org.apache.lucene.analysis.pattern

Class PatternTokenizer

java.lang.Object

org.apache.lucene.util.AttributeSource

org.apache.lucene.analysis.TokenStream

org.apache.lucene.analysis.Tokenizer

org.apache.lucene.analysis.pattern.PatternTokenizer

All Implemented Interfaces:

Closeable, AutoCloseable

public final class PatternTokenizer
extends Tokenizer

This tokenizer uses regex pattern matching to construct distinct tokens for the input stream. It takes two arguments: "pattern" and "group".

• "pattern" is the regular expression.
• "group" says which group to extract into tokens.

group=-1 (the default) is equivalent to "split". In this case, the tokens will be equivalent to the output from (without empty tokens): String.split(java.lang.String)

Using group >= 0 selects the matching group as the token. For example, if you have:

  pattern = \'([^\']+)\'
  group = 0
  input = aaa 'bbb' 'ccc'

the output will be two tokens: 'bbb' and 'ccc' (including the ' marks). With the same input but using group=1, the output would be: bbb and ccc (no ' marks)

NOTE: This Tokenizer does not output tokens that are of zero length.

See Also:

Pattern

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.lucene.util.AttributeSource

AttributeSource.AttributeFactory, AttributeSource.State

Constructor Summary

Constructors

Constructor and Description
PatternTokenizer(AttributeSource.AttributeFactory factory, Reader input, Pattern pattern, int group) creates a new PatternTokenizer returning tokens from group (-1 for split functionality)
PatternTokenizer(Reader input, Pattern pattern, int group) creates a new PatternTokenizer returning tokens from group (-1 for split functionality)

Method Summary

Modifier and Type	Method and Description
void	end() This method is called by the consumer after the last token has been consumed, after TokenStream.incrementToken() returned false (using the new TokenStream API).
boolean	incrementToken() Consumers (i.e., IndexWriter) use this method to advance the stream to the next token.
void	reset() This method is called by a consumer before it begins consumption using TokenStream.incrementToken().

Methods inherited from class org.apache.lucene.analysis.Tokenizer

close, setReader

Methods inherited from class org.apache.lucene.util.AttributeSource

addAttribute, addAttributeImpl, captureState, clearAttributes, cloneAttributes, copyTo, equals, getAttribute, getAttributeClassesIterator, getAttributeFactory, getAttributeImplsIterator, hasAttribute, hasAttributes, hashCode, reflectAsString, reflectWith, restoreState, toString

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

PatternTokenizer

public PatternTokenizer(Reader input,
                        Pattern pattern,
                        int group)

creates a new PatternTokenizer returning tokens from group (-1 for split functionality)

PatternTokenizer

public PatternTokenizer(AttributeSource.AttributeFactory factory,
                        Reader input,
                        Pattern pattern,
                        int group)

creates a new PatternTokenizer returning tokens from group (-1 for split functionality)

Method Detail

incrementToken

public boolean incrementToken()

Description copied from class: TokenStream

Consumers (i.e., IndexWriter) use this method to advance the stream to the next token. Implementing classes must implement this method and update the appropriate AttributeImpls with the attributes of the next token.

The producer must make no assumptions about the attributes after the method has been returned: the caller may arbitrarily change it. If the producer needs to preserve the state for subsequent calls, it can use AttributeSource.captureState() to create a copy of the current attribute state.

This method is called for every token of a document, so an efficient implementation is crucial for good performance. To avoid calls to AttributeSource.addAttribute(Class) and AttributeSource.getAttribute(Class), references to all AttributeImpls that this stream uses should be retrieved during instantiation.

To ensure that filters and consumers know which attributes are available, the attributes must be added during instantiation. Filters and consumers are not required to check for availability of attributes in TokenStream.incrementToken().

Specified by:

incrementToken in class TokenStream

Returns:

false for end of stream; true otherwise

end

public void end()
         throws IOException

Description copied from class: TokenStream

This method is called by the consumer after the last token has been consumed, after TokenStream.incrementToken() returned false (using the new TokenStream API). Streams implementing the old API should upgrade to use this feature.

This method can be used to perform any end-of-stream operations, such as setting the final offset of a stream. The final offset of a stream might differ from the offset of the last token eg in case one or more whitespaces followed after the last token, but a WhitespaceTokenizer was used.

Additionally any skipped positions (such as those removed by a stopfilter) can be applied to the position increment, or any adjustment of other attributes where the end-of-stream value may be important.

If you override this method, always call super.end().

Overrides:

end in class TokenStream

Throws:

IOException - If an I/O error occurs

reset

public void reset()
           throws IOException

Description copied from class: TokenStream

This method is called by a consumer before it begins consumption using TokenStream.incrementToken().

Resets this stream to a clean state. Stateful implementations must implement this method so that they can be reused, just as if they had been created fresh.

If you override this method, always call super.reset(), otherwise some internal state will not be correctly reset (e.g., Tokenizer will throw IllegalStateException on further usage).

Overrides:

reset in class Tokenizer

Throws:

IOException