Class ReverseStringFilter

All Implemented Interfaces:
Closeable, AutoCloseable, Unwrappable<TokenStream>

public final class ReverseStringFilter extends TokenFilter
Reverse token string, for example "country" => "yrtnuoc".

If marker is supplied, then tokens will be also prepended by that character. For example, with a marker of \u0001, "country" => "\u0001yrtnuoc". This is useful when implementing efficient leading wildcards search.

  • Field Details

    • termAtt

      private final CharTermAttribute termAtt
    • marker

      private final char marker
    • NOMARKER

      private static final char NOMARKER
      See Also:
    • START_OF_HEADING_MARKER

      public static final char START_OF_HEADING_MARKER
      Example marker character: U+0001 (START OF HEADING)
      See Also:
    • INFORMATION_SEPARATOR_MARKER

      public static final char INFORMATION_SEPARATOR_MARKER
      Example marker character: U+001F (INFORMATION SEPARATOR ONE)
      See Also:
    • PUA_EC00_MARKER

      public static final char PUA_EC00_MARKER
      Example marker character: U+EC00 (PRIVATE USE AREA: EC00)
      See Also:
    • RTL_DIRECTION_MARKER

      public static final char RTL_DIRECTION_MARKER
      Example marker character: U+200F (RIGHT-TO-LEFT MARK)
      See Also:
  • Constructor Details

    • ReverseStringFilter

      public ReverseStringFilter(TokenStream in)
      Create a new ReverseStringFilter that reverses all tokens in the supplied TokenStream.

      The reversed tokens will not be marked.

      Parameters:
      in - TokenStream to filter
    • ReverseStringFilter

      public ReverseStringFilter(TokenStream in, char marker)
      Create a new ReverseStringFilter that reverses and marks all tokens in the supplied TokenStream.

      The reversed tokens will be prepended (marked) by the marker character.

      Parameters:
      in - TokenStream to filter
      marker - A character used to mark reversed tokens
  • Method Details

    • 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
    • reverse

      public static String reverse(String input)
      Reverses the given input string
      Parameters:
      input - the string to reverse
      Returns:
      the given input string in reversed order
    • reverse

      public static void reverse(char[] buffer)
      Reverses the given input buffer in-place
      Parameters:
      buffer - the input char array to reverse
    • reverse

      public static void reverse(char[] buffer, int len)
      Partially reverses the given input buffer in-place from offset 0 up to the given length.
      Parameters:
      buffer - the input char array to reverse
      len - the length in the buffer up to where the buffer should be reversed
    • 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.
      Parameters:
      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