断点续传和下载原理分析

末蓝、 2022-06-12 03:22 318阅读 0赞

转载地址：  http://www.cnblogs.com/wangzehuaw/p/5610851.html

# [断点续传和下载原理分析][Link 1] #

断点续传和断点下载都是用的RandomAccessFile, 它具有移动指定的文件大小的位置的功能seek 。

断点续传是由服务器给客户端一个已经上传的位置标记position，然后客户端再将文件指针移动到相应的position，通过输入流将文件剩余部分读出来传输给服务器

断点下载 是由客户端告诉服务器已经下载的大小，然后服务器会将指针移动到相应的position，继续读出，把文件返回给客户端。 当然为了下载的更快一下，也可以多线程下载，那么基本实现就是给每个线程分配固定的字节的文件，分别去读

首先是文件上传，这个要用到服务器

关键代码：

FileServer.java

1.  **import java.io.File;  **
2.  **import java.io.FileInputStream;  **
3.  **import java.io.FileOutputStream;  **
4.  **import java.io.IOException;  **
5.  **import java.io.InputStream;  **
6.  **import java.io.OutputStream;  **
7.  **import java.io.PushbackInputStream;  **
8.  **import java.io.RandomAccessFile;  **
9.  **import java.net.ServerSocket;  **
10. **import java.net.Socket;  **
11. **import java.text.SimpleDateFormat;  **
12. **import java.util.Date;  **
13. **import java.util.HashMap;  **
14. **import java.util.Map;  **
15. **import java.util.Properties;  **
16. **import java.util.Set;  **
17. **import java.util.concurrent.ExecutorService;  **
18. **import java.util.concurrent.Executors;  **
19.   
20. **import util.FileLogInfo;  **
21. **import util.StreamTool;  **
22.   
23.   
24.   
25. **public class FileServer \{  **
26.      **private ExecutorService executorService;//线程池  **
27.      **private int port;//监听端口  **
28.      **private boolean quit = false;//退出  **
29.      **private ServerSocket server;  **
30.      **private Map<Long, FileLogInfo> datas = new HashMap<Long, FileLogInfo>();//存放断点数据,以后改为数据库存放  **
31.      **public FileServer(int port)  **
32.      \{  
33.          **this.port = port;  **
34.          //创建线程池，池中具有(cpu个数\*50)条线程  
35.          executorService = Executors.newFixedThreadPool(Runtime.getRuntime().availableProcessors() \* 50);  
36.      \}  
37.        
38.     /\*\* 
39.       \* 退出 
40.       \*/  
41.      **public void quit()  **
42.      \{  
43.         **this.quit = true;  **
44.         **try   **
45.         \{  
46.             server.close();  
47.         \}**catch (IOException e)   **
48.         \{  
49.             e.printStackTrace();  
50.         \}  
51.      \}  
52.        
53.      /\*\* 
54.       \* 启动服务 
55.       \* @throws Exception 
56.       \*/  
57.      **public void start() throws Exception  **
58.      \{  
59.          server = **new ServerSocket(port);//实现端口监听  **
60.          **while(!quit)  **
61.          \{  
62.              **try   **
63.              \{  
64.                Socket socket = server.accept();  
65.                executorService.execute(**new SocketTask(socket));//为支持多用户并发访问，采用线程池管理每一个用户的连接请求  **
66.              \}**catch (Exception e)   **
67.              \{  
68.                  e.printStackTrace();  
69.              \}  
70.          \}  
71.      \}  
72.        
73.      **private final class SocketTask implements Runnable  **
74.      \{  
75.         **private Socket socket = null;  **
76.         **public SocketTask(Socket socket)   **
77.         \{  
78.             **this.socket = socket;  **
79.         \}  
80.         @Override  
81.         **public void run()   **
82.         \{  
83.             **try   **
84.             \{  
85.                 System.out.println("FileServer accepted connection "+ socket.getInetAddress()+ ":"+ socket.getPort());  
86.                 //得到客户端发来的第一行协议数据：Content-Length=143253434;filename=xxx.3gp;sourceid=  
87.                 //如果用户初次上传文件，sourceid的值为空。  
88.                 InputStream inStream = socket.getInputStream();  
89.                 String head = StreamTool.readLine(inStream);  
90.                 System.out.println("FileServer head:"+head);  
91.                 **if(head!=null)  **
92.                 \{  
93.                     //下面从协议数据中提取各项参数值  
94.                     String\[\] items = head.split(";");  
95.                     String filelength = items\[0\].substring(items\[0\].indexOf("=")+1);  
96.                     String filename = items\[1\].substring(items\[1\].indexOf("=")+1);  
97.                     String sourceid = items\[2\].substring(items\[2\].indexOf("=")+1);        
98.                     //生成资源id，如果需要唯一性，可以采用UUID  
99.                     **long id = System.currentTimeMillis();  **
100.                     FileLogInfo log = **null;  **
101.                     **if(sourceid!=null && !"".equals(sourceid))  **
102.                     \{  
103.                         id = Long.valueOf(sourceid);  
104.                         //查找上传的文件是否存在上传记录  
105.                         log = find(id);  
106.                     \}  
107.                     File file = **null;  **
108.                     **int position = 0;  **
109.                     //如果上传的文件不存在上传记录,为文件添加跟踪记录  
110.                     **if(log==null)  **
111.                     \{  
112.                         //设置存放的位置与当前应用的位置有关  
113.                         File dir = **new File("c:/temp/");  **
114.                         **if(!dir.exists()) dir.mkdirs();  **
115.                         file = **new File(dir, filename);  **
116.                         //如果上传的文件发生重名，然后进行改名  
117.                         **if(file.exists())  **
118.                         \{  
