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 */
018package org.apache.hadoop.fs;
019
020import java.io.FileNotFoundException;
021import java.io.IOException;
022import java.util.EnumSet;
023
024import org.apache.hadoop.HadoopIllegalArgumentException;
025import org.apache.hadoop.classification.InterfaceAudience;
026import 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 * </ol>
048 * 
049 * Following combination is not valid and will result in 
050 * {@link HadoopIllegalArgumentException}:
051 * <ol>
052 * <li> APPEND|OVERWRITE</li>
053 * <li> CREATE|APPEND|OVERWRITE</li>
054 * </ol>
055 *****************************************************************/
056@InterfaceAudience.Public
057@InterfaceStability.Evolving
058public enum CreateFlag {
059
060  /**
061   * Create a file. See javadoc for more description
062   * already exists
063   */
064  CREATE((short) 0x01),
065
066  /**
067   * Truncate/overwrite a file. Same as POSIX O_TRUNC. See javadoc for description.
068   */
069  OVERWRITE((short) 0x02),
070
071  /**
072   * Append to a file. See javadoc for more description.
073   */
074  APPEND((short) 0x04);
075
076  private final short mode;
077
078  private CreateFlag(short mode) {
079    this.mode = mode;
080  }
081
082  short getMode() {
083    return mode;
084  }
085  
086  /**
087   * Validate the CreateFlag and throw exception if it is invalid
088   * @param flag set of CreateFlag
089   * @throws HadoopIllegalArgumentException if the CreateFlag is invalid
090   */
091  public static void validate(EnumSet<CreateFlag> flag) {
092    if (flag == null || flag.isEmpty()) {
093      throw new HadoopIllegalArgumentException(flag
094          + " does not specify any options");
095    }
096    final boolean append = flag.contains(APPEND);
097    final boolean overwrite = flag.contains(OVERWRITE);
098    
099    // Both append and overwrite is an error
100    if (append && overwrite) {
101      throw new HadoopIllegalArgumentException(
102          flag + "Both append and overwrite options cannot be enabled.");
103    }
104  }
105  
106  /**
107   * Validate the CreateFlag for create operation
108   * @param path Object representing the path; usually String or {@link Path}
109   * @param pathExists pass true if the path exists in the file system
110   * @param flag set of CreateFlag
111   * @throws IOException on error
112   * @throws HadoopIllegalArgumentException if the CreateFlag is invalid
113   */
114  public static void validate(Object path, boolean pathExists,
115      EnumSet<CreateFlag> flag) throws IOException {
116    validate(flag);
117    final boolean append = flag.contains(APPEND);
118    final boolean overwrite = flag.contains(OVERWRITE);
119    if (pathExists) {
120      if (!(append || overwrite)) {
121        throw new FileAlreadyExistsException("File already exists: "
122            + path.toString()
123            + ". Append or overwrite option must be specified in " + flag);
124      }
125    } else if (!flag.contains(CREATE)) {
126      throw new FileNotFoundException("Non existing file: " + path.toString()
127          + ". Create option is not specified in " + flag);
128    }
129  }
130}