4.6. Create a Custom Valve

A Valve is a Java class that gets inserted into the request processing pipeline for an application before the application's servlet filters. This can be used to modify the request or perform any other behavior. This task demonstrates the basic steps required for implementing a valve.

Procedure 4.3. Create a Custom Valve

  1. Create the Valve class

    Create a subclass of org.apache.catalina.valves.ValveBase.
    package org.jboss.samplevalves;
    
    import org.apache.catalina.valves.ValveBase;
    import org.apache.catalina.connector.Request;
    import org.apache.catalina.connector.Response;
    
    public class restrictedUserAgentsValve extends ValveBase {
    
    }
    
  2. Implement the invoke method

    The invoke() method is called when this valve is executed in the pipeline. The request and response objects are passed as parameters. Perform any processing and modification of the request and response here.
    public void invoke(Request request, Response response)
    {
    
    }
    
  3. Invoke the next pipeline step

    The last thing the invoke method must do is invoke the next step of the pipeline and pass the modified request and response objects along. This is done using the getNext().invoke() method
    getNext().invoke(request, response);
    
  4. Optional: Specify parameters

    If the valve must be configurable, enable this by adding a parameter. Do this by adding an instance variable and a setter method for each parameter.
    private String restrictedUserAgents = null;
    
    public void setRestricteduseragents(String mystring) 
    {
       this.restrictedUserAgents = mystring;
    }
    

Example 4.2. Sample Custom Valve

package org.jboss.samplevalves;

import java.io.IOException;
import java.util.regex.Pattern;

import javax.servlet.ServletException;
import org.apache.catalina.valves.ValveBase;
import org.apache.catalina.connector.Request;
import org.apache.catalina.connector.Response;

public class restrictedUserAgentsValve extends ValveBase 
{
    private String restrictedUserAgents = null;

    public void setRestricteduseragents(String mystring) 
    {
        this.restrictedUserAgents = mystring;
    }

    public void invoke(Request request, Response response) throws IOException, ServletException 
    {
      String agent = request.getHeader("User-Agent");
      System.out.println("user-agent: " + agent + " : " + restrictedUserAgents);
      if (Pattern.matches(restrictedUserAgents, agent)) 
      {
         System.out.println("user-agent: " + agent + " matches: " + restrictedUserAgents);
         response.addHeader("Connection", "close");
      }
      getNext().invoke(request, response);
    }
}