CharTokenizer.cs
上传用户:zhangkuixh
上传日期:2013-09-30
资源大小:5473k
文件大小:3k
- /*
- * Copyright 2004 The Apache Software Foundation
- *
- * Licensed 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.
- */
- using System;
- namespace Lucene.Net.Analysis
- {
-
- /// <summary>An abstract base class for simple, character-oriented tokenizers.</summary>
- public abstract class CharTokenizer : Tokenizer
- {
- public CharTokenizer(System.IO.TextReader input) : base(input)
- {
- }
-
- private int offset = 0, bufferIndex = 0, dataLen = 0;
- private const int MAX_WORD_LEN = 255;
- private const int IO_BUFFER_SIZE = 1024;
- private char[] buffer = new char[MAX_WORD_LEN];
- private char[] ioBuffer = new char[IO_BUFFER_SIZE];
-
- /// <summary>Returns true iff a character should be included in a token. This
- /// tokenizer generates as tokens adjacent sequences of characters which
- /// satisfy this predicate. Characters for which this is false are used to
- /// define token boundaries and are not included in tokens.
- /// </summary>
- protected internal abstract bool IsTokenChar(char c);
-
- /// <summary>Called on each token character to normalize it before it is added to the
- /// token. The default implementation does nothing. Subclasses may use this
- /// to, e.g., lowercase tokens.
- /// </summary>
- protected internal virtual char Normalize(char c)
- {
- return c;
- }
-
- /// <summary>Returns the next token in the stream, or null at EOS. </summary>
- public override Token Next()
- {
- int length = 0;
- int start = offset;
- while (true)
- {
- char c;
-
- offset++;
- if (bufferIndex >= dataLen)
- {
- dataLen = input.Read((System.Char[]) ioBuffer, 0, ioBuffer.Length);
- bufferIndex = 0;
- }
- ;
- if (dataLen <= 0)
- {
- if (length > 0)
- break;
- else
- return null;
- }
- else
- c = ioBuffer[bufferIndex++];
-
- if (IsTokenChar(c))
- {
- // if it's a token char
-
- if (length == 0)
- // start of token
- start = offset - 1;
-
- buffer[length++] = Normalize(c); // buffer it, normalized
-
- if (length == MAX_WORD_LEN)
- // buffer overflow!
- break;
- }
- else if (length > 0)
- // at non-Letter w/ chars
- break; // return 'em
- }
-
- return new Token(new System.String(buffer, 0, length), start, start + length);
- }
- }
- }