java 按行读取文件内容

String readPath = "";
  String writePath = "";
  
  BufferedReader in = null;
  BufferedWriter os = null;
  
  try {
   // 读取文件（readPaht）内容
   if(null != in){
    in.close();
   }
   in = new BufferedReader(new InputStreamReader(new FileInputStream(readPath)));
   //
   if(null != os){
    os.close();
   }
   os = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(writePath)));
   String line = in.readLine();

   while (null != line && !"".equals(line)) {
    os.write(line);
    os.newLine();
    line = in.readLine();
   }

  } catch (Exception e) {
   e.printStackTrace();
  } finally {
   try{
    if(null != in){
     in.close();
    }
    if(null != os){
     os.close();
    }
   }catch (Exception e) {
    e.printStackTrace();
   }
  }