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Tomcat-Valve-Example

This repository contains a simple maven project with a class extended by tomcat ValueBase, to demonstrate on how to implement a custom valve in tomcat.

This is based as an answer for the following question: https://stackoverflow.com/questions/6573325/implementing-tomcat-custom-valve

The question is on steps required to create a custom valve and use it. So let me explain it step by step for someone else also to take advantage of it. For my example, I will use a Java Maven Project. (Git Project)

Step 1: Open a new or existing maven project (you can also clone from the above repo).

Step 2: Add the following dependency to the pom.xml file.

<dependency>
            <groupId>org.apache.tomcat</groupId>
            <artifactId>tomcat-catalina</artifactId>
            <version>7.0.85</version>
            <scope>provided</scope>
</dependency>

Step 3: Under src/main/java path, create a package and create a new Java Class: TomcatValve.java (could be any name). Extend this class by ValueBase class.

Step 4: With this, you will have to implement its invoke method. The entire class would look something similar to this:

import java.io.IOException;
import java.util.Enumeration;
import java.util.logging.Level;
import java.util.logging.Logger;

import org.apache.catalina.connector.Request;
import org.apache.catalina.connector.Response;
import org.apache.catalina.valves.ValveBase;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;

/**
 * @author Keet Sugathadasa
 */
public class TomcatValve extends ValveBase {
    private static final Logger logger = Logger.getLogger(TomcatValve.class.getName());

    public void invoke(Request request, Response response) throws IOException, ServletException {
        HttpServletRequest httpServletRequest = request.getRequest();

        Enumeration<String> headerNames = httpServletRequest.getHeaderNames();

        logger.info("Receiving request");

        while (headerNames.hasMoreElements()) {
            String header = headerNames.nextElement();
            logger.log(Level.INFO, "Header --> {0} Value --> {1}", new Object[]{header, httpServletRequest.getHeader(header)});
        }

        getNext().invoke(request, response);
    }
}

Step 5: Open a terminal, and run mvn install. Now in the target/ folder, there jar should have been built.

Step 6: Copy this jar to ${TOMCAT_HOME}/lib or ${CATALINA_HOME}/lib folder. This is usually in /usr/local/apache-tomcat9/lib.

Step 7: Go to ${TOMCAT_HOME}/conf or ${CATALINA_HOME}/conf folder and add the following line to server.xml:

Classname: TomcatValve

PackageName: com.keetmalin.tomcat

<Valve className="com.keetmalin.tomcat.TomcatValve"/>

Step 9: Go to ${TOMCAT_HOME}/bin or ${CATALINA_HOME}/bin folder and run the following command in a terminal:

./catalina.sh run

Step 10: Next, your Tomcat server will start. Open a browser and go to http://localhost:8080/ and go back to the terminal. You will see that the logs are being printed. Now instead of printing logs, you can do anything you wish. Hope it helps!

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