Java tutorial
/** * 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.util; import java.io.File; import java.io.FileNotFoundException; import java.io.IOException; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.apache.hadoop.fs.FileStatus; import org.apache.hadoop.fs.FileSystem; import org.apache.hadoop.fs.LocalFileSystem; import org.apache.hadoop.fs.Path; import org.apache.hadoop.fs.permission.FsAction; import org.apache.hadoop.fs.permission.FsPermission; /** * Class that provides utility functions for checking disk problem */ public class DiskChecker { private static final Log LOG = LogFactory.getLog(DiskChecker.class); public static class DiskErrorException extends IOException { public DiskErrorException(String msg) { super(msg); } } public static class DiskOutOfSpaceException extends IOException { public DiskOutOfSpaceException(String msg) { super(msg); } } /** * The semantics of mkdirsWithExistsCheck method is different from the mkdirs * method provided in the Sun's java.io.File class in the following way: * While creating the non-existent parent directories, this method checks for * the existence of those directories if the mkdir fails at any point (since * that directory might have just been created by some other process). * If both mkdir() and the exists() check fails for any seemingly * non-existent directory, then we signal an error; Sun's mkdir would signal * an error (return false) if a directory it is attempting to create already * exists or the mkdir fails. * @param dir * @return true on success, false on failure */ public static boolean mkdirsWithExistsCheck(File dir) { if (dir.mkdir() || dir.exists()) { return true; } File canonDir = null; try { canonDir = dir.getCanonicalFile(); } catch (IOException e) { return false; } String parent = canonDir.getParent(); return (parent != null) && (mkdirsWithExistsCheck(new File(parent)) && (canonDir.mkdir() || canonDir.exists())); } /** * Create the directory if it doesn't exist and * @param dir * @throws DiskErrorException */ public static void checkDir(File dir) throws DiskErrorException { if (!mkdirsWithExistsCheck(dir)) throw new DiskErrorException("can not create directory: " + dir.toString()); if (!dir.isDirectory()) throw new DiskErrorException("not a directory: " + dir.toString()); if (!dir.canRead()) throw new DiskErrorException("directory is not readable: " + dir.toString()); if (!dir.canWrite()) throw new DiskErrorException("directory is not writable: " + dir.toString()); } /** * Create the directory or check permissions if it already exists. * * The semantics of mkdirsWithExistsAndPermissionCheck method is different * from the mkdirs method provided in the Sun's java.io.File class in the * following way: * While creating the non-existent parent directories, this method checks for * the existence of those directories if the mkdir fails at any point (since * that directory might have just been created by some other process). * If both mkdir() and the exists() check fails for any seemingly * non-existent directory, then we signal an error; Sun's mkdir would signal * an error (return false) if a directory it is attempting to create already * exists or the mkdir fails. * @param localFS local filesystem * @param dir directory to be created or checked * @param expected expected permission * @return true on success, false on failure */ public static boolean mkdirsWithExistsAndPermissionCheck(LocalFileSystem localFS, Path dir, FsPermission expected) throws IOException { File directory = new File(dir.makeQualified(localFS).toUri().getPath()); if (!directory.exists()) { boolean created = mkdirsWithExistsCheck(directory); if (created) { localFS.setPermission(dir, expected); return true; } else { return false; } } FsPermission actual = localFS.getFileStatus(dir).getPermission(); if (!actual.equals(expected)) { LOG.warn("Incorrect permissions were set on " + dir + ", expected: " + expected + ", while actual: " + actual + ". Fixing..."); localFS.setPermission(dir, expected); } return true; } /** * Create the local directory if necessary, check permissions and also ensure * it can be read from and written into. * @param localFS local filesystem * @param dir directory * @param expected permission * @throws DiskErrorException * @throws IOException */ public static void checkDir(LocalFileSystem localFS, Path dir, FsPermission expected) throws DiskErrorException, IOException { if (!mkdirsWithExistsAndPermissionCheck(localFS, dir, expected)) throw new DiskErrorException("can not create directory: " + dir.toString()); FileStatus stat = localFS.getFileStatus(dir); FsPermission actual = stat.getPermission(); if (!stat.isDir()) throw new DiskErrorException("not a directory: " + dir.toString()); FsAction user = actual.getUserAction(); if (!user.implies(FsAction.READ)) throw new DiskErrorException("directory is not readable: " + dir.toString()); if (!user.implies(FsAction.WRITE)) throw new DiskErrorException("directory is not writable: " + dir.toString()); } }