| /** |
| * 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.hadoop.hdfs.tools.offlineImageViewer; |
| |
| import java.io.DataInputStream; |
| import java.io.IOException; |
| |
| import org.apache.hadoop.classification.InterfaceAudience; |
| |
| /** |
| * An ImageLoader can accept a DataInputStream to an Hadoop FSImage file |
| * and walk over its structure using the supplied ImageVisitor. |
| * |
| * Each implementation of ImageLoader is designed to rapidly process an |
| * image file. As long as minor changes are made from one layout version |
| * to another, it is acceptable to tweak one implementation to read the next. |
| * However, if the layout version changes enough that it would make a |
| * processor slow or difficult to read, another processor should be created. |
| * This allows each processor to quickly read an image without getting |
| * bogged down in dealing with significant differences between layout versions. |
| */ |
| interface ImageLoader { |
| |
| /** |
| * @param in DataInputStream pointing to an Hadoop FSImage file |
| * @param v Visit to apply to the FSImage file |
| * @param enumerateBlocks Should visitor visit each of the file blocks? |
| */ |
| public void loadImage(DataInputStream in, ImageVisitor v, |
| boolean enumerateBlocks) throws IOException; |
| |
| /** |
| * Can this processor handle the specified version of FSImage file? |
| * |
| * @param version FSImage version file |
| * @return True if this instance can process the file |
| */ |
| public boolean canLoadVersion(int version); |
| |
| /** |
| * Factory for obtaining version of image loader that can read |
| * a particular image format. |
| */ |
| @InterfaceAudience.Private |
| public class LoaderFactory { |
| // Java doesn't support static methods on interfaces, which necessitates |
| // this factory class |
| |
| /** |
| * Find an image loader capable of interpreting the specified |
| * layout version number. If none, return null; |
| * |
| * @param version fsimage layout version number to be processed |
| * @return ImageLoader that can interpret specified version, or null |
| */ |
| static public ImageLoader getLoader(int version) { |
| // Easy to add more image processors as they are written |
| ImageLoader[] loaders = { new ImageLoaderCurrent() }; |
| |
| for (ImageLoader l : loaders) { |
| if (l.canLoadVersion(version)) |
| return l; |
| } |
| |
| return null; |
| } |
| } |
| } |