SLF4J Tool: A servlet filter that adds a generated unique request id to the logging context (MDC)

RequestIdFilter.java

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.HttpServletRequest;

import org.slf4j.MDC;

/**
 * A {@link Filter servlet filter} that adds a generated unique request id to the logging context ({@link MDC})
 * <p>
 * Requires SLF4J as the logging facade API.
 * <p>
 * With a log management system such as ELK, this will help you track a complete callflow, filtering logs from a unique request. Quite valuable when
 * your system processes thousands of requests per second and produces terabytes of logs each day...
 * <p>
 * Note that in a micro-services architecture, upon calling other services you can transfer this generated {@code requestId} in a request header
 * {@code X-Track-RequestId}, thus implementing an end-to-end callflow tracking.
 * <p>
 * The request attribute, MDC attribute and request header can be overridden with Java properties:
 * 
 * <table border=1>
 * <tr>
 * <th>attribute</th>
 * <th>default value</th>
 * <th>Filter config</th>
 * <th>Java property</th>
 * </tr>
 * <tr>
 * <td>request header</td>
 * <td>{@code X-Track-RequestId}</td>
 * <td>{@code header.requestId}</td>
 * <td>{@code slf4j.tools.header.requestId}</td>
 * </tr>
 * <tr>
 * <td>request attribute</td>
 * <td>{@code track.requestId}</td>
 * <td>{@code attribute.requestId}</td>
 * <td>{@code slf4j.tools.attribute.requestId}</td>
 * </tr>
 * <tr>
 * <td>MDC attribute</td>
 * <td>{@code requestId}</td>
 * <td>{@code mdc.requestId}</td>
 * <td>{@code slf4j.tools.mdc.requestId}</td>
 * </tr>
 * </table>
 * 
 * y {@code slf4j.tools.mdc.sessionId}
 * 
 * @author pismy
 */
public class RequestIdFilter implements Filter {

	private String headerName;
	private String attributeName;
	private String mdcName;

	public void init(FilterConfig filterConfig) throws ServletException {
		headerName = getConfig("header.requestId", "X-Track-RequestId", filterConfig);
		attributeName = getConfig("attribute.requestId", "track.requestId", filterConfig);
		mdcName = getConfig("mdc.requestId", "requestId", filterConfig);
	}
	
	private String getConfig(String param, String defaultValue, FilterConfig filterConfig) {
		String valueFromConfig = filterConfig.getInitParameter(param);
		return valueFromConfig != null ? valueFromConfig : System.getProperty("slf4j.tools."+param, defaultValue);
	}

	/**
	 * <ul>
	 * <li>checks whether the current request has an attached request id,
	 * <li>if not, tries to get one from request headers (implements end-to-end callflow traceability),
	 * <li>if not, generates one
	 * <li>attaches it to the request (as an attribute) and to the {@link MDC} context.
	 * </ul>
	 */
	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
		// checks whether the current request has an attached request id
		String reqId = (String) request.getAttribute(attributeName);
		if (reqId == null) {
			// retrieve id from request headers
			if (request instanceof HttpServletRequest) {
				reqId = ((HttpServletRequest) request).getHeader(headerName);
			}
			if (reqId == null) {
				// no requestId (either from attributes or headers): generate one
				reqId = Long.toHexString(System.nanoTime());
			}
			// attach to request
			request.setAttribute(attributeName, reqId);
		}

		// attach to MDC context
		MDC.put(mdcName, reqId);

		try {
			chain.doFilter(request, response);
		} finally {
			// remove from MDC context
			MDC.remove(mdcName);
		}
	}

	public void destroy() {
	}
}