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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.extend;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.directwebremoting.Container;

/**
 * An abstraction of all the common servlet operations that are required to host
 * a DWR service that depends on the servlet spec.
 * It would be good to have a base class for all servlet operations, however
 * lack of MI prevents us from doing this.
 * @author Joe Walker [joe at getahead dot ltd dot uk]
 */
public class ContainerUtil
{
    /**
     * Get an boolean setting from the Container.
     * @param container The container to look into
     * @param name The name of the setting to investigate
     * @param defaultValue The value to return if none is given
     * @return The value of the setting as an boolean, or the defaultValue if the
     * setting is empty or not convertible.
     */
    public static boolean getBooleanSetting(Container container, String name, boolean defaultValue)
    {
        Object value = container.getBean(name);
        if (value == null)
        {
            return defaultValue;
        }
        return Boolean.parseBoolean(value.toString());
    }

    /**
     * Get an integer setting from the Container.
     * @param container The container to look into
     * @param name The name of the setting to investigate
     * @param defaultValue The value to return if none is given
     * @return The value of the setting as an int, or the defaultValue if the
     * setting is empty or not convertible.
     */
    public static int getIntSetting(Container container, String name, int defaultValue)
    {
        Object value = container.getBean(name);
        if (value == null)
        {
            return defaultValue;
        }

        try
        {
            return Integer.parseInt(value.toString());
        }
        catch (NumberFormatException ex)
        {
            log.warn("Failed to convert value '" + value + "' from setting '" + name + "' to an integer: " + ex.getMessage());
            return defaultValue;
        }
    }

    /**
     * Look up the Handler associated with the URL in the named URL property.
     * F ex supply the property name "engineHandlerUrl" to look up EngineHandler.
     *
     * @param container The container to look into
     * @param property a URL property name known by the container (usually
     * declared in defaults.properties)
     * @return the Handler registered on the URL
     */
    public static Handler getHandlerForUrlProperty(Container container, String property)
    {
        String registeredHandlerUrl = (String) container.getBean(property);
        return (Handler) container.getBean("url:" + registeredHandlerUrl);
    }

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