hitcounterfilter.java

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/*
 * @author                        : Reghu
 * @Version                       : 1.0
 *
 * Development Environment        :  Oracle 9i JDeveloper
 * Name of the File               :  HitCounterFilter.java
 * Creation/Modification History  :
 *
 * Reghu    21-march-2002     Created
 *
 */
package oracle.otnsamples.vsm;


// Java IO files
import java.io.IOException;

// Servlet Filter classes
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;

// Servlet related classes
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;


/**
 * This class is implemented as a Servlet Filter class to track the number of
 * hits by users. The hits are incremented for every new session.
 *
 * @author Reghu
 * @version 2.0
 */
public final class HitCounterFilter implements Filter {

  public static int counter;
  
  /** Hit Counter */
  private FilterConfig filterConfig = null; // flter configuration

  /**
   * The servlet container invokes this method before the filter goes
   * into service, and sets the filter's configuration object. The method
   * initializes the counter to the value specified in the init param in
   * web.xml
   *
   * @param <b>config</b> The filter config passed by the servlet engine
   *
   * @throws <b>ServletException</b> if any error in initializing the filter
   */
  public void init(FilterConfig filterConfig) throws ServletException {
    this.filterConfig = filterConfig;

    try {
      counter = Integer.parseInt(filterConfig.getInitParameter("Counter"));
    } catch(Exception ex) {
      counter = 0;
    }
  }
  /**
   * This method performs the actual filtering work .In its doFilter() method,
   * each filter receives the current request and response, as well as a
   * FilterChain containing the filters that still must be processed. If the
   * session is a new one, the counter is incremented and the control is
   * passed down the filter chain
   *
   * @param <b>request</b> The servlet request
   * @param <b>response</b> The servlet response
   * @param <b>chain</b> Object representing the chain of all filters
   *
   * @throws <b>ServletException</b> If there was an error while checking the
   *         role privileges
   * @throws <b>IOException</b>
   */
  public void doFilter(
                       ServletRequest request, ServletResponse response,
                       FilterChain chain) throws IOException, 
                                                 ServletException {

    if(filterConfig == null) {
      return;
    }

    // Get the session object 
    HttpSession session = ((HttpServletRequest) request).getSession();

    // If its a new request, its a new user to the site
    if(session.getAttribute("_counter") == null) {

      // Get the Counter stored as a context attribute.
      counter++;
      session.setAttribute("_counter", "c");
    }

    // Invokes the doFilter of the filter chain object
    chain.doFilter(request, response);
  }
  /**
   * Called by the web container to indicate to a filter that it is being taken
   * out of service. This method is only called once all threads within the
   * filter's doFilter method have exited or after a timeout period has
   * passed. After the web container calls this method, it will not call the
   * doFilter method again on this instance of the filter.  This method gives
   * the filter an opportunity to clean up any resources that are being held
   * (for example, memory, file handles, threads) and make sure that any
   * persistent state is synchronized with the filter's current state in
   * memory.    The method sets the filterConfig to null.
   */
  public void destroy() {
    this.filterConfig = null;
  }
}