org.apache.lucene.analysis

Class Analyzer

java.lang.Object

org.apache.lucene.analysis.Analyzer

All Implemented Interfaces:

Closeable

Direct Known Subclasses:

AnalyzerWrapper

public abstract class Analyzer
extends Object
implements Closeable

An Analyzer builds TokenStreams, which analyze text. It thus represents a policy for extracting index terms from text.

In order to define what analysis is done, subclasses must define their TokenStreamComponents in createComponents(String, Reader). The components are then reused in each call to tokenStream(String, Reader).

Simple example:

 Analyzer analyzer = new Analyzer() {
  @Override
   protected TokenStreamComponents createComponents(String fieldName, Reader reader) {
     Tokenizer source = new FooTokenizer(reader);
     TokenStream filter = new FooFilter(source);
     filter = new BarFilter(filter);
     return new TokenStreamComponents(source, filter);
   }
 };
 

For more examples, see the Analysis package documentation.

For some concrete implementations bundled with Lucene, look in the analysis modules:

• Common: Analyzers for indexing content in different languages and domains.
• ICU: Exposes functionality from ICU to Apache Lucene.
• Kuromoji: Morphological analyzer for Japanese text.
• Morfologik: Dictionary-driven lemmatization for the Polish language.
• Phonetic: Analysis for indexing phonetic signatures (for sounds-alike search).
• Smart Chinese: Analyzer for Simplified Chinese, which indexes words.
• Stempel: Algorithmic Stemmer for the Polish Language.
• UIMA: Analysis integration with Apache UIMA.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	Analyzer.GlobalReuseStrategy Implementation of Analyzer.ReuseStrategy that reuses the same components for every field.
static class	Analyzer.PerFieldReuseStrategy Implementation of Analyzer.ReuseStrategy that reuses components per-field by maintaining a Map of TokenStreamComponent per field name.
static class	Analyzer.ReuseStrategy Strategy defining how TokenStreamComponents are reused per call to tokenStream(String, java.io.Reader).
static class	Analyzer.TokenStreamComponents This class encapsulates the outer components of a token stream.

Constructor Summary

Constructors

Constructor and Description
Analyzer() Create a new Analyzer, reusing the same set of components per-thread across calls to tokenStream(String, Reader).
Analyzer(Analyzer.ReuseStrategy reuseStrategy) Expert: create a new Analyzer with a custom Analyzer.ReuseStrategy.

Method Summary

Methods

Modifier and Type	Method and Description
void	close() Frees persistent resources used by this Analyzer
protected abstract Analyzer.TokenStreamComponents	createComponents(String fieldName, Reader reader) Creates a new Analyzer.TokenStreamComponents instance for this analyzer.
int	getOffsetGap(String fieldName) Just like getPositionIncrementGap(java.lang.String), except for Token offsets instead.
int	getPositionIncrementGap(String fieldName) Invoked before indexing a IndexableField instance if terms have already been added to that field.
protected Reader	initReader(String fieldName, Reader reader) Override this if you want to add a CharFilter chain.
TokenStream	tokenStream(String fieldName, Reader reader) Returns a TokenStream suitable for fieldName, tokenizing the contents of reader.

Methods inherited from class java.lang.Object

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

Constructor Detail

Analyzer

public Analyzer()

Create a new Analyzer, reusing the same set of components per-thread across calls to tokenStream(String, Reader).

Analyzer

public Analyzer(Analyzer.ReuseStrategy reuseStrategy)

Expert: create a new Analyzer with a custom Analyzer.ReuseStrategy.

NOTE: if you just want to reuse on a per-field basis, its easier to use a subclass of AnalyzerWrapper such as PerFieldAnalyerWrapper instead.

Method Detail

createComponents

protected abstract Analyzer.TokenStreamComponents createComponents(String fieldName,
                                              Reader reader)

Creates a new Analyzer.TokenStreamComponents instance for this analyzer.

Parameters:

fieldName - the name of the fields content passed to the Analyzer.TokenStreamComponents sink as a reader

reader - the reader passed to the Tokenizer constructor

Returns:

the Analyzer.TokenStreamComponents for this analyzer.

tokenStream

public final TokenStream tokenStream(String fieldName,
                      Reader reader)
                              throws IOException

Returns a TokenStream suitable for fieldName, tokenizing the contents of reader.

This method uses createComponents(String, Reader) to obtain an instance of Analyzer.TokenStreamComponents. It returns the sink of the components and stores the components internally. Subsequent calls to this method will reuse the previously stored components after resetting them through Analyzer.TokenStreamComponents.setReader(Reader).

NOTE: After calling this method, the consumer must follow the workflow described in TokenStream to properly consume its contents. See the Analysis package documentation for some examples demonstrating this.

Parameters:

fieldName - the name of the field the created TokenStream is used for

reader - the reader the streams source reads from

Returns:

TokenStream for iterating the analyzed content of reader

Throws:

AlreadyClosedException - if the Analyzer is closed.

IOException - if an i/o error occurs.

initReader

protected Reader initReader(String fieldName,
                Reader reader)

Override this if you want to add a CharFilter chain.

The default implementation returns reader unchanged.

Parameters:

fieldName - IndexableField name being indexed

reader - original Reader

Returns:

reader, optionally decorated with CharFilter(s)

getPositionIncrementGap

public int getPositionIncrementGap(String fieldName)

Invoked before indexing a IndexableField instance if terms have already been added to that field. This allows custom analyzers to place an automatic position increment gap between IndexbleField instances using the same field name. The default value position increment gap is 0. With a 0 position increment gap and the typical default token position increment of 1, all terms in a field, including across IndexableField instances, are in successive positions, allowing exact PhraseQuery matches, for instance, across IndexableField instance boundaries.

Parameters:

fieldName - IndexableField name being indexed.

Returns:

position increment gap, added to the next token emitted from tokenStream(String,Reader). This value must be >= 0.

getOffsetGap

public int getOffsetGap(String fieldName)

Just like getPositionIncrementGap(java.lang.String), except for Token offsets instead. By default this returns 1. This method is only called if the field produced at least one token for indexing.

Parameters:

fieldName - the field just indexed

Returns:

offset gap, added to the next token emitted from tokenStream(String,Reader). This value must be >= 0.

close

public void close()

Frees persistent resources used by this Analyzer

Specified by:

close in interface Closeable