RTLのテキストを処理するSolr用CharFilterです

ShowaFilterFactory.java

package analysis;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.Reader;
import java.util.LinkedList;

import org.apache.lucene.analysis.BaseCharFilter;
import org.apache.lucene.analysis.CharReader;
import org.apache.lucene.analysis.CharStream;
import org.apache.solr.analysis.BaseCharFilterFactory;

public class ShowaFilterFactory extends BaseCharFilterFactory {
  
  public CharStream create(CharStream input) {
    return new ShowaFilter(input);
  }
  
  private static class ShowaFilter extends BaseCharFilter {
    
    private String line;
    private int linePos;
    private int currentPos;
    private final BufferedReader reader;
    
    ShowaFilter(CharStream in) {
      super(in);
      reader = new BufferedReader(in);
    }

    ShowaFilter(Reader in) {
      this(CharReader.get(in));
    }

    @Override
    public int read() throws IOException {
      if (readLine() == -1) return -1;
      currentPos++;
      return line.charAt(linePos++);
    }
    
    private int readLine() throws IOException {
      if (line == null || line.length() == linePos) {
        line = reader.readLine();
        if (line == null) return -1;
        int lineLen = line.length();
        linePos = 0;
        char[] chars = line.toCharArray();
        char[] newChars = new char[lineLen];
        for (int i = 0; i < lineLen; i++) {
          newChars[i] = chars[lineLen - i - 1];
          addOffCorrectMap(currentPos + i, 0);
        }
        line = String.valueOf(newChars) + "\n";
        return line.length() + 1;
      }
      return 0;
    }
    
    @Override
    public void close() throws IOException {
      reader.close();
      super.close();
    }

    @Override
    public int read(char[] cbuf, int off, int len) throws IOException {
      int l = 0;
      for(int i = off; i < off + len; i++) {
        int c = read();
        if (c == -1) break;
        cbuf[i] = (char) c;
        l++;
      }
      return l == 0 ? -1 : l;
    }
  }

}