119.                             filename = filename.substring(0, filename.indexOf(".")-1)+ dir.listFiles().length+ filename.substring(filename.indexOf("."));  
120.                             file = **new File(dir, filename);  **
121.                         \}  
122.                         save(id, file);  
123.                     \}  
124.                     // 如果上传的文件存在上传记录,读取上次的断点位置  
125.                     **else  **
126.                     \{  
127.                         System.out.println("FileServer have exits log not null");  
128.                         //从上传记录中得到文件的路径  
129.                         file = **new File(log.getPath());  **
130.                         **if(file.exists())  **
131.                         \{  
132.                             File logFile = **new File(file.getParentFile(), file.getName()+".log");  **
133.                             **if(logFile.exists())  **
134.                             \{  
135.                                 Properties properties = **new Properties();  **
136.                                 properties.load(**new FileInputStream(logFile));  **
137.                                 //读取断点位置  
138.                                 position = Integer.valueOf(properties.getProperty("length"));  
139.                             \}  
140.                         \}  
141.                     \}  
142.                     //\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*上面是对协议头的处理，下面正式接收数据\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*  
143.                     //向客户端请求传输数据  
144.                     OutputStream outStream = socket.getOutputStream();  
145.                     String response = "sourceid="+ id+ ";position="+ position+ "%";  
146.                     //服务器收到客户端的请求信息后，给客户端返回响应信息：sourceid=1274773833264;position=position  
147.                     //sourceid由服务生成，唯一标识上传的文件，position指示客户端从文件的什么位置开始上传  
148.                     outStream.write(response.getBytes());  
149.                     RandomAccessFile fileOutStream = **new RandomAccessFile(file, "rwd");  **
150.                     //设置文件长度  
151.                     **if(position==0) fileOutStream.setLength(Integer.valueOf(filelength));  **
152.                     //移动文件指定的位置开始写入数据  
153.                     fileOutStream.seek(position);  
154.                     **byte\[\] buffer = new byte\[1024\];  **
155.                     **int len = -1;  **
156.                     **int length = position;  **
157.                     //从输入流中读取数据写入到文件中，并将已经传入的文件长度写入配置文件，实时记录文件的最后保存位置  
158.                     **while( (len=inStream.read(buffer)) != -1)  **
159.                     \{  
160.                         fileOutStream.write(buffer, 0, len);  
161.                         length += len;  
162.                         Properties properties = **new Properties();  **
163.                         properties.put("length", String.valueOf(length));  
164.                         FileOutputStream logFile = **new FileOutputStream(new File(file.getParentFile(), file.getName()+".log"));  **
165.                         //实时记录文件的最后保存位置  
166.                         properties.store(logFile, **null);  **
167.                         logFile.close();  
168.                     \}  
169.                     //如果长传长度等于实际长度则表示长传成功  
170.                     **if(length==fileOutStream.length())\{  **
171.                         delete(id);  
172.                     \}  
173.                     fileOutStream.close();                    
174.                     inStream.close();  
175.                     outStream.close();  
176.                     file = **null;  **
177.                 \}  
178.             \}  
179.             **catch (Exception e)   **
180.             \{  
181.                 e.printStackTrace();  
182.             \}  
183.             **finally\{  **
184.                 **try  **
185.                 \{  
186.                     **if(socket!=null && !socket.isClosed()) socket.close();  **
187.                 \}   
188.                 **catch (IOException e)  **
189.                 \{  
190.                     e.printStackTrace();  
191.                 \}  
192.             \}  
193.         \}  
194.      \}  
195.        
196.      /\*\*  
197.       \* 查找在记录中是否有sourceid的文件  
198.       \* @param sourceid  
199.       \* @return  
200.       \*/  
201.      **public FileLogInfo find(Long sourceid)  **
202.      \{  
203.          **return datas.get(sourceid);  **
204.      \}  
205.        
206.      /\*\* 
207.       \* 保存上传记录，日后可以改成通过数据库存放 
208.       \* @param id 
209.       \* @param saveFile 
210.       \*/  
211.      **public void save(Long id, File saveFile)  **
212.      \{  
213.          System.out.println("save logfile "+id);  
214.          datas.put(id, **new FileLogInfo(id, saveFile.getAbsolutePath()));  **
215.      \}  
216.        
217.      /\*\* 
218.       \* 当文件上传完毕，删除记录 
219.       \* @param sourceid 
220.       \*/  
221.      **public void delete(long sourceid)  **
222.      \{  
223.          System.out.println("delete logfile "+sourceid);  
224.          **if(datas.containsKey(sourceid)) datas.remove(sourceid);  **
225.      \}  
226.        
227. \}

