android多執行緒暫停下載-HttpURLConnection

private EditText et_path;
    private LinearLayout ll_pbs;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        et_path = (EditText) findViewById(R.id.et_path);
        ll_pbs = (LinearLayout) findViewById(R.id.ll_pbs);
    }

    public
 
 void startDownload(View view){

        //資源路徑
        final String path = et_path.getText().toString().trim();
        new Thread(new Runnable() {

            @Override
            public void run() {
                URL url;
                try {
                    url = new URL(path);
                    HttpURLConnection conn = (HttpURLConnection) url.openConnection();
                    conn.connect();

                    int
 
 totalSize = conn.getContentLength();
                    int threadCount = 3;

                    //計算每個執行緒下載的位元組數
                    int blockSize = totalSize/3;

                    //目標路徑
                    String target = Environment.getExternalStorageDirectory().getAbsolutePath()+"/bbb.jpg";

                    for
 
 (int i = 1; i <= threadCount; i++) {

                        int id = i;
                        int startIndex = (id-1)*blockSize;
                        int endIndex = -1;

                        if (id==threadCount) {
                            //3*3-1
                            endIndex = totalSize-1;
                        }else {
                            endIndex = id*blockSize-1;
                        }

                        final ProgressBar pb = (ProgressBar) View.inflate(MainActivity.this, R.layout.pb, null);
                        runOnUiThread(new Runnable() {

                            @Override
                            public void run() {
                                ll_pbs.addView(pb);
                            }
                        });

                        DownloadThread downloadThread = new DownloadThread(id,startIndex,endIndex,path,target,pb);
                        downloadThread.start();
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                }

            }
        }).start();
    }

    class DownloadThread extends Thread{

        private int id;
        private int startIndex;
        private int endIndex;
        private String path;
        private String target;
        private File tempFile;
        private ProgressBar pb;
        private int newStartIndex;
        public DownloadThread(int id, int startIndex, int endIndex,String path, String target,ProgressBar pb) {
            super();
            this.id = id;
            this.startIndex = startIndex;
            this.endIndex = endIndex;
            this.path = path;
            this.target = target;
            this.pb = pb;


            tempFile = new File(Environment.getExternalStorageDirectory(),"thread"+id+".tmp");
            try {
                BufferedReader br = new BufferedReader(new FileReader(tempFile));
                String readLine = br.readLine();
                br.close();
                newStartIndex = Integer.parseInt(readLine);
            } catch (Exception e) {
                newStartIndex = startIndex;
            }
            pb.setMax(endIndex-startIndex);
        }

        @Override
        public void run() {

            try {

                URL url = new URL(path);
                HttpURLConnection conn = (HttpURLConnection) url.openConnection();
                conn.setRequestProperty("Range", "bytes="+newStartIndex+"-"+endIndex);
                conn.connect();

                int code = conn.getResponseCode();
                if (206==code) {
                    InputStream inputStream = conn.getInputStream();

                    File file = new File(target);
                    RandomAccessFile raf = new RandomAccessFile(file ,"rwd");
                    raf.seek(newStartIndex);

                    int len=-1;
                    byte[] buffer = new byte[1024];
                    int total =0;
                    while((len=inputStream.read(buffer))!=-1){

                        FileWriter fileWriter = new FileWriter(tempFile);

                        raf.write(buffer,0,len);
                        total+=len;

                        fileWriter.write(""+(newStartIndex+total));
                        fileWriter.close();
                        //當前執行緒下載的總百分比
                        float process =(100.f* (total+newStartIndex-startIndex))/(endIndex-startIndex);
                        System.out.println(id+"下載了"+process);
                        pb.setProgress(total+newStartIndex-startIndex);
                    }
                    System.out.println(id+"已完成");
                    raf.close();
                }
            } catch (Exception e) {
                e.printStackTrace();
            }

        }

    }