Package org.apache.lucene.store

Class Directory

java.lang.Object

org.apache.lucene.store.Directory

All Implemented Interfaces:

Closeable, AutoCloseable

Direct Known Subclasses:

BaseDirectory, FilterDirectory, NRTCachingDirectory

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).

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
class	Directory.IndexInputSlicer	Allows to create one or more sliced IndexInput instances from a single file handle.

Constructor Summary

Constructors

Constructor	Description
Directory()

Method Summary

Modifier and Type	Method	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.
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.
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.
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.
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

equals, 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

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:

• Must throw FileNotFoundException if the file does not exist (not java.nio.file.NoSuchFileException of Java 7).
• 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.

Must throw FileNotFoundException if the file does not exist (not java.nio.file.NoSuchFileException of Java 7).

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 AutoCloseable

Specified by:

close in interface Closeable

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

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.

Must throw FileNotFoundException if the file does not exist (not java.nio.file.NoSuchFileException of Java 7).

Throws:

IOException - if an IOException occurs