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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.spring;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.Map;

import org.directwebremoting.Container;
import org.directwebremoting.impl.DefaultContainer;
import org.directwebremoting.util.Logger;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.BeanFactoryAware;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.beans.factory.ListableBeanFactory;
import org.springframework.util.ClassUtils;

/**
 * A Container implementation that looks up all beans from the
 * configuration specified in a Spring context.
 * It loads the configuration from a Spring web application context.
 * @author Bram Smeets
 * @author Joe Walker [joe at getahead dot ltd dot uk]
 */
public class SpringContainer extends DefaultContainer implements Container, BeanFactoryAware, InitializingBean
{
    /* (non-Javadoc)
     * @see org.springframework.beans.factory.BeanFactoryAware#setBeanFactory(org.springframework.beans.factory.BeanFactory)
     */
    public void setBeanFactory(BeanFactory beanFactory) throws BeansException
    {
        this.beanFactory = beanFactory;
    }

    public void addParameter(Object askFor, Object valueParam)
    throws InstantiationException, IllegalAccessException {
        try {
            Class clz = ClassUtils.forName((String)askFor);
            if (log.isDebugEnabled()) {
                log.debug("trying to resolve the following class from the Spring bean container: " + clz.getName());
            }

            Map beansOfType = ((ListableBeanFactory)beanFactory).getBeansOfType(clz);
            if (log.isDebugEnabled()) {
                log.debug("beans: " + beansOfType + " - " + beansOfType.size());
            }
            if (beansOfType.size() == 0) {
                log.debug("adding parameter the normal way");
                super.addParameter(askFor, valueParam);
            } else if (beansOfType.size() > 1) {
                // TODO: handle multiple declarations
                throw new InstantiationException("multiple beans of type '" + clz.getName() + "' were found in the spring configuration");
            } else {
                this.beans.put(askFor, beansOfType.values().iterator().next());
            }
        } catch (ClassNotFoundException e) {
            super.addParameter(askFor, valueParam);
        }
    }

    /* (non-Javadoc)
     * @see org.directwebremoting.impl.DefaultContainer#getBean(java.lang.String)
     */
    public Object getBean(String id)
    {
        Object reply;
        try {
            reply = beanFactory.getBean(id);
        }
        catch (BeansException ex)
        {
            // Spring throws on not-found, we return null.
            reply = super.getBean(id);
        }

        return reply;
    }

    /* (non-Javadoc)
     * @see org.directwebremoting.impl.DefaultContainer#getBeanNames()
     */
    public Collection getBeanNames()
    {
        List names = new ArrayList();

        // Snarf the beans from Spring
        if (beanFactory instanceof ListableBeanFactory)
        {
            ListableBeanFactory listable = (ListableBeanFactory) beanFactory;
            names.addAll(Arrays.asList(listable.getBeanDefinitionNames()));
        }
        else
        {
            log.warn("List of beanNames does not include Spring beans since your BeanFactory is not a ListableBeanFactory.");
        }

        // And append the DWR ones
        names.addAll(super.getBeanNames());

        return Collections.unmodifiableCollection(names);
    }

    /**
     * Avoids initialization of lazy-init beans in Spring context.
     */
    protected void callInitializingBeans()
    {
        callInitializingBeans(super.getBeanNames());
    }
    
    
    /* (non-Javadoc)
     * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet()
     */
    public void afterPropertiesSet() throws Exception
    {
        // This needs to be implemented, but the work that would normally be done here
        // is done in callInitializingBeans.  DWR-561.
    }

    /**
     * The Spring BeanFactory that we read from
     */
    protected BeanFactory beanFactory;

    /**
     * The log stream
     */
    private static final Logger log = Logger.getLogger(SpringContainer.class);
}