org.apache.lucene.analysis
Class Token

java.lang.Object
  org.apache.lucene.analysis.Token

All Implemented Interfaces:

Cloneable

public class Token
extends Object
implements Cloneable

A Token is an occurence of a term from the text of a field. It consists of a term's text, the start and end offset of the term in the text of the field, and a type string.

The start and end offsets permit applications to re-associate a token with its source text, e.g., to display highlighted query terms in a document browser, or to show matching text fragments in a KWIC (KeyWord In Context) display, etc.

The type is an interned string, assigned by a lexical analyzer (a.k.a. tokenizer), naming the lexical or syntactic class that the token belongs to. For example an end of sentence marker token might be implemented with type "eos". The default token type is "word".

A Token can optionally have metadata (a.k.a. Payload) in the form of a variable length byte array. Use TermPositions.getPayloadLength() and TermPositions.getPayload(byte[], int) to retrieve the payloads from the index.

WARNING: The status of the Payloads feature is experimental. The APIs introduced here might change in the future and will not be supported anymore in such a case.

NOTE: As of 2.3, Token stores the term text internally as a malleable char[] termBuffer instead of String termText. The indexing code and core tokenizers have been changed re-use a single Token instance, changing its buffer and other fields in-place as the Token is processed. This provides substantially better indexing performance as it saves the GC cost of new'ing a Token and String for every term. The APIs that accept String termText are still available but a warning about the associated performance cost has been added (below). The termText() method has been deprecated.

Tokenizers and filters should try to re-use a Token instance when possible for best performance, by implementing the TokenStream.next(Token) API. Failing that, to create a new Token you should first use one of the constructors that starts with null text. Then you should call either termBuffer() or resizeTermBuffer(int) to retrieve the Token's termBuffer. Fill in the characters of your term into this buffer, and finally call setTermLength(int) to set the length of the term text. See LUCENE-969 for details.

See Also:

Payload

Field Summary

static String

DEFAULT_TYPE

Constructor Summary

Token()
Constructs a Token will null text.

Token(int start, int end)
Constructs a Token with null text and start & end offsets.

Token(int start, int end, String typ)
Constructs a Token with null text and start & end offsets plus the Token type.

Token(String text, int start, int end)
Constructs a Token with the given term text, and start & end offsets.

Token(String text, int start, int end, String typ)
Constructs a Token with the given text, start and end offsets, & type.

Method Summary

void	clear() Resets the term text, payload, and positionIncrement to default.
Object	clone()
int	endOffset() Returns this Token's ending offset, one greater than the position of the last character corresponding to this token in the source text.
Payload	getPayload() Returns this Token's payload.
int	getPositionIncrement() Returns the position increment of this Token.
char[]	resizeTermBuffer(int newSize) Grows the termBuffer to at least size newSize.
void	setEndOffset(int offset) Set the ending offset.
void	setPayload(Payload payload) Sets this Token's payload.
void	setPositionIncrement(int positionIncrement) Set the position increment.
void	setStartOffset(int offset) Set the starting offset.
void	setTermBuffer(char[] buffer, int offset, int length) Copies the contents of buffer, starting at offset for length characters, into the termBuffer array.
void	setTermLength(int length) Set number of valid characters (length of the term) in the termBuffer array.
void	setTermText(String text) Sets the Token's term text.
void	setType(String type) Set the lexical type.
int	startOffset() Returns this Token's starting offset, the position of the first character corresponding to this token in the source text.
char[]	termBuffer() Returns the internal termBuffer character array which you can then directly alter.
int	termLength() Return number of valid characters (length of the term) in the termBuffer array.
String	termText() Deprecated. Use termBuffer() and termLength() instead.
String	toString()
String	type() Returns this Token's lexical type.

Methods inherited from class java.lang.Object

equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

DEFAULT_TYPE

public static final String DEFAULT_TYPE

See Also:

Constant Field Values

Constructor Detail

Token

public Token()

Constructs a Token will null text.

Token

public Token(int start,
             int end)

Constructs a Token with null text and start & end offsets.

