Spring的注解@Qualifier小结
近期在捯饬spring的注解，现将遇到的问题记录下来，以供遇到同样问题的童鞋解决~
先说明下场景，代码如下
有如下接口：
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public interface EmployeeService { public EmployeeDto getEmployeeById(Long id); } |
同时有下述两个实现类 EmployeeServiceImpl和EmployeeServiceImpl1：
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@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(); } } |
调用代码如下：
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@Controller @RequestMapping ( "/emplayee.do" ) public class EmployeeInfoControl { @Autowired EmployeeService employeeService; @RequestMapping (params = "method=showEmplayeeInfo" ) public void showEmplayeeInfo(HttpServletRequest request, HttpServletResponse response, EmployeeDto dto) { #略 } } |
在启动tomcat时报如下错误：
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]
其实报错信息已经说得很明确了,在autoware时，由于有两个类实现了EmployeeService接口，所以Spring不知道应该绑定哪个实现类，所以抛出了如上错误。
这个时候就要用到@Qualifier注解了，qualifier的意思是合格者，通过这个标示，表明了哪个实现类才是我们所需要的，我们修改调用代码，添加@Qualifier注解，需要注意的是@Qualifier的参数名称必须为我们之前定义@Service注解的名称之一！
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@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 } } |
问题解决！
@qualifier注解
@Qualifier限定哪个bean应该被自动注入。当Spring无法判断出哪个bean应该被注入时，@Qualifier注解有助于消除歧义bean的自动注入。
参见下面的例子
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public class Staff{ @Autowired private user user; } |
我们有两个bean定义为Person类的实例。
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< 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 知道哪个bean应该自动注入？不。当您运行上面的例子时，抛出如下异常:
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]
要解决以上问题，你需要使用@Quanlifier注解告诉Spring 哪个bean应该被autowired的。
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public class Staff { @Autowired @Qualifier ( "user1" ) private User user; } |
以上为个人经验，希望能给大家一个参考，也希望大家多多支持。
原文链接：https://HdhCmsTestcnblogs测试数据/smileLuckBoy/p/5801678.html
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