Spring13 - 自动注入@Autowired
@Autowired注入
单独使用@Autowired注解,默认根据类型装配。【默认是byType】
查看源码:
package org.springframework.beans.factory.annotation;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
@Target({ElementType.CONSTRUCTOR, ElementType.METHOD, ElementType.PARAMETER, ElementType.FIELD, ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Autowired {
boolean required() default true;
}
源码中有两处需要注意:
-
第一处:该注解可以标注在哪里?
-
- 构造方法上
- 方法上
- 形参上
- 属性上
- 注解上
-
第二处:该注解有一个required属性,默认值是true,表示在注入的时候要求被注入的Bean必须是存在的,如果不存在则报错。如果required属性设置为false,表示注入的Bean存在或者不存在都没关系,存在的话就注入,不存在的话,也不报错。
①场景一:属性注入
创建UserDao接口
package com.atguigu.spring6.dao;
public interface UserDao {
public void print();
}
创建UserDaoImpl实现
package com.atguigu.spring6.dao.impl;
import com.atguigu.spring6.dao.UserDao;
import org.springframework.stereotype.Repository;
@Repository
public class UserDaoImpl implements UserDao {
@Override
public void print() {
System.out.println("Dao层执行结束");
}
}
创建UserService接口
package com.atguigu.spring6.service;
public interface UserService {
public void out();
}
创建UserServiceImpl实现类
package com.atguigu.spring6.service.impl;
import com.atguigu.spring6.dao.UserDao;
import com.atguigu.spring6.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
@Service
public class UserServiceImpl implements UserService {
@Autowired
private UserDao userDao;
@Override
public void out() {
userDao.print();
System.out.println("Service层执行结束");
}
}
创建UserController类
package com.atguigu.spring6.controller;
import com.atguigu.spring6.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
@Controller
public class UserController {
@Autowired
private UserService userService;
public void out() {
userService.out();
System.out.println("Controller层执行结束。");
}
}
测试一
package com.atguigu.spring6.bean;
import com.atguigu.spring6.controller.UserController;
import org.junit.jupiter.api.Test;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class UserTest {
private Logger logger = LoggerFactory.getLogger(UserTest.class);
@Test
public void testAnnotation(){
ApplicationContext context = new ClassPathXmlApplicationContext("Beans.xml");
UserController userController = context.getBean("userController", UserController.class);
userController.out();
logger.info("执行成功");
}
}
测试结果:
以上构造方法和setter方法都没有提供,经过测试,仍然可以注入成功。
②场景二:set注入
修改UserServiceImpl类
package com.atguigu.spring6.service.impl;
import com.atguigu.spring6.dao.UserDao;
import com.atguigu.spring6.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
@Service
public class UserServiceImpl implements UserService {
private UserDao userDao;
@Autowired
public void setUserDao(UserDao userDao) {
this.userDao = userDao;
}
@Override
public void out() {
userDao.print();
System.out.println("Service层执行结束");
}
}
修改UserController类
package com.atguigu.spring6.controller;
import com.atguigu.spring6.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
@Controller
public class UserController {
private UserService userService;
@Autowired
public void setUserService(UserService userService) {
this.userService = userService;
}
public void out() {
userService.out();
System.out.println("Controller层执行结束。");
}
}
测试:成功调用
③场景三:构造方法注入
修改UserServiceImpl类
package com.atguigu.spring6.service.impl;
import com.atguigu.spring6.dao.UserDao;
import com.atguigu.spring6.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
@Service
public class UserServiceImpl implements UserService {
private UserDao userDao;
@Autowired
public UserServiceImpl(UserDao userDao) {
this.userDao = userDao;
}
@Override
public void out() {
userDao.print();
System.out.println("Service层执行结束");
}
}
修改UserController类
package com.atguigu.spring6.controller;
import com.atguigu.spring6.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
@Controller
public class UserController {
private UserService userService;
@Autowired
public UserController(UserService userService) {
this.userService = userService;
}
public void out() {
userService.out();
System.out.println("Controller层执行结束。");
}
}
测试:成功调用
④场景四:形参上注入
修改UserServiceImpl类
package com.atguigu.spring6.service.impl;
import com.atguigu.spring6.dao.UserDao;
import com.atguigu.spring6.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
@Service
public class UserServiceImpl implements UserService {
private UserDao userDao;
public UserServiceImpl(@Autowired UserDao userDao) {
this.userDao = userDao;
}
@Override
public void out() {
userDao.print();
System.out.println("Service层执行结束");
}
}
修改UserController类
package com.atguigu.spring6.controller;
import com.atguigu.spring6.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
@Controller
public class UserController {
private UserService userService;
public UserController(@Autowired UserService userService) {
this.userService = userService;
}
public void out() {
userService.out();
System.out.println("Controller层执行结束。");
}
}
测试:成功调用
⑤场景五:只有一个有参构造函数,注解可以省略
修改UserServiceImpl类
package com.atguigu.spring6.service.impl;
import com.atguigu.spring6.dao.UserDao;
import com.atguigu.spring6.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Service;
@Service
public class UserServiceImpl implements UserService {
@Autowired
private UserDao userDao;
public UserServiceImpl(UserDao userDao) {
this.userDao = userDao;
}
@Override
public void out() {
userDao.print();
System.out.println("Service层执行结束");
}
}
测试通过
当有参数的构造方法只有一个时,@Autowired注解可以省略。
说明:有多个构造方法时呢?大家可以测试(再添加一个无参构造函数),测试报错
⑥场景六:@Autowired注解和@Qualifier注解联合
添加dao层实现
package com.atguigu.spring6.dao.impl;
import com.atguigu.spring6.dao.UserDao;
import org.springframework.stereotype.Repository;
@Repository
public class UserDaoRedisImpl implements UserDao {
@Override
public void print() {
System.out.println("Redis Dao层执行结束");
}
}
测试:测试异常
错误信息中说:不能装配,UserDao这个Bean的数量等于2
怎么解决这个问题呢?当然要byName,根据名称进行装配了。
修改UserServiceImpl类
package com.atguigu.spring6.service.impl;
import com.atguigu.spring6.dao.UserDao;
import com.atguigu.spring6.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
@Service
public class UserServiceImpl implements UserService {
@Autowired
@Qualifier("userDaoImpl") // 指定bean的名字
private UserDao userDao;
@Override
public void out() {
userDao.print();
System.out.println("Service层执行结束");
}
}
总结
- @Autowired注解可以出现在:属性上、构造方法上、构造方法的参数上、setter方法上。
- 当带参数的构造方法只有一个,@Autowired注解可以省略。()
- @Autowired注解默认根据类型注入。如果要根据名称注入的话,需要配合@Qualifier注解一起使用。
分类:
SSM / Spring6
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