Parameters:

start - start offset

end - end offset

Token

public Token(int start,
             int end,
             String typ)

Constructs a Token with null text and start & end offsets plus the Token type.

Parameters:

start - start offset

end - end offset

Token

public Token(String text,
             int start,
             int end)

Constructs a Token with the given term text, and start & end offsets. The type defaults to "word." NOTE: for better indexing speed you should instead use the char[] termBuffer methods to set the term text.

Parameters:

text - term text

start - start offset

end - end offset

Token

public Token(String text,
             int start,
             int end,
             String typ)

Constructs a Token with the given text, start and end offsets, & type. NOTE: for better indexing speed you should instead use the char[] termBuffer methods to set the term text.

Parameters:

text - term text

start - start offset

end - end offset

typ - token type

Method Detail

setPositionIncrement

public void setPositionIncrement(int positionIncrement)

Set the position increment. This determines the position of this token relative to the previous Token in a TokenStream, used in phrase searching.

The default value is one.

Some common uses for this are:

• Set it to zero to put multiple terms in the same position. This is useful if, e.g., a word has multiple stems. Searches for phrases including either stem will match. In this case, all but the first stem's increment should be set to zero: the increment of the first instance should be one. Repeating a token with an increment of zero can also be used to boost the scores of matches on that token.
• Set it to values greater than one to inhibit exact phrase matches. If, for example, one does not want phrases to match across removed stop words, then one could build a stop word filter that removes stop words and also sets the increment to the number of stop words removed before each non-stop word. Then exact phrase queries will only match when the terms occur with no intervening stop words.

See Also:

TermPositions

getPositionIncrement

public int getPositionIncrement()

Returns the position increment of this Token.

See Also:

setPositionIncrement(int)

setTermText

public void setTermText(String text)

Sets the Token's term text. NOTE: for better indexing speed you should instead use the char[] termBuffer methods to set the term text.

termText

public final String termText()

Deprecated. Use termBuffer() and termLength() instead.

Returns the Token's term text.

setTermBuffer

public final void setTermBuffer(char[] buffer,
                                int offset,
                                int length)

Copies the contents of buffer, starting at offset for length characters, into the termBuffer array. NOTE: for better indexing speed you should instead retrieve the termBuffer, using termBuffer() or resizeTermBuffer(int), and fill it in directly to set the term text. This saves an extra copy.

termBuffer

public final char[] termBuffer()

Returns the internal termBuffer character array which you can then directly alter. If the array is too small for your token, use resizeTermBuffer(int) to increase it. After altering the buffer be sure to call setTermLength(int) to record the number of valid characters that were placed into the termBuffer.

resizeTermBuffer

public char[] resizeTermBuffer(int newSize)

Grows the termBuffer to at least size newSize.

Parameters:

newSize - minimum size of the new termBuffer

Returns:

newly created termBuffer with length >= newSize

termLength

public final int termLength()

Return number of valid characters (length of the term) in the termBuffer array.

setTermLength

public final void setTermLength(int length)

Set number of valid characters (length of the term) in the termBuffer array.

startOffset

public final int startOffset()

Returns this Token's starting offset, the position of the first character corresponding to this token in the source text. Note that the difference between endOffset() and startOffset() may not be equal to termText.length(), as the term text may have been altered by a stemmer or some other filter.

setStartOffset

public void setStartOffset(int offset)

Set the starting offset.

See Also:

startOffset()

endOffset

public final int endOffset()

Returns this Token's ending offset, one greater than the position of the last character corresponding to this token in the source text.

setEndOffset

public void setEndOffset(int offset)

Set the ending offset.

See Also:

endOffset()

type

public final String type()

Returns this Token's lexical type. Defaults to "word".

setType

public final void setType(String type)

Set the lexical type.

See Also:

type()

getPayload

public Payload getPayload()

Returns this Token's payload.

setPayload

public void setPayload(Payload payload)

Sets this Token's payload.

toString

public String toString()

Overrides:

toString in class Object

clear

public void clear()

Resets the term text, payload, and positionIncrement to default. Other fields such as startOffset, endOffset and the token type are not reset since they are normally overwritten by the tokenizer.

clone

public Object clone()

Overrides:

clone in class Object