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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 Ahmed Hashim
 *
 * 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.create;

import java.lang.reflect.Method;

import org.directwebremoting.extend.Creator;
import org.directwebremoting.util.LocalUtil;
import org.directwebremoting.util.Messages;

/**
 * A {@link Creator} that uses an instance method to create singletons.
 * By default this creator uses a static method with the signature:
 * SomeClass.getInstance() to create new instances. The name of
 * the singleton constructor method can be customized using the
 * getInstance parameter.
 * @author Ahmed Hashim [hashim at egjug dot org]
 * @author Joe Walker [joe at getahead dot ltd dot uk]
 */
public class SingletonCreator extends AbstractCreator implements Creator
{
    /**
     * What sort of class do we create?
     * @param classname The name of the class
     */
    public void setClass(String classname)
    {
        try
        {
            clazz = LocalUtil.classForName(classname);
        }
        catch (ClassNotFoundException ex)
        {
            throw new IllegalArgumentException(Messages.getString("Creator.ClassNotFound", classname));
        }
    }

    /* (non-Javadoc)
     * @see org.directwebremoting.extend.Creator#getInstance()
     */
    public Object getInstance() throws InstantiationException
    {
        try
        {
            Method method = clazz.getMethod(factoryMethod);
            return method.invoke(new SingletonCreator());
        }
        catch (Exception ex)
        {
            // JDK5: We should really be passing the exception on
            throw new InstantiationException(Messages.getString("Creator.IllegalAccess"));
        }
    }

    /* (non-Javadoc)
     * @see org.directwebremoting.extend.Creator#getType()
     */
    public Class getType()
    {
        return clazz;
    }
    
    /**
     * @return the factoryMethod function name
     * */
    public String getFactoryMethod()
    {
        return factoryMethod;
    }
    
    /**
     * @param functionToCall the name of the factory function. 
     * */
    public void setFactoryMethod(String functionToCall)
    {
        this.factoryMethod = functionToCall;
    }

    /**
     * The function which will return an instance from the object, the common 
     * function name used in singleton class is 'getInstance', this will be the
     * default value. 
     * */
    private String factoryMethod = "getInstance";

    /**
     * The type of the object that we create
     */
    private Class clazz;
}