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Commons Collections example source code file (InstantiateFactory.java)

This example Commons Collections source code file (InstantiateFactory.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Commons Collections tags/keywords

class, class, constructor, constructor, factory, functorexception, illegalaccessexception, illegalargumentexception, instantiatefactory, instantiatefactory, instantiationexception, io, object, object, reflection, serializable

The Commons Collections InstantiateFactory.java source code

/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You 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.apache.commons.collections.functors;

import java.io.Serializable;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;

import org.apache.commons.collections.Factory;
import org.apache.commons.collections.FunctorException;

/**
 * Factory implementation that creates a new object instance by reflection.
 * 
 * @since Commons Collections 3.0
 * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
 *
 * @author Stephen Colebourne
 */
public class InstantiateFactory implements Factory, Serializable {

    /** The serial version */
    private static final long serialVersionUID = -7732226881069447957L;

    /** The class to create */
    private final Class iClassToInstantiate;
    /** The constructor parameter types */
    private final Class[] iParamTypes;
    /** The constructor arguments */
    private final Object[] iArgs;
    /** The constructor */
    private transient Constructor iConstructor = null;

    /**
     * Factory method that performs validation.
     * 
     * @param classToInstantiate  the class to instantiate, not null
     * @param paramTypes  the constructor parameter types
     * @param args  the constructor arguments
     * @return a new instantiate factory
     */
    public static Factory getInstance(Class classToInstantiate, Class[] paramTypes, Object[] args) {
        if (classToInstantiate == null) {
            throw new IllegalArgumentException("Class to instantiate must not be null");
        }
        if (((paramTypes == null) && (args != null))
            || ((paramTypes != null) && (args == null))
            || ((paramTypes != null) && (args != null) && (paramTypes.length != args.length))) {
            throw new IllegalArgumentException("Parameter types must match the arguments");
        }

        if (paramTypes == null || paramTypes.length == 0) {
            return new InstantiateFactory(classToInstantiate);
        } else {
            paramTypes = (Class[]) paramTypes.clone();
            args = (Object[]) args.clone();
            return new InstantiateFactory(classToInstantiate, paramTypes, args);
        }
    }

    /**
     * Constructor that performs no validation.
     * Use <code>getInstance if you want that.
     * 
     * @param classToInstantiate  the class to instantiate
     */
    public InstantiateFactory(Class classToInstantiate) {
        super();
        iClassToInstantiate = classToInstantiate;
        iParamTypes = null;
        iArgs = null;
        findConstructor();
    }

    /**
     * Constructor that performs no validation.
     * Use <code>getInstance if you want that.
     * 
     * @param classToInstantiate  the class to instantiate
     * @param paramTypes  the constructor parameter types, not cloned
     * @param args  the constructor arguments, not cloned
     */
    public InstantiateFactory(Class classToInstantiate, Class[] paramTypes, Object[] args) {
        super();
        iClassToInstantiate = classToInstantiate;
        iParamTypes = paramTypes;
        iArgs = args;
        findConstructor();
    }

    /**
     * Find the Constructor for the class specified.
     */
    private void findConstructor() {
        try {
            iConstructor = iClassToInstantiate.getConstructor(iParamTypes);

        } catch (NoSuchMethodException ex) {
            throw new IllegalArgumentException("InstantiateFactory: The constructor must exist and be public ");
        }
    }

    /**
     * Creates an object using the stored constructor.
     * 
     * @return the new object
     */
    public Object create() {
        // needed for post-serialization
        if (iConstructor == null) {
            findConstructor();
        }

        try {
            return iConstructor.newInstance(iArgs);

        } catch (InstantiationException ex) {
            throw new FunctorException("InstantiateFactory: InstantiationException", ex);
        } catch (IllegalAccessException ex) {
            throw new FunctorException("InstantiateFactory: Constructor must be public", ex);
        } catch (InvocationTargetException ex) {
            throw new FunctorException("InstantiateFactory: Constructor threw an exception", ex);
        }
    }
    
}

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