org.apache.lucene.analysis.pattern

Class PatternCaptureGroupTokenFilter

  • All Implemented Interfaces:
    Closeable, AutoCloseable


    public final class PatternCaptureGroupTokenFilter
    extends TokenFilter
    CaptureGroup uses Java regexes to emit multiple tokens - one for each capture group in one or more patterns.

    For example, a pattern like:

    "(https?://([a-zA-Z\-_0-9.]+))"

    when matched against the string "http://www.foo.com/index" would return the tokens "https://www.foo.com" and "www.foo.com".

    If none of the patterns match, or if preserveOriginal is true, the original token will be preserved.

    Each pattern is matched as often as it can be, so the pattern "(...)", when matched against "abcdefghi" would produce ["abc","def","ghi"]

    A camelCaseFilter could be written as:

    "([A-Z]{2,})", "(?<![A-Z])([A-Z][a-z]+)", "(?:^|\\b|(?<=[0-9_])|(?<=[A-Z]{2}))([a-z]+)", "([0-9]+)"

    plus if preserveOriginal is true, it would also return "camelCaseFilter"

    • Constructor Detail

      • PatternCaptureGroupTokenFilter

        public PatternCaptureGroupTokenFilter(TokenStream input,
                                              boolean preserveOriginal,
                                              Pattern... patterns)
        Parameters:
        input - the input TokenStream
        preserveOriginal - set to true to return the original token even if one of the patterns matches
        patterns - an array of Pattern objects to match against each token
    • Method Detail

      • incrementToken

        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
        Returns:
        false for end of stream; true otherwise
        Throws:
        IOException
      • reset

        public void reset()
                   throws IOException
        Description copied from class: TokenFilter
        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).

        NOTE: The default implementation chains the call to the input TokenStream, so be sure to call super.reset() when overriding this method.

        Overrides:
        reset in class TokenFilter
        Throws:
        IOException