LUCENE3.0 自学吧 7 CharTokenizer

CharTokenizer 是一个抽象类，它主要是对西文字符进行分词处理的。常见的英文中，是以空格、标点为分隔符号的，在分词的时候，就是以这些分隔符作为分词的间隔符的。

 

 

package org.apache.lucene.analysis;

import java.io.IOException;
import java.io.Reader;

import org.apache.lucene.analysis.tokenattributes.OffsetAttribute;
import org.apache.lucene.analysis.tokenattributes.TermAttribute;
import org.apache.lucene.util.AttributeSource;

//CharTokenizer是一个抽象类，貌似只有
// CharTokenizer token5 = new LetterTokenizer(input); 去实例化？
public abstract class CharTokenizer extends Tokenizer {
  public CharTokenizer(Reader input) {
    super(input);
    offsetAtt = addAttribute(OffsetAttribute.class);
    termAtt = addAttribute(TermAttribute.class);
  }

  public CharTokenizer(AttributeSource source, Reader input) {
    super(source, input);
    offsetAtt = addAttribute(OffsetAttribute.class);
    termAtt = addAttribute(TermAttribute.class);
  }

  public CharTokenizer(AttributeFactory factory, Reader input) {
    super(factory, input);
    offsetAtt = addAttribute(OffsetAttribute.class);
    termAtt = addAttribute(TermAttribute.class);
  }

  private int offset = 0, bufferIndex = 0, dataLen = 0;
  private static final int MAX_WORD_LEN = 255;
  private static final int IO_BUFFER_SIZE = 4096;
  private final char[] ioBuffer = new char[IO_BUFFER_SIZE];

  private TermAttribute termAtt;
  private OffsetAttribute offsetAtt;

  protected abstract boolean isTokenChar(char c);
// 对字符进行处理，可以在CharTokenizer 的子类中实现
  protected char normalize(char c) {
    return c;
  }

  @Override
  public final boolean incrementToken() throws IOException {
    clearAttributes();
    int length = 0;
    int start = bufferIndex;
    char[] buffer = termAtt.termBuffer();
    while (true) {

      if (bufferIndex >= dataLen) {
        offset += dataLen;
        dataLen = input.read(ioBuffer);
        if (dataLen == -1) {
          dataLen = 0;                            // so next offset += dataLen won't decrement offset
          if (length > 0)
            break;
          else
            return false;
        }
        bufferIndex = 0;
      }

      final char c = ioBuffer[bufferIndex++];

      if (isTokenChar(c)) {               // if it's a token char

        if (length == 0)                 // start of token
          start = offset + bufferIndex - 1;
        else if (length == buffer.length)
          buffer = termAtt.resizeTermBuffer(1+length);

        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
    }

    termAtt.setTermLength(length);
    offsetAtt.setOffset(correctOffset(start), correctOffset(start+length));
    return true;
  }

  @Override
  public final void end() {
    // set final offset
    int finalOffset = correctOffset(offset);
    offsetAtt.setOffset(finalOffset, finalOffset);
  }

  @Override
  public void reset(Reader input) throws IOException {
    super.reset(input);
    bufferIndex = 0;
    offset = 0;
    dataLen = 0;
  }
}

 

实现 CharTokenizer 的具体类有 1 个，分别为： LetterTokenizer( 仅在核心包 ) 、

 

看看 LetterTokenizer 类：

 

 

package org.apache.lucene.analysis;

import java.io.Reader;

// 只要读取到非字符的符号，就分词

public class LetterTokenizer extends CharTokenizer {

public LetterTokenizer(Reader in) {
    super(in);
}


protected boolean isTokenChar(char c) {
    return Character.isLetter(c);
}
}

 

做个测试就可以看到：

 

 

package com.fpi.lucene.studying.test;

import java.io.IOException;
import java.io.Reader;
import java.io.StringReader;

import org.apache.lucene.analysis.CharTokenizer;
import org.apache.lucene.analysis.LetterTokenizer;
import org.apache.lucene.analysis.Tokenizer;
import org.apache.lucene.analysis.cjk.CJKTokenizer;
import org.apache.lucene.analysis.cn.ChineseTokenizer;

public class JustTest {
       public static void main(String[] args) {
         Reader read = new StringReader("what are you doing,man?It's none of your business!");
       LetterTokenizer token5 = new LetterTokenizer(read);
       try {
                     while(token5.incrementToken()){
                             System.out.println(token5.toString());
                      }
              } catch (IOException e) {
                     // TODO Auto-generated catch block
                     e.printStackTrace();
              }
       }
}

 

运行结果如下：

(startOffset=0,endOffset=4,term=what)

(startOffset=5,endOffset=8,term=are)

(startOffset=9,endOffset=12,term=you)

(startOffset=13,endOffset=18,term=doing)

(startOffset=19,endOffset=22,term=man)

(startOffset=23,endOffset=25,term=It)

(startOffset=26,endOffset=27,term=s)

(startOffset=28,endOffset=32,term=none)

(startOffset=33,endOffset=35,term=of)

(startOffset=36,endOffset=40,term=your)

(startOffset=41,endOffset=49,term=business)     

 

看到了吗？不但逗号和问号被分开，而且连 It’s 这个也被分解为 It 和 s 了。

 

没有非字符的英文字母串就可以作为一个词条，一个词条长度的限制为 255 个字符，可以在 CharTokenizer 抽象类中看到定义：

 

private static final int MAX_WORD_LEN = 255

 

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