Android中使用Socket怎么实现文件断点上传功能

package com.android.upload; import java.io.File;  import java.io.OutputStream;  import java.io.PushbackInputStream;  import java.io.RandomAccessFile;  import java.net.Socket;    import android.app.Activity;  import android.os.Bundle;  import android.os.Environment;  import android.os.Handler;  import android.os.Message;  import android.view.View;  import android.view.View.OnClickListener; import android.widget.Button;  import android.widget.EditText;  import android.widget.ProgressBar;  import android.widget.TextView;  import android.widget.Toast;    import com.android.service.UploadLogService;  import com.android.socket.utils.StreamTool;    public class UploadActivity extends Activity {    private EditText filenameText;    private TextView resulView;    private ProgressBar uploadbar;    private UploadLogService logService;    private boolean start=true;   private Handler handler = new Handler(){      @Override      public void handleMessage(Message msg) {        int length = msg.getData().getInt("size");        uploadbar.setProgress(length);        float num = (float)uploadbar.getProgress()/(float)uploadbar.getMax();        int result = (int)(num * 100);        resulView.setText(result+ "%");        if(uploadbar.getProgress()==uploadbar.getMax()){          Toast.makeText(UploadActivity.this, R.string.success, 1).show();        }      }    };        @Override    public void onCreate(Bundle savedInstanceState) {      super.onCreate(savedInstanceState);      setContentView(R.layout.main);            logService = new UploadLogService(this);      filenameText = (EditText)this.findViewById(R.id.filename);      uploadbar = (ProgressBar) this.findViewById(R.id.uploadbar);      resulView = (TextView)this.findViewById(R.id.result);      Button button =(Button)this.findViewById(R.id.button);      Button button1 =(Button)this.findViewById(R.id.stop);      button1 .setOnClickListener(new OnClickListener() {              @Override       public void onClick(View v) {         start=false;                }     });     button.setOnClickListener(new View.OnClickListener() {        @Override        public void onClick(View v) {          start=true;         String filename = filenameText.getText().toString();          if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){            File uploadFile = new File(Environment.getExternalStorageDirectory(), filename);            if(uploadFile.exists()){              uploadFile(uploadFile);            }else{              Toast.makeText(UploadActivity.this, R.string.filenotexsit, 1).show();            }          }else{            Toast.makeText(UploadActivity.this, R.string.sdcarderror, 1).show();          }        }      });    }        private void uploadFile(final File uploadFile) {      new Thread(new Runnable() {             @Override        public void run() {          try {            uploadbar.setMax((int)uploadFile.length());            String souceid = logService.getBindId(uploadFile);            String head = "Content-Length="+ uploadFile.length() + ";filename="+ uploadFile.getName() + ";sourceid="+              (souceid==null? "" : souceid)+"\r\n";            Socket socket = new Socket("192.168.1.78",7878);            OutputStream outStream = socket.getOutputStream();            outStream.write(head.getBytes());                        PushbackInputStream inStream = new PushbackInputStream(socket.getInputStream());              String response = StreamTool.readLine(inStream);            String[] items = response.split(";");            String responseid = items[0].substring(items[0].indexOf("=")+1);            String position = items[1].substring(items[1].indexOf("=")+1);            if(souceid==null){//代表原来没有上传过此文件，往数据库添加一条绑定记录              logService.save(responseid, uploadFile);            }            RandomAccessFile fileOutStream = new RandomAccessFile(uploadFile, "r");            fileOutStream.seek(Integer.valueOf(position));            byte[] buffer = new byte[1024];            int len = -1;            int length = Integer.valueOf(position);            while(start&&(len = fileOutStream.read(buffer)) != -1){              outStream.write(buffer, 0, len);              length += len;              Message msg = new Message();              msg.getData().putInt("size", length);              handler.sendMessage(msg);            }            fileOutStream.close();            outStream.close();            inStream.close();            socket.close();            if(length==uploadFile.length()) logService.delete(uploadFile);          } catch (Exception e) {            e.printStackTrace();          }        }      }).start();    }  }