java - Spring Data JPA 自定义 findBy 不起作用

Question

这个问题已经有答案了:

What is a NullPointerException, and how do I fix it? (12 个回答)

Why is my Spring @Autowired field null? (21 个回答)

已关闭 3 年前。

我调用该方法的服务

public String deleteEmployeeByID(int id){
    if(employeeRepository.existsById(id))
    {
        List<Task> tasks;
        tasks=(List<Task>)taskRepository.findByEmployee_EmployeeId(id);

出现此错误

2020-02-13 12:15:32.707 INFO 20380 --- [nio-8080-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring DispatcherServlet 'dispatcherServlet' 2020-02-13 12:15:32.707 INFO 20380 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet : Initializing Servlet 'dispatcherServlet' 2020-02-13 12:15:32.741 INFO 20380 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet : Completed initialization in 33 ms 2020-02-13 12:15:33.628 ERROR 20380 --- [nio-8080-exec-1] o.a.c.c.C.[.[.[/].[dispatcherServlet] : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is java.lang.NullPointerException] with root cause

java.lang.NullPointerException: null at com.example.presentation.EmployeeService.deleteEmployeeByID(EmployeeService.java:101) ~[classes/:na] at com.example.presentation.EmployeeController.deleteEmployeeByID(EmployeeController.java:60) ~[classes/:na] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_242] at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_242] at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_242] at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_242] at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:190) ~[spring-web-5.2.3.RELEASE.jar:5.2.3.RELEASE] at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138) ~[spring-web-5.2.3.RELEASE.jar:5.2.3.RELEASE] at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:106) ~[spring-webmvc-5.2.3.RELEASE.jar:5.2.3.RELEASE] at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:888) ~[spring-webmvc-5.2.3.RELEASE.jar:5.2.3.RELEASE] at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:793) ~[spring-webmvc-5.2.3.RELEASE.jar:5.2.3.RELEASE] at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.2.3.RELEASE.jar:5.2.3.RELEASE] at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1040) ~[spring-webmvc-5.2.3.RELEASE.jar:5.2.3.RELEASE] at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:943) ~[spring-webmvc-5.2.3.RELEASE.jar:5.2.3.RELEASE] at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) ~[spring-webmvc-5.2.3.RELEASE.jar:5.2.3.RELEASE] at org.springframework.web.servlet.FrameworkServlet.doDelete(FrameworkServlet.java:931) ~[spring-webmvc-5.2.3.RELEASE.jar:5.2.3.RELEASE] at javax.servlet.http.HttpServlet.service(HttpServlet.java:666) ~[tomcat-embed-core-9.0.30.jar:9.0.30] at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) ~[spring-webmvc-5.2.3.RELEASE.jar:5.2.3.RELEASE] at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) ~[tomcat-embed-core-9.0.30.jar:9.0.30] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-9.0.30.jar:9.0.30] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.30.jar:9.0.30] at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.30.jar:9.0.30] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.30.jar:9.0.30] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.30.jar:9.0.30] at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.2.3.RELEASE.jar:5.2.3.RELEASE] at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.3.RELEASE.jar:5.2.3.RELEASE] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.30.jar:9.0.30] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.30.jar:9.0.30] at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.2.3.RELEASE.jar:5.2.3.RELEASE] at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.3.RELEASE.jar:5.2.3.RELEASE] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.30.jar:9.0.30] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.30.jar:9.0.30] at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.2.3.RELEASE.jar:5.2.3.RELEASE] at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.3.RELEASE.jar:5.2.3.RELEASE] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.30.jar:9.0.30] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.30.jar:9.0.30] at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202) ~[tomcat-embed-core-9.0.30.jar:9.0.30] at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) [tomcat-embed-core-9.0.30.jar:9.0.30] at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541) [tomcat-embed-core-9.0.30.jar:9.0.30] at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) [tomcat-embed-core-9.0.30.jar:9.0.30] at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) [tomcat-embed-core-9.0.30.jar:9.0.30] at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) [tomcat-embed-core-9.0.30.jar:9.0.30] at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) [tomcat-embed-core-9.0.30.jar:9.0.30] at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:367) [tomcat-embed-core-9.0.30.jar:9.0.30] at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) [tomcat-embed-core-9.0.30.jar:9.0.30] at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:860) [tomcat-embed-core-9.0.30.jar:9.0.30] at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1598) [tomcat-embed-core-9.0.30.jar:9.0.30] at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-9.0.30.jar:9.0.30] at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_242] at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_242] at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-9.0.30.jar:9.0.30] at java.lang.Thread.run(Thread.java:748) [na:1.8.0_242]

此存储库

public interface TaskRepository extends JpaRepository<Task, Integer>{
        public  List<Task> findByEmployee_EmployeeId(int id);

Answer 1

如果您发布了相关代码，而不仅仅是您认为有疑问的区域，那就太好了。尝试 @Autowired 您正在使用的服务，并将您的方法替换为:

findByEmployeeId(Integer id);