foreachtag.java

这是学习Java必须读懂两套源代码

/**
 * Copyright (C) 2001 Yasna.com. All rights reserved.
 *
 * ===================================================================
 * The Apache Software License, Version 1.1
 *
 * 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 acknowledgment:
 *       "This product includes software developed by
 *        Yasna.com (http://www.yasna.com)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Yazd" and "Yasna.com" must not be used to
 *    endorse or promote products derived from this software without
 *    prior written permission. For written permission, please
 *    contact [e-mail].
 *
 * 5. Products derived from this software may not be called "Yazd",
 *    nor may "Yazd" appear in their name, without prior written
 *    permission of Yasna.com.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL YASNA.COM OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of Yasna.com. For more information
 * on Yasna.com, please see <http://www.yasna.com>.
 */

/**
 * Copyright (C) 2000 CoolServlets.com. All rights reserved.
 *
 * ===================================================================
 * The Apache Software License, Version 1.1
 *
 * 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 acknowledgment:
 *       "This product includes software developed by
 *        CoolServlets.com (http://www.coolservlets.com)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Jive" and "CoolServlets.com" must not be used to
 *    endorse or promote products derived from this software without
 *    prior written permission. For written permission, please
 *    contact [e-mail].
 *
 * 5. Products derived from this software may not be called "Jive",
 *    nor may "Jive" appear in their name, without prior written
 *    permission of CoolServlets.com.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL COOLSERVLETS.COM OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of CoolServlets.com. For more information
 * on CoolServlets.com, please see <http://www.coolservlets.com>.
 */

package com.Yasna.forum.tags;

import java.io.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.jsp.*;
import javax.servlet.jsp.tagext.*;
import javax.servlet.http.*;
import com.Yasna.forum.*;
import com.Yasna.forum.tags.*;

/**
 * JSP Tag <b>foreach</b>, used to implement a simple numbered loop.
 * <p>
 * Requires that attribute <b>id</b> be set to the name of a
 * script variable for later use in JSP to retrieve the value
 * of the loop counter using &lt;jsp:getProperty/&gt;.
 * <p>
 * Requires that attribute <b>begin</b> be set to the number at
 * which the foreach loop should start.
 * <p>
 * Requires that attribute <b>end</b> be set to the number at
 * which the foreach loop should end.
 * <p>
 * Optional attribute <b>step</b> specifies how much the foreach
 * counter should be incremented for each loop, default is 1.
 * <p>
 * During each loop the body of the foreach tag is processed.
 * <p>
 * JSP Tag Lib Descriptor
 * <p><pre>
 *  &lt;name&gt;foreach&lt;/name&gt;
 *  &lt;tagclass&gt;com.Yasna.forum.tags.ForEachTag&lt;/tagclass&gt;
 *  &lt;teiclass&gt;com.Yasna.forum.tags.ForEachTEI&lt;/teiclass&gt;
 *  &lt;bodycontent&gt;JSP&lt;/bodycontent&gt;
 *  &lt;info&gt;Implement a loop.&lt;/info&gt;
 *  &lt;attribute&gt;
 *    &lt;name&gt;id&lt;/name&gt;
 *    &lt;required&gt;true&lt;/required&gt;
 *    &lt;rtexprvalue&gt;false&lt;/rtexprvalue&gt;
 *  &lt;/attribute&gt;
 *  &lt;attribute&gt;
 *    &lt;name&gt;begin&lt;/name&gt;
 *    &lt;required&gt;true&lt;/required&gt;
 *    &lt;rtexprvalue&gt;false&lt;/rtexprvalue&gt;
 *  &lt;/attribute&gt;
 *  &lt;attribute&gt;
 *    &lt;name&gt;end&lt;/name&gt;
 *    &lt;required&gt;true&lt;/required&gt;
 *    &lt;rtexprvalue&gt;false&lt;/rtexprvalue&gt;
 *  &lt;/attribute&gt;
 *  &lt;attribute&gt;
 *    &lt;name&gt;step&lt;/name&gt;
 *    &lt;required&gt;false&lt;/required&gt;
 *    &lt;rtexprvalue&gt;false&lt;/rtexprvalue&gt;
 *  &lt;/attribute&gt;
 * </pre>
 *
 * @author Glenn Nielsen
 */
public class ForEachTag extends BodyTagSupport
{
  private int begin = 0;
  private int end = 0;
  private int index = 0;
  private int step = 1;

  /**
   * Method called at start of foreach Tag
   *
   * @return an EVAL_BODY_TAG if foreach should loop, or a SKIP_BODY if foreach is completed.
   */
  public final int doStartTag() throws JspException
  {
    // Save the script variable for use by JSP getProperty
    pageContext.setAttribute(id,this,PageContext.PAGE_SCOPE);
    if( index > end )
      return SKIP_BODY;
    return EVAL_BODY_TAG;
  }

  /**
   * Method called at end of a foreach loop
   *
   * @return an EVAL_BODY_TAG if foreach should loop again, or a SKIP_BODY if foreach is completed.
   */
  public final int doAfterBody() throws JspException
  {
    index += step;
    if( index > end )
      return SKIP_BODY;
    return EVAL_BODY_TAG;
  }

  /**
   * Method called at end of foreach Tag
   * @return EVAL_PAGE
   */
  public final int doEndTag() throws JspException
  {
    try
    {
      if(bodyContent != null)
        bodyContent.writeOut(bodyContent.getEnclosingWriter());
    } catch(java.io.IOException e)
    {
      throw new JspException("IO Error: " + e.getMessage());
    }
    return EVAL_PAGE;
  }

  /**
   * Set the beginning index of the foreach loop
   */
  public final void setBegin(String beg)
  {
    index = begin = Integer.valueOf(beg).intValue();
  }

  /**
   * Set the ending index of the foreach loop
   */
  public final void setEnd(String last)
  {
    end = Integer.valueOf(last).intValue();
  }

  /**
   * Set the index step of the foreach loop
   */
  public final void setStep(String last)
  {
    step = Integer.valueOf(last).intValue();
  }

  /**
   * foreach loop value property which can be obtained by the JSP page
   * using &lt;jsp:getProperty name=<i>"id"</i> property="value"/&gt;
   *
   * @return String - current value of the foreach counter
   */
  public final String getValue()
  {
    return "" + index;
  }

  /**
   * Remove the script variable after foreach tag closed out
   */
  public final void release()
  {
    if( id != null && id.length() > 0 )
      pageContext.removeAttribute(id,PageContext.PAGE_SCOPE);
  }

}