Java/Servlets/Exception
Exceptions in Servlet
/*
<?xml version="1.0" encoding="ISO-8859-1"?>
<web-app xmlns="http://java.sun.ru/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.ru/xml/ns/j2ee
http://java.sun.ru/xml/ns/j2ee/web-app_2_4.xsd" version="2.4">
<servlet>
<servlet-name>DeliberateException</servlet-name>
<servlet-class>DeliberateException</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>DeliberateException</servlet-name>
<url-pattern>/deliberateException</url-pattern>
</servlet-mapping>
</web-app>
*/
import java.io.IOException;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class DeliberateException extends HttpServlet {
public void init(ServletConfig config) throws ServletException {
super.init(config);
throw new NullPointerException();
}
public void doGet(HttpServletRequest req, HttpServletResponse res)
throws IOException, ServletException {
ServletOutputStream out = res.getOutputStream();
res.setContentType("text/html");
out.println("<html><head><title>Exception Thrower</title></head>");
out.println("<body>You"ll never see this!</body></html>");
}
}
ForwardException - show forwarding an exception to an error page
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
/*
* ForwardException - show forwarding an exception to an error page.
*
* @author Ian Darwin
* @version $Id: ForwardException.java,v 1.2 2002/03/13 21:50:30 ian Exp $
*/
public class ForwardException extends HttpServlet
{
/** Called in response to a GET request (data encoded in the URL) */
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
ServletContext application = getServletContext();
// BOILERPLATE beginning
response.setContentType("text/html");
PrintWriter out = response.getWriter();
try {
// to do: logic code and main HTML goes here.
// simulate an error condition happening at run time.
if (this instanceof Servlet)
throw new RuntimeException("Test exception");
out.println("<!DOCTYPE html PUBLIC " +
"\"-//W3C//DTD XHTML 1.0 Transitional//EN\"\n" +
"\"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd\"\n" +
">");
out.println("<html>");
out.println("<head><title>Servlet Output</title></head>");
out.println("<body>");
// BOILERPLATE ending
out.println("</body>");
out.println("</html>");
out.close();
} catch (Exception exc) {
// dispatch to JSP to display the error.
RequestDispatcher rd = application.getRequestDispatcher("/oops.jsp");
request.setAttribute("javax.servlet.jsp.jspException", exc);
rd.forward(request, response);
}
}
}
javax.servlet.error.request_uri
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class ErrorDisplay extends HttpServlet {
public void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException,
IOException {
res.setContentType("text/html");
PrintWriter out = res.getWriter();
String code = null, message = null, type = null, uri = null;
Object codeObj, messageObj, typeObj;
Throwable throwable;
codeObj = req.getAttribute("javax.servlet.error.status_code");
messageObj = req.getAttribute("javax.servlet.error.message");
typeObj = req.getAttribute("javax.servlet.error.exception_type");
throwable = (Throwable) req.getAttribute("javax.servlet.error.exception");
uri = (String) req.getAttribute("javax.servlet.error.request_uri");
if (uri == null) {
uri = req.getRequestURI(); // in case there"s no URI given
}
// Convert the attributes to string values
if (codeObj != null)
code = codeObj.toString();
if (messageObj != null)
message = messageObj.toString();
if (typeObj != null)
type = typeObj.toString();
// The error reason is either the status code or exception type
String reason = (code != null ? code : type);
out.println("<HTML>");
out.println("<HEAD><TITLE>" + reason + ": " + message + "</TITLE></HEAD>");
out.println("<BODY>");
out.println("<H1>" + reason + "</H1>");
out.println("<H2>" + message + "</H2>");
out.println("<PRE>");
if (throwable != null) {
throwable.printStackTrace(out);
}
out.println("</PRE>");
out.println("<HR>");
out.println("<I>Error accessing " + uri + "</I>");
out.println("</BODY></HTML>");
}
}
