Spring的注解@Qualifier
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:
public interface EmployeeService { public EmployeeDto getEmployeeById(Long id); }
同时有下述两个实现类 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(); } }
调用代码如下:
@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!
@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 } }
装载自:https://www.cnblogs.com/smileLuckBoy/p/5801678.html
@Autowired 注解 是根据类型自动注入,如果<bean>中有多个该类型的bean,自动注入的时候会报BeanCreationException异常。所以通常通过@Autowired和@Qualifier一起配合着注解。
举例:例如bean中配了多个数据源。
<bean class="org.springframework.jdbc.core.JdbcTemplate"> <qualifier value="dataSource1"/> <property name="dataSource" ref="dataSource1" /> </bean> <bean class="org.springframework.jdbc.core.JdbcTemplate"> <qualifier value="dataSource2"/> <property name="dataSource" ref="dataSource2" /> </bean>
在代码中用到的地方可以通过如下代码进行注解,这样防止冲突
@Autowired() @Qualifier("dataSource1") private JdbcTemplate jdbcTemplate;
@Autowired() @Qualifier("dataSource2") private JdbcTemplate jdbcTemplate;