Can we have a filter to handle all the apps in a container?

Question

Hi,
I have a simple (Stupid) question.
Can I configure a Servlet filter to intercept requests to all the applications (a.k.a all the ServletContexts)? All I know is we can configure a filter for each ServletContext (application), but I am wondering if there is any way.
The reason I am asking is because, if there is a way to do so, I can configure my filter to provide me the debug output (Such as CGI, session, request, and ServletContext variables) on all the applications on development servers and when I can get rid of debugging on production servers (by not deploying the filter).
Thanx in advance,
Thirupati Panyala

Answer 1

Thanks for the reply Sudhir.
I tried it in Tomcat 4.x. It works for only the root resources even though I configured the filter for /* which is expected to include all the resources including root (for ex: /examples/...).
So, I understand, the web.xml under /conf will be overriden by that of the respective apps as you go further down the context paths (apps). That's why the container was not executing my filter when I went to the next level of the URI (http://localhost:8080/index.html WORKED, but NOT http://localhost:8080/examples/jsp/num/numguess.jsp).
If you want to try it for yourself, here is the piece of code I tried with (This is taken from Apache Tomcat source):
package filters;
import java.io.IOException;
import java.io.PrintWriter;
import java.io.StringWriter;
import java.sql.Timestamp;
import java.util.Enumeration;
import java.util.Locale;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServletRequest;
* Example filter that dumps interesting state information about a request
* to the associated servlet context log file, before allowing the servlet
* to process the request in the usual way. This can be installed as needed
* to assist in debugging problems.
* @author Craig McClanahan
* @version $Revision: 1.5 $ $Date: 2001/05/23 22:26:17 $
public final class RequestDumperFilter implements Filter {
// ----------------------------------------------------- Instance Variables
* The filter configuration object we are associated with. If this value
* is null, this filter instance is not currently configured.
private FilterConfig filterConfig = null;
// --------------------------------------------------------- Public Methods
* Take this filter out of service.
public void destroy() {
this.filterConfig = null;
* Time the processing that is performed by all subsequent filters in the
* current filter stack, including the ultimately invoked servlet.
* @param request The servlet request we are processing
* @param result The servlet response we are creating
* @param chain The filter chain we are processing
* @exception IOException if an input/output error occurs
* @exception ServletException if a servlet error occurs
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain)
     throws IOException, ServletException {
if (filterConfig == null)
     return;
     // Render the generic servlet request properties
     StringWriter sw = new StringWriter();
     PrintWriter writer = new PrintWriter(sw);
     writer.println("Request Received at " +
          (new Timestamp(System.currentTimeMillis())));
     writer.println(" characterEncoding=" + request.getCharacterEncoding());
     writer.println(" contentLength=" + request.getContentLength());
     writer.println(" contentType=" + request.getContentType());
     writer.println(" locale=" + request.getLocale());
     writer.print(" locales=");
     Enumeration locales = request.getLocales();
     boolean first = true;
     while (locales.hasMoreElements()) {
     Locale locale = (Locale) locales.nextElement();
     if (first)
     first = false;
     else
     writer.print(", ");
     writer.print(locale.toString());
     writer.println();
     Enumeration names = request.getParameterNames();
     while (names.hasMoreElements()) {
     String name = (String) names.nextElement();
     writer.print(" parameter=" + name + "=");
     String values[] = request.getParameterValues(name);
     for (int i = 0; i < values.length; i++) {
     if (i > 0)
          writer.print(", ");
          writer.print(values);
     writer.println();
     writer.println(" protocol=" + request.getProtocol());
     writer.println(" remoteAddr=" + request.getRemoteAddr());
     writer.println(" remoteHost=" + request.getRemoteHost());
     writer.println(" scheme=" + request.getScheme());
     writer.println(" serverName=" + request.getServerName());
     writer.println(" serverPort=" + request.getServerPort());
     writer.println(" isSecure=" + request.isSecure());
     // Render the HTTP servlet request properties
     if (request instanceof HttpServletRequest) {
     writer.println("---------------------------------------------");
     HttpServletRequest hrequest = (HttpServletRequest) request;
     writer.println(" contextPath=" + hrequest.getContextPath());
     Cookie cookies[] = hrequest.getCookies();
if (cookies == null)
cookies = new Cookie[0];
     for (int i = 0; i < cookies.length; i++) {
     writer.println(" cookie=" + cookies[i].getName() +
               "=" + cookies[i].getValue());
     names = hrequest.getHeaderNames();
     while (names.hasMoreElements()) {
     String name = (String) names.nextElement();
          String value = hrequest.getHeader(name);
     writer.println(" header=" + name + "=" + value);
     writer.println(" method=" + hrequest.getMethod());
     writer.println(" pathInfo=" + hrequest.getPathInfo());
     writer.println(" queryString=" + hrequest.getQueryString());
     writer.println(" remoteUser=" + hrequest.getRemoteUser());
     writer.println("requestedSessionId=" +
               hrequest.getRequestedSessionId());
     writer.println(" requestURI=" + hrequest.getRequestURI());
     writer.println(" servletPath=" + hrequest.getServletPath());
     writer.println("=============================================");
     // Log the resulting string
     writer.flush();
     response.getWriter().print(sw.getBuffer().toString());
     // Pass control on to the next filter
chain.doFilter(request, response);
* Place this filter into service.
* @param filterConfig The filter configuration object
public void init(FilterConfig filterConfig) throws ServletException {
     this.filterConfig = filterConfig;
* Return a String representation of this object.
public String toString() {
     if (filterConfig == null)
     return ("RequestDumperFilter()");
     StringBuffer sb = new StringBuffer("RequestDumperFilter(");
     sb.append(filterConfig);
     sb.append(")");
     return (sb.toString());
And the config in web.xml is :
<filter>
<filter-name>Request Dumper Filter</filter-name>
<filter-class>filters.RequestDumperFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>Request Dumper Filter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
Thanx
Thirupati Panyala