斷點續傳和下載原理分析

阿新 • • 發佈：2018-11-07

斷點續傳和下載原理分析

斷點續傳和斷點下載都是用的RandomAccessFile, 它具有移動指定的檔案大小的位置的功能seek 。

斷點續傳是由伺服器給客戶端一個已經上傳的位置標記position，然後客戶端再將檔案指標移動到相應的position，通過輸入流將檔案剩餘部分讀出來傳輸給伺服器

斷點下載是由客戶端告訴伺服器已經下載的大小，然後伺服器會將指標移動到相應的position，繼續讀出，把檔案返回給客戶端。當然為了下載的更快一下，也可以多執行緒下載，那麼基本實現就是給每個執行緒分配固定的位元組的檔案，分別去讀

首先是檔案上傳，這個要用到伺服器

關鍵程式碼：

FileServer.java

Java程式碼

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;

import java.io.OutputStream;
import java.io.PushbackInputStream;
import java.io.RandomAccessFile;
import java.net.ServerSocket;
import java.net.Socket;
import java.text.SimpleDateFormat;

import java.util.Date;
import java.util.HashMap;
import java.util.Map;
import java.util.Properties;
import java.util.Set;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import util.FileLogInfo;
import util.StreamTool;
public class FileServer {
private ExecutorService executorService;//執行緒池
private int port;//監聽埠
private boolean quit = false;//退出
private ServerSocket server;
private Map<Long, FileLogInfo> datas = new HashMap<Long, FileLogInfo>();//存放斷點資料,以後改為資料庫存放
public FileServer(int port)
{
this.port = port;
//建立執行緒池，池中具有(cpu個數*50)條執行緒
executorService = Executors.newFixedThreadPool(Runtime.getRuntime().availableProcessors() * 50);
}
/**
* 退出
*/
public void quit()
{
this.quit = true;
try
{
server.close();
}catch (IOException e)
{
e.printStackTrace();
}
}
/**
* 啟動服務
* @throws Exception
*/
public void start() throws Exception
{
server = new ServerSocket(port);//實現埠監聽
while(!quit)
{
try
{
Socket socket = server.accept();
executorService.execute(new SocketTask(socket));//為支援多使用者併發訪問，採用執行緒池管理每一個使用者的連線請求
}catch (Exception e)
{
e.printStackTrace();
}
}
}
private final class SocketTask implements Runnable
{
private Socket socket = null;
public SocketTask(Socket socket)
{
this.socket = socket;
}
@Override
public void run()
{
try
{
System.out.println("FileServer accepted connection "+ socket.getInetAddress()+ ":"+ socket.getPort());
//得到客戶端發來的第一行協議資料：Content-Length=143253434;filename=xxx.3gp;sourceid=
//如果使用者初次上傳檔案，sourceid的值為空。
InputStream inStream = socket.getInputStream();
String head = StreamTool.readLine(inStream);
System.out.println("FileServer head:"+head);
if(head!=null)
{
//下面從協議資料中提取各項引數值
String[] items = head.split(";");
String filelength = items[0].substring(items[0].indexOf("=")+1);
String filename = items[1].substring(items[1].indexOf("=")+1);
String sourceid = items[2].substring(items[2].indexOf("=")+1);
//生成資源id，如果需要唯一性，可以採用UUID
long id = System.currentTimeMillis();
FileLogInfo log = null;
if(sourceid!=null && !"".equals(sourceid))
{
id = Long.valueOf(sourceid);
//查詢上傳的檔案是否存在上傳記錄
log = find(id);
}
File file = null;
int position = 0;
