Source Code Cross Referenced for EdgeNGramTokenizer.java in  » Net » lucene-connector » org » apache » lucene » analysis » ngram » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » Net » lucene connector » org.apache.lucene.analysis.ngram 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        package org.apache.lucene.analysis.ngram;
002:
003:        /**
004:         * Licensed to the Apache Software Foundation (ASF) under one or more
005:         * contributor license agreements.  See the NOTICE file distributed with
006:         * this work for additional information regarding copyright ownership.
007:         * The ASF licenses this file to You under the Apache License, Version 2.0
008:         * (the "License"); you may not use this file except in compliance with
009:         * the License.  You may obtain a copy of the License at
010:         *
011:         *     http://www.apache.org/licenses/LICENSE-2.0
012:         *
013:         * Unless required by applicable law or agreed to in writing, software
014:         * distributed under the License is distributed on an "AS IS" BASIS,
015:         * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
016:         * See the License for the specific language governing permissions and
017:         * limitations under the License.
018:         */
019:
020:        import org.apache.lucene.analysis.Token;
021:        import org.apache.lucene.analysis.Tokenizer;
022:
023:        import java.io.IOException;
024:        import java.io.Reader;
025:
026:        /**
027:         * Tokenizes the input from an edge into n-grams of given size(s).
028:         * @author Otis Gospodnetic
029:         * @author Adam Hiatt
030:         */
031:        public class EdgeNGramTokenizer extends Tokenizer {
032:            public static final Side DEFAULT_SIDE = Side.FRONT;
033:            public static final int DEFAULT_MAX_GRAM_SIZE = 1;
034:            public static final int DEFAULT_MIN_GRAM_SIZE = 1;
035:
036:            // Replace this with an enum when the Java 1.5 upgrade is made, the impl will be simplified
037:            /** Specifies which side of the input the n-gram should be generated from */
038:            public static class Side {
039:                private String label;
040:
041:                /** Get the n-gram from the front of the input */
042:                public static Side FRONT = new Side("front");
043:
044:                /** Get the n-gram from the end of the input */
045:                public static Side BACK = new Side("back");
046:
047:                // Private ctor
048:                private Side(String label) {
049:                    this .label = label;
050:                }
051:
052:                public String getLabel() {
053:                    return label;
054:                }
055:
056:                // Get the appropriate Side from a string
057:                public static Side getSide(String sideName) {
058:                    if (FRONT.getLabel().equals(sideName)) {
059:                        return FRONT;
060:                    } else if (BACK.getLabel().equals(sideName)) {
061:                        return BACK;
062:                    }
063:                    return null;
064:                }
065:            }
066:
067:            private int minGram;
068:            private int maxGram;
069:            private int gramSize;
070:            private Side side;
071:            private boolean started = false;
072:            private int inLen;
073:            private String inStr;
074:
075:            /**
076:             * Creates EdgeNGramTokenizer that can generate n-grams in the sizes of the given range
077:             *
078:             * @param input Reader holding the input to be tokenized
079:             * @param side the {@link Side} from which to chop off an n-gram
080:             * @param minGram the smallest n-gram to generate
081:             * @param maxGram the largest n-gram to generate
082:             */
083:            public EdgeNGramTokenizer(Reader input, Side side, int minGram,
084:                    int maxGram) {
085:                super (input);
086:
087:                if (side == null) {
088:                    throw new IllegalArgumentException(
089:                            "sideLabel must be either front or back");
090:                }
091:
092:                if (minGram < 1) {
093:                    throw new IllegalArgumentException(
094:                            "minGram must be greater than zero");
095:                }
096:
097:                if (minGram > maxGram) {
098:                    throw new IllegalArgumentException(
099:                            "minGram must not be greater than maxGram");
100:                }
101:
102:                this .minGram = minGram;
103:                this .maxGram = maxGram;
104:                this .side = side;
105:            }
106:
107:            /**
108:             * Creates EdgeNGramTokenizer that can generate n-grams in the sizes of the given range
109:             *
110:             * @param input Reader holding the input to be tokenized
111:             * @param sideLabel the name of the {@link Side} from which to chop off an n-gram
112:             * @param minGram the smallest n-gram to generate
113:             * @param maxGram the largest n-gram to generate
114:             */
115:            public EdgeNGramTokenizer(Reader input, String sideLabel,
116:                    int minGram, int maxGram) {
117:                this (input, Side.getSide(sideLabel), minGram, maxGram);
118:            }
119:
120:            /** Returns the next token in the stream, or null at EOS. */
121:            public final Token next() throws IOException {
122:                // if we are just starting, read the whole input
123:                if (!started) {
124:                    started = true;
125:                    char[] chars = new char[1024];
126:                    input.read(chars);
127:                    inStr = new String(chars).trim(); // remove any trailing empty strings
128:                    inLen = inStr.length();
129:                    gramSize = minGram;
130:                }
131:
132:                // if the remaining input is too short, we can't generate any n-grams
133:                if (gramSize > inLen) {
134:                    return null;
135:                }
136:
137:                // if we have hit the end of our n-gram size range, quit
138:                if (gramSize > maxGram) {
139:                    return null;
140:                }
141:
142:                Token tok;
143:                if (side == Side.FRONT) {
144:                    tok = new Token(inStr.substring(0, gramSize), 0, gramSize);
145:                } else {
146:                    tok = new Token(inStr.substring(inLen - gramSize), inLen
147:                            - gramSize, inLen);
148:                }
149:
150:                gramSize++;
151:                return tok;
152:            }
153:        }
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