spring boot + jpa访问数据库时报这个错,调用CrudRepository保存的时候

java.lang.NullPointerException: null
at com.yd.cn.controller.SampleController.hello(SampleController.java:26) ~[classes/:na]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_102]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_102]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_102]
at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_102]
at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:221) ~[spring-web-4.2.5.RELEASE.jar:4.2.5.RELEASE]
at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:136) ~[spring-web-4.2.5.RELEASE.jar:4.2.5.RELEASE]
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:110) ~[spring-webmvc-4.2.5.RELEASE.jar:4.2.5.RELEASE]
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:817) ~[spring-webmvc-4.2.5.RELEASE.jar:4.2.5.RELEASE]
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:731) ~[spring-webmvc-4.2.5.RELEASE.jar:4.2.5.RELEASE]
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85) ~[spring-webmvc-4.2.5.RELEASE.jar:4.2.5.RELEASE]
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:959) ~[spring-webmvc-4.2.5.RELEASE.jar:4.2.5.RELEASE]
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893) ~[spring-webmvc-4.2.5.RELEASE.jar:4.2.5.RELEASE]
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:968) ~[spring-webmvc-4.2.5.RELEASE.jar:4.2.5.RELEASE]
at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:859) ~[spring-webmvc-4.2.5.RELEASE.jar:4.2.5.RELEASE]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:622) ~[servlet-api.jar:na]
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:844) ~[spring-webmvc-4.2.5.RELEASE.jar:4.2.5.RELEASE]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729) ~[servlet-api.jar:na]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:230) ~[catalina.jar:8.5.11]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) ~[catalina.jar:8.5.11]
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) ~[tomcat-websocket.jar:8.5.11]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) ~[catalina.jar:8.5.11]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) ~[catalina.jar:8.5.11]
at org.springframework.boot.actuate.autoconfigure.EndpointWebMvcAutoConfiguration$ApplicationContextHeaderFilter.doFilterInternal(EndpointWebMvcAutoConfiguration.java:237) ~[spring-boot-actuator-1.3.3.RELEASE.jar:1.3.3.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.2.5.RELEASE.jar:4.2.5.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) ~[catalina.jar:8.5.11]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) ~[catalina.jar:8.5.11]
at org.springframework.boot.actuate.trace.WebRequestTraceFilter.doFilterInternal(WebRequestTraceFilter.java:112) ~[spring-boot-actuator-1.3.3.RELEASE.jar:1.3.3.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.2.5.RELEASE.jar:4.2.5.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) ~[catalina.jar:8.5.11]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) ~[catalina.jar:8.5.11]
at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) ~[spring-web-4.2.5.RELEASE.jar:4.2.5.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.2.5.RELEASE.jar:4.2.5.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) ~[catalina.jar:8.5.11]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) ~[catalina.jar:8.5.11]
at org.springframework.web.filter.HttpPutFormContentFilter.doFilterInternal(HttpPutFormContentFilter.java:87) ~[spring-web-4.2.5.RELEASE.jar:4.2.5.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.2.5.RELEASE.jar:4.2.5.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) ~[catalina.jar:8.5.11]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) ~[catalina.jar:8.5.11]
at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:77) ~[spring-web-4.2.5.RELEASE.jar:4.2.5.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.2.5.RELEASE.jar:4.2.5.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) ~[catalina.jar:8.5.11]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) ~[catalina.jar:8.5.11]
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:121) ~[spring-web-4.2.5.RELEASE.jar:4.2.5.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.2.5.RELEASE.jar:4.2.5.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) ~[catalina.jar:8.5.11]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) ~[catalina.jar:8.5.11]
at org.springframework.boot.actuate.autoconfigure.MetricsFilter.doFilterInternal(MetricsFilter.java:103) ~[spring-boot-actuator-1.3.3.RELEASE.jar:1.3.3.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.2.5.RELEASE.jar:4.2.5.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) ~[catalina.jar:8.5.11]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) ~[catalina.jar:8.5.11]
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198) ~[catalina.jar:8.5.11]
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) [catalina.jar:8.5.11]
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:474) [catalina.jar:8.5.11]
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140) [catalina.jar:8.5.11]
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79) [catalina.jar:8.5.11]
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87) [catalina.jar:8.5.11]
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:349) [catalina.jar:8.5.11]
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:783) [tomcat-coyote.jar:8.5.11]
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) [tomcat-coyote.jar:8.5.11]
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:798) [tomcat-coyote.jar:8.5.11]
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1434) [tomcat-coyote.jar:8.5.11]
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-coyote.jar:8.5.11]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [na:1.8.0_102]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_102]
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-util.jar:8.5.11]
at java.lang.Thread.run(Thread.java:745) [na:1.8.0_102]

错误就是在第一行,,没有指向,没有你的代码,具体不知道是什么错误.你可以去百度搜一下第一行,结合你自己的代码,可以找出答案的

ava.lang.NullPointerException: null
at com.yd.cn.controller.SampleController.hello(SampleController.java:26) ~[classes/:na]

你这里空指针，是不是有对象没有实例化

SampleController.java:26

这个类的地26行,自己打断点很快就出来了