Annotation 注解

注入注解：@Autowired 注入

1.加在set方法上， 默认按类型by type，如果在 spring 容器中能够找到多个相同的类型，就从这多个类型找查找有没有一个key的值跟我们的 set 方法的参数名相同，如果有，就注入；没有的话，就无法判断要注入哪一个，导致报错

如果想用byName，使用@Qulifie 需要写在参数上

文件目录

代码：配置文件：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" 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-4.0.xsd"> <context:component-scan base-package="com.neudeu.service,com.neuedu.dao"></context:component-scan> </beans> 

base-package="com.neudeu.service,com.neuedu.dao  扫描这两个包

Test.java

package com.neuedu.test; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; public class Test { public static void main(String[] args) { ApplicationContext ac = new ClassPathXmlApplicationContext("beans.xml"); } } 

UserDao.java

package com.neuedu.dao; import org.springframework.stereotype.Component; @Component //注解方式 //Spring 自动地给这个类创建对象并将这个类放到 String 容器中去 public class UserDao { public UserDao() { System.out.println("UserDao..."); } public void save(){ System.out.println("保存用户信息..."); } } 

@Component   //注解方式

UserService.java

package com.neudeu.service; import org.springframework.stereotype.Component; import com.neuedu.dao.UserDao; @Component public class UserService { public UserService() { System.out.println("UserService..."); } private UserDao userDao; public void save(){ userDao.save(); } } 

输出：

修改代码：
UserService.java

package com.neudeu.service; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Component; import com.neuedu.dao.UserDao; @Component public class UserService { public UserService() { System.out.println("UserService..."); } private UserDao userDao; public void save(){ userDao.save(); } @Autowired //自动的将 userDao的属性注入进来 //修改代码 public void setUserDao(UserDao userDao) { //修改代码 System.out.println("setUserDao..."); //修改代码 this.userDao = userDao; //修改代码 } } 

输出：    @Autowired  //自动的将 userDao的属性注入进来

修改代码：

Test.java

package com.neuedu.test; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; import com.neudeu.service.UserService; public class Test { public static void main(String[] args) { ApplicationContext ac = new ClassPathXmlApplicationContext("beans.xml"); UserService userService = ac.getBean(UserService.class); userService.save(); } } 

输出：

set 注入 byName，按名称注入

修改代码：配置文件：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" 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-4.0.xsd"> <context:component-scan base-package="com.neudeu.service,com.neuedu.dao"></context:component-scan> <bean id="ud" class="com.neuedu.dao.UserDao"></bean> </beans> 

输出：byName，按名称注入

 

修改代码：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" 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-4.0.xsd"> <context:component-scan base-package="com.neudeu.service,com.neuedu.dao"></context:component-scan> <bean id="ud" class="com.neuedu.dao.UserDao"></bean> <bean id="ud1" class="com.neuedu.dao.UserDao"></bean> //修改代码 </beans> 

UserService.java

package com.neudeu.service; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.beans.factory.annotation.Qualifier; import org.springframework.stereotype.Component; import com.neuedu.dao.UserDao; @Component public class UserService { public UserService() { System.out.println("UserService..."); } private UserDao userDao; public void save(){ userDao.save(); } @Autowired //自动的将 userDao的属性注入进来 public void setUserDao(@Qualifier("ud1") UserDao userDao) { //修改代码 System.out.println("setUserDao..."); this.userDao = userDao; } } 

输出：

2.加在属性上，默认按类型bytype； 如果想用byName，使用@Qulifie 

修改代码：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" 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-4.0.xsd"> <context:component-scan base-package="com.neudeu.service,com.neuedu.dao"></context:component-scan> <bean id="ud" class="com.neuedu.dao.UserDao"></bean> <bean id="userDao" class="com.neuedu.dao.UserDao"></bean> //修改代码 </beans> 

UserService.java

package com.neudeu.service; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.beans.factory.annotation.Qualifier; import org.springframework.stereotype.Component; import com.neuedu.dao.UserDao; @Component public class UserService { @Autowired //自动的将 userDao的属性注入进来 @Qualifier("ud") private UserDao userDao; public UserService() { System.out.println("UserService..."); } public void save(){ userDao.save(); } } 

输出：

@Resource 注入

 默认按名称，名称找不到，按类型；可以指定特定名称

修改代码：

UserService.java

package com.neudeu.service; import javax.annotation.Resource; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.beans.factory.annotation.Qualifier; import org.springframework.stereotype.Component; import com.neuedu.dao.UserDao; @Component public class UserService { @Resource //修改代码 @Qualifier("ud") private UserDao userDao; public UserService() { System.out.println("UserService..."); } public void save(){ userDao.save(); } } 

输出：@Resource 作用和 Autowired 一样，不过注入方式不同，前者默认按名称byName，后者默认按类型bytype

强制按名称，找不到则报错

UserService.java

package com.neudeu.service; import javax.annotation.Resource; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.beans.factory.annotation.Qualifier; import org.springframework.stereotype.Component; import com.neuedu.dao.UserDao; @Component public class UserService { //@Autowired //自动的将 userDao的属性注入进来 @Resource(name="ud1") //修改代码 //@Qualifier("ud") private UserDao userDao; public UserService() { System.out.println("UserService..."); } public void save(){ userDao.save(); } } 

输出：

 组件注解

 @Component,@Controller,@Service,@Repository

初始化的名字默认为类名首字母小写，可以指定初始化bean的名字；

实质没有任何区别，功能都一样，在哪个层都可以随意调用，但推荐尽量遵从规范。