【已解决】org.springframework.web.util.NestedServletException: Request processing failed; nested exceptio

exception

org.springframework.web.util.NestedServletException: Request processing failed; nested exception is java.lang.NullPointerException org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:982) org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:872) javax.servlet.http.HttpServlet.service(HttpServlet.java:648) org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846) javax.servlet.http.HttpServlet.service(HttpServlet.java:729) org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

root cause

java.lang.NullPointerException com.rgl.controller.UserController.login(UserController.java:48) sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) java.lang.reflect.Method.invoke(Method.java:498) org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:220) org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:134) org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:116) org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827) org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738) org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85) org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:963) org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:897) org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970) org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:872) javax.servlet.http.HttpServlet.service(HttpServlet.java:648) org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846) javax.servlet.http.HttpServlet.service(HttpServlet.java:729) org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) ＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝分割线＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝ 之所以出现这个Ｅｘｃｅｐｔｉｏｎ，是因为我用【User user =this.userService.....】这句话对user进行了初始化，但等号【＝】后面的句子执行失败，最后导致对象初始化失败。 解决方法：等号后面的句子有问题。经过检查，发现调用的方法在一个接口类中，但我并没有注入那个被调用的类，因此，只需要进行注入就好了。 　　　　在UserController中加上@Autowired就行了。源代码如下所示：  修正前： import javax.servlet.http.HttpServletRequest; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Controller; import org.springframework.ui.Model; import org.springframework.web.bind.annotation.RequestMapping; import com.rgl.domain.User; import com.rgl.service.IUserService; @Controller @RequestMapping("/user") public class UserController {     public IUserService userService;              @RequestMapping("/signIn.do")     public String login(HttpServletRequest httpServletRequest,Model model) throws Exception{         String username=httpServletRequest.getParameter("username");         String password=httpServletRequest.getParameter("password");         /*try{             User user=this.userService.selectByNamePassword(username, password);             model.addAttribute("user", user);             return "user/showUser";         }catch (Exception e) {             // TODO: handle exception             return "fail";         }*/         User user=this.userService.selectByNamePassword(username, password);         System.out.print(user.getUserid()+":"+user.getName());         model.addAttribute("user", user);         return "user/showUser";     } } 修正后： import javax.servlet.http.HttpServletRequest; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Controller; import org.springframework.ui.Model; import org.springframework.web.bind.annotation.RequestMapping; import com.rgl.domain.User; import com.rgl.service.IUserService; @Controller @RequestMapping("/user") public class UserController {     @Autowired     public IUserService userService;          @RequestMapping("/signIn.do")     public String login(HttpServletRequest httpServletRequest,Model model) throws Exception{         String username=httpServletRequest.getParameter("username");         String password=httpServletRequest.getParameter("password");         /*try{             User user=this.userService.selectByNamePassword(username, password);             model.addAttribute("user", user);             return "user/showUser";         }catch (Exception e) {             // TODO: handle exception             return "fail";         }*/         User user=this.userService.selectByNamePassword(username, password);         System.out.print(user.getUserid()+":"+user.getName());         model.addAttribute("user", user);         return "user/showUser";     } }