org.apache.hadoop.hdfs.tools.offlineImageViewer.ImageLoader Maven / Gradle / Ivy
/**
* 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;
}
}
}