examplefilter.java

《J2EE企业级应用开发》一书的配套源代码

/*
 * $Header: /home/cvs/jakarta-tomcat-4.0/webapps/examples/WEB-INF/classes/filters/ExampleFilter.java,v 1.4 2001/03/17 00:39:30 craigmcc Exp $
 * $Revision: 1.4 $
 * $Date: 2001/03/17 00:39:30 $
 *
 * ====================================================================
 *
 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 1999 The Apache Software Foundation.  All rights
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution, if
 *    any, must include the following acknowlegement:
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowlegement may appear in the software itself,
 *    if and wherever such third-party acknowlegements normally appear.
 *
 * 4. The names "The Jakarta Project", "Tomcat", and "Apache Software
 *    Foundation" must not be used to endorse or promote products derived
 *    from this software without prior written permission. For written
 *    permission, please contact [e-mail].
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 * 5. Products derived from this software may not be called "Apache"
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 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
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 * ====================================================================
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 * This software consists of voluntary contributions made by many
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 * <http://www.apache.org/>.
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 * [Additional notices, if required by prior licensing conditions]
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 */


package filters;


import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletContext;
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
 * @version $Revision: 1.4 $ $Date: 2001/03/17 00:39:30 $
 */

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.
     */
    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 result 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
     */
    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 filterConfig The filter configuration object
     */
    public void init(FilterConfig filterConfig) throws ServletException {

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

    }


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

	if (filterConfig == null)
	    return ("InvokerFilter()");
	StringBuffer sb = new StringBuffer("InvokerFilter(");
	sb.append(filterConfig);
	sb.append(")");
	return (sb.toString());

    }


}