org.apache.lucene.store
Class Directory

java.lang.Object
  extended by org.apache.lucene.store.Directory
All Implemented Interfaces:
Closeable
Direct Known Subclasses:
CompoundFileDirectory, FileSwitchDirectory, FSDirectory, NRTCachingDirectory, RAMDirectory, RateLimitedDirectoryWrapper, TrackingDirectoryWrapper

public abstract class Directory
extends Object
implements Closeable

A Directory is a flat list of files. Files may be written once, when they are created. Once a file is created it may only be opened for read, or deleted. Random access is permitted both when reading and writing.

Java's i/o APIs not used directly, but rather all i/o is through this API. This permits things such as:

Directory locking is implemented by an instance of LockFactory, and can be changed for each Directory instance using setLockFactory(org.apache.lucene.store.LockFactory).


Nested Class Summary
 class Directory.IndexInputSlicer
          Allows to create one or more sliced IndexInput instances from a single file handle.
 
Field Summary
protected  boolean isOpen
           
protected  LockFactory lockFactory
          Holds the LockFactory instance (implements locking for this Directory instance).
 
Constructor Summary
Directory()
           
 
Method Summary
 void clearLock(String name)
          Attempt to clear (forcefully unlock and remove) the specified lock.
abstract  void close()
          Closes the store.
 void copy(Directory to, String src, String dest, IOContext context)
          Copies the file src to Directory to under the new file name dest.
abstract  IndexOutput createOutput(String name, IOContext context)
          Creates a new, empty file in the directory with the given name.
 Directory.IndexInputSlicer createSlicer(String name, IOContext context)
          Creates an Directory.IndexInputSlicer for the given file name.
abstract  void deleteFile(String name)
          Removes an existing file in the directory.
protected  void ensureOpen()
           
abstract  boolean fileExists(String name)
          Returns true iff a file with the given name exists.
abstract  long fileLength(String name)
          Returns the length of a file in the directory.
 LockFactory getLockFactory()
          Get the LockFactory that this Directory instance is using for its locking implementation.
 String getLockID()
          Return a string identifier that uniquely differentiates this Directory instance from other Directory instances.
abstract  String[] listAll()
          Returns an array of strings, one for each file in the directory.
 Lock makeLock(String name)
          Construct a Lock.
abstract  IndexInput openInput(String name, IOContext context)
          Returns a stream reading an existing file, with the specified read buffer size.
 void setLockFactory(LockFactory lockFactory)
          Set the LockFactory that this Directory instance should use for its locking implementation.
abstract  void sync(Collection<String> names)
          Ensure that any writes to these files are moved to stable storage.
 String toString()
           
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
 

Field Detail

isOpen

protected volatile boolean isOpen

lockFactory

protected LockFactory lockFactory
Holds the LockFactory instance (implements locking for this Directory instance).

Constructor Detail

Directory

public Directory()
Method Detail

listAll

public abstract String[] listAll()
                          throws IOException
Returns an array of strings, one for each file in the directory.

Throws:
NoSuchDirectoryException - if the directory is not prepared for any write operations (such as createOutput(String, IOContext)).
IOException - in case of other IO errors

fileExists

public abstract boolean fileExists(String name)
                            throws IOException
Returns true iff a file with the given name exists.

Throws:
IOException

deleteFile

public abstract void deleteFile(String name)
                         throws IOException
Removes an existing file in the directory.

Throws:
IOException

fileLength

public abstract long fileLength(String name)
                         throws IOException
Returns the length of a file in the directory. This method follows the following contract:

Parameters:
name - the name of the file for which to return the length.
Throws:
FileNotFoundException - if the file does not exist.
IOException - if there was an IO error while retrieving the file's length.

createOutput

public abstract IndexOutput createOutput(String name,
                                         IOContext context)
                                  throws IOException
Creates a new, empty file in the directory with the given name. Returns a stream writing this file.

Throws:
IOException

sync

public abstract void sync(Collection<String> names)
                   throws IOException
Ensure that any writes to these files are moved to stable storage. Lucene uses this to properly commit changes to the index, to prevent a machine/OS crash from corrupting the index.

NOTE: Clients may call this method for same files over and over again, so some impls might optimize for that. For other impls the operation can be a noop, for various reasons.

Throws:
IOException

openInput

public abstract IndexInput openInput(String name,
                                     IOContext context)
                              throws IOException
Returns a stream reading an existing file, with the specified read buffer size. The particular Directory implementation may ignore the buffer size. Currently the only Directory implementations that respect this parameter are FSDirectory and CompoundFileDirectory.

Throws:
IOException

makeLock

public Lock makeLock(String name)
Construct a Lock.

Parameters:
name - the name of the lock file

clearLock

public void clearLock(String name)
               throws IOException
Attempt to clear (forcefully unlock and remove) the specified lock. Only call this at a time when you are certain this lock is no longer in use.

Parameters:
name - name of the lock to be cleared.
Throws:
IOException

close

public abstract void close()
                    throws IOException
Closes the store.

Specified by:
close in interface Closeable
Throws:
IOException

setLockFactory

public void setLockFactory(LockFactory lockFactory)
                    throws IOException
Set the LockFactory that this Directory instance should use for its locking implementation. Each * instance of LockFactory should only be used for one directory (ie, do not share a single instance across multiple Directories).

Parameters:
lockFactory - instance of LockFactory.
Throws:
IOException

getLockFactory

public LockFactory getLockFactory()
Get the LockFactory that this Directory instance is using for its locking implementation. Note that this may be null for Directory implementations that provide their own locking implementation.


getLockID

public String getLockID()
Return a string identifier that uniquely differentiates this Directory instance from other Directory instances. This ID should be the same if two Directory instances (even in different JVMs and/or on different machines) are considered "the same index". This is how locking "scopes" to the right index.


toString

public String toString()
Overrides:
toString in class Object

copy

public void copy(Directory to,
                 String src,
                 String dest,
                 IOContext context)
          throws IOException
Copies the file src to Directory to under the new file name dest.

If you want to copy the entire source directory to the destination one, you can do so like this:

 Directory to; // the directory to copy to
 for (String file : dir.listAll()) {
   dir.copy(to, file, newFile); // newFile can be either file, or a new name
 }
 

NOTE: this method does not check whether dest exist and will overwrite it if it does.

Throws:
IOException

createSlicer

public Directory.IndexInputSlicer createSlicer(String name,
                                               IOContext context)
                                        throws IOException
Creates an Directory.IndexInputSlicer for the given file name. IndexInputSlicer allows other Directory implementations to efficiently open one or more sliced IndexInput instances from a single file handle. The underlying file handle is kept open until the Directory.IndexInputSlicer is closed.

Throws:
IOException - if an IOException occurs
WARNING: This API is experimental and might change in incompatible ways in the next release.
NOTE: This API is for internal purposes only and might change in incompatible ways in the next release.

ensureOpen

protected final void ensureOpen()
                         throws AlreadyClosedException
Throws:
AlreadyClosedException - if this Directory is closed


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