spring自动装配

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:p="http://www.springframework.org/schema/p"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context.xsd" default-autowire="byName">
	
	<!-- ###############自动装配############### -->  
	<bean id="userDao" class="cn.itcast.d_auto.UserDao"></bean>	
	<bean id="userService" class="cn.itcast.d_auto.UserService"></bean>
	
	<!-- 如果根据类型自动装配： 必须确保IOC容器中只有一个该类型的对象 -->
	<bean id="userAction" class="cn.itcast.d_auto.UserAction"></bean>
	
	<!--   报错： 因为上面已经有一个该类型的对象，且使用了根据类型自动装配
	<bean id="userService_test" class="cn.itcast.d_auto.UserService" autowire="byType"></bean>
	 -->
</beans>      

public class App {

	// 创建容器对象
	private ApplicationContext ac = new ClassPathXmlApplicationContext("cn/itcast/d_auto/bean.xml");
	@Test
	public void testExecuteAction() {
		// 从容器中获取Action
		UserAction userAction = (UserAction) ac.getBean("userAction");
		userAction.execute();
	}
}

public class UserAction {

	private UserService userService;
	public void setUserService(UserService userService) {
		this.userService = userService;
	}

	public String execute() {
		userService.save();
		return null;
	}
}

public class UserService {
	private UserDao userDao; // = new UserDao();
	public void setUserDao(UserDao userDao) {
		this.userDao = userDao;
	}

	public void save() {
		userDao.save();
	}
}

public class UserDao {

	public void save() {
		System.out.println("DB:保存用户...");
	}
}