org.apache.lucene.analysis
Class ASCIIFoldingFilter

java.lang.Object
  org.apache.lucene.util.AttributeSource
      org.apache.lucene.analysis.TokenStream
          org.apache.lucene.analysis.TokenFilter
              org.apache.lucene.analysis.ASCIIFoldingFilter

All Implemented Interfaces:

Closeable

public final class ASCIIFoldingFilter
extends TokenFilter

This class converts alphabetic, numeric, and symbolic Unicode characters which are not in the first 127 ASCII characters (the "Basic Latin" Unicode block) into their ASCII equivalents, if one exists. Characters from the following Unicode blocks are converted; however, only those characters with reasonable ASCII alternatives are converted:

• C1 Controls and Latin-1 Supplement: http://www.unicode.org/charts/PDF/U0080.pdf
• Latin Extended-A: http://www.unicode.org/charts/PDF/U0100.pdf
• Latin Extended-B: http://www.unicode.org/charts/PDF/U0180.pdf
• Latin Extended Additional: http://www.unicode.org/charts/PDF/U1E00.pdf
• Latin Extended-C: http://www.unicode.org/charts/PDF/U2C60.pdf
• Latin Extended-D: http://www.unicode.org/charts/PDF/UA720.pdf
• IPA Extensions: http://www.unicode.org/charts/PDF/U0250.pdf
• Phonetic Extensions: http://www.unicode.org/charts/PDF/U1D00.pdf
• Phonetic Extensions Supplement: http://www.unicode.org/charts/PDF/U1D80.pdf
• General Punctuation: http://www.unicode.org/charts/PDF/U2000.pdf
• Superscripts and Subscripts: http://www.unicode.org/charts/PDF/U2070.pdf
• Enclosed Alphanumerics: http://www.unicode.org/charts/PDF/U2460.pdf
• Dingbats: http://www.unicode.org/charts/PDF/U2700.pdf
• Supplemental Punctuation: http://www.unicode.org/charts/PDF/U2E00.pdf
• Alphabetic Presentation Forms: http://www.unicode.org/charts/PDF/UFB00.pdf
• Halfwidth and Fullwidth Forms: http://www.unicode.org/charts/PDF/UFF00.pdf

See: http://en.wikipedia.org/wiki/Latin_characters_in_Unicode The set of character conversions supported by this class is a superset of those supported by Lucene's ISOLatin1AccentFilter which strips accents from Latin1 characters. For example, 'à' will be replaced by 'a'.

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.lucene.util.AttributeSource

AttributeSource.AttributeFactory, AttributeSource.State

Field Summary

Fields inherited from class org.apache.lucene.analysis.TokenFilter

input

Constructor Summary

ASCIIFoldingFilter(TokenStream input)

Method Summary

void	foldToASCII(char[] input, int length) Converts characters above ASCII to their ASCII equivalents.
static int	foldToASCII(char[] input, int inputPos, char[] output, int outputPos, int length) Converts characters above ASCII to their ASCII equivalents.
boolean	incrementToken() Consumers (i.e., IndexWriter) use this method to advance the stream to the next token.

Methods inherited from class org.apache.lucene.analysis.TokenFilter

close, end, reset

Methods inherited from class org.apache.lucene.util.AttributeSource

addAttribute, addAttributeImpl, captureState, clearAttributes, cloneAttributes, copyTo, equals, getAttribute, getAttributeClassesIterator, getAttributeFactory, getAttributeImplsIterator, hasAttribute, hasAttributes, hashCode, reflectAsString, reflectWith, restoreState, toString

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

ASCIIFoldingFilter

public ASCIIFoldingFilter(TokenStream input)

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

foldToASCII

public void foldToASCII(char[] input,
                        int length)

Converts characters above ASCII to their ASCII equivalents. For example, accents are removed from accented characters.

Parameters:

input - The string to fold

length - The number of characters in the input string

foldToASCII

public static final int foldToASCII(char[] input,
                                    int inputPos,
                                    char[] output,
                                    int outputPos,
                                    int length)

Converts characters above ASCII to their ASCII equivalents. For example, accents are removed from accented characters.

Parameters:

input - The characters to fold

inputPos - Index of the first character to fold

output - The result of the folding. Should be of size >= length * 4.

outputPos - Index of output where to put the result of the folding

length - The number of characters to fold

Returns:

length of output

NOTE: This API is for internal purposes only and might change in incompatible ways in the next release.