CreateFlag.java
/**
* 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),
/**
* Advise that a block replica NOT be written to the local rack DataNode where
* 'local' means the same rack as the client is being run on.
*/
NO_LOCAL_RACK((short) 0x120);
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.
*
* @param flag enum set flag.
*/
public static void validateForAppend(EnumSet<CreateFlag> flag) {
validate(flag);
if (!flag.contains(APPEND)) {
throw new HadoopIllegalArgumentException(flag
+ " does not contain APPEND");
}
}
}