basedatatagiteratorcollection.java

这是一个mvc模式

package jsp.tags.dapact.tags.data;

import java.util.Collection;
import java.util.Iterator;
import jsp.tags.dapact.conf.UserClassFactory;
import jsp.tags.dapact.tags.ChainedJspException;
/**
 * Title:        Data Aware Processing And Control Tags
 * Description:  Tag library for the processing and controlling the input and output of data.
 * Copyright:    LGPL (http://www.gnu.org/copyleft/lesser.html)
 * Compile Date: @compile_date@
 * @author Allen M Servedio
 * @amp_sign@version @VERSION@
 */

/**
 * Data tag iterator that iterates over a collection (supplied by the subclass... if you want
 * it supplied by doing a lookup, use jsp.tags.dapact.tags.data.DataTagIteratorUsingAssignData).
 * It uses its name as the key to the value (i.e. when a call to
 * {@link #retrieveValueByName(Object, String)} comes in, it only returns a value if
 * the name parameter matches the name property.
 */
public abstract class BaseDataTagIteratorCollection extends BaseDataTagIterator
{
  /**
   * Default constructor...
   */
  public BaseDataTagIteratorCollection()
  {
  }

  /**
   * Called when the starting tag is found - if an exception occurs while processing
   * the super class, this will call the close() method or if there is nothing to iterate
   * over, it will call the close() method.
   *
   * @return EVAL_BODY_TAG so that it processes what ever is in the body or SKIP_BODY
   * if no collection (or iterator from the collection) is supplied or it is empty.
   */
  public int doStartTag() throws ChainedJspException
  {
    super.doStartTag();
    int result = SKIP_BODY;

    Collection collection = getCollection();
    if (collection != null)
    {
      iterator = collection.iterator();
      if ((iterator != null) && (iterator.hasNext()))
      {
        result = EVAL_BODY_TAG;
        value = iterator.next();
      }
    }

    // If the result is to skip the body, close any open resources.
    if (result == SKIP_BODY)
    {
      try
      {
        close();
      }
      catch (DataException ex)
      {
        UserClassFactory.getLogger().log("Exception while closing resources because there was no data to process.", ex);
      }
    }
    return result;
  }

  /**
   * Called by objects that want to request a value by its name, it only returns a value if
   * the name parameter matches the name property.
   *
   * @param requestor the object requesting the value or the object that the value
   *   is being requested for (like with a lookup: you would pass the TagSupport
   *   object, not the lookup which is what actually calls this function).
   * @param name the name of the value to retrieve.
   *
   * @return the value that was found by the name supplied.
   */
  public Object retrieveValueByName(Object requestor, String name)
  {
    Object result = null;
    if (getName().equals(name))
    {
      result = value;
    }
    return result;
  }

  /**
   * When there is an exception or the result set has been processed, this method will be called.
   */
  public void close() throws DataException
  {
    iterator = null;
    value = null;
    setDone(true);
  }

  /**
   * This function is called to get the next entry in the collection.
   *
   * @return this function returns <code>true</code> until there is no more data,
   *   then it returns <code>false</code>.
   */
  public boolean next() throws DataException
  {
    boolean result = false;
    if ((iterator != null) && (iterator.hasNext()) && (!isDone()))
    {
      value = iterator.next();
      result = true;
    }
    setDone(!result);
    return result;
  }

  /**
   * Called by the container to free the tag's resources - super class calls the close()
   * method from the RetrieveValueByNameIteratorInf interface to close any open resources.
   */
  public void release()
  {
    super.release();
    iterator = null;
    value = null;
  }

  /**
   * Method that must be implemented by sub classes to return the collection to be
   * iterated over - this will be called in the doStartTag() function.
   *
   * @return collection to be iterated over.
   */
  protected abstract Collection getCollection();

  private Iterator iterator;
  private Object value;
}