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前言

【第8章】全注解开发介绍了全注解开发,有使用到@Autowired注解,关于它为什么要单独开一章呢,因为它太重要了,还经常拿来和@Resource做对比。

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一、@Autowired注入

本章内容基于前面章节基础,基于不重复造轮子理论,只提供样例代码

@Autowired根据对象的类型去容器中查找:

• 未找到,会抛出异常
• 找到一个,完成注入
• 存在多个,注入失败,抛出异常

1. 属性注入

package org.example.autowired.controller;

import org.example.autowired.service.UserService;
import org.springframework.stereotype.Controller;

/**
 * Create by zjg on 2024/4/5
 */
@Controller
public class UserController {
    //属性注入
    @Autowired
    UserService userService;
    public void addUser(){
        System.out.println("执行...UserController");
        userService.addUserService();
    }
}

2. 构造方法注入

package org.example.autowired.controller;

import org.example.autowired.service.UserService;
import org.springframework.stereotype.Controller;

/**
 * Create by zjg on 2024/4/5
 */
@Controller
public class UserController {
	//构造方法注入
    UserService userService;
    @Autowired
    public UserController(UserService userService) {
        this.userService = userService;
    }
    public void addUser(){
        System.out.println("执行...UserController");
        userService.addUserService();
    }
}

3. set方法注入

package org.example.autowired.controller;

import org.example.autowired.service.UserService;
import org.springframework.stereotype.Controller;

/**
 * Create by zjg on 2024/4/5
 */
@Controller
public class UserController {
	//set方法注入
    UserService userService;
    @Autowired
    public void setUserService(UserService userService) {
        this.userService = userService;
    }
    public void addUser(){
        System.out.println("执行...UserController");
        userService.addUserService();
    }
}

4. 形参注入

package org.example.autowired.controller;

import org.example.autowired.service.UserService;
import org.springframework.stereotype.Controller;

/**
 * Create by zjg on 2024/4/5
 */
@Controller
public class UserController {
	//形参注入
    UserService userService;
    public UserController(@Autowired(required = false) UserService userService) {
        this.userService = userService;
    }
    public void addUser(){
        System.out.println("执行...UserController");
        userService.addUserService();
    }
}

5. byName注入

5.1 新增实现类

UserService 是一个接口,有UserServiceImpl和AdminServiceImpl 两个实现类

package org.example.autowired.service.impl;

import org.example.autowired.dao.UserDao;
import org.example.autowired.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

/**
 * Create by zjg on 2024/4/5
 */
@Service
public class AdminServiceImpl implements UserService {
    @Autowired
    UserDao userDao;

    @Override
    public void addUserService() {
        System.out.println("执行...AdminServiceImpl");
        userDao.addUserDao();
    }
}

5.2 注入

package org.example.autowired.controller;

import org.example.autowired.service.UserService;
import org.springframework.stereotype.Controller;

/**
 * Create by zjg on 2024/4/5
 */
@Controller
public class UserController {
	//byName注入
    @Autowired
    @Qualifier(value = "adminServiceImpl")
    UserService userService;
    public void addUser(){
        System.out.println("执行...UserController");
        userService.addUserService();
    }
}

二、@Resource

自从oracle收购了sun公司,搞出了一堆幺蛾子,java跟长了腿似的,版本蹭蹭往上涨,指不定后面还有收费

@Resource注解在JDK1.8中是自带的,JDK17中已经不再提供了,需要我们单独去下载,没办法整呗

1.引入库

<!-- https://mvnrepository.com/artifact/jakarta.annotation/jakarta.annotation-api -->
<dependency>
    <groupId>jakarta.annotation</groupId>
    <artifactId>jakarta.annotation-api</artifactId>
    <version>2.1.1</version>
</dependency>

2.使用

2.1 根据注解的name值注入

import jakarta.annotation.Resource;
import org.example.autowired.service.UserService;
import org.springframework.stereotype.Controller;

@Controller
public class UserController {
    @Resource(name="userServiceImpl")
    UserService userService;
    public void addUser(){
        System.out.println("执行...UserController");
        userService.addUserService();
    }
}

2.2 根据对象变量名注入

import jakarta.annotation.Resource;
import org.example.autowired.service.UserService;
import org.springframework.stereotype.Controller;

@Controller
public class UserController {
    @Resource
    UserService userServiceImpl;
    public void addUser(){
        System.out.println("执行...UserController");
        userServiceImpl.addUserService();
    }
}

2.3 根据对象类型注入

根据类型注入,需要保证只有一个实现类被匹配到,否则会抛出异常

import jakarta.annotation.Resource;
import org.example.autowired.service.UserService;
import org.springframework.stereotype.Controller;

@Controller
public class UserController {
   @Resource
    UserService userService;
    public void addUser(){
        System.out.println("执行...UserController");
        userService.addUserService();
    }
}

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总结

回到顶部
官方网站
官方文档
视频学习

个人感觉@Resource的匹配机制要更灵活一些,两者除了使用方式和匹配机制不同,基本上都能满足业务需要,具体使用哪个看项目而定吧,项目中大量使用哪个咱们就用哪个,如果是新项目需要使用到spring框架那就用@Autowired,毕竟是自家产品兼容性可能更好一些,其他情况完全可以用@Resource。