Servlet exception handler

package com.ack.web.servlet;

import java.io.ByteArrayOutputStream;

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;

/**

 * Map the location of the servlet to handle at error

 * with the supplied status code

 *

 <web-app>

 ...

 <error-page>

 <exception-type>javax.servlet.ServletException</exception-type>

 <location>/servlet/com.ack.web.servlet.ServletExceptionHandler</location>

 </error-page>

 </web-app>

 */

public class ServletExceptionHandler extends HttpServlet {

  public void doGet( HttpServletRequest req, HttpServletResponse res )

      throws ServletException, IOException {

    res.setContentType( "text/html" );

    PrintWriter pw = res.getWriter();

    String exceptionType = getRequestAttribute( req,

                                                "javax.servlet.error.exception_type",

                                                "status code not supplied" );

    String errorMsg = getRequestAttribute( req,

                                           "javax.servlet.error.message",

                                           "error msg not supplied" );

    // exception attribute available as of servlet 2.3 API

    Object exception = req.getAttribute( "javax.servlet.error.exception" );

    pw.println( "<h1>Custom Exception Handler</h1>" );

    pw.println( "<h2>Exception type: " + exceptionType + "</h1>" );

    pw.println( "<h2>Exception Message: " + errorMsg + "</h1>" );

    pw.println( "<p>Problem accessing: " + req.getRequestURI() + "</p>" );

    // if we have the exception dump it out to the page

    if( exception != null ) {

      ByteArrayOutputStream bos = null;

      try {

        pw.println( "<p><hr noshade><p><pre>" );

        bos = new ByteArrayOutputStream();

        PrintWriter writer = new PrintWriter( bos, true );

        ( (Exception) exception ).printStackTrace( writer );

        pw.println( bos.toString() );

      }

      finally {

        pw.println( "</pre>" );

        if( bos != null ) bos.close();

      }

    }

    // output date and time of error

    pw.println( "<p><hr><p>" );

    pw.println( new java.util.Date( System.currentTimeMillis() ) );

  }

  private String getRequestAttribute( HttpServletRequest req,

                                      String name,

                                      String defaultValue ) {

    Object value = req.getAttribute( name );

    return ( value != null ) ? value.toString() : defaultValue;

  }

}