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.fs; import java.io.FileNotFoundException; import java.io.IOException; import java.util.EnumSet; import org.apache.hadoop.HadoopIllegalArgumentException; import org.apache.hadoop.classification.InterfaceAudience; import org.apache.hadoop.classification.InterfaceStability; /**************************************************************** * CreateFlag specifies the file create semantic. Users can combine flags like: <br> * <code> * EnumSet.of(CreateFlag.CREATE, CreateFlag.APPEND) * <code> * <p> * * Use the CreateFlag as follows: * <ol> * <li> CREATE - to create a file if it does not exist, * else throw FileAlreadyExists.</li> * <li> APPEND - to append to a file if it exists, * else throw FileNotFoundException.</li> * <li> OVERWRITE - to truncate a file if it exists, * else throw FileNotFoundException.</li> * <li> CREATE|APPEND - to create a file if it does not exist, * else append to an existing file.</li> * <li> CREATE|OVERWRITE - to create a file if it does not exist, * else overwrite an existing file.</li> * <li> SYNC_BLOCK - to force closed blocks to the disk device. * In addition {@link Syncable#hsync()} should be called after each write, * if true synchronous behavior is required.</li> * <li> LAZY_PERSIST - Create the block on transient storage (RAM) if * available.</li> * <li> APPEND_NEWBLOCK - Append data to a new block instead of end of the last * partial block.</li> * </ol> * * Following combinations are not valid and will result in * {@link HadoopIllegalArgumentException}: * <ol> * <li> APPEND|OVERWRITE</li> * <li> CREATE|APPEND|OVERWRITE</li> * </ol> *****************************************************************/ @InterfaceAudience.Public @InterfaceStability.Evolving public enum CreateFlag { /** * Create a file. See javadoc for more description * already exists */ CREATE((short) 0x01), /** * Truncate/overwrite a file. Same as POSIX O_TRUNC. See javadoc for description. */ OVERWRITE((short) 0x02), /** * Append to a file. See javadoc for more description. */ APPEND((short) 0x04), /** * Force closed blocks to disk. Similar to POSIX O_SYNC. See javadoc for description. */ SYNC_BLOCK((short) 0x08), /** * Create the block on transient storage (RAM) if available. If * transient storage is unavailable then the block will be created * on disk. * * HDFS will make a best effort to lazily write these files to persistent * storage, however file contents may be lost at any time due to process/ * node restarts, hence there is no guarantee of data durability. * * This flag must only be used for intermediate data whose loss can be * tolerated by the application. */ LAZY_PERSIST((short) 0x10), /** * Append data to a new block instead of the end of the last partial block. * This is only useful for APPEND. */ NEW_BLOCK((short) 0x20), /** * Advise that a block replica NOT be written to the local DataNode where * 'local' means the same host as the client is being run on. */ @InterfaceAudience.LimitedPrivate({ "HBase" }) NO_LOCAL_WRITE((short) 0x40), /** * Enforce the file to be a replicated file, no matter what its parent * directory's replication or erasure coding policy is. */ SHOULD_REPLICATE((short) 0x80), /** * Advise that the first block replica NOT take into account DataNode * locality. The first block replica should be placed randomly within the * cluster. Subsequent block replicas should follow DataNode locality rules. */ IGNORE_CLIENT_LOCALITY((short) 0x100); private final short mode; private CreateFlag(short mode) { this.mode = mode; } short getMode() { return mode; } /** * Validate the CreateFlag and throw exception if it is invalid * @param flag set of CreateFlag * @throws HadoopIllegalArgumentException if the CreateFlag is invalid */ public static void validate(EnumSet<CreateFlag> flag) { if (flag == null || flag.isEmpty()) { throw new HadoopIllegalArgumentException(flag + " does not specify any options"); } final boolean append = flag.contains(APPEND); final boolean overwrite = flag.contains(OVERWRITE); // Both append and overwrite is an error if (append && overwrite) { throw new HadoopIllegalArgumentException(flag + "Both append and overwrite options cannot be enabled."); } } /** * Validate the CreateFlag for create operation * @param path Object representing the path; usually String or {@link Path} * @param pathExists pass true if the path exists in the file system * @param flag set of CreateFlag * @throws IOException on error * @throws HadoopIllegalArgumentException if the CreateFlag is invalid */ public static void validate(Object path, boolean pathExists, EnumSet<CreateFlag> flag) throws IOException { validate(flag); final boolean append = flag.contains(APPEND); final boolean overwrite = flag.contains(OVERWRITE); if (pathExists) { if (!(append || overwrite)) { throw new FileAlreadyExistsException("File already exists: " + path.toString() + ". Append or overwrite option must be specified in " + flag); } } else if (!flag.contains(CREATE)) { throw new FileNotFoundException( "Non existing file: " + path.toString() + ". Create option is not specified in " + flag); } } /** * Validate the CreateFlag for the append operation. The flag must contain * APPEND, and cannot contain OVERWRITE. */ public static void validateForAppend(EnumSet<CreateFlag> flag) { validate(flag); if (!flag.contains(APPEND)) { throw new HadoopIllegalArgumentException(flag + " does not contain APPEND"); } } }