Class SynonymFilter

  extended by org.apache.lucene.util.AttributeSource
      extended by org.apache.lucene.analysis.TokenStream
          extended by org.apache.lucene.analysis.TokenFilter
              extended by org.apache.lucene.analysis.synonym.SynonymFilter
All Implemented Interfaces:

public final class SynonymFilter
extends TokenFilter

Matches single or multi word synonyms in a token stream. This token stream cannot properly handle position increments != 1, ie, you should place this filter before filtering out stop words.

Note that with the current implementation, parsing is greedy, so whenever multiple parses would apply, the rule starting the earliest and parsing the most tokens wins. For example if you have these rules:

   a -> x
   a b -> y
   b c d -> z
Then input a b c d e parses to y b c d, ie the 2nd rule "wins" because it started earliest and matched the most input tokens of other rules starting at that point.

A future improvement to this filter could allow non-greedy parsing, such that the 3rd rule would win, and also separately allow multiple parses, such that all 3 rules would match, perhaps even on a rule by rule basis.

NOTE: when a match occurs, the output tokens associated with the matching rule are "stacked" on top of the input stream (if the rule had keepOrig=true) and also on top of aother matched rule's output tokens. This is not a correct solution, as really the output should be an abitrary graph/lattice. For example, with the above match, you would expect an exact PhraseQuery "y b c" to match the parsed tokens, but it will fail to do so. This limitations is necessary because Lucene's TokenStream (and index) cannot yet represent an arbitrary graph.

NOTE: If multiple incoming tokens arrive on the same position, only the first token at that position is used for parsing. Subsequent tokens simply pass through and are not parsed. A future improvement would be to allow these tokens to also be matched.

Nested Class Summary
Nested classes/interfaces inherited from class org.apache.lucene.util.AttributeSource
AttributeSource.AttributeFactory, AttributeSource.State
Field Summary
static String TYPE_SYNONYM
Fields inherited from class org.apache.lucene.analysis.TokenFilter
Constructor Summary
SynonymFilter(TokenStream input, SynonymMap synonyms, boolean ignoreCase)
Method Summary
 boolean incrementToken()
          Consumers (i.e., IndexWriter) use this method to advance the stream to the next token.
 void reset()
          Reset the filter as well as the input TokenStream.
Methods inherited from class org.apache.lucene.analysis.TokenFilter
close, end
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
clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail


public static final String TYPE_SYNONYM
See Also:
Constant Field Values
Constructor Detail


public SynonymFilter(TokenStream input,
                     SynonymMap synonyms,
                     boolean ignoreCase)
input - input tokenstream
synonyms - synonym map
ignoreCase - case-folds input for matching with Character.toLowerCase(int). Note, if you set this to true, its your responsibility to lowercase the input entries when you create the SynonymMap
Method Detail


public boolean incrementToken()
                       throws IOException
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
false for end of stream; true otherwise


public void reset()
           throws IOException
Description copied from class: TokenFilter
Reset the filter as well as the input TokenStream.

reset in class TokenFilter

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