【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.NullPointerExceptionorg.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.NullPointerExceptioncom.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";    }}