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's from JSP's. So the app is all kinds of messed up. Most of the data is fetched via stored procedures, which are being called by iBatis ORM/Spring. Sometimes when an error happens on the SP side it will display an ugly message to the user such as below:

javax.servlet.ServletException: org.springframework.jdbc.BadSqlGrammarException: SqlMapClient operation; bad SQL grammar []; nested exception is com.ibatis.common.jdbc.exception.NestedSQLException:   
--- The error occurred in debtowed.xml.  
--- The error occurred while applying a parameter map.  
--- Check the debtowed.getFormerTenantData.  
--- Check the statement (update procedure failed).  
--- Cause: java.sql.SQLException: ORA-06550: line 1, column 11:
PLS-00905: object package.GET_FORMER_ADDRESS is invalid
ORA-06550: line 1, column 7:
PL/SQL: Statement ignored

Caused by: java.sql.SQLException: ORA-06550: line 1, column 11:
PLS-00905: object package.GET_FORMER_ADDRESS is invalid
ORA-06550: line 1, column 7:
PL/SQL: Statement ignored

At this point the above information is displayed in the browser and logged to server.log.
However, I want to do following:

• Present user with custom error page
• log the errors in myapp.log instead of server.log (we do this in some other places as we use log4j)

Plese tell me what is the best way of doing this? Should I be adding something in web.xml? like a listener? will that be the only change or will I have to change existing code?

The code does not do any error checking. it just calls the SP like below

getSqlMapClientTemplate().queryForList("sp.getfmrAddy", paramMap);

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:

<filter>
  <filter-name>ExceptionFilter</filter-name>
  <filter-class>com.example.ExceptionFilter</filter-class>
</filter>

<filter-mapping>
  <filter-name>ExceptionFilter</filter-name>
  <servlet-name>MyMainServlet</servlet-name>
</filter-mapping>

then add filter mappings for all your servlets.

Hope that helps.