Spring IOC @Autowired、@Qualifier 、@Primary 注解说明

旧城等待， 2024-04-19 11:06 150阅读 0赞

## ##

### 1.@Autowired ###

依赖注入的注解

### 2.@Primary ###

官网文档的解释：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3MzA2MDQx_size_16_color_FFFFFF_t_70][]

**对应的翻译，来自搜狗（凑合可以看懂）**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3MzA2MDQx_size_16_color_FFFFFF_t_70 1][]

**代码示例：**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3MzA2MDQx_size_16_color_FFFFFF_t_70 2][]

**个人理解：在通过javaconfig进行声明bean时，加上该注解后，那个bean时首要选择。**

### 3.@Qualifier ###

**标识符，**因为@Autowired默认时按照bean的类型注入（bytype）,当别注入的接口有多个实现时，如果不加以区分，程序将会出现异常，使用@Qualifier进行标识来解决这个问题

示例：

**声明的bean**

package com.lhj.service;
    
    public interface UserService {
    
        void eat();
    }
    
    
    -------------------------------------------------------------
    
    package com.lhj.service.impl;
    
    import com.lhj.service.UserService;
    import org.springframework.beans.factory.annotation.Qualifier;
    import org.springframework.stereotype.Service;
    
    @Service
    public class UserServiceImpl implements UserService {
        public void eat() {
            System.out.println("UserServiceImpl");
        }
    }
    
    -------------------------------------------------------------
    package com.lhj.service.impl;
    
    import com.lhj.service.UserService;
    import org.springframework.stereotype.Service;
    
    @Service
    public class UserServiceExtendImpl implements UserService {
        public void eat() {
            System.out.println("UserServiceExtendImpl");
        }
    }

**注入并使用bean**

package com.lhj.service;
    
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.beans.factory.annotation.Qualifier;
    import org.springframework.stereotype.Service;
    
    @Service
    public class UserDemoService {
    
        @Autowired
        @Qualifier("userServiceExtendImpl")
        private UserService userService;
    }

**添加@Qualifier来区分这里的UserServiceImpl 和UserServiceExtendImpl 两个bean ,@Qualifier括号内的值可以是bean的id或name值**

**官网文档说明：**

![20190917165301803.png][]

**搜狗翻译**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3MzA2MDQx_size_16_color_FFFFFF_t_70 3][]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3MzA2MDQx_size_16_color_FFFFFF_t_70]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/18/68ff915afa7d46399d1f20a4b6e10a93.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3MzA2MDQx_size_16_color_FFFFFF_t_70 1]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/18/7d2de9b937454468bbd59d3e4fc523d0.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3MzA2MDQx_size_16_color_FFFFFF_t_70 2]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/18/feb5c09a584141d1aa7d8c6fb265d732.png
[20190917165301803.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/18/d6ecb093f49f48a1bbab9a93b63c7f73.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3MzA2MDQx_size_16_color_FFFFFF_t_70 3]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/18/35bc193c0b9a4fd28d4ff8ee5a6df0fb.png