Apache Lucene TokenStream 合同违规

Question

Using Appache Lucene TokenStream to remove stopwords causes an error:

TokenStream contract violation: reset()/close() call missing, reset() called multiple times, or subclass does not call super.reset(). Please see Javadocs of TokenStream class for more information about the correct consuming workflow.

I use this code:

public static String removeStopWords(String string) throws IOException {
    TokenStream tokenStream = new StandardTokenizer(Version.LUCENE_47, new StringReader(string));
    TokenFilter tokenFilter = new StandardFilter(Version.LUCENE_47, tokenStream);
    TokenStream stopFilter = new StopFilter(Version.LUCENE_47, tokenFilter, StandardAnalyzer.STOP_WORDS_SET);
    StringBuilder stringBuilder = new StringBuilder();

    CharTermAttribute token = tokenStream.getAttribute(CharTermAttribute.class);

    while(stopFilter.incrementToken()) {
        if(stringBuilder.length() > 0 ) {
            stringBuilder.append(" ");
        }

        stringBuilder.append(token.toString());
    }

    stopFilter.end();
    stopFilter.close();

    return stringBuilder.toString();
}

But as you can see i never call reset() or close().

So why am i getting this error?

Answer 1

i never call reset() or close().

Well, that is your problem. If you care to read TokenStream javadoc, you would find the following:

The workflow of the new TokenStream API is as follows:

1. Instantiation of TokenStream / TokenFilter s which add/get attributes to/from the AttributeSource .
2. The consumer calls TokenStream#reset()
3. ...

I only had to add one line with reset() to your code and it worked.

...    
CharTermAttribute token = tokenStream.getAttribute(CharTermAttribute.class);
tokenStream.reset();   // I added this 
while(stopFilter.incrementToken()) {
...

Answer 2

I meet the error when reuse the same Tokenizer. The reason just in the comments. The solution is set a new reader or create a new Tokenizer.

  /** Expert: Set a new reader on the Tokenizer.  Typically, an
   *  analyzer (in its tokenStream method) will use
   *  this to re-use a previously created tokenizer. */
  public final void setReader(Reader input) {
    if (input == null) {
      throw new NullPointerException("input must not be null");
    } else if (this.input != ILLEGAL_STATE_READER) {
      throw new IllegalStateException("TokenStream contract violation: close() call missing");
    }
    this.inputPending = input;
    setReaderTestPoint();
  }