java.lang.IllegalStateException：在servlet中提交响应后无法转发

在我的项目中，我禁止用户每个页面只有他已经登录。 这就是我写下面代码的原因。 当我输入浏览器时，例如， http：// localhost：8080 / JSP1 / Students ，我来到login.jsp页面。 但在输入loginid和密码后，只显示空白页http：// localhost：8080 / JSP1 / Logged ，GlassFish表示存在exception

 if (userPath.equals("/Students")){ RequestDispatcher requestDispatcher = request.getRequestDispatcher("/Students.jsp"); requestDispatcher.forward(request, response); } java.lang.IllegalStateException: PWC1227: Cannot forward after response has been committed 

doGet和doPost的完整代码：

  @Override protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { HttpSession ses = request.getSession(); String login = (String)ses.getAttribute("login"); String password = (String)ses.getAttribute("password"); if ((login==null)|(password==null)){ RequestDispatcher requestDispatcher = request.getRequestDispatcher("/login.jsp"); requestDispatcher.forward(request, response); } //Now we think that we are successfully logged in String userPath = request.getServletPath(); // System.out.println(userPath); if (userPath.equals("/Login")){ RequestDispatcher requestDispatcher = request.getRequestDispatcher("/login.jsp"); requestDispatcher.forward(request, response); } if (userPath.equals("/Students")){ RequestDispatcher requestDispatcher = request.getRequestDispatcher("/Students.jsp"); requestDispatcher.forward(request, response); } if (userPath.equals("/Student")){ RequestDispatcher requestDispatcher = request.getRequestDispatcher("/Student.jspx"); requestDispatcher.forward(request, response); } if (userPath.equals("/StudentEdit")){ RequestDispatcher requestDispatcher = request.getRequestDispatcher("/StudentEdit.jsp"); requestDispatcher.forward(request, response); } } @Override protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // processRequest(request, response); PrintWriter out = response.getWriter(); String userPath = request.getServletPath(); System.out.println(userPath); if (request.getRequestURI().equals("/Logged")){ String Login = request.getParameter("login"); String Password = request.getParameter("password"); request.getSession().setAttribute("login", Login); request.getSession().setAttribute("password", Password); RequestDispatcher requestDispatcher = request.getRequestDispatcher("/Students.jsp"); requestDispatcher.forward(request, response); } if (userPath.equals("/addStudent")) { // System.out.println(request.getContextPath()); String Name = request.getParameter("name"); String Surname = request.getParameter("surname"); String Login = request.getParameter("login"); String Password = request.getParameter("password"); Student student = new Student(Name,Surname,Login,Password); if (student != null) { dao.insertStudent(student); } else { System.out.println("Not valid parameter!!!"); } RequestDispatcher requestDispatcher = request.getRequestDispatcher("/Students.jsp"); requestDispatcher.forward(request, response); } if (request.getRequestURI().equals("/Edit")) { System.out.println("We work with students!!!"); String delete = request.getParameter("Add_new_student"); if (delete != null){ RequestDispatcher requestDispatcher = request.getRequestDispatcher("/Student.jspx"); requestDispatcher.forward(request, response); } Enumeration parameters = request.getParameterNames(); while (parameters.hasMoreElements()) { String parameterName = (String) parameters.nextElement(); String parameterValue = request.getParameter(parameterName); String norder = parameterName.substring(parameterName.indexOf("_")+1); ArrayList curStudents = dao.getAllStudents(); int norderint = Integer.parseInt(norder); Student studentToWork = curStudents.get(norderint); String actionToDo = parameterName.substring(0, parameterName.indexOf("_")); if (actionToDo.equals("Edit")){ RequestDispatcher requestDispatcher = request.getRequestDispatcher("/StudentEdit.jsp"); ServletContext cont = request.getServletContext(); cont.setAttribute("studentToEdit", studentToWork); requestDispatcher.forward(request, response); } else { boolean attemp = dao.deleteStudent(studentToWork); if (attemp){ RequestDispatcher requestDispatcher = request.getRequestDispatcher("/Students.jsp"); requestDispatcher.forward(request, response); } else { out.println("Unsuccessfull attemp to delete a Student"); } } } } if (userPath.equals("/EditStudent")){ System.out.println("We work with StudentEdit!"); Student studentToEdit = (Student)request.getSession().getAttribute("studentToEdit"); String newName = request.getParameter("name"); String newSurname = request.getParameter("surname"); String newLogin = request.getParameter("login"); String newPassword = request.getParameter("password"); Student newStudent = new Student(newName, newSurname,newLogin,newPassword); boolean update = dao.updateStudent(studentToEdit, newStudent); if (update){ out.println("
You have successfully edited a Student=" + studentToEdit.toString() + " to Student="+ newStudent.toString()); } else { out.println("
Unsuccessful attempt to edit!
" ); } } } 

login.jsp很简单：

         
 
 
 
Login:
 
 
 
 
 
Password 
 
 >
 
 
 
 
 
 
 
  

我无法弄清楚发生了什么。

Answer 1

如果未提供登录和/或密码，您不会在转发后返回。 启动者之间的一个常见误解是， forward()方法神奇地终止了代码执行并以某种方式跳出了方法。 因此不是这样。 您必须从方法返回并自行停止执行代码的残余。

你需要添加一个return;

 if ((login==null)|(password==null)){ RequestDispatcher requestDispatcher = request.getRequestDispatcher("/login.jsp"); requestDispatcher.forward(request, response); return; } 

或者添加else

 if ((login==null)|(password==null)){ RequestDispatcher requestDispatcher = request.getRequestDispatcher("/login.jsp"); requestDispatcher.forward(request, response); } else { // Now we think that we are successfully logged in. // Yes, that above comment is now finally true. // Put your bunch of non-DRY if-else code here. } 

也可以看看：

• java.lang.IllegalStateException：提交响应后不能（转发| sendRedirect |创建会话）