nested exception is java.lang.NullPointerException

i am new to spring and hibernate . its a basic crud app. add and delete works .
when i edit and hit submit i get this exception.

HTTP Status 500 - Request processing failed; nested exception is java.lang.NullPointerException

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type Exception report

message Request processing failed; nested exception is java.lang.NullPointerException

description The server encountered an internal error that prevented it from fulfilling this request.

exception

org.springframework.web.util.NestedServletException: Request processing failed; nested exception is java.lang.NullPointerException
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:659)
org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:563)
javax.servlet.http.HttpServlet.service(HttpServlet.java:646)
javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)


root cause

java.lang.NullPointerException
com.mayur.dao.ProductDAOImpl.updateProduct(ProductDAOImpl.java:36)
com.mayur.service.ProductServiceImpl.updateProduct(ProductServiceImpl.java:34)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
java.lang.reflect.Method.invoke(Method.java:606)
org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:307)
org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:183)
org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:150)
org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:108)
org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:202)
com.sun.proxy.$Proxy19.updateProduct(Unknown Source)
com.mayur.Controller.ProductController.editProduct(ProductController.java:75)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
java.lang.reflect.Method.invoke(Method.java:606)
org.springframework.web.bind.annotation.support.HandlerMethodInvoker.doInvokeMethod(HandlerMethodInvoker.java:710)
org.springframework.web.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(HandlerMethodInvoker.java:167)
org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:414)
org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:402)
org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:771)
org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:716)
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:647)
org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:563)
javax.servlet.http.HttpServlet.service(HttpServlet.java:646)
javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

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following are other files

Product.java


ProductDAOImpl.java



ProductServiceImpl.java



ProductController.java



please help me.

The most important thing in the error is: com.mayur.dao.ProductDAOImpl.updateProduct(ProductDAOImpl.java:36)

What is on line 36 of that class? (In the posted version it is blank so it looks like different line #s are used.)

these are the 3 line the errors are pointing to
ProductDAOImpl.java
Product productToUpdate = getProductById(product.getId());
ProductServiceImpl.java
productDAO.updateProduct(product);
ProductController.java
productService.updateProduct(product);

How can there be 3 lines on line 36?. Look exactly at line 36


NullPointer Exception usually happens when you try to call a method on a null reference. You need to look at line 36 and see what references are being used in line 36. One of them has got to be Null

i forgot to set product id; solved it by adding product.setId(id) in controller.
thanks for your help