由于在上面的流程图中已经进行了详细的分析，我在这儿就不讲了，只是在存储数据的时候服务器没有用数据库去存储，这儿只是为了方便，所以要想测试断点上传，服务器是不能停的，否则数据就没有了，在以后改进的时候应该用数据库去存储数据。

文件上传客户端：

关键代码：

UploadActivity.java

1.  **package com.hao;  **
2.    
3.  **import java.io.File;  **
4.  **import java.util.List;  **
5.    
6.  **import com.hao.upload.UploadThread;  **
7.  **import com.hao.upload.UploadThread.UploadProgressListener;  **
8.  **import com.hao.util.ConstantValues;  **
9.  **import com.hao.util.FileBrowserActivity;  **
10.   
11. **import android.app.Activity;  **
12. **import android.app.Dialog;  **
13. **import android.app.ProgressDialog;  **
14. **import android.content.DialogInterface;  **
15. **import android.content.Intent;  **
16. **import android.content.res.Resources;  **
17. **import android.net.Uri;  **
18. **import android.os.Bundle;  **
19. **import android.os.Environment;  **
20. **import android.os.Handler;  **
21. **import android.os.Message;  **
22. **import android.util.Log;  **
23. **import android.view.View;  **
24. **import android.view.View.OnClickListener;  **
25. **import android.widget.Button;  **
26. **import android.widget.TextView;  **
27. **import android.widget.Toast;  **
28. /\*\* 
29.  \*  
30.  \* @author Administrator 
31.  \* 
32.  \*/  
33. **public class UploadActivity extends Activity implements OnClickListener\{  **
34.     **private static final String TAG = "SiteFileFetchActivity";  **
35.     **private Button download, upload, select\_file;  **
36.     **private TextView info;  **
37.     **private static final int PROGRESS\_DIALOG = 0;  **
38.     **private ProgressDialog progressDialog;  **
39.     **private UploadThread uploadThread;  **
40.     **private String uploadFilePath = null;  **
41.     **private String fileName;  **
42.     /\*\* Called when the activity is first created. \*/  
43.     @Override  
44.     **public void onCreate(Bundle savedInstanceState) \{  **
45.         **super.onCreate(savedInstanceState);  **
46.         setContentView(R.layout.upload);  
47.         initView();  
48.     \}  
49.       
50.     **private void initView()\{  **
51.         download = (Button) findViewById(R.id.download);  
52.         download.setOnClickListener(**this);  **
53.         upload = (Button) findViewById(R.id.upload);  
54.         upload.setOnClickListener(**this);  **
55.         info = (TextView) findViewById(R.id.info);  
56.         select\_file = (Button) findViewById(R.id.select\_file);  
57.         select\_file.setOnClickListener(**this);  **
58.     \}  
59.       
60.     @Override  
61.     **protected void onActivityResult(int requestCode, int resultCode, Intent data) \{  **
62.         // TODO Auto-generated method stub  
63.         **super.onActivityResult(requestCode, resultCode, data);  **
64.         **if (resultCode == RESULT\_OK) \{  **
65.                   **if (requestCode == 1) \{  **
66.                            Uri uri = data.getData();    // 接收用户所选文件的路径  
67.                            info.setText("select: " + uri); // 在界面上显示路径  
68.                            uploadFilePath = uri.getPath();  
69.                            **int last = uploadFilePath.lastIndexOf("/");  **
70.                            uploadFilePath = uri.getPath().substring(0, last+1);  
71.                            fileName = uri.getLastPathSegment();  
72.                   \}  
73.         \}  
74.     \}  
75.       
76.     **protected Dialog onCreateDialog(int id) \{  **
77.         **switch(id) \{  **
78.         **case PROGRESS\_DIALOG:  **
79.             progressDialog = **new ProgressDialog(UploadActivity.this);  **
80.             progressDialog.setProgressStyle(ProgressDialog.STYLE\_HORIZONTAL);  
81.             progressDialog.setButton("暂停", **new DialogInterface.OnClickListener() \{  **
82.                 @Override  
83.                 **public void onClick(DialogInterface dialog, int which) \{  **
84.                     // TODO Auto-generated method stub  
85.                     uploadThread.closeLink();  
86.                     dialog.dismiss();  
87.                 \}  
88.             \});  
89.             progressDialog.setMessage("正在上传...");  
90.             progressDialog.setMax(100);  
91.             **return progressDialog;  **
92.         **default:  **
93.             **return null;  **
94.         \}  
95.     \}  
96.       
97.     /\*\*  
98.      \* 使用Handler给创建他的线程发送消息，  
99.      \* 匿名内部类  
100.      \*/    
101.     **private Handler handler = new Handler()    **
102.     \{    
103.         @Override  
104.         **public void handleMessage(Message msg)     **
105.         \{    
106.             //获得上传长度的进度    
107.             **int length = msg.getData().getInt("size");    **
108.             progressDialog.setProgress(length);    
109.             **if(progressDialog.getProgress()==progressDialog.getMax())//上传成功    **
110.             \{    
111.                 progressDialog.dismiss();  
112.                 Toast.makeText(UploadActivity.**this, getResources().getString(R.string.upload\_over), 1).show();    **
113.             \}    
114.         \}    
115.     \};     
116.   
117.     @Override  
118.     **public void onClick(View v) \{  **
119.         // TODO Auto-generated method stub  
120.         Resources r = getResources();  
121.         **switch(v.getId())\{  **
122.             **case R.id.select\_file:  **
123.                 Intent intent = **new Intent();  **
124.                 //设置起始目录和查找的类型  
125.                 intent.setDataAndType(Uri.fromFile(**new File("/sdcard")), "\*/\*");//"\*/\*"表示所有类型，设置起始文件夹和文件类型  **
126.                 intent.setClass(UploadActivity.**this, FileBrowserActivity.class);  **
127.                 startActivityForResult(intent, 1);  
128.                 **break;  **
129.             **case R.id.download:  **
130.                 startActivity(**new Intent(UploadActivity.this, SmartDownloadActivity.class));  **
131.                 **break;  **
132.             **case R.id.upload:  **
133.                 **if(Environment.getExternalStorageState().equals(Environment.MEDIA\_MOUNTED))//判断SDCard是否存在    **
134.                 \{    
135.                     **if(uploadFilePath == null)\{  **
136.                         Toast.makeText(UploadActivity.**this, "还没设置上传文件", 1).show();  **
137.                     \}  
138.                     System.out.println("uploadFilePath:"+uploadFilePath+" "+fileName);  
139.                     //取得SDCard的目录    
140.                     File uploadFile = **new File(new File(uploadFilePath), fileName);    **
141.                     Log.i(TAG, "filePath:"+uploadFile.toString());  
142.                     **if(uploadFile.exists())    **
143.                     \{    
144.                         showDialog(PROGRESS\_DIALOG);  
145.                         info.setText(uploadFile+" "+ConstantValues.HOST+":"+ConstantValues.PORT);  
146.                         progressDialog.setMax((**int) uploadFile.length());//设置长传文件的最大刻度  **
147.                         uploadThread = **new UploadThread(UploadActivity.this, uploadFile, ConstantValues.HOST, ConstantValues.PORT);  **
148.                         uploadThread.setListener(**new UploadProgressListener() \{  **
149.                               
150.                             @Override  
151.                             **public void onUploadSize(int size) \{  **
152.                                 // TODO Auto-generated method stub  
153.                                 Message msg = **new Message();  **
154.                                 msg.getData().putInt("size", size);  
155.                                 handler.sendMessage(msg);  
156.                             \}  
157.                         \});  
158.                         uploadThread.start();  
159.                     \}    
160.                     **else    **
161.                     \{    
162.                         Toast.makeText(UploadActivity.**this, "文件不存在", 1).show();    **
163.                     \}    
164.                 \}    
165.                 **else    **
166.                 \{    
167.                     Toast.makeText(UploadActivity.**this, "SDCard不存在！", 1).show();    **
168.                 \}    
169.                 **break;  **
170.         \}  
171.               
172.     \}  
173.       
174.       
175. \}

