问题
I have a custom error page setup for basic debugging whilst I'm programming and for some reason none of the values from the try catches get through. The error page just says: "Null null null". If anyone can help with this I'd be very grateful.
Servlet:
package com.atrium.userServlets;
import java.io.IOException;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import com.atrium.DAOs.UserDAO;
import com.atrium.userBeans.UserRegistrationBean;
@WebServlet("/Register")
public class UserRegistrationServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
public UserRegistrationServlet() {
super();
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
try {
HttpSession session = request.getSession(false);
if (session == null) {
response.sendRedirect(this.getServletContext() + "/Authenticate");
return;
}
request.getRequestDispatcher("/WEB-INF/register.jsp").forward(request, response);
}
catch(Throwable exception) {
String errorMessage = exception.getMessage();
Throwable errorCause = exception.getCause();
String errorLocation = this.getServletName();
request.setAttribute("ErrorMessage", errorMessage);
request.setAttribute("ErrorCause", errorCause);
request.setAttribute("ErrorLocation", errorLocation);
request.getRequestDispatcher("/WEB-INF/errorDisplay.jsp").forward(request, response);
}
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
try {
String ErrorMessage = "";
//Check user name is supplied
if (request.getParameter("Username") == null || request.getParameter("Username") == "") {
ErrorMessage = "You must enter a username!";
request.setAttribute("ErrorMessage", ErrorMessage);
request.getRequestDispatcher("/WEB-INF/register.jsp").forward(request, response);
return;
}
//Check user name for maximum length
if (request.getParameter("Username").length() > 16) {
ErrorMessage = "The username you entered was too long! Only 16 characters are allowed.";
request.setAttribute("ErrorMessage", ErrorMessage);
request.getRequestDispatcher("/WEB-INF/register.jsp").forward(request, response);
return;
}
//Check password is supplied
if (request.getParameter("Password") == null || request.getParameter("Password") == "") {
ErrorMessage = "You must enter a password!";
request.setAttribute("ErrorMessage", ErrorMessage);
request.getRequestDispatcher("/WEB-INF/register.jsp").forward(request, response);
return;
}
//Check verify password is supplied
if (request.getParameter("vPassword") == null || request.getParameter("vPassword") == "") {
ErrorMessage = "You must enter your password twice!";
request.setAttribute("ErrorMessage", ErrorMessage);
request.getRequestDispatcher("/WEB-INF/register.jsp").forward(request, response);
return;
}
//Check password is equal to verify password
if (((String)request.getParameter("Password")).equals((String)request.getParameter("vPassword"))) {}
else {
ErrorMessage = "The passwords you entered do not match!";
request.setAttribute("ErrorMessage", ErrorMessage);
request.getRequestDispatcher("/WEB-INF/register.jsp").forward(request, response);
return;
}
//Check password for complexity
/*--------------------------------------------------------
(?=.*[0-9]) a digit must occur at least once
(?=.*[a-z]) a lower case letter must occur at least once
(?=.*[A-Z]) an upper case letter must occur at least once
(?=[\\S]+$) no whitespace allowed in the entire string
.{6,16} at least 6 to 16 characters
---------------------------------------------------------*/
Pattern passwordPattern = Pattern.compile("((?=.*[0-9])(?=.*[a-z])(?=.*[A-Z])(?=[\\S]+$).{6,16})");
Matcher passwordMatcher = passwordPattern.matcher(request.getParameter("Password"));
if (passwordMatcher.find() == false) {
ErrorMessage = "The password you entered does not abide by the strength rules!";
request.setAttribute("ErrorMessage", ErrorMessage);
request.getRequestDispatcher("/WEB-INF/register.jsp").forward(request, response);
return;
}
//Check email is supplied
if (request.getParameter("Email") == null || request.getParameter("Username") == "") {
ErrorMessage = "You must enter an email!";
request.setAttribute("ErrorMessage", ErrorMessage);
request.getRequestDispatcher("/WEB-INF/register.jsp").forward(request, response);
return;
}
//Check verify email is supplied
if (request.getParameter("vEmail") == null || request.getParameter("vEmail") == "") {
ErrorMessage = "You must enter your email twice!";
request.setAttribute("ErrorMessage", ErrorMessage);
request.getRequestDispatcher("/WEB-INF/register.jsp").forward(request, response);
return;
}
//Check email is equal to verify email
if (((String)request.getParameter("Email")).equals((String)request.getParameter("vEmail"))) {}
else {
ErrorMessage = "The emails you entered did not match!";
request.setAttribute("ErrorMessage", ErrorMessage);
request.getRequestDispatcher("/WEB-INF/register.jsp").forward(request, response);
return;
}
//Validate email - *@*
Pattern emailPattern = Pattern.compile(".+@.+\\.[a-z]+", Pattern.CASE_INSENSITIVE);
Matcher emailMatcher = emailPattern.matcher(request.getParameter("Email"));
if (emailMatcher.find() == false) {
ErrorMessage = "The email you entered is not valid!";
request.setAttribute("ErrorMessage", ErrorMessage);
request.getRequestDispatcher("/WEB-INF/register.jsp").forward(request, response);
return;
}
