Package org.apache.lucene.analysis.util

Class CharTokenizer

  • All Implemented Interfaces:
    Closeable, AutoCloseable
    Direct Known Subclasses:
    LetterTokenizer, WhitespaceTokenizer
    public abstract class CharTokenizer
extends Tokenizer
    An abstract base class for simple, character-oriented tokenizers.

    The base class also provides factories to create instances of CharTokenizer using Java 8 lambdas or method references. It is possible to create an instance which behaves exactly like LetterTokenizer: 

     Tokenizer tok = CharTokenizer.fromTokenCharPredicate(Character::isLetter);

    • Constructor Detail

      • CharTokenizer

        public CharTokenizer()
        Creates a new CharTokenizer instance

      • CharTokenizer

        public CharTokenizer​(AttributeFactory factory,
                     int maxTokenLen)
        Creates a new CharTokenizer instance
        Parameters:
        factory - the attribute factory to use for this Tokenizer
        maxTokenLen - maximum token length the tokenizer will emit. Must be greater than 0 and less than MAX_TOKEN_LENGTH_LIMIT (1024*1024)
        Throws:
        IllegalArgumentException - if maxTokenLen is invalid.

    • Method Detail

      • fromTokenCharPredicate

        public static CharTokenizer fromTokenCharPredicate​(IntPredicate tokenCharPredicate)
        Creates a new instance of CharTokenizer using a custom predicate, supplied as method reference or lambda expression. The predicate should return true for all valid token characters.

        This factory is intended to be used with lambdas or method references. E.g., an elegant way to create an instance which behaves exactly as LetterTokenizer is: 

         Tokenizer tok = CharTokenizer.fromTokenCharPredicate(Character::isLetter);

      • fromTokenCharPredicate

        public static CharTokenizer fromTokenCharPredicate​(AttributeFactory factory,
                                                   IntPredicate tokenCharPredicate)
        Creates a new instance of CharTokenizer with the supplied attribute factory using a custom predicate, supplied as method reference or lambda expression. The predicate should return true for all valid token characters.

        This factory is intended to be used with lambdas or method references. E.g., an elegant way to create an instance which behaves exactly as LetterTokenizer is: 

         Tokenizer tok = CharTokenizer.fromTokenCharPredicate(factory, Character::isLetter);

      • fromSeparatorCharPredicate

        public static CharTokenizer fromSeparatorCharPredicate​(IntPredicate separatorCharPredicate)
        Creates a new instance of CharTokenizer using a custom predicate, supplied as method reference or lambda expression. The predicate should return true for all valid token separator characters. This method is provided for convenience to easily use predicates that are negated (they match the separator characters, not the token characters).

        This factory is intended to be used with lambdas or method references. E.g., an elegant way to create an instance which behaves exactly as WhitespaceTokenizer is: 

         Tokenizer tok = CharTokenizer.fromSeparatorCharPredicate(Character::isWhitespace);

      • fromSeparatorCharPredicate

        public static CharTokenizer fromSeparatorCharPredicate​(AttributeFactory factory,
                                                       IntPredicate separatorCharPredicate)
        Creates a new instance of CharTokenizer with the supplied attribute factory using a custom predicate, supplied as method reference or lambda expression. The predicate should return true for all valid token separator characters.

        This factory is intended to be used with lambdas or method references. E.g., an elegant way to create an instance which behaves exactly as WhitespaceTokenizer is: 

         Tokenizer tok = CharTokenizer.fromSeparatorCharPredicate(factory, Character::isWhitespace);

      • isTokenChar

        protected abstract boolean isTokenChar​(int c)
        Returns true iff a codepoint should be included in a token. This tokenizer generates as tokens adjacent sequences of codepoints which satisfy this predicate. Codepoints for which this is false are used to define token boundaries and are not included in tokens.

      • incrementToken

        public final 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

      • end

        public final void end()
               throws IOException
        Description copied from class: TokenStream
        This method is called by the consumer after the last token has been consumed, after TokenStream.incrementToken() returned false (using the new TokenStream API). Streams implementing the old API should upgrade to use this feature.

        This method can be used to perform any end-of-stream operations, such as setting the final offset of a stream. The final offset of a stream might differ from the offset of the last token eg in case one or more whitespaces followed after the last token, but a WhitespaceTokenizer was used.

        Additionally any skipped positions (such as those removed by a stopfilter) can be applied to the position increment, or any adjustment of other attributes where the end-of-stream value may be important.

        If you override this method, always call super.end().

        Overrides:
        end in class TokenStream
        Throws:
        IOException - If an I/O error occurs

      • reset

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

        Overrides:
        reset in class Tokenizer
        Throws:
        IOException