Request processing failed; nested exception is java.lang.NullPointerException] with root cause

严重: Servlet.service() for servlet [SpringMVC] in context with path [/ssm] threw exception [Request processing failed; nested exception is java.lang.NullPointerException] with root cause

java.lang.NullPointerException

at weihang.service.impl.NovelDetailIServiceImpl.selectByNovelId(NovelDetailIServiceImpl.java:21)

at weihang.controller.UserController.novelDetail(UserController.java:98)

at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)

at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)

at java.lang.reflect.Method.invoke(Method.java:498)

at org.springframework.web.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(HandlerMethodInvoker.java:175)

at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:446)

at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:434)

at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:945)

at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:876)

at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:961)

at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:852)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:622)

at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:292)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)

at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)

at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)

at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:108)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)

at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:212)

at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)

at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)

at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:141)

at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)

at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:616)

at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)

at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:528)

at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1100)

at org.apache.coyote.AbstractProtocolAbstractConnectionHandler.process(AbstractProtocol.java:687)atorg.apache.tomcat.util.net.NioEndpointAbstractConnectionHandler.process(AbstractProtocol.java:687)atorg.apache.tomcat.util.net.NioEndpointSocketProcessor.doRun(NioEndpoint.java:1520)

at org.apache.tomcat.util.net.NioEndpointSocketProcessor.run(NioEndpoint.java:1476)atjava.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)atjava.util.concurrent.ThreadPoolExecutorSocketProcessor.run(NioEndpoint.java:1476)atjava.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)atjava.util.concurrent.ThreadPoolExecutorWorker.run(ThreadPoolExecutor.java:624)

at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)

at java.lang.Thread.run(Thread.java:748)

这个报错是因为在impl实现接口的时候,从mapper里面申明接口的时候没有加上@Resource注解,加上即可