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Apache Commons VFS is a Virtual File System library.
There is a newer version: 2.9.0
/*
 * 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.vfs2.operations;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;

import org.apache.commons.vfs2.FileObject;
import org.apache.commons.vfs2.FileSystemException;

/**
 *
 * @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 Collection of operations that are available for that scheme.
     */
    private final 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 specified 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 FileSystemException if list of operations cannot be retrieved.
     */
    @Override
    public final void collectOperations(final Collection> operationsList,
            final FileObject file) throws FileSystemException {
        doCollectOperations(operations, operationsList, file);
    }

    /**
     * Gather available operations for the specified FileObject and put them into specified operationsList.
     *
     * @param availableOperations the list of available operations for the specified FileObject.
     * @param resultList List to be filled with applicable operations.
     * @param file the FileObject for which we want to get the list of available operations.
     * @throws FileSystemException if list of operations cannot be retrieved.
     * @see #collectOperations(Collection operationsList, FileObject file)
     */
    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 required operation instance.
     * @throws FileSystemException if operation cannot be retrieved.
     */
    @Override
    public final FileOperation getOperation(final FileObject file, final Class operationClass)
            throws FileSystemException {
        final Class implementation = lookupOperation(operationClass);

        final FileOperation operationInstance = instantiateOperation(file, implementation);

        return operationInstance;
    }

    /**
     * Get operation instance for specified FileOperation subclass.
     *
     * @param file the file this operation should act on.
     * @param operationClass the class of an file operation interface to instantiate.
     * @return a new file operation
     * @throws FileSystemException if operation cannot be instantiated.
     */
    protected abstract FileOperation instantiateOperation(final FileObject file,
            final Class operationClass) throws FileSystemException;

    /**
     * Find class implementing a specific operation interface.
     *
     * @param operationClass the interface which is requested.
     * @return never returns null
     * @throws FileSystemException if operationClass is not a known FileOperation interface.
     */
    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;
        final Iterator> iterator = operations.iterator();
        while (iterator.hasNext()) {
            final Class operation = iterator.next();
            if (operationClass.isAssignableFrom(operation)) {
                foundClass = operation;
                break;
            }
        }

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

        return foundClass;
    }

    /**
     * Add new FileOperation to list of known operations.
     *
     * @param operationClass a class implementing FileOperation.
     * @throws FileSystemException if instances of the class cannot be assigned to FileOperation.
     */
    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);
    }
}