HTTP Status 500 -type Exception reportmessage description The server encountered an internal error that prevented it from fulfilling this request.exception java.lang.NullPointerException com.yudn.action.AdminAction.validate(AdminAction.java:44) com.opensymphony.xwork2.validator.ValidationInterceptor.doBeforeInvocation(ValidationInterceptor.java:251) com.opensymphony.xwork2.validator.ValidationInterceptor.doIntercept(ValidationInterceptor.java:263) org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor.doIntercept(AnnotationValidationInterceptor.java:68) com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98) com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:249) com.opensymphony.xwork2.interceptor.ConversionErrorInterceptor.intercept(ConversionErrorInterceptor.java:138) com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:249) com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:236) com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98) com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:249) com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:236) com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98) com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:249) com.opensymphony.xwork2.interceptor.StaticParametersInterceptor.intercept(StaticParametersInterceptor.java:190) com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:249) org.apache.struts2.interceptor.MultiselectInterceptor.intercept(MultiselectInterceptor.java:75) com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:249) org.apache.struts2.interceptor.CheckboxInterceptor.intercept(CheckboxInterceptor.java:90) com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:249) org.apache.struts2.interceptor.FileUploadInterceptor.intercept(FileUploadInterceptor.java:243) com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:249) com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor.intercept(ModelDrivenInterceptor.java:100) com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:249) com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor.intercept(ScopedModelDrivenInterceptor.java:141) com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:249) com.opensymphony.xwork2.interceptor.ChainingInterceptor.intercept(ChainingInterceptor.java:145) com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:249) com.opensymphony.xwork2.interceptor.PrepareInterceptor.doIntercept(PrepareInterceptor.java:171) com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98) com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:249) com.opensymphony.xwork2.interceptor.I18nInterceptor.intercept(I18nInterceptor.java:176) com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:249) org.apache.struts2.interceptor.ServletConfigInterceptor.intercept(ServletConfigInterceptor.java:164) com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:249) com.opensymphony.xwork2.interceptor.AliasInterceptor.intercept(AliasInterceptor.java:192) com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:249) com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept(ExceptionMappingInterceptor.java:187) com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:249) org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:54) org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:511) org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:77) org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:91)note The full stack trace of the root cause is available in the Apache Tomcat/7.0.68 logs.package com.yudn.action;import com.opensymphony.xwork2.ModelDriven;import com.yudn.entity.Users;import com.yudn.service.UsersDAO;import com.yudn.service.impl.UsersDAOImpl;public class UsersAction extends SuperAction implements ModelDriven<Users>{?? ??? ?/**?? ? * ?? ? */?? ?private static final long serialVersionUID = 1L;?? ?private Users users = new Users();?? ??? ?//用戶登錄動作處理獲取表單驗證?? ?public String login()?? ?{?? ??? ?UsersDAO uDao = new UsersDAOImpl();?? ??? ?if(uDao.usersLogin(users)){?? ??? ??? ?if ("admin".equals(users.getUsername().trim())) {?? ??? ??? ??? ? this.addFieldError("usernameError", "用戶名不能為空");?? ??? ??? ?}?? ??? ??? ?if ("admin".equals(users.getPassword().length() < 6)) {?? ??? ??? ??? ? this.addFieldError("password","密碼長度不能小于6位");?? ??? ??? ?}?? ??? ??? ?super.validate();?? ??? ??? ?// 在session中保存登錄成功的用戶名。?? ??? ??? ?session.setAttribute("loginUserName", users.getUsername());?? ??? ??? ?return SUCCESS;?? ??? ?}?? ??? ?else{?? ??? ??? ?return? ERROR;?? ??? ?}?? ?}?? ?public void validate(){?? ??? ?if ("admin".equals(users.getUsername().trim())) {?? ??? ??? ?// this.addFieldError("usernameError", "用戶名不能為空");?? ??? ?}?? ??? ?if ("admin".equals(users.getPassword().length() < 6)) {?? ??? ??? ?// this.addFieldError("password","密碼長度不能小于6位");?? ??? ?}?? ??? ?super.validate();?? ?}?? ?//用戶注冊動作處理獲取表單?? ?public String regist(){?? ??? ?Users u=new Users();?? ??? ?u.setUsername(request.getParameter("username"));?? ??? ?u.setPassword(request.getParameter("password"));?? ??? ?UsersDAO uDao = new UsersDAOImpl();?? ??? ?uDao.usersRegist(u);?? ??? ?return SUCCESS;?? ??? ?}?? ?public Users getModel() {?? ??? ?return this.users;?? ?}}