cachetag.java

J2EE的经典案例。宠物商店。绝对是值得好好学习的经典源码。学javar必看的源码

/*
 * Copyright 2002 Sun Microsystems, Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 *
 * - Redistribution 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.
 *
 * Neither the name of Sun Microsystems, Inc. or the names of
 * contributors may be used to endorse or promote products derived
 * from this software without specific prior written permission.
 *
 * This software is provided "AS IS," without a warranty of any
 * kind. ALL EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND
 * WARRANTIES, INCLUDING ANY IMPLIED WARRANTY OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT, ARE HEREBY
 * EXCLUDED. SUN AND ITS LICENSORS SHALL NOT BE LIABLE FOR ANY DAMAGES
 * SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR
 * DISTRIBUTING THE SOFTWARE OR ITS DERIVATIVES. IN NO EVENT WILL SUN
 * OR ITS LICENSORS BE LIABLE FOR ANY LOST REVENUE, PROFIT OR DATA, OR
 * FOR DIRECT, INDIRECT, SPECIAL, CONSEQUENTIAL, INCIDENTAL OR
 * PUNITIVE DAMAGES, HOWEVER CAUSED AND REGARDLESS OF THE THEORY OF
 * LIABILITY, ARISING OUT OF THE USE OF OR INABILITY TO USE SOFTWARE,
 * EVEN IF SUN HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
 *
 * You acknowledge that Software is not designed, licensed or intended
 * for use in the design, construction, operation or maintenance of
 * any nuclear facility.
 */

package com.sun.j2ee.blueprints.waf.view.taglibs.smart;

import java.io.IOException;
import java.util.Calendar;
import java.util.Date;
import javax.servlet.jsp.JspTagException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.tagext.BodyContent;
import javax.servlet.jsp.tagext.BodyTagSupport;
import javax.servlet.http.HttpServletRequest;

/**
 * A naive caching tag.
 */
public class CacheTag extends BodyTagSupport {

    private String scope;
    private String name;
    private long duration;
    private Entry entry;

    public void setScope(String s) { scope = s; }

    public void setName(String n) { name = n; }

    public void setDuration(long d) { duration = d; }

    public int doStartTag() throws JspTagException {
        entry = getEntry();
        if ((entry != null) && entry.isExpired()) {
            entry = null;
            removeEntry();
        }
        return (entry == null) ? EVAL_BODY_BUFFERED : SKIP_BODY;
    }

    private String getKey() {
            HttpServletRequest req =
            ((HttpServletRequest) pageContext.getRequest());
            return  (req.getRequestURL().toString()
                            + '#' + name
                            + '?' + req.getQueryString());
    }


    private Entry getEntry() {
        String key = getKey();
         if ("context".equals(scope)) {
                    return (Entry)pageContext.getServletContext().getAttribute(key);
          } else if ("session".equals(scope)) {
                    return (Entry)pageContext.getSession().getAttribute(key);
         } else if ("request".equals(scope)) {
                    return (Entry)pageContext.getRequest().getAttribute(key);
         } else if ("page".equals(scope)) {
                    return (Entry)pageContext.getAttribute(key);
         }
        return null;
    }

    private void removeEntry() {
        String key = getKey();
         if ("context".equals(scope)) {
                   pageContext.getServletContext().removeAttribute(key);
          }else if ("session".equals(scope)) {
                   pageContext.getSession().removeAttribute(key);
         } else if ("request".equals(scope)) {
                    pageContext.getRequest().removeAttribute(key);
         } else if ("page".equals(scope)) {
                    pageContext.removeAttribute(key);
         }
    }

    public int doEndTag() throws JspTagException {
        if (entry == null) {
            BodyContent bc = getBodyContent();
            if (bc != null) {
                String content = bc.getString();
                entry = new Entry(content, duration);
                if ("context".equals(scope)) {
                    pageContext.getServletContext().setAttribute(getKey(), entry);
                }else if ("session".equals(scope)) {
                    pageContext.getSession().setAttribute(getKey(), entry);
                } else if ("request".equals(scope)) {
                    pageContext.getRequest().setAttribute(getKey(), entry);
                } else if ("page".equals(scope)) {
                    pageContext.setAttribute(getKey(), entry);
                }

                try {
                    JspWriter out = bc.getEnclosingWriter();
                    out.print(content);
                }
                catch (IOException ioe) {
                    System.err.println("ChacheTag: Problems with writing...");
                }
            }
        } else {
            try {
                JspWriter out = pageContext.getOut();
                out.print(entry.getContent());
            } catch (IOException ioe) {
                System.err.println("CacheTag: Problems with writing...");
            }
        }
        // reset everything
        scope = null;
        name = null;
        duration = 0;
        entry = null;


        return EVAL_PAGE;
    }

    /*
     * An entry in the cache.
     */
    class Entry {

        String content;
        long timestamp;
        long duration;

        public Entry(String content, long duration) {
            this.content = content;
            timestamp = System.currentTimeMillis();
            this.duration = duration;
        }

        public String getContent() { return content; }

        public boolean isExpired() {
            long currentTime = System.currentTimeMillis();
            return ((currentTime - timestamp) > duration);
        }
    }
}