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}
然后再写这个接⼝的实现类UserServiceImpl:
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package com.bean;
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import com.dao.UserDAO;
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public class UserServiceImpl implements UserService {
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private UserDAO userDAO;
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public UserDAO getUserDAO() {
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return userDAO;
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}
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//设值注⼊为UserDAO的注⼊做准备
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public void setUserDAO(UserDAO userDAO) {
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this.userDAO = userDAO;
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}
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//实现负责业务逻辑的add⽅法
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@Override
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public void add(User user) {
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/
/ TODO Auto-generated method stub
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userDAO.save(user);
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}
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}
⑥、在src下创建Spring配置⽂件，命名为l，在其中配置数据访问类和业务逻辑实现类：
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<?xml version="1.0" encoding="UTF-8"?>
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<beans xmlns="/schema/beans" xmlns:context="/schema/context"
xmlns:xsi="/2001/XMLSchema-instance" xmlns:aop="/schema/aop"
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xmlns:util="/schema/util" xmlns:jdbc="/schema/jdbc"
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xmlns:cache="/schema/cache"
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xsi:schemaLocation="
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/schema/context
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/schema/context/spring-context.xsd
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/schema/beans
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/schema/beans/spring-beans.xsd
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/schema/tx
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/schema/tx/spring-tx.xsd
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/schema/jdbc
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/schema/jdbc/spring-jdbc-3.1.xsd
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/schema/cache
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/schema/cache/spring-cache-3.1.xsd
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/schema/aop
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/schema/aop/spring-aop.xsd
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/schema/util
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/schema/util/spring-util.xsd">
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<!-- 配置数据访问类，实例名称为u -->
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<bean id="u" class="com.dao.UserDAOImpl">
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</bean>
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<bean id="user" class="com.bean.User">
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</bean>
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<!-- 设值注⼊配置业务逻辑实现类，实例名称为userService-->
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<bean id="userService" class="com.bean.UserServiceImpl">
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<!-- 在这⾥实现注⼊，注⼊实例名称为u的实例到该实例的userDAO属性 -->
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<property name="userDAO">
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<ref bean="u" />
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</property>
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</bean>
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</beans>
⑦、写⼀个测试⽅法进⾏测试(为了简洁，这⾥没有加上测试类，也没有引⼊包，读者写的时候需要注意)
//设值注⼊测试
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public static void setValDI(){
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//初始化容器
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ApplicationContext ctx = new ClassPathXmlApplicationContext("l");
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UserServiceImpl service = (Bean("userService");
实例化bean的三种方式
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User u=(Bean("user");
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u.setPassword("123456");
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u.setUsername("test");
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service.add(u);
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}
2、构造⽅法注⼊
①、修改UserServiceImpl类加上构造⽅法
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package com.bean;
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import com.dao.UserDAO;
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public class UserServiceImpl implements UserService {
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private UserDAO userDAO;
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public UserDAO getUserDAO() {
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return userDAO;
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}
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public void setUserDAO(UserDAO userDAO) {
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this.userDAO = userDAO;
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}
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//如果需要构造⽅法注⼊则这⾥必须写上构造⽅法
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public UserServiceImpl(UserDAO userDAO) {
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super();
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this.userDAO = userDAO;
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}
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