AbstractFileOperationProvider.java

/*
 * 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.vfs.operations;

import org.apache.commons.vfs.FileSystemException;
import org.apache.commons.vfs.FileObject;

import java.util.*;

/**
 * todo: add class description here
 * 
 * @author Siarhei Baidun
 * @since 0.1
 */
public abstract class AbstractFileOperationProvider implements
		FileOperationProvider
{

	/**
	 * Available operations. Operations could be registered for different schemes.
	 * Some operations can work only for "file" scheme, other - for "svnhttp(s)",
	 * "svn", "svnssh", but not for "file", etc. The Map has scheme as a key and
	 * Colleaction of operations that are available for that scheme.
	 */
	private Collection operations = new ArrayList();

	/**
	 * Gather available operations for the specified FileObject and put them into
	 * specified operationsList.
	 * 
	 * @param operationsList
	 *            the list of available operations for the specivied FileObject.
	 *            The operationList contains classes of available operations, e.g.
	 *            Class objects.
	 * @param file
	 *            the FileObject for which we want to get the list of available
	 *            operations.
	 * @throws org.apache.commons.vfs.FileSystemException
	 *             if list of operations cannto be retrieved.
	 */
	public final void collectOperations(final Collection operationsList,
			final FileObject file) throws FileSystemException
	{

		doCollectOperations(operations, operationsList, file);
	}

	/**
	 * 
	 * @throws FileSystemException
	 */
	protected abstract void doCollectOperations(
			final Collection availableOperations, final Collection resultList,
			final FileObject file) throws FileSystemException;

	/**
	 * @param file
	 *            the FileObject for which we need a operation.
	 * @param operationClass
	 *            the Class which instance we are needed.
	 * @return the requried operation instance.
	 * @throws org.apache.commons.vfs.FileSystemException
	 *             if operation cannot be retrieved.
	 */
	public final FileOperation getOperation(FileObject file, Class operationClass)
			throws FileSystemException
	{
		Class implementation = lookupOperation(operationClass);

		FileOperation operationInstance = instantiateOperation(file, implementation);

		return operationInstance;
	}

	/**
	 * 
	 * @param operationClass
	 * @return
	 * @throws FileSystemException
	 */
	protected abstract FileOperation instantiateOperation(final FileObject file,
			final Class operationClass) throws FileSystemException;

	/**
	 * 
	 * @param operationClass
	 * @return never returns null
	 */
	protected final Class lookupOperation(final Class operationClass)
			throws FileSystemException
	{
		// check validity of passed class
		if (!FileOperation.class.isAssignableFrom(operationClass))
		{
			throw new FileSystemException("vfs.operation/wrong-type.error", operationClass);
		}

		// find appropriate class
		Class foundClass = null;
		Iterator iterator = operations.iterator();
		while (iterator.hasNext())
		{
			Class operation = (Class) iterator.next();
			if (operationClass.isAssignableFrom(operation))
			{
				foundClass = operation;
				break;
			}
		}

		if (foundClass == null)
		{
			throw new FileSystemException("vfs.operation/not-found.error", operationClass);
		}

		return foundClass;
	}

	/**
	 * 
	 * @param operationClass
	 * @throws FileSystemException
	 */
	protected final void addOperation(final Class operationClass)
			throws FileSystemException
	{
		// check validity of passed class
		if (!FileOperation.class.isAssignableFrom(operationClass))
		{
			throw new FileSystemException("vfs.operation/cant-register.error", operationClass);
		}

		// ok, lets add it to the list
		operations.add(operationClass);
	}
}