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java.lang.IllegalStateException: Cannot (forward | sendRedirect | create session) after response has been committed8个
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,只显示空白页面 http://localhost:8080/JSP1/Logged,而GlassFish表示存在异常
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,只显示空白页面 http://localhost:8080/JSP1/Logged,而GlassFish表示存在异常
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
完整的doGet和doPost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,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<Student> 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("<p>You have successfully edited a Student=" + studentToEdit.toString() + " to Student="+ newStudent.toString());
} else {
out.println("<p>Unsuccessful attempt to edit!</p>" );
}
}
}
login.jsp很简单：
<%@page contentType="text/html" pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<Meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>JSP Page</title>
</head>
<body>
<form action="/JSP1/Logged" method="POST">
<table>
<tr>
<td>Login:</td>
<td><input type="text" name="login" value=""/> </td>
</tr>
<tr>
<td>Password </td>
<td><input type="password" name="password"/> ></td>
</tr>
<tr>
<td><input type="submit" name="OK" value="OK" /> </td>
</tr>
</table>
</form>
</body>
我无法弄清楚发生了什么.
解决方法
如果未提供登录和/或密码,您不会在转发后返回.在初学者中常见的误解是,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.
你需要添加一个回报;
if ((login==null)|(password==null)){
RequestDispatcher requestDispatcher = request.getRequestDispatcher("/login.jsp");
requestDispatcher.forward(request,response);
return;
}
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.
}
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