--- /dev/null
+package org.apache.lucene.analysis.ngram;
+
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import org.apache.lucene.analysis.TokenFilter;
+import org.apache.lucene.analysis.TokenStream;
+import org.apache.lucene.analysis.tokenattributes.OffsetAttribute;
+import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
+
+import java.io.IOException;
+
+/**
+ * Tokenizes the given token into n-grams of given size(s).
+ * <p>
+ * This {@link TokenFilter} create n-grams from the beginning edge or ending edge of a input token.
+ * </p>
+ */
+public final class EdgeNGramTokenFilter extends TokenFilter {
+ public static final Side DEFAULT_SIDE = Side.FRONT;
+ public static final int DEFAULT_MAX_GRAM_SIZE = 1;
+ public static final int DEFAULT_MIN_GRAM_SIZE = 1;
+
+ /** Specifies which side of the input the n-gram should be generated from */
+ public static enum Side {
+
+ /** Get the n-gram from the front of the input */
+ FRONT {
+ @Override
+ public String getLabel() { return "front"; }
+ },
+
+ /** Get the n-gram from the end of the input */
+ BACK {
+ @Override
+ public String getLabel() { return "back"; }
+ };
+
+ public abstract String getLabel();
+
+ // Get the appropriate Side from a string
+ public static Side getSide(String sideName) {
+ if (FRONT.getLabel().equals(sideName)) {
+ return FRONT;
+ }
+ if (BACK.getLabel().equals(sideName)) {
+ return BACK;
+ }
+ return null;
+ }
+ }
+
+ private final int minGram;
+ private final int maxGram;
+ private Side side;
+ private char[] curTermBuffer;
+ private int curTermLength;
+ private int curGramSize;
+ private int tokStart;
+
+ private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);
+ private final OffsetAttribute offsetAtt = addAttribute(OffsetAttribute.class);
+
+ /**
+ * Creates EdgeNGramTokenFilter that can generate n-grams in the sizes of the given range
+ *
+ * @param input {@link TokenStream} holding the input to be tokenized
+ * @param side the {@link Side} from which to chop off an n-gram
+ * @param minGram the smallest n-gram to generate
+ * @param maxGram the largest n-gram to generate
+ */
+ public EdgeNGramTokenFilter(TokenStream input, Side side, int minGram, int maxGram) {
+ super(input);
+
+ if (side == null) {
+ throw new IllegalArgumentException("sideLabel must be either front or back");
+ }
+
+ if (minGram < 1) {
+ throw new IllegalArgumentException("minGram must be greater than zero");
+ }
+
+ if (minGram > maxGram) {
+ throw new IllegalArgumentException("minGram must not be greater than maxGram");
+ }
+
+ this.minGram = minGram;
+ this.maxGram = maxGram;
+ this.side = side;
+ }
+
+ /**
+ * Creates EdgeNGramTokenFilter that can generate n-grams in the sizes of the given range
+ *
+ * @param input {@link TokenStream} holding the input to be tokenized
+ * @param sideLabel the name of the {@link Side} from which to chop off an n-gram
+ * @param minGram the smallest n-gram to generate
+ * @param maxGram the largest n-gram to generate
+ */
+ public EdgeNGramTokenFilter(TokenStream input, String sideLabel, int minGram, int maxGram) {
+ this(input, Side.getSide(sideLabel), minGram, maxGram);
+ }
+
+ @Override
+ public final boolean incrementToken() throws IOException {
+ while (true) {
+ if (curTermBuffer == null) {
+ if (!input.incrementToken()) {
+ return false;
+ } else {
+ curTermBuffer = termAtt.buffer().clone();
+ curTermLength = termAtt.length();
+ curGramSize = minGram;
+ tokStart = offsetAtt.startOffset();
+ }
+ }
+ if (curGramSize <= maxGram) {
+ if (! (curGramSize > curTermLength // if the remaining input is too short, we can't generate any n-grams
+ || curGramSize > maxGram)) { // if we have hit the end of our n-gram size range, quit
+ // grab gramSize chars from front or back
+ int start = side == Side.FRONT ? 0 : curTermLength - curGramSize;
+ int end = start + curGramSize;
+ clearAttributes();
+ offsetAtt.setOffset(tokStart + start, tokStart + end);
+ termAtt.copyBuffer(curTermBuffer, start, curGramSize);
+ curGramSize++;
+ return true;
+ }
+ }
+ curTermBuffer = null;
+ }
+ }
+
+ @Override
+ public void reset() throws IOException {
+ super.reset();
+ curTermBuffer = null;
+ }
+}
fnp / pylucene.git / blobdiff