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From Jose Fernandez <>
Subject RE: custom token filter generates empty tokens
Date Thu, 09 Oct 2014 16:29:32 GMT
When you return true from incrementToken() you tell Lucene to add your token to the token stream.
At the end of incrementToken() check for an empty token. If it's empty then return incrementToken()
to process the next token. This will affect your positions so if you're doing phrase search
you will need to adjust the position attribute to account for the now-empty token.

-----Original Message-----
From: G.Long [] 
Sent: Thursday, October 09, 2014 7:54 AM
Subject: custom token filter generates empty tokens

Hi :)

I wrote a custom token filter which removes special characters. 
Sometimes, all characters of the token are removed so the filter procudes an empty token.
I would like to remove this token from the tokenstream but i'm not sure how to do that.

Is there something missing in my custom token filter or do I need to chain another custom
token filter to remove empty tokens?

Regards :)


this is the code of my custom filter :

public class SpecialCharFilter extends TokenFilter {

     private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);

     protected SpecialCharFilter(TokenStream input) {

     public boolean incrementToken() throws IOException {

         if (!input.incrementToken()) {
             return false;

         final char[] buffer = termAtt.buffer();
         final int length = termAtt.length();
         final char[] newBuffer = new char[length];

         int newIndex = 0;
         for (int i = 0; i < length; i++) {
             if (!isFilteredChar(buffer[i])) {
                 newBuffer[newIndex] = buffer[i];

         String term = new String(newBuffer);
         term = term.trim();
         char[] characters = term.toCharArray();
         termAtt.copyBuffer(characters, 0, characters.length);

         return true;

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