Java agent API: Error Grouping with a Custom Callback Implementation

package test;
import java.io.IOException;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.newrelic.api.agent.ErrorGroupCallback;
import com.newrelic.api.agent.NewRelic;

public class MyServletContextListener implements ServletContextListener {

@Override
public void contextDestroyed(ServletContextEvent arg0) {
// Do any cleanup if needed
  }

@Override
public void contextInitialized(ServletContextEvent arg0) {
// Register the error grouping callback on application startup
NewRelic.setErrorGroupCallback(new MyErrorGrouper());
  }
}

public class MyErrorGrouper implements ErrorGroupCallback {

public String generateGroupingString(ErrorData errorData) {
String clazz = errorData.getErrorClass();
String txnName = errorData.getTransactionName();

return (clazz.isEmpty() || txnName.isEmpty()) ? null : clazz + "_" + txnName;
  }
}

public class TestServlet extends HttpServlet {

private static final long serialVersionUID = 1L;

protected void processRequest(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
// Simulate an exception
  throw new ServletException("Simulated ServletException");
  }

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
  processRequest(req, resp);
  }

@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp)
  throws ServletException, IOException {
  processRequest(req, resp);
  }
}