lookupvaluebyparamcontextdata.java

这是一个mvc模式

package jsp.tags.dapact.lookup;

import javax.servlet.jsp.PageContext;
import javax.servlet.jsp.tagext.TagSupport;
import jsp.tags.dapact.BaseDataBodyTagSupport;
import jsp.tags.dapact.BaseDataTagSupport;
import jsp.tags.dapact.conf.UserClassFactory;

/**
 * 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@
 */

/**
 * Looks up the value by looking in the parameter list in the request, then the contexts,
 * and finally the data objects.
 * @todo rewrite to make one parameter driven class that uses properties as default.
 */
public class LookupValueByParamContextData extends LookupValueByParamContext
{
  /**
   * Default constructor...
   */
  public LookupValueByParamContextData()
  {
  }

  /**
   * This function will be called by the tags when they want to lookup a general
   * non-String object - in this case, it returns the value of a HTTP request parameter,
   * if that is null it looks in the contexts (page, request, session, and then application [servlet]),
   * or if that is also null look in the tag data objects for the value.
   *
   * @param key the key of the value to be saved.
   * @param value the value to be added - this will be overridden by what is returned by
   *   this function.
   * @param tag the tag that will be used to save the value.
   * @param pc the page context associated with the tag that is also a parameter. This
   *   will be used to search parameters and contexts (page, session, request, and servlet).
   *
   * @return the lookedup value or null if not found.
   */
  public Object lookupValue(String key, Object value, TagSupport tag, PageContext pc)
  {
    Object result = super.lookupValue(key, value, tag, pc);
    if ((result == null) && (key != null) && (tag != null))
    {
      String dataTagName = null;
      if (tag instanceof BaseDataTagSupport)
      {
        dataTagName = ((BaseDataTagSupport)tag).getDataTagName();
      }
      else if (tag instanceof BaseDataBodyTagSupport)
      {
        dataTagName = ((BaseDataBodyTagSupport)tag).getDataTagName();
      }
      result = LookupUtil.findValueInDataTag(key, dataTagName, tag);
    }
    return result;
  }

  /**
   * This function will be called by the tags when they want to lookup a string object
   * (most common case: storing attributes) - in this case, it returns the value of a HTTP request parameter,
   * if that is null it looks in the contexts (page, request, session, and then application [servlet]),
   * or if that is also null look in the tag data objects for the value.
   *
   * @param key the key of the value to be saved.
   * @param value the value to be added - this will be overridden by what is returned by
   *   this function.
   * @param tag the tag that will be used to save the value.
   * @param pc the page context associated with the tag that is also a parameter. This
   *   will be used to search parameters and contexts (page, session, request, and servlet).
   *
   * @return the lookedup value.
   */
  public String lookupValue(String key, String value, TagSupport tag, PageContext pc)
  {
    String result = super.lookupValue(key, value, tag, pc);
    if ((result == null) && (key != null) && (tag != null))
    {
      try
      {
        String dataTagName = null;
        if (tag instanceof BaseDataTagSupport)
        {
          dataTagName = ((BaseDataTagSupport)tag).getDataTagName();
        }
        else if (tag instanceof BaseDataBodyTagSupport)
        {
          dataTagName = ((BaseDataBodyTagSupport)tag).getDataTagName();
        }
        result = (String)LookupUtil.findValueInDataTag(key, dataTagName, tag);
      }
      catch (ClassCastException e)
      {
        // Catch this exception and log it and return null.
        UserClassFactory.getLogger().log("The lookup value for the following name is not a String: " + key, e);
      }
    }
    return result;
  }
}