org.apache.lucene.store

Class Directory

java.lang.Object

org.apache.lucene.store.Directory

All Implemented Interfaces:

Closeable, AutoCloseable

Direct Known Subclasses:

BaseDirectory, FilterDirectory

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:

• implementation of RAM-based indices;
• implementation indices stored in a database, via JDBC;
• implementation of an index as a single file;

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

Constructor Summary

Constructors

Constructor and Description
Directory()

Method Summary

Methods

Modifier and Type	Method and Description
abstract 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.
abstract void	deleteFile(String name) Removes an existing file in the directory.
protected void	ensureOpen()
abstract boolean	fileExists(String name) Deprecated. This method will be removed in 5.0
abstract long	fileLength(String name) Returns the length of a file in the directory.
abstract 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.
abstract Lock	makeLock(String name) Construct a Lock.
ChecksumIndexInput	openChecksumInput(String name, IOContext context) Returns a stream reading an existing file, computing checksum as it reads
abstract IndexInput	openInput(String name, IOContext context) Returns a stream reading an existing file, with the specified read buffer size.
abstract 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

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

@Deprecated
public abstract boolean fileExists(String name)
                            throws IOException

Deprecated. This method will be removed in 5.0

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:

• Throws FileNotFoundException or NoSuchFileException if the file does not exist.
• Returns a value ≥0 if the file exists, which specifies its length.

Parameters:

name - the name of the file for which to return the length.

Throws:

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 FileNotFoundException or NoSuchFileException if the file does not exist.

Throws:

IOException

openChecksumInput

public ChecksumIndexInput openChecksumInput(String name,
                                   IOContext context)
                                     throws IOException

Returns a stream reading an existing file, computing checksum as it reads

Throws:

IOException

makeLock

public abstract Lock makeLock(String name)

Construct a Lock.

Parameters:

name - the name of the lock file

clearLock

public abstract 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

Specified by:

close in interface AutoCloseable

Throws:

IOException

setLockFactory

public abstract 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 abstract 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, IOContext.DEFAULT); // 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

ensureOpen

protected void ensureOpen()
                   throws AlreadyClosedException

Throws:

AlreadyClosedException - if this Directory is closed