UploadThread.java

1.  **package com.hao.upload;  **
2.    
3.  **import java.io.File;  **
4.  **import java.io.IOException;  **
5.  **import java.io.InputStream;  **
6.  **import java.io.OutputStream;  **
7.  **import java.io.RandomAccessFile;  **
8.  **import java.net.Socket;  **
9.    
10. **import android.content.Context;  **
11. **import android.util.Log;  **
12.   
13. **import com.hao.db.UploadLogService;  **
14. **import com.hao.util.StreamTool;  **
15.   
16. **public class UploadThread extends Thread \{  **
17.   
18.     **private static final String TAG = "UploadThread";  **
19.     /\*需要上传文件的路径\*/  
20.     **private File uploadFile;  **
21.     /\*上传文件服务器的IP地址\*/  
22.     **private String dstName;  **
23.     /\*上传服务器端口号\*/  
24.     **private int dstPort;  **
25.     /\*上传socket链接\*/  
26.     **private Socket socket;  **
27.     /\*存储上传的数据库\*/  
28.     **private UploadLogService logService;   **
29.     **private UploadProgressListener listener;  **
30.     **public UploadThread(Context context, File uploadFile, final String dstName,final int dstPort)\{  **
31.         **this.uploadFile = uploadFile;  **
32.         **this.dstName = dstName;  **
33.         **this.dstPort = dstPort;  **
34.         logService = **new UploadLogService(context);  **
35.     \}  
36.       
37.     **public void setListener(UploadProgressListener listener) \{  **
38.         **this.listener = listener;  **
39.     \}  
40.   
41.     /\*\* 
42.      \* 模拟断开连接 
43.      \*/  
44.     **public void closeLink()\{  **
45.         **try\{  **
46.             **if(socket != null) socket.close();  **
47.         \}**catch(IOException e)\{  **
48.             e.printStackTrace();  
49.             Log.e(TAG, "close socket fail");  
50.         \}  
51.     \}  
52.   
53.     @Override  
54.     **public void run() \{  **
55.         // TODO Auto-generated method stub  
56.         **try \{  **
57.             // 判断文件是否已有上传记录  
58.             String souceid = logService.getBindId(uploadFile);  
59.             // 构造拼接协议  
60.             String head = "Content-Length=" + uploadFile.length()  
61.                     + ";filename=" + uploadFile.getName() + ";sourceid="  
62.                     + (souceid == **null ? "" : souceid) + "%";  **
63.             // 通过Socket取得输出流  
64.             socket = **new Socket(dstName, dstPort);  **
65.             OutputStream outStream = socket.getOutputStream();  
66.             outStream.write(head.getBytes());  
67.             Log.i(TAG, "write to outStream");  
68.   
69.             InputStream inStream = socket.getInputStream();  
70.             // 获取到字符流的id与位置  
71.             String response = StreamTool.readLine(inStream);  
72.             Log.i(TAG, "response:" + response);  
73.             String\[\] items = response.split(";");  
74.             String responseid = items\[0\].substring(items\[0\].indexOf("=") + 1);  
75.             String position = items\[1\].substring(items\[1\].indexOf("=") + 1);  
76.             // 代表原来没有上传过此文件，往数据库添加一条绑定记录  
77.             **if (souceid == null) \{  **
78.                 logService.save(responseid, uploadFile);  
79.             \}  
80.             RandomAccessFile fileOutStream = **new RandomAccessFile(uploadFile, "r");  **
81.             // 查找上次传送的最终位置，并从这开始传送  
82.             fileOutStream.seek(Integer.valueOf(position));  
83.             **byte\[\] buffer = new byte\[1024\];  **
84.             **int len = -1;  **
85.             // 初始化上传的数据长度  
86.             **int length = Integer.valueOf(position);  **
87.             **while ((len = fileOutStream.read(buffer)) != -1) \{  **
88.                 outStream.write(buffer, 0, len);  
89.                 // 设置长传数据长度  
90.                 length += len;  
91.                 listener.onUploadSize(length);  
92.             \}  
93.             fileOutStream.close();  
94.             outStream.close();  
95.             inStream.close();  
96.             socket.close();  
97.             // 判断上传完则删除数据  
98.             **if (length == uploadFile.length())  **
99.                 logService.delete(uploadFile);  
100.         \} **catch (Exception e) \{  **
101.             e.printStackTrace();  
102.         \}  
103.     \}  
104.       
105.     **public interface UploadProgressListener\{  **
106.         **void onUploadSize(int size);  **
107.     \}  
108. \}

