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 {@link org.apache.lucene.codecs.PostingsFormat}
- DocValues - see {@link org.apache.lucene.codecs.DocValuesFormat}
- Stored fields - see {@link org.apache.lucene.codecs.StoredFieldsFormat}
- Term vectors - see {@link org.apache.lucene.codecs.TermVectorsFormat}
- FieldInfos - see {@link org.apache.lucene.codecs.FieldInfosFormat}
- SegmentInfo - see {@link org.apache.lucene.codecs.SegmentInfoFormat}
- Norms - see {@link org.apache.lucene.codecs.NormsFormat}
- Live documents - see {@link org.apache.lucene.codecs.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 {@link org.apache.lucene.codecs.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 {@link java.util.ServiceLoader 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 {@link org.apache.lucene.codecs.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 {@link org.apache.lucene.codecs.lucene46.Lucene46Codec} and override {@link org.apache.lucene.codecs.lucene46.Lucene46Codec#getPostingsFormatForField(String)} to return your custom postings format.

Similarly, if you just want to customise the {@link org.apache.lucene.codecs.DocValuesFormat} per-field, have a look at {@link org.apache.lucene.codecs.lucene46.Lucene46Codec#getDocValuesFormatForField(String)}.