# Package org.apache.lucene.codecs

Codecs API: API for customization of the encoding and structure of the index.

See: Description

Class Summary
Class | Description
--- | ---
BlockTermState | Holds all state required for `PostingsReaderBase` to produce a `DocsEnum` without re-seeking the terms dict.
BlockTreeTermsReader | A block-based terms index and dictionary that assigns terms to variable length blocks according to how they share prefixes.
BlockTreeTermsReader.Stats | BlockTree statistics for a single field returned by `BlockTreeTermsReader.FieldReader.computeStats()`.
BlockTreeTermsWriter | Block-based terms index and dictionary writer.
Codec | Encodes/decodes an inverted index segment.
CodecUtil | Utility class for reading and writing versioned headers.
DocValuesConsumer | Abstract API that consumes numeric, binary and sorted docvalues.
DocValuesFormat | Encodes/decodes per-document values.
DocValuesProducer | Abstract API that produces numeric, binary and sorted docvalues.
FieldInfosFormat | Encodes/decodes `FieldInfos`
FieldInfosReader | Codec API for reading `FieldInfos`.
FieldInfosWriter | Codec API for writing `FieldInfos`.
FieldsConsumer | Abstract API that consumes terms, doc, freq, prox, offset and payloads postings.
FieldsProducer | Abstract API that produces terms, doc, freq, prox, offset and payloads postings.
FilterCodec | A codec that forwards all its method calls to another codec.
LiveDocsFormat | Format for live/deleted documents
MappingMultiDocsAndPositionsEnum | Exposes flex API, merged from flex API of sub-segments, remapping docIDs (this is used for segment merging).
MappingMultiDocsEnum | Exposes flex API, merged from flex API of sub-segments, remapping docIDs (this is used for segment merging).
MultiLevelSkipListReader | This abstract class reads skip lists with multiple levels.
MultiLevelSkipListWriter | This abstract class writes skip lists with multiple levels.
NormsFormat | Encodes/decodes per-document score normalization values.
PostingsBaseFormat | Provides a `PostingsReaderBase` and `PostingsWriterBase`.
PostingsConsumer | Abstract API that consumes postings for an individual term.
PostingsFormat | Encodes/decodes terms, postings, and proximity data.
PostingsReaderBase | The core terms dictionaries (BlockTermsReader, BlockTreeTermsReader) interact with a single instance of this class to manage creation of `DocsEnum` and `DocsAndPositionsEnum` instances.
PostingsWriterBase | Extension of `PostingsConsumer` to support pluggable term dictionaries.
SegmentInfoFormat | Expert: Controls the format of the `SegmentInfo` (segment metadata file).
SegmentInfoReader | Specifies an API for classes that can read `SegmentInfo` information.
SegmentInfoWriter | Specifies an API for classes that can write out `SegmentInfo` data.
StoredFieldsFormat | Controls the format of stored fields
StoredFieldsReader | Codec API for reading stored fields.
StoredFieldsWriter | Codec API for writing stored fields:
TermsConsumer | Abstract API that consumes terms for an individual field.
TermStats | Holder for per-term statistics.
TermVectorsFormat | Controls the format of term vectors
TermVectorsReader | Codec API for reading term vectors:
TermVectorsWriter | Codec API for writing term vectors:

## Package org.apache.lucene.codecs Description

Codecs API: API for customization of the encoding and structure of the index.

The Codec API allows you to customise the way the following pieces of index information are stored:

- Postings lists - see `PostingsFormat`
- DocValues - see `DocValuesFormat`
- Stored fields - see `StoredFieldsFormat`
- Term vectors - see `TermVectorsFormat`
- FieldInfos - see `FieldInfosFormat`
- SegmentInfo - see `SegmentInfoFormat`
- Norms - see `NormsFormat`
- Live documents - see `LiveDocsFormat`

For some concrete implementations beyond Lucene's official index format, see the Codecs module.

Codecs are identified by name through the Java Service Provider Interface. To create your own codec, extend `Codec` and pass the new codec's name to the super() constructor:

    public class MyCodec extends Codec {

        public MyCodec() {
            super("MyCodecName");
        }

        ...
    }

You will need to register the Codec class so that the `ServiceLoader` can find it, by including a META-INF/services/org.apache.lucene.codecs.Codec file on your classpath that contains the package-qualified name of your codec.

If you just want to customise the `PostingsFormat`, or use different postings formats for different fields, then you can register your custom postings format in the same way (in META-INF/services/org.apache.lucene.codecs.PostingsFormat), and then extend the default `Lucene42Codec` and override `Lucene42Codec.getPostingsFormatForField(String)` to return your custom postings format.