//如果上傳的檔案不存在上傳記錄,為檔案新增跟蹤記錄
if(log==null)
{
//設定存放的位置與當前應用的位置有關
File dir = new File("c:/temp/");
if(!dir.exists()) dir.mkdirs();
file = new File(dir, filename);
//如果上傳的檔案發生重名，然後進行改名
if(file.exists())
{
filename = filename.substring(0, filename.indexOf(".")-1)+ dir.listFiles().length+ filename.substring(filename.indexOf("."));
file = new File(dir, filename);
}
save(id, file);
}
// 如果上傳的檔案存在上傳記錄,讀取上次的斷點位置
else
{
System.out.println("FileServer have exits log not null");
//從上傳記錄中得到檔案的路徑
file = new File(log.getPath());
if(file.exists())
{
File logFile = new File(file.getParentFile(), file.getName()+".log");
if(logFile.exists())
{
Properties properties = new Properties();
properties.load(new FileInputStream(logFile));
//讀取斷點位置
position = Integer.valueOf(properties.getProperty("length"));
}
}
}
//***************************上面是對協議頭的處理，下面正式接收資料***************************************
//向客戶端請求傳輸資料
OutputStream outStream = socket.getOutputStream();
String response = "sourceid="+ id+ ";position="+ position+ "%";
//伺服器收到客戶端的請求資訊後，給客戶端返回響應資訊：sourceid=1274773833264;position=position
//sourceid由服務生成，唯一標識上傳的檔案，position指示客戶端從檔案的什麼位置開始上傳
outStream.write(response.getBytes());
RandomAccessFile fileOutStream = new RandomAccessFile(file, "rwd");
//設定檔案長度
if(position==0) fileOutStream.setLength(Integer.valueOf(filelength));
//移動檔案指定的位置開始寫入資料
fileOutStream.seek(position);
byte[] buffer = new byte[1024];
int len = -1;
int length = position;
//從輸入流中讀取資料寫入到檔案中，並將已經傳入的檔案長度寫入配置檔案，實時記錄檔案的最後儲存位置
while( (len=inStream.read(buffer)) != -1)
{
fileOutStream.write(buffer, 0, len);
length += len;
Properties properties = new Properties();
properties.put("length", String.valueOf(length));
FileOutputStream logFile = new FileOutputStream(new File(file.getParentFile(), file.getName()+".log"));
//實時記錄檔案的最後儲存位置
properties.store(logFile, null);
logFile.close();
}
//如果長傳長度等於實際長度則表示長傳成功
if(length==fileOutStream.length()){
delete(id);
}
fileOutStream.close();
inStream.close();
outStream.close();
file = null;
}
}
catch (Exception e)
{
e.printStackTrace();
}
finally{
try
{
if(socket!=null && !socket.isClosed()) socket.close();
}
catch (IOException e)
{
e.printStackTrace();
}
}
}
}
/**
* 查詢在記錄中是否有sourceid的檔案
* @param sourceid
* @return
*/
public FileLogInfo find(Long sourceid)
{
return datas.get(sourceid);
}
/**
* 儲存上傳記錄，日後可以改成通過資料庫存放
* @param id
* @param saveFile
*/
public void save(Long id, File saveFile)
{
System.out.println("save logfile "+id);
datas.put(id, new FileLogInfo(id, saveFile.getAbsolutePath()));
}
/**
* 當檔案上傳完畢，刪除記錄
* @param sourceid
*/
public void delete(long sourceid)
{
System.out.println("delete logfile "+sourceid);
if(datas.containsKey(sourceid)) datas.remove(sourceid);
}
}

