beanwalker.java

webwork source

/*
 * WebWork, Web Application Framework
 *
 * Distributable under Apache license.
 * See terms of license at opensource.org
 */
package webwork.view.xslt.SAXAdapter;

import org.apache.commons.logging.*;
import org.xml.sax.ContentHandler;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.AttributesImpl;

import java.beans.IntrospectionException;
import java.beans.Introspector;
import java.beans.PropertyDescriptor;
import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class BeanWalker extends AbstractWalker
{

   private static final Object[] NULLPARAMS = new Object[0];

   /**
    * Cache can savely be static because the cached information is
    * the same for all instances of this class.
    */
   private static Map propertyDescriptorCache;

   public void doWalk(XMLWalker rootWalker, ContentHandler contentHandler, Object value, String attributeName, List walkedInstances) throws SAXException
   {
      if (value == null)
      {
         LogFactory.getLog(this.getClass()).error(attributeName + " == null, returning!");
         return;
      } // Guardclause

      walkedInstances.add(value);

      try
      {
         Class type = value.getClass();
         PropertyDescriptor[] props = getPropertyDescriptors(value);
         if (props.length > 0)
         {
            AttributesImpl attributes = new AttributesImpl();
            attributes.addAttribute("", "class", "", "CDATA", type.getName());
            contentHandler.startElement("", attributeName, "", attributes);
            for (int i = 0; i < props.length; i++)
            {
               Method m = props[i].getReadMethod();
               if (m == null)
               {
                  //FIXME: write only property or indexed access
                  continue;
               }
               String propertyName = props[i].getName();
               Object propertyValue;
               /** 999 white magic hack start 999 **
                * some property accessors will throw exceptions,
                * e.g. getLocale() in webwork.ActionSupport *grrr*
                * IMHO property accessor should not have those side
                * effects - [e-mail]
                */
               try
               {
                  propertyValue = m.invoke(value, NULLPARAMS);
               }
               catch (Exception e)
               {
                  continue;
               }
               /** 999 white magic hack end 999 **/

               rootWalker.walk(contentHandler, propertyValue, propertyName, walkedInstances);

            }
            contentHandler.endElement("", attributeName, "");
         }
         else
         {
            // No properties found
            LogFactory.getLog(this.getClass()).debug("Class " + type.getName() + " has no readable properties, " + " trying to walk with toStringWalker...");
            rootWalker.getToStringWalker().walk(rootWalker, contentHandler, value, attributeName, walkedInstances);
         }
      }
      catch (IntrospectionException e)
      {
         throw new SAXException(e);
      }
   }

   /**
    * @return A private Class not visible from outside.
    *         This walker is not really used by the registry in XMLReaderAdapter.
    *         If it would match java.lang.Object the fall back for primitives and java.lang.Number
    *         would not work any more.
    */
   public final Class getWalkedType()
   {
      return NoClass.class;
   }

   /**
    * This private class is returned by @see getWalkedType pro forma.
    */
   private class NoClass
   {
   }

   /**
    * Caching facade method to Introspector.getBeanInfo(Class, Class).getPropertyDescriptors();
    **/
   private synchronized PropertyDescriptor[] getPropertyDescriptors(Object bean) throws IntrospectionException
   {
      if (propertyDescriptorCache == null)
      {
         propertyDescriptorCache = new HashMap();
      }

      PropertyDescriptor[] props = (PropertyDescriptor[]) propertyDescriptorCache.get(bean.getClass());
      if (props == null)
      {
         LogFactory.getLog(this.getClass()).debug("Caching property descriptor for " + bean.getClass().getName());
         props = Introspector.getBeanInfo(bean.getClass(), Object.class).getPropertyDescriptors();
         propertyDescriptorCache.put(bean.getClass(), props);
      }
      return props;
   }
}