public final class SynonymFilter extends TokenFilter
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 -> zThen 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.
AttributeSource.AttributeFactory, AttributeSource.State| Modifier and Type | Field and Description |
|---|---|
static String |
TYPE_SYNONYM |
input| Constructor and Description |
|---|
SynonymFilter(TokenStream input,
SynonymMap synonyms,
boolean ignoreCase) |
| Modifier and Type | Method and Description |
|---|---|
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.
|
close, endaddAttribute, addAttributeImpl, captureState, clearAttributes, cloneAttributes, copyTo, equals, getAttribute, getAttributeClassesIterator, getAttributeFactory, getAttributeImplsIterator, hasAttribute, hasAttributes, hashCode, reflectAsString, reflectWith, restoreState, toStringpublic static final String TYPE_SYNONYM
public SynonymFilter(TokenStream input, SynonymMap synonyms, boolean ignoreCase)
input - input tokenstreamsynonyms - synonym mapignoreCase - 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 SynonymMappublic boolean incrementToken()
throws IOException
TokenStreamIndexWriter) 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().
incrementToken in class TokenStreamIOExceptionpublic void reset()
throws IOException
TokenFilterreset in class TokenFilterIOException