org.apache.hadoop.fs

Enum CreateFlag

java.lang.Object

java.lang.Enum<CreateFlag>

org.apache.hadoop.fs.CreateFlag

All Implemented Interfaces:

Serializable, Comparable<CreateFlag>

@InterfaceAudience.Public
@InterfaceStability.Evolving
public enum CreateFlag
extends Enum<CreateFlag>

CreateFlag specifies the file create semantic. Users can combine flags like:
EnumSet.of(CreateFlag.CREATE, CreateFlag.APPEND)

Use the CreateFlag as follows:

1. CREATE - to create a file if it does not exist, else throw FileAlreadyExists.
2. APPEND - to append to a file if it exists, else throw FileNotFoundException.
3. OVERWRITE - to truncate a file if it exists, else throw FileNotFoundException.
4. CREATE|APPEND - to create a file if it does not exist, else append to an existing file.
5. CREATE|OVERWRITE - to create a file if it does not exist, else overwrite an existing file.
6. SYNC_BLOCK - to force closed blocks to the disk device. In addition Syncable.hsync() should be called after each write, if true synchronous behavior is required.
7. LAZY_PERSIST - Create the block on transient storage (RAM) if available.
8. APPEND_NEWBLOCK - Append data to a new block instead of end of the last partial block.

Following combinations are not valid and will result in HadoopIllegalArgumentException:

1. APPEND|OVERWRITE
2. CREATE|APPEND|OVERWRITE

Enum Constant Summary

Enum Constants

Enum Constant and Description
APPEND Append to a file.
CREATE Create a file.
LAZY_PERSIST Create the block on transient storage (RAM) if available.
NEW_BLOCK Append data to a new block instead of the end of the last partial block.
NO_LOCAL_WRITE 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.
OVERWRITE Truncate/overwrite a file.
SYNC_BLOCK Force closed blocks to disk.

Method Summary

Methods

Modifier and Type	Method and Description
static void	validate(EnumSet<CreateFlag> flag) Validate the CreateFlag and throw exception if it is invalid
static void	validate(Object path, boolean pathExists, EnumSet<CreateFlag> flag) Validate the CreateFlag for create operation
static void	validateForAppend(EnumSet<CreateFlag> flag) Validate the CreateFlag for the append operation.
static CreateFlag	valueOf(String name) Returns the enum constant of this type with the specified name.
static CreateFlag[]	values() Returns an array containing the constants of this enum type, in the order they are declared.

Methods inherited from class java.lang.Enum

clone, compareTo, equals, finalize, getDeclaringClass, hashCode, name, ordinal, toString, valueOf

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Enum Constant Detail

CREATE

public static final CreateFlag CREATE

Create a file. See javadoc for more description already exists

OVERWRITE

public static final CreateFlag OVERWRITE

Truncate/overwrite a file. Same as POSIX O_TRUNC. See javadoc for description.

APPEND

public static final CreateFlag APPEND

Append to a file. See javadoc for more description.

SYNC_BLOCK

public static final CreateFlag SYNC_BLOCK

Force closed blocks to disk. Similar to POSIX O_SYNC. See javadoc for description.

LAZY_PERSIST

public static final CreateFlag LAZY_PERSIST

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.

NEW_BLOCK

public static final CreateFlag NEW_BLOCK

Append data to a new block instead of the end of the last partial block. This is only useful for APPEND.

NO_LOCAL_WRITE

@InterfaceAudience.LimitedPrivate(value="HBase")
public static final CreateFlag NO_LOCAL_WRITE

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.

Method Detail

values

public static CreateFlag[] values()

Returns an array containing the constants of this enum type, in the order they are declared. This method may be used to iterate over the constants as follows:

for (CreateFlag c : CreateFlag.values())
    System.out.println(c);

Returns:

an array containing the constants of this enum type, in the order they are declared

valueOf

public static CreateFlag valueOf(String name)

Returns the enum constant of this type with the specified name. The string must match exactly an identifier used to declare an enum constant in this type. (Extraneous whitespace characters are not permitted.)

Parameters:

name - the name of the enum constant to be returned.

Returns:

the enum constant with the specified name

Throws:

IllegalArgumentException - if this enum type has no constant with the specified name

NullPointerException - if the argument is null

validate

public static void validate(EnumSet<CreateFlag> flag)

Validate the CreateFlag and throw exception if it is invalid

Parameters:

flag - set of CreateFlag

Throws:

HadoopIllegalArgumentException - if the CreateFlag is invalid

validate

public static void validate(Object path,
            boolean pathExists,
            EnumSet<CreateFlag> flag)
                     throws IOException

Validate the CreateFlag for create operation

Parameters:

path - Object representing the path; usually String or Path

pathExists - pass true if the path exists in the file system

flag - set of CreateFlag

Throws:

IOException - on error

HadoopIllegalArgumentException - if the CreateFlag is invalid

validateForAppend

public static void validateForAppend(EnumSet<CreateFlag> flag)

Validate the CreateFlag for the append operation. The flag must contain APPEND, and cannot contain OVERWRITE.