MDC (Mapped Diagnostic Context) Filter

Problem:

I wanted to add username and ip address to each logging entry of my Java web application.  I assumed I would have to go through each logging entry and add it manually, or perform some sort of fancy find/replace.

Research:

After consulting my best friend Google, I discovered that an MDC servlet filter was the correct approach.  However, I wasn’t sure of how much effort was required.  After some pondering I decided the correct approach is what I needed to do.

Solution:

I required a new class (see below):

package com.example;

import org.jboss.logging.MDC;
import org.springframework.security.core.Authentication;
import org.springframework.security.core.context.SecurityContextHolder;

import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import java.io.IOException;

public class MDCFilter implements Filter {

@Override
 public void init(FilterConfig filterConfig) throws ServletException {
 }

@Override
 public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain)
 throws IOException, ServletException {
 Authentication authentication =
 SecurityContextHolder.getContext().getAuthentication();
 if (authentication != null) {
 MDC.put(Constants.mdc_username, authentication.getName());
 }
 HttpServletRequest httpRequest = (HttpServletRequest) req;
 String ipAddress = httpRequest.getHeader("X-FORWARDED-FOR");
 if (ipAddress == null) {
 ipAddress = req.getRemoteAddr();
 }
 MDC.put(Constants.mdc_ipaddress, ipAddress);
 try {
 chain.doFilter(req, resp);
 } finally {
 if (authentication != null) {
 MDC.remove(Constants.mdc_username);
 }
 MDC.remove(Constants.mdc_ipaddress);
 }
 }

@Override
 public void destroy() {
 }

}

Additionally, I required a modification to the web.xml:

 <filter>
 <filter-name>mdcFilter</filter-name>
 <filter-class>com.example.MDCFilter</filter-class>
 </filter>

 <filter-mapping>
 <filter-name>mdcFilter</filter-name>
 <url-pattern>/*</url-pattern>
 </filter-mapping>

Final Thoughts:

Considering how little work was required I’m convinced I made the right decision.  Also, if I need to add any additional fields to my log entries I simply need to modify the MDCFilter class.  That’s it.

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