下面是多线程下载

SmartDownloadActivity.java

1.  **package com.hao;  **
2.    
3.  **import java.io.File;  **
4.    
5.  **import com.hao.R;  **
6.  **import com.hao.R.id;  **
7.  **import com.hao.R.layout;  **
8.  **import com.hao.download.SmartFileDownloader;  **
9.  **import com.hao.download.SmartFileDownloader.SmartDownloadProgressListener;  **
10. **import com.hao.util.ConstantValues;  **
11.   
12. **import android.app.Activity;  **
13. **import android.os.Bundle;  **
14. **import android.os.Environment;  **
15. **import android.os.Handler;  **
16. **import android.os.Message;  **
17. **import android.view.View;  **
18. **import android.widget.Button;  **
19. **import android.widget.ProgressBar;  **
20. **import android.widget.TextView;  **
21. **import android.widget.Toast;  **
22.   
23. /\*\* 
24.  \*  
25.  \* @author Administrator 
26.  \*  
27.  \*/  
28. **public class SmartDownloadActivity extends Activity \{  **
29.     **private ProgressBar downloadbar;  **
30.     **private TextView resultView;  **
31.     **private String path = ConstantValues.DOWNLOAD\_URL;  **
32.     SmartFileDownloader loader;  
33.     **private Handler handler = new Handler() \{  **
34.         @Override  
35.         // 信息  
36.         **public void handleMessage(Message msg) \{  **
37.             **switch (msg.what) \{  **
38.             **case 1:  **
39.                 **int size = msg.getData().getInt("size");  **
40.                 downloadbar.setProgress(size);  
41.                 **float result = (float) downloadbar.getProgress() / (float) downloadbar.getMax();  **
42.                 **int p = (int) (result \* 100);  **
43.                 resultView.setText(p + "%");  
44.                 **if (downloadbar.getProgress() == downloadbar.getMax())  **
45.                     Toast.makeText(SmartDownloadActivity.**this, "下载成功", 1).show();  **
46.                 **break;  **
47.             **case -1:  **
48.                 Toast.makeText(SmartDownloadActivity.**this, msg.getData().getString("error"), 1).show();  **
49.                 **break;  **
50.             \}  
51.   
52.         \}  
53.     \};  
54.   
55.     **public void onCreate(Bundle savedInstanceState) \{  **
56.         **super.onCreate(savedInstanceState);  **
57.         setContentView(R.layout.download);  
58.   
59.         Button button = (Button) **this.findViewById(R.id.button);  **
60.         Button closeConn = (Button) findViewById(R.id.closeConn);  
61.         closeConn.setOnClickListener(**new View.OnClickListener() \{  **
62.               
63.             @Override  
64.             **public void onClick(View v) \{  **
65.                 // TODO Auto-generated method stub  
66.                 **if(loader != null)\{  **
67.                     finish();  
68.                 \}**else\{  **
69.                     Toast.makeText(SmartDownloadActivity.**this, "还没有开始下载，不能暂停", 1).show();  **
70.                 \}  
71.             \}  
72.         \});  
73.         downloadbar = (ProgressBar) **this.findViewById(R.id.downloadbar);  **
74.         resultView = (TextView) **this.findViewById(R.id.result);  **
75.         resultView.setText(path);  
76.         button.setOnClickListener(**new View.OnClickListener() \{  **
77.             @Override  
78.             **public void onClick(View v) \{  **
79.                 **if (Environment.getExternalStorageState().equals(Environment.MEDIA\_MOUNTED)) \{  **
80.                     download(path, ConstantValues.FILE\_PATH);  
81.                 \} **else \{  **
82.                     Toast.makeText(SmartDownloadActivity.**this, "没有SDCard", 1).show();  **
83.                 \}  
84.             \}  
85.         \});  
86.     \}  
87.   
88.     // 对于UI控件的更新只能由主线程(UI线程)负责，如果在非UI线程更新UI控件，更新的结果不会反映在屏幕上，某些控件还会出错  
89.     **private void download(final String path, final File dir) \{  **
90.         **new Thread(new Runnable() \{  **
91.             @Override  
92.             **public void run() \{  **
93.                 **try \{  **
94.                     loader = **new SmartFileDownloader(SmartDownloadActivity.this, path, dir, 3);  **
95.                     **int length = loader.getFileSize();// 获取文件的长度  **
96.                     downloadbar.setMax(length);  
97.                     loader.download(**new SmartDownloadProgressListener() \{  **
98.                         @Override  
99.                         **public void onDownloadSize(int size) \{ // 可以实时得到文件下载的长度  **
100.                             Message msg = **new Message();  **
101.                             msg.what = 1;  
102.                             msg.getData().putInt("size", size);  
103.                             handler.sendMessage(msg);  
104.                         \}  
105.                     \});  
106.                 \} **catch (Exception e) \{  **
107.                     Message msg = **new Message();// 信息提示  **
108.                     msg.what = -1;  
109.                     msg.getData().putString("error", "下载失败");// 如果下载错误，显示提示失败！  
110.                     handler.sendMessage(msg);  
111.                 \}  
112.             \}  
113.         \}).start();// 开始  
114.   
115.     \}  
116. \}

