How do I write the Java logger Servlet?

Question

I want to do some log in my system, like user action, and I know in the servelet I can get the request with all the session,parameter..etc

So I want to write the Servlet

public class UserActionCheck extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        HttpSession session = request.getSession();
        Map map = request.getParameterMap();
        Set keSet = map.entrySet();
        for (Iterator itr = keSet.iterator(); itr.hasNext(); ) {
            Map.Entry me = (Map.Entry) itr.next();
            Object ok = me.getKey();
            Object ov = me.getValue();
            String[] value = new String[1];
            if (ov instanceof String[]) {
                value = (String[]) ov;
            } else {
                value[0] = ov.toString();
            }

            for (int k = 0; k < value.length; k++) {
                System.out.println(ok + "=" + value[k]);
            }
        }
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        //HttpSession session = request.getSession();
    }
}

then I can see the parameter output in the tomcat console..but I get the blank page..

It seems the page is stop after doGet method..

so how should I make it continue?

use that RequestDispatcher ?

also how to handle in the doPost ?

Answer 1

For your purpose, the best way would be to use a Filter .

Example :

@WebFilter(filterName = "monitoringFilter", urlPatterns = { "/*" })
public class MonitoringFilter implements Filter
{
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
    {
        // Right here do your stuff pretty much like in a servlet
        request // ... get information you need

        // Process request as normal
        chain.doFilter(request,response);
    }

    @Override
    public void init(FilterConfig config) throws ServletException
    {

    }

    @Override
    public void destroy()
    {

    }
}

More info :

• Filter

Answer 2

You ask the question

so how should I make it continue?

The idea of the doGet method is that it should write to the response object, the html (or data) that should be written in the browser;

For example you could write

PrintWriter out = response.getWriter();
for(int k=0;k<value.length;k++){
            out.println(ok+"="+value[k]);
}

Have a look at http://www.apl.jhu.edu/~hall/java/Servlet-Tutorial/Servlet-Tutorial-First-Servlets.html

doPost can also be treated similarly but is usually used for POST'd data - it is called when a HTML form is submitted.

Answer 3

You should use log4j and FileAppender to implement logging in your application. Something like this :::

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
class A{
  static Log log = LogFactory.getLog(A.class);
  void methodA(){
   try{
    log.info("I am inside A");
   } catch(Exception e) {
      log.error("error" , e);
     }
  }

}