simple edge n-gram prefix filter

gistfile1.java

package service.search;

import java.io.Reader;

import org.apache.lucene.analysis.LowerCaseFilter;
import org.apache.lucene.analysis.LowerCaseTokenizer;
import org.apache.lucene.analysis.ReusableAnalyzerBase;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.Tokenizer;
import org.apache.lucene.analysis.WhitespaceTokenizer;
import org.apache.lucene.analysis.ngram.EdgeNGramTokenFilter;
import org.apache.lucene.analysis.ngram.EdgeNGramTokenFilter.Side;
import org.apache.lucene.util.Version;

public final class LowerCaseNGramPrefixAnalyzer extends ReusableAnalyzerBase {
	private final Version matchVersion;

	public LowerCaseNGramPrefixAnalyzer(Version matchVersion) {
		this.matchVersion = matchVersion;
	}

	@Override
	protected TokenStreamComponents createComponents(String fieldName,
			Reader reader) {
		Tokenizer source = new WhitespaceTokenizer(matchVersion, reader);

		TokenStream sink = new LowerCaseFilter(Version.LUCENE_35, source);
		
		return new TokenStreamComponents(source, new EdgeNGramTokenFilter(
				sink, Side.FRONT, 3, 15));
	}
}