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DWR is easy Ajax for Java. It makes it simple to call Java code directly from Javascript. It gets rid of almost all the boiler plate code between the web browser and your Java code.

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/*
 * Copyright 2005 Joe Walker
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.directwebremoting.hibernate;

import java.beans.PropertyDescriptor;

import javax.servlet.ServletContext;

import org.directwebremoting.ConversionException;
import org.directwebremoting.WebContextFactory;
import org.directwebremoting.extend.Property;
import org.directwebremoting.extend.PropertyDescriptorProperty;
import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.engine.SessionImplementor;
import org.hibernate.proxy.HibernateProxy;
import org.hibernate.proxy.LazyInitializer;

/**
 * A {@link Property} that catches Hibernate exceptions.
 * This is useful for Hibernate 2 where lazy loading results in an exception
 * and you are unable to detect and prevent this.
 * @author Joe Walker [joe at getahead dot ltd dot uk]
 */
public class H3PropertyDescriptorProperty extends PropertyDescriptorProperty
{
    /**
     * Simple constructor
     * @param descriptor The PropertyDescriptor that we are proxying to
     */
    public H3PropertyDescriptorProperty(PropertyDescriptor descriptor)
    {
        super(descriptor);
    }

    /* (non-Javadoc)
     * @see org.directwebremoting.impl.PropertyDescriptorProperty#getValue(java.lang.Object)
     */
    @Override
    public Object getValue(Object bean) throws ConversionException
    {
        if (!(bean instanceof HibernateProxy))
        {
            // This is not a hibernate dynamic proxy, just use it
            return super.getValue(bean);
        }
        else
        {
            // If the property is already initialized, use it
            boolean initialized = Hibernate.isPropertyInitialized(bean, descriptor.getName());
            if (initialized)
            {
                // This might be a lazy-collection so we need to double check
                Object reply = super.getValue(bean);
                initialized = Hibernate.isInitialized(reply);
            }

            if (initialized)
            {
                return super.getValue(bean);
            }
            else
            {
                // If the session bound to the property is live, use it
                HibernateProxy proxy = (HibernateProxy) bean;
                LazyInitializer initializer = proxy.getHibernateLazyInitializer();
                SessionImplementor implementor = initializer.getSession();
                if (implementor.isOpen())
                {
                    return super.getValue(bean);
                }

                // So the property needs database access, and the session is closed
                // We'll need to try get another session
                ServletContext context = WebContextFactory.get().getServletContext();
                Session session = H3SessionAjaxFilter.getCurrentSession(context);

                if (session != null)
                {
                    session.update(bean);
                    return super.getValue(bean);
                }

                return null;
            }
        }
    }
}