how do I catch errors globally, log them and show user an error page in J2EE app

Question

I have searched this topic on google a bit and seen some best practices. But I need some specific advice. I am working on a J2EE app that has servlets/Struts2/Call to DAO\'

Answer 1

I expect this is already solved in some way by Struts - so best check struts docco. If i were you i'd write an ExceptionFilter that can wrap your servlet calls:

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletResponse;

import org.apache.log4j.Logger;

public class ExceptionFilter implements Filter{

private static final Logger logger = Logger.getLogger(ExceptionFilter.class);
private ExceptionService exceptionService = null;
@Override
public void destroy() {
    exceptionService.shutdown();
}

@Override
public void doFilter(ServletRequest rq, ServletResponse rs, FilterChain chain) throws IOException, ServletException {
    try {
        chain.doFilter(rq, rs); // this calls the servlet which is where your exceptions will bubble up from
    } catch (Throwable t) {
        // deal with exception, then do redirect to custom jsp page
        logger.warn(t);
        exceptionService.dealWithException(t); // you could have a service to track counts of exceptions / log them to DB etc
        HttpServletResponse response = (HttpServletResponse) resp;
        response.sendRedirect("somejsp.jsp");
    }
}

@Override
public void init(FilterConfig arg0) throws ServletException {
    // TODO Auto-generated method stub
    exceptionService = new ExceptionService();
}

}

and add this to your web.xml:

  ExceptionFilter
  com.example.ExceptionFilter



  ExceptionFilter
  MyMainServlet

then add filter mappings for all your servlets.

Hope that helps.