FTPClient client = new FTPClient();
client.connect(serverIp, port); //连接到FTP服务器
client.login(userName, passsword);

int reply = client.getReplyCode();
if (!FTPReply.isPositiveCompletion(reply)) {
  client.disconnect();
  Log.d(TAG, "无法连接到ftp服务器，错误码为：" + reply);
  return;
 }

String remotePath = "/upload/qjnn.apk"; //FTP服务器上文件路径
FTPFile[] files = client.listFiles(remotePath);
FTPFile file = files[0]; //文件信息
long size = file.getSize();
String fileaName = file.getName();

String remotePath = "/upload/qjnn.apk"; //FTP服务器上文件路径

String charSet = "UTF-8";
if (!FTPReply.isPositiveCompletion(client.sendCommand("OPTS UTF8", "ON"))) {  //向服务器请求使用"UTF-8"编码
  charSet = "GBK";
}
FTPFile[] files = client.listFiles(new String(remotePath.getBytes(charSet), "ISO-8859-1")); //对remotePath进行编码转换
FTPFile file = files[0]; //文件信息
long size = file.getSize();
String fileaName = new String(fileName.getBytes(), Charset.forName(charSet));

long fileLength = mEntity.getFileSize();
Properties pro = CommonUtil.loadConfig(mConfigFile);
int blockSize = (int) (fileLength / mThreadNum);
int[] recordL = new int[mThreadNum];
for (int i = 0; i < mThreadNum; i++) {
 recordL[i] = -1;
}
int rl = 0;
for (int i = 0; i < mThreadNum; i++) {
 long startL = i * blockSize, endL = (i + 1) * blockSize;
 Object state = pro.getProperty(mTempFile.getName() + "_state_" + i);
 if (state != null && Integer.parseInt(state + "") == 1) { //该线程已经完成
  if (resumeRecordLocation(i, startL, endL)) return;
  continue;
 }
 //分配下载位置
 Object record = pro.getProperty(fileName + "_record_" + i);
 //如果有记录，则恢复下载
 if (record != null && Long.parseLong(record + "") >= 0) {
  Long r = Long.parseLong(record + "");
  mConstance.CURRENT_LOCATION += r - startL;
  Log.d(TAG, "任务【" + mEntity.getFileName() + "】线程__" + i + "__恢复下载");
  startL = r;
  recordL[rl] = i;
  rl++;
 } else {
  recordL[rl] = i;
  rl++;
 }
 //最后一个线程的结束位置即为文件的总长度
 if (i == (mThreadNum - 1)) endL = fileLength;
 //创建分段线程
 AbsThreadTask task = createSingThreadTask(i, startL, endL, fileLength);
 if (task == null) return;
 mTask.put(i, task);
}
startSingleTask(recordL);

 client.enterLocalPassiveMode();  //设置被动模式
 client.setFileType(FTP.BINARY_FILE_TYPE); //设置文件传输模式
 client.setRestartOffset(mConfig.START_LOCATION);  //设置恢复下载的位置
 client.allocate(mBufSize);
 is = client.retrieveFileStream(new String(remotePath.getBytes(charSet), SERVER_CHARSET));
 //发送第二次指令时，还需要再做一次判断
 reply = client.getReplyCode();
 if (!FTPReply.isPositivePreliminary(reply)) {
  client.disconnect();
  fail(mChildCurrentLocation, "获取文件信息错误，错误码为：" + reply, null);
  return;
 }
 file = new BufferedRandomAccessFile(mConfig.TEMP_FILE, "rwd", mBufSize);
 file.seek(mConfig.START_LOCATION);
 byte[] buffer = new byte[mBufSize];
 int len;
 while ((len = is.read(buffer)) != -1) { 
  //如果该条线程读取的数据长度大于所分配的区间长度，则只能读到区间的最大长度
  if (mChildCurrentLocation + len >= mConfig.END_LOCATION) {
    len = (int) (mConfig.END_LOCATION - mChildCurrentLocation);
    file.write(buffer, 0, len);
    progress(len);
    break;
  } else {
    file.write(buffer, 0, len);
    progress(len);
  }
 }