Class PostingsFormat

  extended by org.apache.lucene.codecs.PostingsFormat
All Implemented Interfaces:
Direct Known Subclasses:
Lucene40PostingsFormat, Lucene41PostingsFormat, 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:
WARNING: This API is experimental and might change in incompatible ways in the next release.

Field Summary
static PostingsFormat[] EMPTY
          Zero-length PostingsFormat array.
Constructor Summary
protected PostingsFormat(String name)
          Creates a new postings format.
Method Summary
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


public static final PostingsFormat[] EMPTY
Zero-length PostingsFormat array.

Constructor Detail


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).

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


public final String getName()
Returns this posting format's name

Specified by:
getName in interface NamedSPILoader.NamedSPI


public abstract FieldsConsumer fieldsConsumer(SegmentWriteState state)
                                       throws IOException
Writes a new segment



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.



public String toString()
toString in class Object


public static PostingsFormat forName(String name)
looks up a format by name


public static Set<String> availablePostingsFormats()
returns a list of all available format names


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!

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