UserRegistrationBean user = new UserRegistrationBean();
user.setUsername(request.getParameter("Username"));
user.setPassword(request.getParameter("Password"));
user.setEmail(request.getParameter("Email"));
user = UserDAO.register(user);
if (user.getExists() == true) {
ErrorMessage = "The user name you entered has already been registered!";
request.setAttribute("ErrorMessage", ErrorMessage);
request.getRequestDispatcher("/WEB-INF/register.jsp").forward(request, response);
return;
}
}
catch(Throwable exception) {
String errorMessage = exception.getMessage();
Throwable errorCause = exception.getCause();
String errorLocation = this.getServletName();
request.setAttribute("ErrorMessage", errorMessage);
request.setAttribute("ErrorCause", errorCause);
request.setAttribute("ErrorLocation", errorLocation);
request.getRequestDispatcher("/WEB-INF/errorDisplay.jsp").forward(request, response);
}
}
}
JSP Error Page:
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Exception Details</title>
</head>
<body>
<% final String errorMessage = (String)request.getAttribute("ErrorMessage"); %>
<% final Throwable errorCause = (Throwable)request.getAttribute("ErrorCause"); %>
<% final String errorLocation = (String)request.getAttribute("ErrorLocation"); %>
<h1>An Error Occurred...</h1>
<p>
<%= errorMessage %><br><br>
<%= errorCause %><br><br>
<%= errorLocation %>
</p>
回答1:
Make these changes to your catch block:
catch(Throwable errorMessage) {
request.setAttribute("errorMessage", (String)errorMessage.getMessage());
request.setAttribute("errorCause", errorMessage.getCause());
request.setAttribute("errorLocation", (String)this.getServletName());
request.getRequestDispatcher("/WEB-INF/errorDisplay.jsp").forward(request, response);
}
Try this on your jsp page:
<body>
<h1>An Error Occurred...</h1>
<p>
${requestScope.errorMessage}<br><br>
${requestScope.errorCause}<br><br>
${requestScope.errorLocation}
</p>
</body>
回答2:
You can provide an error handler servlet like this :
@WebServlet("/error")
public class ErrorHandler extends HttpServlet {
private static final long serialVersionUID = 1L;
/***** This Method Is Called By The Servlet Container To Process A 'GET' Request *****/
public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {
handleRequest(request, response);
}
public void handleRequest(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {
/***** Analyze The Servlet Exception *****/
Integer statusCode = (Integer) request.getAttribute("javax.servlet.error.status_code");
String servletName = (String) request.getAttribute("javax.servlet.error.servlet_name");
Throwable throwable = (Throwable) request.getAttribute("javax.servlet.error.exception");
if (servletName == null) {
servletName = "Unknown";
}
String requestUri = (String) request.getAttribute("javax.servlet.error.request_uri");
if (requestUri == null) {
requestUri = "Unknown";
}
/***** Set Response Content Type *****/
response.setContentType("text/html");
/***** Print The Response *****/
PrintWriter out = response.getWriter();
String title = "Error/Exception Information";
String docType = "<!DOCTYPE html>\n";
out.println(docType
+ "<html>\n" + "<head><meta http-equiv=\"Content-Type\" content=\"text/html; charset=UTF-8\"><title>" + title + "</title></head>\n" + "<body>");
if (throwable == null && statusCode == null) {
out.println("<h3>Error Information Is Missing</h3>");
} else if (statusCode != 500) {
out.write("<h3>Error Details</h3>");
out.write("<ul><li><strong>Status Code</strong>?= "+ statusCode + "</li>");
out.write("<li><strong>Requested URI</strong>?= "+ requestUri + "</li></ul>");
} else {
out.println("<h3>Exception Details</h3>");
out.println("<ul><li><strong>Servlet Name</strong>?= " + servletName + "</li>");
out.println("<li><strong>Exception Name</strong>?= " + throwable.getClass( ).getName( ) + "</li>");
out.println("<li><strong>Requested URI</strong>?= " + requestUri + "</li>");
out.println("<li><strong>Exception Message</strong>?= " + throwable.getMessage( ) + "</li></ul>");
}
out.println("<div> </div>Click <a id=\"homeUrl\" href=\"index.jsp\">home</a>");
out.println("</body>\n</html>");
out.close();
}
}
Then register it to handle the error cases in web.xml like :
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" version="3.0">
<display-name>Error/Exception Information</display-name>
<!-- Error Code Related Error Pages -->
<error-page>
<error-code>404</error-code>
<location>/error</location>
</error-page>
<error-page>
<error-code>403</error-code>
<location>/error</location>
</error-page>
<!-- Exception Type Related Error Pages -->
<error-page>
<exception-type>javax.servlet.ServletException</exception-type>
<location>/error</location>
</error-page>
<error-page>
<exception-type>java.io.IOException</exception-type>
<location>/error</location>
</error-page>
</web-app>
So you just need to throw the exception from all other servlets in case of any exception and it will be handled automatically by this error servlet that we have defined.So, throw the exception from your servlet like :
@WebServlet("/myExceptionServlet")
public class MyExceptionServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
throw new ServletException("HTTP GET Method Is Not Supported.");
}
}
来源：https://stackoverflow.com/questions/23267506/java-servlet-jsp-custom-error-page