利用RandomAccessFile快速读取文件最后一行

public static String readLastLine(File file, String charset) throws IOException {  
  if (!file.exists() || file.isDirectory() || !file.canRead()) {  
    return null;  
  }  
  RandomAccessFile raf = null;  
  try {  
    raf = new RandomAccessFile(file, "r");  
    long len = raf.length();  
    if (len == 0L) {  
      return "";  
    } else {  
      long pos = len - 1;  
      while (pos > 0) {  
        pos--;  
        raf.seek(pos);  
        if (raf.readByte() == '\n') {  
          break;  
        }  
      }  
      if (pos == 0) {  
        raf.seek(0);  
      }  
      byte[] bytes = new byte[(int) (len - pos)];  
      raf.read(bytes);  
      if (charset == null) {  
        return new String(bytes);  
      } else {  
        return new String(bytes, charset);  
      }  
    }  
  } catch (FileNotFoundException e) {  
  } finally {  
    if (raf != null) {  
      try {  
        raf.close();  
      } catch (Exception e2) {  
      }  
    }  
  }  
  return null;  
}