Loop issue in ExceptionHandlerServlet

[Haifeng Jiang]

I want to handle non-business exception in the BPIMSExceptionHandlerServlet . So I make a BPIMSExceptionHandlerServlet class below.

/**
 * 
 */
package com.ibm.partnerworld.incentives.management.action;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.struts.Globals;

/**
 * @author jianghaifeng
 * 
 */
public class BPIMSExceptionHandlerServlet extends HttpServlet {
	/**
	 * 
	 */
	private static final long serialVersionUID = 1L;

	public void doPost(HttpServletRequest request,
			HttpServletResponse response) throws ServletException, IOException {
		try {

			Throwable exception = null;
			
			// Check if struts has placed an exception object in request
			Object obj = request.getAttribute(Globals.EXCEPTION_KEY);

			if (obj == null) {
				// Since no struts exception is found,
				// check if a JSP exception is available in request.
				obj = request.getAttribute("javax.servlet.jsp.jspException");
			}

			if ((obj != null) && (obj instanceof Throwable)) {
				exception = (Throwable) obj;
			}

			// request uri containing the original URL value will be available
			// only on servers implementing servlet 2.4 spec
//			String requestURI = (String) request
//					.getAttribute("errorPageURL");
			
			String url = getServletConfig().getInitParameter("errorPageURL");
			System.out.println("url is     " + url);
			response.sendRedirect("url");
			
		} catch (Exception e) {
			// Throwing exceptions from this method can result in request
			// going in to an infinite loop forwarding to the error servlet
			// recursively.
			e.printStackTrace();
		}
	}
	
	public void doGet(HttpServletRequest request,
			HttpServletResponse response) throws ServletException, IOException {
		doPost(request, response);
	}
}

And my web.xml file is:

<?xml version="1.0" encoding="UTF-8"?>
<web-app id="WebApp_ID" version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
	<display-name>partnerworld_incentives_management</display-name>
	<distributable />
	<servlet>
		<servlet-name>action</servlet-name>
		<servlet-class>com.ibm.partnerworld.incentives.management.action.BPIMSActionServlet</servlet-class>
		
		<init-param>
			<param-name>config</param-name>
			<param-value>/WEB-INF/struts-config.xml</param-value>
		</init-param>
		<init-param>
			<param-name>debug</param-name>
			<param-value>2</param-value>
		</init-param>
		<init-param>
			<param-name>detail</param-name>
			<param-value>2</param-value>
		</init-param>
		<init-param>
			<param-name>validate</param-name>
			<param-value>true</param-value>
		</init-param>
		<load-on-startup>2</load-on-startup>
	</servlet>
	
	<servlet>
		<servlet-name>exceptionHandler</servlet-name>
		<servlet-class>com.ibm.partnerworld.incentives.management.action.BPIMSExceptionHandlerServlet</servlet-class>
		<init-param>
			<param-name>errorPageURL</param-name>
			<param-value>/WEB-INF/jsp/common/error.html</param-value>
		</init-param>
		<load-on-startup>3</load-on-startup>
	</servlet>

	<servlet-mapping>
		<servlet-name>action</servlet-name>
		<url-pattern>*.wss</url-pattern>
	</servlet-mapping>
	
	<servlet-mapping>
		<servlet-name>exceptionHandler</servlet-name>
		<url-pattern>/error</url-pattern>
	</servlet-mapping>

	<error-page>
		<exception-type>java.lang.Throwable</exception-type>
		<location>/error</location>
	</error-page>
        ...

Now I just create one NullPointerException in one Action class manually.

		List tList = new ArrayList();
		tList = null;
		
		tList.add(new Object());

When I run the project, the BPIMSExceptionHandlerServlet catched the NullPointerException. But the problem is the program keep running. It seems a loop in doPost method. It just keeps running. I have debug the project. The program keep running from the first line to the last line in doPost method. Anybody know what's wrong here? Thanks in advance.

[Sagar Rohankar]

Just a wild guess, change the name of html file

 
 <init-param>  
           <param-name>errorPageURL</param-name>  
           <param-value>/WEB-INF/jsp/common/error.html</param-value>  
</init-param>   

into

 
 <init-param>  
           <param-name>errorPageURL</param-name>  
           <param-value>/WEB-INF/jsp/common/someother.html</param-value>  
</init-param>   

Afterthoughts: It look like this part of the code is recalling the ExceptionHandlerServlet

 
  String url = getServletConfig().getInitParameter("errorPageURL");  
  System.out.println("url is     " + url);  
  response.sendRedirect("url");    

OR you may have some unhandled Exception in ExceptionHandlerServlet code, itself

[David Newton]

Not sure what this has to do with Struts.

response.sendRedirect("url");      

Is that really what you mean to do?

In any case, the ability to redirect also depends on not having written anything to the response yet.

[Sagar Rohankar]

David Newton wrote:
In any case, the ability to redirect also depends on not having written anything to the response yet.

Yes, David is more precise than me :thumbup:

[Haifeng Jiang]

Sagar Rohankar wrote:

David Newton wrote:
In any case, the ability to redirect also depends on not having written anything to the response yet.

Yes, David is more precise than me :thumbup:

Thanks for your reply.

Now I correct the code.

request.sendRedirect("/WEB-INF/jsp/common/error.html");

but the program cannot find the error.html file. Give me a 404 error code. I also tried "error.html" or "/error.html". none of them work. Now I don't know what is the correct path in the sendRedirect() method. Do you know how to write in the method?

My project structure is:
BPIMS_Web --- WebContent --- WEB-INF --- jsp --- common --- error.html
- --- welcome.jsp
error.html and welcome.jsp are in the same directory.

In the application.xml:

...
	<module id="WebModule_1228351345750">
		<web>
			<web-uri>BPIMS_Web.war</web-uri>
			<context-root>/partnerworld/incentives/management</context-root>
		</web>
	</module>
...

I use below url to access my project:
http://localhost:9080/partnerworld/incentives/management/welcome.wss?user=eric
when I click one link in the welcome page to trigger the exception to throw out to the servlet level, the servlet can catch the exception. But the redirect method doesn't work. Kindly advise.

[Haifeng Jiang]

Now I got the solution. Add one Action in the struct config file to handle the redirected uri. Then redirect to the url which you want.

[Sagar Rohankar]

Why don't you try Exception Handling + Struts. Struts provides Global exception handling for your web app.

[Haifeng Jiang]

Sagar Rohankar wrote:Why don't you try Exception Handling + Struts. Struts provides Global exception handling for your web app.

As you may know if the jspException throwed from jsp level. Struts will not able to cacth this type of exception. So I have to think out a solution to handle it. Thanks

[Sagar Rohankar]

Eric Jiang wrote:

Sagar Rohankar wrote:Why don't you try Exception Handling + Struts. Struts provides Global exception handling for your web app.

As you may know if the jspException throwed from jsp level. Struts will not able to cacth this type of exception.

Hmm, I know about jspException, but never cared about it, Anyways, thanks.

[Haifeng Jiang]

Sagar Rohankar wrote:

Eric Jiang wrote:

Sagar Rohankar wrote:Why don't you try Exception Handling + Struts. Struts provides Global exception handling for your web app.

As you may know if the jspException throwed from jsp level. Struts will not able to cacth this type of exception.

Hmm, I know about jspException, but never cared about it, Anyways, thanks.

welcome.
Now I do a test. If I create NullPointerException manually in jsp. the servlet cannot catch it. Don't know why. Anybody can help on this?Thanks.