Class ASCIIFoldingFilter

  extended by org.apache.lucene.util.AttributeSource
      extended by org.apache.lucene.analysis.TokenStream
          extended by org.apache.lucene.analysis.TokenFilter
              extended by org.apache.lucene.analysis.ASCIIFoldingFilter
All Implemented Interfaces:

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:

See: 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
Constructor Summary
ASCIIFoldingFilter(TokenStream input)
Method Summary
 void foldToASCII(char[] input, 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, equals, getAttribute, getAttributeClassesIterator, getAttributeFactory, getAttributeImplsIterator, hasAttribute, hasAttributes, hashCode, restoreState, toString
Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Detail


public ASCIIFoldingFilter(TokenStream input)
Method Detail


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


public void foldToASCII(char[] input,
                        int length)
Converts characters above ASCII to their ASCII equivalents. For example, accents are removed from accented characters.

input - The string to fold
length - The number of characters in the input string

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