@Autowired 和 @Resource 的区别

🏷️ MyBatis Spring Boot

1. @Resource 默认是 按照名称 来装配注入的；

   <bean id="daoConfigDev" class="liujiajia.me.learning.mybatis.DaoConfig">
       <property name="username" value="jiajia" />
       <property name="password" value="jiajiaspassword"/>
   </bean>
   <bean id="daoConfigRelease" class="liujiajia.me.learning.mybatis.DaoConfig">
       <property name="username" value="admin" />
       <property name="password" value="adminspassword"/>
   </bean>

   @Resource
   DaoConfig daoConfigDev;
   
   @Resource
   DaoConfig daoConfigRelease;

   名称可以通过 name 属性进行指定，如果没有指定 name 属性，当注解写在字段上时，默认取 字段名 ，按照名称查找，如果注解写在 setter 方法上默认取 属性名 进行装配；

   import org.springframework.stereotype.Component;
   
   import javax.annotation.Resource;
   
   /**
   * Created by liujiajia on 2019/1/24.
   */
   @Component
   public class Configs {
       // 会优先使用 name 属性指定的名称来装配
       @Resource(name = "daoConfigRelease")
       private DaoConfig daoConfig;
       @Resource
       private DaoConfig daoConfigDev;
       @Resource
       private DaoConfig daoConfigRelease;
   
       // getter setter ...
   }

   @Resource(name = "daoConfigRelease")
   public void setDaoConfig(DaoConfig daoConfig) {
       this.daoConfig = daoConfig;
   }
   @Resource
   public void setDaoConfigDev(DaoConfig daoConfigDev) {
       this.daoConfigDev = daoConfigDev;
   }
   @Resource
   public void setDaoConfigRelease(DaoConfig daoConfigRelease) {
       this.daoConfigRelease = daoConfigRelease;
   }

   只有当找不到与名称匹配的 bean 才会按照类型来装配注入；

   如果有多个同类型的 bean 则启动时会发生 NoUniqueBeanDefinitionException 异常：

   org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'configController': Injection of resource dependencies failed; nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'liujiajia.me.learning.mybatis.DaoConfig' available: expected single matching bean but found 2: daoConfigDev,daoConfigRelease

2. @Autowired 默认是 按照类型 装配注入的；

   @Autowired
   private DaoConfig daoConfig;

   如果想按照名称来装配注入，则需要结合 @Qualifier 一起使用；

   import org.springframework.beans.factory.annotation.Autowired;
   import org.springframework.beans.factory.annotation.Qualifier;
   import org.springframework.stereotype.Component;
   
   import javax.annotation.Resource;
   
   /**
   * Created by liujiajia on 2019/1/24.
   */
   @Component
   public class Configs {
       // 会优先使用 name 属性指定的名称来装配
       @Autowired
       @Qualifier("daoConfigRelease")
       private DaoConfig daoConfig;
       @Autowired
       @Qualifier("daoConfigDev")
       private DaoConfig daoConfigDev;
       @Autowired
       @Qualifier("daoConfigRelease")
       private DaoConfig daoConfigRelease;
   
       public DaoConfig getDaoConfig() {
           return daoConfig;
       }
   
       // getter setter ...
   }

   否则启动时会报错。

   Field daoConfig in liujiajia.me.learning.mybatis.Configs required a single bean, but 2 were found:
   - daoConfigDev: defined in class path resource [applicationContext.xml]
   - daoConfigRelease: defined in class path resource [applicationContext.xml]

3. @Resource 注解是由 JDK 提供，而 @Autowired 是由 Spring 提供；

4. @Resource 和 @Autowired 都可以书写标注在字段或者该字段的 setter 方法之上；

   @Autowired
   private DaoConfig daoConfig;
   
   @Resource
   private DaoConfig daoConfig;

   @Autowired
   public void setDaoConfig(DaoConfig daoConfig) {
       this.daoConfig = daoConfig;
   }
   
   @Resource
   public void setDaoConfig(DaoConfig daoConfig) {
       this.daoConfig = daoConfig;
   }

详细的解释可以参考 @Autowired 和@Resource 的区别是什么？、@Resource 和@Autowire 的区别