Class ReversedWildcardFilter

  • All Implemented Interfaces:
    Closeable, AutoCloseable

    public final class ReversedWildcardFilter
    extends TokenFilter
    This class produces a special form of reversed tokens, suitable for better handling of leading wildcards. Tokens from the input TokenStream are reversed and prepended with a special "reversed" marker character. If withOriginal argument is true then first the original token is returned, and then the reversed token (with positionIncrement == 0) is returned. Otherwise only reversed tokens are returned.

    Note: this filter doubles the number of tokens in the input stream when withOriginal == true, which proportionally increases the size of postings and term dictionary in the index.

    • 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
        false for end of stream; true otherwise
      • reverse

        public static void reverse(char[] buffer,
                                   int start,
                                   int len)
        Partially reverses the given input buffer in-place from the given offset up to the given length, keeping surrogate pairs in the correct (non-reversed) order.
        buffer - the input char array to reverse
        start - the offset from where to reverse the buffer
        len - the length in the buffer up to where the buffer should be reversed
      • 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.

        reset in class TokenFilter