Package org.apache.lucene.codecs

Class PostingsFormat

java.lang.Object

org.apache.lucene.codecs.PostingsFormat

All Implemented Interfaces:

NamedSPILoader.NamedSPI

Direct Known Subclasses:

Lucene99PostingsFormat, PerFieldPostingsFormat

public abstract class PostingsFormat
extends Object
implements NamedSPILoader.NamedSPI

Encodes/decodes terms, postings, and proximity data.

Note, when extending this class, the name (getName()) may written into the index in certain configurations. In order for the segment to be read, the name must resolve to your implementation via forName(String). This method uses Java's Service Provider Interface (SPI) to resolve format names.

If you implement your own format, make sure that it has a no-arg constructor so SPI can load it.

See Also:

ServiceLoader

WARNING: This API is experimental and might change in incompatible ways in the next release.

Field Summary

Fields

Modifier and Type	Field	Description
static PostingsFormat[]	EMPTY	Zero-length PostingsFormat array.

Constructor Summary

Constructors

Modifier	Constructor	Description
protected	PostingsFormat(String name)	Creates a new postings format.

Method Summary

Modifier and Type	Method	Description
static Set<String>	availablePostingsFormats()	returns a list of all available format names
abstract FieldsConsumer	fieldsConsumer(SegmentWriteState state)	Writes a new segment
abstract FieldsProducer	fieldsProducer(SegmentReadState state)	Reads a segment.
static PostingsFormat	forName(String name)	looks up a format by name
String	getName()	Returns this posting format's name
static void	reloadPostingsFormats(ClassLoader classloader)	Reloads the postings format list from the given ClassLoader.
String	toString()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

EMPTY

public static final PostingsFormat[] EMPTY

Zero-length PostingsFormat array.

Constructor Detail

PostingsFormat

protected PostingsFormat(String name)

Creates a new postings format.

The provided name will be written into the index segment in some configurations (such as when using PerFieldPostingsFormat): in such configurations, for the segment to be read this class should be registered with Java's SPI mechanism (registered in META-INF/ of your jar file, etc).

Parameters:

name - must be all ascii alphanumeric, and less than 128 characters in length.

Method Detail

getName

public final String getName()

Returns this posting format's name

Specified by:

getName in interface NamedSPILoader.NamedSPI

fieldsConsumer

public abstract FieldsConsumer fieldsConsumer(SegmentWriteState state)
                                       throws IOException

Writes a new segment

Throws:

IOException

fieldsProducer

public abstract FieldsProducer fieldsProducer(SegmentReadState state)
                                       throws IOException

Reads a segment. NOTE: by the time this call returns, it must hold open any files it will need to use; else, those files may be deleted. Additionally, required files may be deleted during the execution of this call before there is a chance to open them. Under these circumstances an IOException should be thrown by the implementation. IOExceptions are expected and will automatically cause a retry of the segment opening logic with the newly revised segments.

Throws:

IOException

toString

public String toString()

Overrides:

toString in class Object

forName

public static PostingsFormat forName(String name)

looks up a format by name

availablePostingsFormats

public static Set<String> availablePostingsFormats()

returns a list of all available format names

reloadPostingsFormats

public static void reloadPostingsFormats(ClassLoader classloader)

Reloads the postings format list from the given ClassLoader. Changes to the postings formats are visible after the method ends, all iterators (availablePostingsFormats(),...) stay consistent.

NOTE: Only new postings formats are added, existing ones are never removed or replaced.

This method is expensive and should only be called for discovery of new postings formats on the given classpath/classloader!