Java框架--注解模式：@Repository @Service @Controller @Autowired

Java面向对象本质：

找到类--创建对象--给属性赋值--调用方法xml--bean(找到类)--beanFactory(创建对象-反射)--property(set注入、构造注入、工厂注入)--getBean(从beanFactory)获取对象--对象调用方法注解模式--context扫包--给类加@Component注解(找到类)--beanFactory(创建对象-反射)--@Autowired--getBean(从beanFactory)获取对象--对象调用方法

注解配置步骤：

1、扫包    <context:component-scan base-package="com.ioc.dao"></context:component-scan>2、加注解@Component组件注解--其他地方都是用@Component   在spring3.x以后延伸了3个和@Component等效的注解   @Repository  用于DAO实现类的注解--单例模式@Scope("singleton")   @Service     用于Servers实现类的注解--单例模式@Scope("singleton")   @Controller  用于Controller实现类的注解，spring将@Controller设置为--多例模式@Scope("prototype")3、key由来：第一种：将注解类的类名第一个字母小写   UserController==userController第二种：注解中标注别名 @Controller("usercon")4、@Autowired默认注入方式是根据类型(类)去注入，而不是根据id

代码测试：

DAO层定义一个interfacepackage com.ioc.dao;public interface IUserDao {public void addUser();}定义一个实现类package com.ioc.dao;import org.springframework.stereotype.Repository;@Repositorypublic class UserDao implements IUserDao{@Overridepublic void addUser() {System.out.println("调用了UserDao的addUser方法！");}}Service层package com.ioc.service;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.stereotype.Service;import com.ioc.dao.IUserDao;@Service//@Component  等同于  @Servicepublic class UserService {@Autowiredprivate IUserDao userDao;public void addUser() {userDao.addUser();}}Controller层package com.ioc.web;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.stereotype.Controller;import com.ioc.service.UserService;@Controllerpublic class UserController {@Autowired(required=false)//required=false  依赖的UserDao  bean没注册，也不报错private UserService userServer;public void addUser(){userServer.addUser();}}测试类：package com.test;import org.springframework.context.ApplicationContext;import org.springframework.context.support.ClassPathXmlApplicationContext;import com.ioc.web.UserController;public class Test3 {public static void main(String[] args) {ApplicationContext context = new ClassPathXmlApplicationContext("classpath:applicationContext.xml");UserController userController = (UserController) context.getBean("userController");userController.addUser();}}运行结果：十二月 15, 2016 3:39:23 下午 org.springframework.context.support.ClassPathXmlApplicationContext prepareRefresh信息: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@579bb367: startup date [Thu Dec 15 15:39:23 CST 2016]; root of context hierarchy十二月 15, 2016 3:39:24 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions信息: Loading XML bean definitions from class path resource [applicationContext.xml]调用了UserDao的addUser方法！

注解：@Resource、@Autowired、@Qualifier

定义第二个接口的实现类package com.ioc.dao;import org.springframework.stereotype.Repository;@Repositorypublic class UserDao2 implements IUserDao {@Overridepublic void addUser() {System.out.println("调用了UserDao的addUser222222方法！");}}修改service层public class UserService {@Autowiredprivate IUserDao xxx;public void addUser() {xxx.addUser();}}会报错：Error creating bean with name 'userService': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private com.ioc.dao.IUserDao com.ioc.service.UserService.xxx; nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type [com.ioc.dao.IUserDao] is defined: expected single matching bean but found 2: userDao,userDao2如果此时想调用UserDao2，并且写法private IUserDao xxx;需要修改service层public class UserService {@Autowired@Qualifier("userDao2")  //private IUserDao xxx;public void addUser() {xxx.addUser();}}@Resource(name="userDao2")等同于@Autowired@Qualifier("userDao2")注意：@Resource的作用相当于@Autowired，只不过@Autowired按byType自动注入，如果发现找到多个bean，则，又按照byName方式比对，如果还有多个，则报出异常 而@Resource默认按byName自动注入罢了。其实spring注解，最常用的还是根据名称，根据类型啊，构造方法啊，用的非常少。所以在多个实现的时候我们定义好bean的名称就行，就不会错乱。