这个单个的下载线程

SmartDownloadThread.java

1.  **package com.hao.download;  **
2.    
3.  **import java.io.File;  **
4.  **import java.io.InputStream;  **
5.  **import java.io.RandomAccessFile;  **
6.  **import java.net.HttpURLConnection;  **
7.  **import java.net.URL;  **
8.    
9.  **import android.util.Log;  **
10.   
11. /\*\* 
12.  \* 线程下载 
13.  \* @author Administrator 
14.  \*  
15.  \*/  
16. **public class SmartDownloadThread extends Thread \{  **
17.     **private static final String TAG = "SmartDownloadThread";  **
18.     **private File saveFile;  **
19.     **private URL downUrl;  **
20.     **private int block;  **
21.     /\*  \*下载开始位置 \*/  
22.     **private int threadId = -1;  **
23.     **private int downLength;  **
24.     **private boolean finish = false;  **
25.     **private SmartFileDownloader downloader;  **
26.   
27.     **public SmartDownloadThread(SmartFileDownloader downloader, URL downUrl,  **
28.             File saveFile, **int block, int downLength, int threadId) \{  **
29.         **this.downUrl = downUrl;  **
30.         **this.saveFile = saveFile;  **
31.         **this.block = block;  **
32.         **this.downloader = downloader;  **
33.         **this.threadId = threadId;  **
34.         **this.downLength = downLength;  **
35.     \}  
36.   
37.     @Override  
38.     **public void run() \{  **
39.         **if (downLength < block) \{ // 未下载完成  **
40.             **try \{  **
41.                 HttpURLConnection http = (HttpURLConnection) downUrl  
42.                         .openConnection();  
43.                 http.setConnectTimeout(5 \* 1000);  
44.                 http.setRequestMethod("GET");  
45.                 http.setRequestProperty("Accept","image/gif, image/jpeg, image/pjpeg, image/pjpeg, application/x-shockwave-flash, application/xaml+xml, application/vnd.ms-xpsdocument, application/x-ms-xbap, application/x-ms-application, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, \*/\*");  
46.                 http.setRequestProperty("Accept-Language", "zh-CN");  
47.                 http.setRequestProperty("Referer", downUrl.toString());  
48.                 http.setRequestProperty("Charset", "UTF-8");  
49.                 **int startPos = block \* (threadId - 1) + downLength;// 开始位置  **
50.                 **int endPos = block \* threadId - 1;// 结束位置  **
51.                 http.setRequestProperty("Range", "bytes=" + startPos + "-" + endPos);// 设置获取实体数据的范围  
52.                 http.setRequestProperty("User-Agent","Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.2; Trident/4.0; .NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)");  
53.                 http.setRequestProperty("Connection", "Keep-Alive");  
54.   
55.                 InputStream inStream = http.getInputStream();  
56.                 **byte\[\] buffer = new byte\[1024\];  **
57.                 **int offset = 0;  **
58.                 print("Thread " + **this.threadId + " start download from position " + startPos);  **
59.                 RandomAccessFile threadfile = **new RandomAccessFile(this.saveFile, "rwd");  **
60.                 threadfile.seek(startPos);  
61.                 **while ((offset = inStream.read(buffer, 0, 1024)) != -1) \{  **
62.                     threadfile.write(buffer, 0, offset);  
63.                     downLength += offset;  
64.                     downloader.update(**this.threadId, downLength);  **
65.                     downloader.saveLogFile();  
66.                     downloader.append(offset);  
67.                 \}  
68.                 threadfile.close();  
69.                 inStream.close();  
70.                 print("Thread " + **this.threadId + " download finish");  **
71.                 **this.finish = true;  **
72.             \} **catch (Exception e) \{  **
73.                 **this.downLength = -1;  **
74.                 print("Thread " + **this.threadId + ":" + e);  **
75.             \}  
76.         \}  
77.     \}  
78.   
79.     **private static void print(String msg) \{  **
80.         Log.i(TAG, msg);  
81.     \}  
82.   
83.     /\*\*  
84.      \* 下载是否完成  
85.      \* @return  
86.      \*/  
87.     **public boolean isFinish() \{  **
88.         **return finish;  **
89.     \}  
90.   
91.     /\*\* 
92.      \* 已经下载的内容大小 
93.      \* @return 如果返回值为-1,代表下载失败 
94.      \*/  
95.     **public long getDownLength() \{  **
96.         **return downLength;  **
97.     \}  
98. \}

