第二章 IoC 构造器注入

UserDao与UserDaoImpl:

public interface UserDao {
    public void save();
}  

public class UserDaoImpl implements UserDao {
    public void save() {
        System.out.println("保存用户...");
    }
}  

UserService接口及其实现类UserServiceImpl:

public interface UserService {
    public void addUser();
}  

public class UserServiceImpl implements UserService {
	private UserDao userDao;
	private String username;

	//这里的成员变量不需要setter方法。这是与setter注入不同的地方	

	public UserServiceImpl(UserDao userDao, String username) {
		this.userDao = userDao;
		this.username = username;
	}

	public void addUser() {
		System.out.println(username);
		userDao.save();
	}
}

配置:

<bean id="userDao" class="cn.framelife.spring.dao.impl.UserDaoImpl"></bean>
	<!-- index表示的是构造方法中的第几个参数。从0开始。 -->
	<bean id="userService" class="cn.framelife.spring.service.impl.UserServiceImpl">
		<constructor-arg index="0" ref="userDao"></constructor-arg>
		<constructor-arg index="1" value="zhangsan"></constructor-arg>
	</bean>