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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 2007 Tim Peierls
 *
 * 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.guice;

import org.directwebremoting.create.NewCreator;
import org.directwebremoting.extend.Creator;
import org.directwebremoting.util.LocalUtil;

import com.google.inject.Injector;

import static org.directwebremoting.guice.DwrGuiceUtil.*;

/**
 * A creator that uses Guice dependency injection to create remoted objects.
 * @author Tim Peierls [tim at peierls dot net]
 */
public class GuiceCreator extends NewCreator implements Creator
{

    public GuiceCreator()
    {
        this.injector = getInjector();
    }

    /**
     * Specified via {@link org.directwebremoting.annotations.RemoteProxy @RemoteProxy}
     * or via a parameter in XML configuration.
     */
    @Override
    public void setClass(String classname)
    {
        try
        {
            // Don't use LocalUtil.classForName because it insists
            // on a default constructor, and we want to be able to
            // use an @Inject constructor.
            this.type = LocalUtil.classForName(classname);
        }
        catch (ClassNotFoundException ex)
        {
            throw new IllegalArgumentException(String.format("GuiceCreator: class %s not found", classname));
        }
    }

    /**
     * The class named through {@link GuiceCreator#setClass setClass}.
     */
    @Override
    public Class getType()
    {
        return type;
    }

    /**
     * Looks up an instance of this creator's type with an
     * {@link com.google.inject.Injector Injector}.
     */
    @Override
    public Object getInstance()
    {
        return injector.getInstance(type);
    }

    /**
     * The type of object being created.
     */
    private volatile Class type;

    /**
     * The Injector with which objects are created.
     */
    private final Injector injector;
}