Spring的注解@Qualifier小結(jié)

近期在捯飭spring的注解，現(xiàn)將遇到的問(wèn)題記錄下來(lái)，以供遇到同樣問(wèn)題的童鞋解決~

先說(shuō)明下場(chǎng)景，代碼如下

有如下接口：

public interface EmployeeService {
    public EmployeeDto getEmployeeById(Long id);
}

同時(shí)有下述兩個(gè)實(shí)現(xiàn)類(lèi) EmployeeServiceImpl和EmployeeServiceImpl1：

@Service("service")
public class EmployeeServiceImpl implements EmployeeService {
    public EmployeeDto getEmployeeById(Long id) {
        return new EmployeeDto();
    }
}
@Service("service1")
public class EmployeeServiceImpl1 implements EmployeeService {
    public EmployeeDto getEmployeeById(Long id) {
        return new EmployeeDto();
    }
}

調(diào)用代碼如下：

@Controller
@RequestMapping("/emplayee.do")
public class EmployeeInfoControl {    
    @Autowired
    EmployeeService employeeService;     
    @RequestMapping(params = "method=showEmplayeeInfo")
    public void showEmplayeeInfo(HttpServletRequest request, HttpServletResponse response, EmployeeDto dto) {
        #略
    }
}

在啟動(dòng)tomcat時(shí)報(bào)如下錯(cuò)誤：

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'employeeInfoControl': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: com.test.service.EmployeeService com.test.controller.EmployeeInfoControl.employeeService; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No unique bean of type [com.test.service.EmployeeService] is defined: expected single matching bean but found 2: [service1, service2]

其實(shí)報(bào)錯(cuò)信息已經(jīng)說(shuō)得很明確了,在autoware時(shí)，由于有兩個(gè)類(lèi)實(shí)現(xiàn)了EmployeeService接口，所以Spring不知道應(yīng)該綁定哪個(gè)實(shí)現(xiàn)類(lèi)，所以拋出了如上錯(cuò)誤。

這個(gè)時(shí)候就要用到@Qualifier注解了，qualifier的意思是合格者，通過(guò)這個(gè)標(biāo)示，表明了哪個(gè)實(shí)現(xiàn)類(lèi)才是我們所需要的，我們修改調(diào)用代碼，添加@Qualifier注解，需要注意的是@Qualifier的參數(shù)名稱(chēng)必須為我們之前定義@Service注解的名稱(chēng)之一！

@Controller
@RequestMapping("/emplayee.do")
public class EmployeeInfoControl {    
    @Autowired
    @Qualifier("service")
    EmployeeService employeeService;    
    @RequestMapping(params = "method=showEmplayeeInfo")
    public void showEmplayeeInfo(HttpServletRequest request, HttpServletResponse response, EmployeeDto dto) {
        #略
    }
}

問(wèn)題解決！

@qualifier注解

@Qualifier限定哪個(gè)bean應(yīng)該被自動(dòng)注入。當(dāng)Spring無(wú)法判斷出哪個(gè)bean應(yīng)該被注入時(shí)，@Qualifier注解有助于消除歧義bean的自動(dòng)注入。

參見(jiàn)下面的例子

public class Staff{    
    @Autowired    
    private user user;
}

我們有兩個(gè)bean定義為Person類(lèi)的實(shí)例。

<beanid="staff"class="com.test.Staff"/> 
<beanid="user1"class="com.test.User">
<property name="name"value="zhangsan"/></bean> 
<beanid="user2"class="com.test.User">
<property name="name"value="lisi"/></bean>

Spring 知道哪個(gè)bean應(yīng)該自動(dòng)注入？不。當(dāng)您運(yùn)行上面的例子時(shí)，拋出如下異常:

Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No unique bean of type [com.test.User] is defined: expected single matching bean but found2: [user1, user2]

要解決以上問(wèn)題，你需要使用@Quanlifier注解告訴Spring 哪個(gè)bean應(yīng)該被autowired的。

public class Staff
{
    @Autowired
    @Qualifier("user1")
    private User user;
}

以上為個(gè)人經(jīng)驗(yàn)，希望能給大家一個(gè)參考，也希望大家多多支持腳本之家。

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