总得下载线程

SmartFileDownloader.java

1.  1.  **package com.hao.download;  **
    2.    
    3.  **import java.io.File;  **
    4.  **import java.io.RandomAccessFile;  **
    5.  **import java.net.HttpURLConnection;  **
    6.  **import java.net.URL;  **
    7.  **import java.util.LinkedHashMap;  **
    8.  **import java.util.Map;  **
    9.  **import java.util.UUID;  **
    10. **import java.util.concurrent.ConcurrentHashMap;  **
    11. **import java.util.regex.Matcher;  **
    12. **import java.util.regex.Pattern;  **
    13.   
    14. **import com.hao.db.DownloadFileService;  **
    15.   
    16. **import android.content.Context;  **
    17. **import android.util.Log;  **
    18.   
    19. /\*\* 
    20.  \* 文件下载主程序 
    21.  \* @author Administrator 
    22.  \*  
    23.  \*/  
    24. **public class SmartFileDownloader \{  **
    25.     **private static final String TAG = "SmartFileDownloader";  **
    26.     **private Context context;  **
    27.     **private DownloadFileService fileService;  **
    28.     /\* 已下载文件长度 \*/  
    29.     **private int downloadSize = 0;  **
    30.     /\* 原始文件长度 \*/  
    31.     **private int fileSize = 0;  **
    32.     /\*原始文件名\*/  
    33.     **private String fileName;  **
    34.     /\* 线程数 \*/  
    35.     **private SmartDownloadThread\[\] threads;  **
    36.     /\* 本地保存文件 \*/  
    37.     **private File saveFile;  **
    38.     /\* 缓存各线程下载的长度 \*/  
    39.     **private Map<Integer, Integer> data = new ConcurrentHashMap<Integer, Integer>();  **
    40.     /\* 每条线程下载的长度 \*/  
    41.     **private int block;  **
    42.     /\* 下载路径 \*/  
    43.     **private String downloadUrl;  **
    44.   
    45.     /\*\* 
    46.      \* 获取文件名 
    47.      \*/  
    48.     **public String getFileName()\{  **
    49.         **return this.fileName;  **
    50.     \}  
    51.     /\*\* 
    52.      \* 获取线程数 
    53.      \*/  
    54.     **public int getThreadSize() \{  **
    55.         **return threads.length;  **
    56.     \}  
    57.   
    58.     /\*\* 
    59.      \* 获取文件大小 
    60.      \* @return 
    61.      \*/  
    62.     **public int getFileSize() \{  **
    63.         **return fileSize;  **
    64.     \}  
    65.   
    66.     /\*\* 
    67.      \* 累计已下载大小 
    68.      \* @param size 
    69.      \*/  
    70.     **protected synchronized void append(int size) \{  **
    71.         downloadSize += size;  
    72.     \}  
    73.   
    74.     /\*\* 
    75.      \* 更新指定线程最后下载的位置 
    76.      \* @param threadId 线程id 
    77.      \* @param pos 最后下载的位置 
    78.      \*/  
    79.     **protected void update(int threadId, int pos) \{  **
    80.         **this.data.put(threadId, pos);  **
    81.     \}  
    82.   
    83.     /\*\* 
    84.      \* 保存记录文件 
    85.      \*/  
    86.     **protected synchronized void saveLogFile() \{  **
    87.         **this.fileService.update(this.downloadUrl, this.data);  **
    88.     \}  
    89.   
    90.     /\*\* 
    91.      \* 构建文件下载器 
    92.      \* @param downloadUrl 下载路径 
    93.      \* @param fileSaveDir 文件保存目录 
    94.      \* @param threadNum 下载线程数 
    95.      \*/  
    96.     **public SmartFileDownloader(Context context, String downloadUrl,  **
    97.             File fileSaveDir, **int threadNum) \{  **
    98.         **try \{  **
    99.             **this.context = context;  **
    100.             **this.downloadUrl = downloadUrl;  **
    101.             fileService = **new DownloadFileService(this.context);  **
    102.             URL url = **new URL(this.downloadUrl);  **
    103.             **if (!fileSaveDir.exists()) fileSaveDir.mkdirs();  **
    104.             **this.threads = new SmartDownloadThread\[threadNum\];  **
    105.             HttpURLConnection conn = (HttpURLConnection) url.openConnection();  
    106.             conn.setConnectTimeout(5 \* 1000);  
    107.             conn.setRequestMethod("GET");  
    108.             conn.setRequestProperty("Accept", "image/gif, image/jpeg, image/pjpeg, image/pjpeg, application/x-shockwave-flash, application/xaml+xml, application/vnd.ms-xpsdocument, application/x-ms-xbap, application/x-ms-application, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, \*/\*");  
    109.             conn.setRequestProperty("Accept-Language", "zh-CN");  
    110.             conn.setRequestProperty("Referer", downloadUrl);  
    111.             conn.setRequestProperty("Charset", "UTF-8");  
    112.             conn.setRequestProperty("User-Agent", "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.2; Trident/4.0; .NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)");  
    113.             conn.setRequestProperty("Connection", "Keep-Alive");  
    114.             conn.connect();  
    115.             printResponseHeader(conn);  
    116.             **if (conn.getResponseCode() == 200) \{  **
    117.                 **this.fileSize = conn.getContentLength();// 根据响应获取文件大小  **
    118.                 **if (this.fileSize <= 0)  **
    119.                     **throw new RuntimeException("Unkown file size ");  **
    120.   
    121.                 fileName = getFileName(conn);  
    122.                 **this.saveFile = new File(fileSaveDir, fileName);/\* 保存文件 \*/  **
    123.                 Map<Integer, Integer> logdata = fileService.getData(downloadUrl);  
    124.                 **if (logdata.size() > 0) \{  **
    125.                     **for (Map.Entry<Integer, Integer> entry : logdata.entrySet())  **
    126.                         data.put(entry.getKey(), entry.getValue());  
    127.                 \}  
    128.                 //划分每个线程下载文件长度  
    129.                 **this.block = (this.fileSize % this.threads.length) == 0 ? this.fileSize / this.threads.length  **
    130.                         : **this.fileSize / this.threads.length + 1;  **
    131.                 **if (this.data.size() == this.threads.length) \{  **
    132.                     **for (int i = 0; i < this.threads.length; i++) \{  **
    133.                         **this.downloadSize += this.data.get(i + 1);  **
    134.                     \}  
    135.                     print("已经下载的长度" + **this.downloadSize);  **
    136.                 \}  
    137.             \} **else \{  **
    138.                 **throw new RuntimeException("server no response ");  **
    139.             \}  
