basetagsupport.java

这是一个mvc模式

package jsp.tags.dapact;

import java.util.Enumeration;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.TagSupport;
import jsp.tags.dapact.conf.UserClassFactory;
import jsp.tags.dapact.lookup.TagDataParamNames;
import jsp.tags.dapact.util.TagUtil;
/**
 * 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@
 */

/**
 * Base class for all tags that need to implement the Tag interface by providing
 * an implementation of the interface that works with the tag library to add further
 * functionality.
 */
public class BaseTagSupport extends TagSupport
{
  /**
   * Default constructor.
   */
  public BaseTagSupport()
  {
  }

  /**
   * Called when the starting tag is found.
   *
   * @return EVAL_BODY_INCLUDE so that it processes what ever is in the body.
   */
  public int doStartTag() throws JspException
  {
    super.doStartTag();
    return EVAL_BODY_INCLUDE;
  }

 /**
   * Called at the end of the tag.
   *
   * @exception JspException general JSP exception.
   *
   * @return EVAL_PAGE so that it continues to process the rest of the page.
   */
  public int doEndTag() throws JspException
  {
    super.doEndTag();
    return EVAL_PAGE;
  }

  /**
   * Call this to set an object value for a specific key. This is useful for storing
   * non-Sting objects in a tag for later retrieval. The value passed in will be processed
   * by a call to TagUtil.filterValue(String, Object, TagSupport, PageContext). If
   * that filter returns a null, it will remove the key-value from storage.
   *
   * @param key the key to reference the object with - remember, these keys will be mixed
   *   with the ones from the setValue(String, String) function call. If this is null, the
   *   filter will not be called and nothing will happen.
   * @param value the object to store for the key.
   */
  public void setValue(String key, Object value)
  {
    if (key != null)
    {
      Object newValue = UserClassFactory.getFilterValueInstance(getFilterValueName()).lookupValue(key, value, this, pageContext);
      if (newValue != null)
      {
        super.setValue(key, newValue);
        String name = isPublishableAttr(key, newValue);
        if (name != null)
        {
          pageContext.setAttribute(name, newValue);
        }
      }
      else
      {
        removeValue(key);
        String name = isReleasableAttr(key);
        if (name != null)
        {
          pageContext.removeAttribute(name);
        }
      }
    }
  }

  /**
   * Call this to set a string value for a specific key. This is useful for storing
   * non-Object objects in a tag for later retrieval - like the value of tag attributes.
   * The value passed in will be processed by a call to TagUtil.filterValue(String, Object, TagSupport, PageContext).
   * If that filter returns a null, it will remove the key-value from storage.
   *
   * @param key the key to reference the object with - remember, these keys will be mixed
   *   with the ones from the setValue(String, Object) function call. If this is null, the
   *   filter will not be called and nothing will happen.
   * @param value the string to store for the key.
   */
  public void setValue(String key, String value)
  {
    if (key != null)
    {
      Object newValue = UserClassFactory.getFilterValueInstance(getFilterValueName()).lookupValue(key, value, this, pageContext);
      if (newValue != null)
      {
        super.setValue(key, newValue);
        String name = isPublishableAttr(key, newValue);
        if (name != null)
        {
          pageContext.setAttribute(name, newValue);
        }
      }
      else
      {
        removeValue(key);
        String name = isReleasableAttr(key);
        if (name != null)
        {
          pageContext.removeAttribute(name);
        }
      }
    }
  }

  /**
   * Retrieves a value as a String.
   *
   * @param key the key to be used to look up the value.
   *
   * @return the value as a string or null if it was not found.
   */
  public String getValueAsString(String key)
  {
    String result = null;
    if (key != null)
    {
      Object value = getValue(key);
      if (value != null)
      {
        result = value.toString();
      }
    }
    return result;
  }

  /**
   * Called by the container to free the tag's resources - this also releases any published
   * attributes. This is called after the end tag.
   */
  public void release()
  {
    // Releases the tag
    Enumeration attrs = getValues();
    if (attrs != null)
    {
      while (attrs.hasMoreElements())
      {
        String key = (String)attrs.nextElement();
        String name = isReleasableAttr(key);
        if (name != null)
        {
          pageContext.removeAttribute(name);
        }
      }
    }
    super.release();
  }

  /**
   * Checks to see if the attribute should be published (and, if so, with what name).
   * This base implementation always returns null - the subclass should make the decision.
   * This implementation will therefore only mandate that this function be overridden
   * when the subclass wants to publish some attributes.
   *
   * @param attr the attribute under consideration.
   * @param value the attribute's current value.
   *
   * @return <code>null</code> if it should not be published, otherwise the name that will be
   *  used to publish it (set it as an attribute of the page context).
   */
  public String isPublishableAttr(String attr, Object value)
  {
    return null;
  }

  /**
   * Checks to see if the attribute should be released (and, if so, with what name).
   * This base implementation always returns null - the subclass should make the decision.
   * This implementation will therefore only mandate that this function be overridden
   * when the subclass wants to release some attributes.
   *
   * @param attr the attribute under consideration.
   * @param value the attribute's current value.
   *
   * @return <code>null</code> if it should not be released, otherwise the name that will be
   *  used to release it (from the page context).
   */
  public String isReleasableAttr(String attr)
  {
    return null;
  }

  /**
   * Retrieve the name of the filter value object to create (will be used to look up
   * the filter value object class name).
   */
  protected String getFilterValueName()
  {
    String name = null;
    try
    {
      name = (String)pageContext.findAttribute(TagDataParamNames.FILTER_VALUE_NAME_DATA_NAME);
    }
    catch (ClassCastException e)
    {
      // Just log exception.
      UserClassFactory.getLogger().log("Filter value name found but is not a string.", e);
    }
    return name;
  }

  /**
   * @return Retrieve the name of the lookup value object to create (will be used to look up
   * the lookup value object class name).
   */
  protected String getLookupValueName()
  {
    String name = null;
    try
    {
      name = (String)pageContext.findAttribute(TagDataParamNames.LOOKUP_VALUE_NAME_DATA_NAME);
    }
    catch (ClassCastException e)
    {
      // Just log exception.
      UserClassFactory.getLogger().log("Lookup value name found but is not a string.", e);
    }
    return name;
  }

  /*=============================================================================*/
  /*                           PROPERTIES/ATTRIBUTES                             */
  /*=============================================================================*/
  /**
   * A string constant that is used to retrieve and set the value of the lookup name property.
   */
  public static final String LOOKUP_NAME_CONST = TagUtil.HIDE_ATTR_CHAR + "lookupName";
  /**
   * Get the lookup name of the object.
   */
  public String getLookupName()
  {
    return (String)getValue(LOOKUP_NAME_CONST);
  }
  /**
   * Set the lookup name of the object.
   */
  public void setLookupName(String lookupName)
  {
    this.setValue(LOOKUP_NAME_CONST, lookupName);
  }

  /**
   * A string constant that is used to retrieve and set the value of the name property.
   */
  public static final String NAME_CONST = "name";
  /**
   * Get the name of the object.
   */
  public String getName()
  {
    return (String)getValue(NAME_CONST);
  }
  /**
   * Set the name of the object.
   */
  public void setName(String name)
  {
    this.setValue(NAME_CONST, name);
  }
}