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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.List;
import java.util.Map;

import javax.servlet.ServletContext;
import javax.servlet.http.HttpServletRequest;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.directwebremoting.ServerContextFactory;
import org.directwebremoting.WebContextFactory;
import org.directwebremoting.extend.AbstractCreator;
import org.directwebremoting.extend.Creator;
import org.directwebremoting.util.LocalUtil;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.web.servlet.support.RequestContextUtils;
import org.springframework.web.context.support.WebApplicationContextUtils;

/**
 * A creator that relies on a spring bean factory.
 * @author Joe Walker [joe at getahead dot ltd dot uk]
 */
public class SpringCreator extends AbstractCreator implements Creator
{
    /**
     * @return Returns the beanName.
     */
    public String getBeanName()
    {
        return beanName;
    }

    /**
     * @param beanName The beanName to set.
     */
    public void setBeanName(String beanName)
    {
        this.beanName = beanName;
    }

    /**
     * What sort of class do we create?
     * @param classname The name of the class
     */
    public void setClass(String classname)
    {
        try
        {
            this.clazz = LocalUtil.classForName(classname);
        }
        catch (ClassNotFoundException ex)
        {
            throw new IllegalArgumentException("Class not found: " + classname, ex);
        }
    }

    /* (non-Javadoc)
     * @see org.directwebremoting.create.Creator#init(org.w3c.dom.Element)
     */
    @Override
    public void setProperties(Map params) throws IllegalArgumentException
    {
        List locValues = new ArrayList();

        for (Map.Entry entry : params.entrySet())
        {
            String key = entry.getKey();
            String value = entry.getValue();

            if (key.startsWith("location"))
            {
                log.debug("Adding configLocation: " + value + " from parameter: " + key);
                locValues.add(value);
            }
        }

        configLocation = locValues.toArray(new String[locValues.size()]);
    }

    /* (non-Javadoc)
     * @see org.directwebremoting.Creator#getType()
     */
    public Class getType()
    {
        if (clazz == null)
        {
            try
            {
                clazz = getInstance().getClass();
            }
            catch (InstantiationException ex)
            {
                log.error("Failed to instansiate object to detect type.", ex);
                return Object.class;
            }
        }

        return clazz;
    }

    /* (non-Javadoc)
     * @see org.directwebremoting.Creator#getInstance()
     */
    public Object getInstance() throws InstantiationException
    {
        try
        {
            if (overrideFactory != null)
            {
                return overrideFactory.getBean(beanName);
            }

            if (factory == null)
            {
                factory = getBeanFactory();
            }

            if (factory == null)
            {
                log.error("DWR can't find a spring config. See following info logs for solutions");
                log.info("- Option 1. In dwr.xml,  add  for each spring config file.");
                log.info("- Option 2. Use a spring org.springframework.web.context.ContextLoaderListener.");
                log.info("- Option 3. Call SpringCreator.setOverrideBeanFactory() from your web-app");
                throw new InstantiationException("DWR can't find a spring config. See the logs for solutions");
            }

            return factory.getBean(beanName);
        }
        catch (InstantiationException ex)
        {
            throw ex;
        }
        catch (Exception ex)
        {
            throw new InstantiationException("Illegal Access to default constructor on " + clazz.getName() + " due to: " + ex);
        }
    }

    /**
     * @return A found BeanFactory configuration
     */
    private BeanFactory getBeanFactory()
    {
        // If someone has set a resource name then we need to load that.
        if (configLocation != null && configLocation.length > 0)
        {
            log.info("Spring BeanFactory via ClassPathXmlApplicationContext using " + configLocation.length + "configLocations.");
            return new ClassPathXmlApplicationContext(configLocation);
        }

        ServletContext srvCtx = ServerContextFactory.get().getServletContext();

        HttpServletRequest request = null;
        try
        {
            request = WebContextFactory.get().getHttpServletRequest();
        }
        catch (Exception ex)
        {
            // Probably on boot time
        }
        return request != null ? RequestContextUtils.getWebApplicationContext(request, srvCtx) : WebApplicationContextUtils.getWebApplicationContext(srvCtx);
    }

    /**
     * Set a web-app wide BeanFactory.
     * This method is misnamed (The parameter is a BeanFactory and not a
     * XmlBeanFactory)
     * @param factory The factory to set.
     * @deprecated This method is misnamed use setOverrideBeanFactory
     */
    @Deprecated
    public static void setXmlBeanFactory(BeanFactory factory)
    {
        overrideFactory = factory;
    }

    /**
     * Set a web-app wide BeanFactory.
     * @param factory The factory to set.
     */
    public static void setOverrideBeanFactory(BeanFactory factory)
    {
        overrideFactory = factory;
    }

    /**
     * The name of the spring bean we want to create
     */
    private String beanName = null;

    /**
     * The log stream
     */
    private static final Log log = LogFactory.getLog(SpringCreator.class);

    /**
     * The Spring beans factory from which we get our beans.
     */
    private BeanFactory factory = null;

    /**
     * An web-app wide BeanFactory that we can use to override any calculated
     * ones.
     */
    private static BeanFactory overrideFactory = null;

    /**
     * The cached type of bean that we are creating
     */
    private Class clazz = null;

    /**
     * An array of locations to search through for a beans.xml file
     */
    private String[] configLocation = null;
}