    140.         \} **catch (Exception e) \{  **
    141.             print(e.toString());  
    142.             **throw new RuntimeException("don't connection this url");  **
    143.         \}  
    144.     \}  
    145.   
    146.     /\*\* 
    147.      \* 获取文件名 
    148.      \*/  
    149.     **private String getFileName(HttpURLConnection conn) \{  **
    150.         String filename = **this.downloadUrl.substring(this.downloadUrl.lastIndexOf('/') + 1);//链接的最后一个/就是文件名  **
    151.         **if (filename == null || "".equals(filename.trim())) \{ // 如果获取不到文件名称  **
    152.             **for (int i = 0;; i++) \{  **
    153.                 String mine = conn.getHeaderField(i);  
    154.                 print("ConnHeader:"+mine+" ");  
    155.                 **if (mine == null)  **
    156.                     **break;  **
    157.                 **if ("content-disposition".equals(conn.getHeaderFieldKey(i).toLowerCase())) \{  **
    158.                     Matcher m = Pattern.compile(".\*filename=(.\*)").matcher(mine.toLowerCase());  
    159.                     **if (m.find())  **
    160.                         **return m.group(1);  **
    161.                 \}  
    162.             \}  
    163.             filename = UUID.randomUUID() + ".tmp";// 默认取一个文件名  
    164.         \}  
    165.         **return filename;  **
    166.     \}  
    167.   
    168.     /\*\* 
    169.      \* 开始下载文件 
    170.      \*  
    171.      \* @param listener 
    172.      \*            监听下载数量的变化,如果不需要了解实时下载的数量,可以设置为null 
    173.      \* @return 已下载文件大小 
    174.      \* @throws Exception 
    175.      \*/  
    176.     **public int download(SmartDownloadProgressListener listener)  **
    177.             **throws Exception \{  **
    178.         **try \{  **
    179.             RandomAccessFile randOut = **new RandomAccessFile(this.saveFile, "rw");  **
    180.             **if (this.fileSize > 0)  **
    181.                 randOut.setLength(**this.fileSize);  **
    182.             randOut.close();  
    183.             URL url = **new URL(this.downloadUrl);  **
    184.             **if (this.data.size() != this.threads.length) \{  **
    185.                 **this.data.clear();// 清除数据  **
    186.                 **for (int i = 0; i < this.threads.length; i++) \{  **
    187.                     **this.data.put(i + 1, 0);  **
    188.                 \}  
    189.             \}  
    190.             **for (int i = 0; i < this.threads.length; i++) \{  **
    191.                 **int downLength = this.data.get(i + 1);  **
    192.                 **if (downLength < this.block && this.downloadSize < this.fileSize) \{ // 该线程未完成下载时,继续下载  **
    193.                     **this.threads\[i\] = new SmartDownloadThread(this, url,  **
    194.                             **this.saveFile, this.block, this.data.get(i + 1), i + 1);  **
    195.                     **this.threads\[i\].setPriority(7);  **
    196.                     **this.threads\[i\].start();  **
    197.                 \} **else \{  **
    198.                     **this.threads\[i\] = null;  **
    199.                 \}  
    200.             \}  
    201.             **this.fileService.save(this.downloadUrl, this.data);  **
    202.             **boolean notFinish = true;// 下载未完成  **
    203.             **while (notFinish) \{ // 循环判断是否下载完毕  **
    204.                 Thread.sleep(900);  
    205.                 notFinish = **false;// 假定下载完成  **
    206.                 **for (int i = 0; i < this.threads.length; i++) \{  **
    207.                     **if (this.threads\[i\] != null && !this.threads\[i\].isFinish()) \{  **
    208.                         notFinish = **true;// 下载没有完成  **
    209.                         **if (this.threads\[i\].getDownLength() == -1) \{ // 如果下载失败,再重新下载  **
    210.                             **this.threads\[i\] = new SmartDownloadThread(this,  **
    211.                                     url, **this.saveFile, this.block, this.data.get(i + 1), i + 1);  **
    212.                             **this.threads\[i\].setPriority(7);  **
    213.                             **this.threads\[i\].start();  **
    214.                         \}  
    215.                     \}  
    216.                 \}  
    217.                 **if (listener != null)  **
    218.                     listener.onDownloadSize(**this.downloadSize);  **
    219.             \}  
    220.             fileService.delete(**this.downloadUrl);  **
    221.         \} **catch (Exception e) \{  **
    222.             print(e.toString());  
    223.             **throw new Exception("file download fail");  **
    224.         \}  
    225.         **return this.downloadSize;  **
    226.     \}  
    227.   
    228.     /\*\* 
    229.      \* 获取Http响应头字段 
    230.      \*  
    231.      \* @param http 
    232.      \* @return 
    233.      \*/  
    234.     **public static Map<String, String> getHttpResponseHeader(  **
    235.             HttpURLConnection http) \{  
    236.         Map<String, String> header = **new LinkedHashMap<String, String>();  **
    237.         **for (int i = 0;; i++) \{  **
    238.             String mine = http.getHeaderField(i);  
    239.             **if (mine == null)  **
    240.                 **break;  **
    241.             header.put(http.getHeaderFieldKey(i), mine);  
    242.         \}  
    243.         **return header;  **
    244.     \}  
    245.   
    246.     /\*\* 
    247.      \* 打印Http头字段 
    248.      \*  
    249.      \* @param http 
    250.      \*/  
    251.     **public static void printResponseHeader(HttpURLConnection http) \{  **
    252.         Map<String, String> header = getHttpResponseHeader(http);  
    253.         **for (Map.Entry<String, String> entry : header.entrySet()) \{  **
    254.             String key = entry.getKey() != **null ? entry.getKey() + ":" : "";  **
    255.             print(key + entry.getValue());  
    256.         \}  
    257.     \}  
    258.   
    259.     // 打印日志  
    260.     **private static void print(String msg) \{  **
    261.         Log.i(TAG, msg);  
    262.     \}  
    263.   
    264.     **public interface SmartDownloadProgressListener \{  **
    265.         **public void onDownloadSize(int size);  **
    266.     \}  
    267. \}  
    268.

[Link 1]: http://www.cnblogs.com/wangzehuaw/p/5610851.html