How to attach a filter to a servlet or URL pattern

Question

I was ordered to use ExampleFilter.java to check response time of the wep application. But i don't how to do this yet. I get this ExampleFilter.java from Tomcat. I want to know how to attached it with servlet or url pattern.

 * Example filter that can be attached to either an individual servlet
 * or to a URL pattern.  This filter performs the following functions:
 * <ul>
 * <li>Attaches itself as a request attribute, under the attribute name
 *     defined by the value of the <code>attribute</code> initialization
 *     parameter.</li>
 * <li>Calculates the number of milliseconds required to perform the
 *     servlet processing required by this request, including any
 *     subsequently defined filters, and logs the result to the servlet
 *     context log for this application.
 * </ul>
 *






/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements.  See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License.  You may obtain a copy of the License at
*
*     http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/



import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;


/**
 * Example filter that can be attached to either an individual servlet
 * or to a URL pattern.  This filter performs the following functions:
 * <ul>
 * <li>Attaches itself as a request attribute, under the attribute name
 *     defined by the value of the <code>attribute</code> initialization
 *     parameter.</li>
 * <li>Calculates the number of milliseconds required to perform the
 *     servlet processing required by this request, including any
 *     subsequently defined filters, and logs the result to the servlet
 *     context log for this application.
 * </ul>
 *
 * @author Craig McClanahan
 */
public final class ExampleFilter implements Filter {


    // ----------------------------------------------------- Instance Variables


    /**
     * The request attribute name under which we store a reference to ourself.
     */
    private String attribute = null;


    /**
     * The filter configuration object we are associated with.  If this value
     * is null, this filter instance is not currently configured.
     */
    private FilterConfig filterConfig = null;


    // --------------------------------------------------------- Public Methods


    /**
     * Take this filter out of service.
     */
    @Override
    public void destroy() {

        this.attribute = null;
        this.filterConfig = null;

    }


    /**
     * Time the processing that is performed by all subsequent filters in the
     * current filter stack, including the ultimately invoked servlet.
     *
     * @param request The servlet request we are processing
     * @param response The servlet response we are creating
     * @param chain The filter chain we are processing
     *
     * @exception IOException if an input/output error occurs
     * @exception ServletException if a servlet error occurs
     */
    @Override
    public void doFilter(ServletRequest request, ServletResponse response,
                         FilterChain chain)
        throws IOException, ServletException {

        // Store ourselves as a request attribute (if requested)
        if (attribute != null)
            request.setAttribute(attribute, this);

        // Time and log the subsequent processing
        long startTime = System.currentTimeMillis();
        chain.doFilter(request, response);
        long stopTime = System.currentTimeMillis();
        filterConfig.getServletContext().log
            (this.toString() + ": " + (stopTime - startTime) +
             " milliseconds");

    }


    /**
     * Place this filter into service.
     *
     * @param fConfig The filter configuration object
     */
    @Override
    public void init(FilterConfig fConfig) throws ServletException {

        this.filterConfig = fConfig;
        this.attribute = fConfig.getInitParameter("attribute");

    }


    /**
     * Return a String representation of this object.
     */
    @Override
    public String toString() {

        if (filterConfig == null)
            return ("TimingFilter()");
        StringBuilder sb = new StringBuilder("TimingFilter(");
        sb.append(filterConfig);
        sb.append(")");
        return (sb.toString());

    }


}

I try to create the object of this class in my servlet but it now work. I don't know how to make it work. Please help me! can you help and show me how to use this ?

Answer 1

Add this annotation to the Filter class. It maps all the requests to this filter. If you are interested in only specific requests url's you should map only those url patterns.

@WebFilter("/*")
public class ExampleFilter implements Filter {
     // your filter..
}