001 /**
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements. See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership. The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License. You may obtain a copy of the License at
009 *
010 * http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018 package org.apache.hadoop.fs;
019
020 import java.io.FileNotFoundException;
021 import java.io.IOException;
022 import java.util.EnumSet;
023
024 import org.apache.hadoop.HadoopIllegalArgumentException;
025 import org.apache.hadoop.classification.InterfaceAudience;
026 import org.apache.hadoop.classification.InterfaceStability;
027
028 /****************************************************************
029 * CreateFlag specifies the file create semantic. Users can combine flags like: <br>
030 * <code>
031 * EnumSet.of(CreateFlag.CREATE, CreateFlag.APPEND)
032 * <code>
033 * <p>
034 *
035 * Use the CreateFlag as follows:
036 * <ol>
037 * <li> CREATE - to create a file if it does not exist,
038 * else throw FileAlreadyExists.</li>
039 * <li> APPEND - to append to a file if it exists,
040 * else throw FileNotFoundException.</li>
041 * <li> OVERWRITE - to truncate a file if it exists,
042 * else throw FileNotFoundException.</li>
043 * <li> CREATE|APPEND - to create a file if it does not exist,
044 * else append to an existing file.</li>
045 * <li> CREATE|OVERWRITE - to create a file if it does not exist,
046 * else overwrite an existing file.</li>
047 * <li> SYNC_BLOCK - to force closed blocks to the disk device.
048 * In addition {@link Syncable#hsync()} should be called after each write,
049 * if true synchronous behavior is required.</li>
050 * </ol>
051 *
052 * Following combination is not valid and will result in
053 * {@link HadoopIllegalArgumentException}:
054 * <ol>
055 * <li> APPEND|OVERWRITE</li>
056 * <li> CREATE|APPEND|OVERWRITE</li>
057 * </ol>
058 *****************************************************************/
059 @InterfaceAudience.Public
060 @InterfaceStability.Evolving
061 public enum CreateFlag {
062
063 /**
064 * Create a file. See javadoc for more description
065 * already exists
066 */
067 CREATE((short) 0x01),
068
069 /**
070 * Truncate/overwrite a file. Same as POSIX O_TRUNC. See javadoc for description.
071 */
072 OVERWRITE((short) 0x02),
073
074 /**
075 * Append to a file. See javadoc for more description.
076 */
077 APPEND((short) 0x04),
078
079 /**
080 * Force closed blocks to disk. Similar to POSIX O_SYNC. See javadoc for description.
081 */
082 SYNC_BLOCK((short) 0x08),
083
084 /**
085 * Create the block on transient storage (RAM) if available. If
086 * transient storage is unavailable then the block will be created
087 * on disk.
088 *
089 * HDFS will make a best effort to lazily write these files to persistent
090 * storage, however file contents may be lost at any time due to process/
091 * node restarts, hence there is no guarantee of data durability.
092 *
093 * This flag must only be used for intermediate data whose loss can be
094 * tolerated by the application.
095 */
096 LAZY_PERSIST((short) 0x10);
097
098 private final short mode;
099
100 private CreateFlag(short mode) {
101 this.mode = mode;
102 }
103
104 short getMode() {
105 return mode;
106 }
107
108 /**
109 * Validate the CreateFlag and throw exception if it is invalid
110 * @param flag set of CreateFlag
111 * @throws HadoopIllegalArgumentException if the CreateFlag is invalid
112 */
113 public static void validate(EnumSet<CreateFlag> flag) {
114 if (flag == null || flag.isEmpty()) {
115 throw new HadoopIllegalArgumentException(flag
116 + " does not specify any options");
117 }
118 final boolean append = flag.contains(APPEND);
119 final boolean overwrite = flag.contains(OVERWRITE);
120
121 // Both append and overwrite is an error
122 if (append && overwrite) {
123 throw new HadoopIllegalArgumentException(
124 flag + "Both append and overwrite options cannot be enabled.");
125 }
126 }
127
128 /**
129 * Validate the CreateFlag for create operation
130 * @param path Object representing the path; usually String or {@link Path}
131 * @param pathExists pass true if the path exists in the file system
132 * @param flag set of CreateFlag
133 * @throws IOException on error
134 * @throws HadoopIllegalArgumentException if the CreateFlag is invalid
135 */
136 public static void validate(Object path, boolean pathExists,
137 EnumSet<CreateFlag> flag) throws IOException {
138 validate(flag);
139 final boolean append = flag.contains(APPEND);
140 final boolean overwrite = flag.contains(OVERWRITE);
141 if (pathExists) {
142 if (!(append || overwrite)) {
143 throw new FileAlreadyExistsException("File already exists: "
144 + path.toString()
145 + ". Append or overwrite option must be specified in " + flag);
146 }
147 } else if (!flag.contains(CREATE)) {
148 throw new FileNotFoundException("Non existing file: " + path.toString()
149 + ". Create option is not specified in " + flag);
150 }
151 }
152 }