由於在上面的流程圖中已經進行了詳細的分析，我在這兒就不講了，只是在儲存資料的時候伺服器沒有用資料庫去儲存，這兒只是為了方便，所以要想測試斷點上傳，伺服器是不能停的，否則資料就沒有了，在以後改進的時候應該用資料庫去儲存資料。

檔案上傳客戶端：

關鍵程式碼：

UploadActivity.java

Java程式碼

package com.hao;
import java.io.File;
import java.util.List;
import com.hao.upload.UploadThread;
import com.hao.upload.UploadThread.UploadProgressListener;
import com.hao.util.ConstantValues;
import com.hao.util.FileBrowserActivity;
import android.app.Activity;
import android.app.Dialog;
import android.app.ProgressDialog;
import android.content.DialogInterface;
import android.content.Intent;
import android.content.res.Resources;
import android.net.Uri;
import android.os.Bundle;
import android.os.Environment;
import android.os.Handler;
import android.os.Message;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;
/**
*
* @author Administrator
*
*/
public class UploadActivity extends Activity implements OnClickListener{
private static final String TAG = "SiteFileFetchActivity";
private Button download, upload, select_file;
private TextView info;
private static final int PROGRESS_DIALOG = 0;
private ProgressDialog progressDialog;
private UploadThread uploadThread;
private String uploadFilePath = null;
private String fileName;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.upload);
initView();
}
private void initView(){
download = (Button) findViewById(R.id.download);
download.setOnClickListener(this);
upload = (Button) findViewById(R.id.upload);
upload.setOnClickListener(this);
info = (TextView) findViewById(R.id.info);
select_file = (Button) findViewById(R.id.select_file);
select_file.setOnClickListener(this);
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
// TODO Auto-generated method stub
super.onActivityResult(requestCode, resultCode, data);
if (resultCode == RESULT_OK) {
if (requestCode == 1) {
Uri uri = data.getData(); // 接收使用者所選檔案的路徑
info.setText("select: " + uri); // 在介面上顯示路徑
uploadFilePath = uri.getPath();
int last = uploadFilePath.lastIndexOf("/");
uploadFilePath = uri.getPath().substring(0, last+1);
fileName = uri.getLastPathSegment();
}
}
}
protected Dialog onCreateDialog(int id) {
switch(id) {
case PROGRESS_DIALOG:
progressDialog = new ProgressDialog(UploadActivity.this);
progressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
progressDialog.setButton("暫停", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
// TODO Auto-generated method stub
uploadThread.closeLink();
dialog.dismiss();
}
});
progressDialog.setMessage("正在上傳...");
progressDialog.setMax(100);
return progressDialog;
default:
return null;
}
}
/**
* 使用Handler給建立他的執行緒傳送訊息，
* 匿名內部類
*/
private Handler handler = new Handler()
{
@Override
public void handleMessage(Message msg)
{
//獲得上傳長度的進度
int length = msg.getData().getInt("size");
progressDialog.setProgress(length);
if(progressDialog.getProgress()==progressDialog.getMax())//上傳成功
{
progressDialog.dismiss();
Toast.makeText(UploadActivity.this, getResources().getString(R.string.upload_over), 1).show();
}
}
};
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
Resources r = getResources();
switch(v.getId()){
case R.id.select_file:
Intent intent = new Intent();
//設定起始目錄和查詢的型別
intent.setDataAndType(Uri.fromFile(new File("/sdcard")), "*/*");//"*/*"表示所有型別，設定起始資料夾和檔案型別
intent.setClass(UploadActivity.this, FileBrowserActivity.class);
startActivityForResult(intent, 1);
break;
case R.id.download:
startActivity(new Intent(UploadActivity.this, SmartDownloadActivity.class));
break;
case R.id.upload:
if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED))//判斷SDCard是否存在
{
if(uploadFilePath == null){
Toast.makeText(UploadActivity.this, "還沒設定上傳檔案", 1).show();
}
System.out.println("uploadFilePath:"+uploadFilePath+" "+fileName);
//取得SDCard的目錄
File uploadFile = new File(new File(uploadFilePath), fileName);
Log.i(TAG, "filePath:"+uploadFile.toString());
if(uploadFile.exists())
{
showDialog(PROGRESS_DIALOG);
info.setText(uploadFile+" "+ConstantValues.HOST+":"+ConstantValues.PORT);
progressDialog.setMax((int) uploadFile.length());//設定長傳檔案的最大刻度
uploadThread = new UploadThread(UploadActivity.this, uploadFile, ConstantValues.HOST, ConstantValues.PORT);
uploadThread.setListener(new UploadProgressListener() {
@Override
public void onUploadSize(int size) {
// TODO Auto-generated method stub
Message msg = new Message();
msg.getData().putInt("size", size);
handler.sendMessage(msg);
}
});
uploadThread.start();
}
else
{
Toast.makeText(UploadActivity.this, "檔案不存在", 1).show();
}
}
else
{
Toast.makeText(UploadActivity.this, "SDCard不存在！", 1).show();
}
break;
}
}
}

UploadThread.java

Java程式碼

package com.hao.upload;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.RandomAccessFile;
import java.net.Socket;
import android.content.Context;
import android.util.Log;
import com.hao.db.UploadLogService;
import com.hao.util.StreamTool;
public class UploadThread extends Thread {
private static final String TAG = "UploadThread";
/*需要上傳檔案的路徑*/
private File uploadFile;
/*上傳檔案伺服器的IP地址*/
private String dstName;
/*上傳伺服器埠號*/
private int dstPort;
/*上傳socket連結*/
private Socket socket;
/*儲存上傳的資料庫*/
private UploadLogService logService;
private UploadProgressListener listener;
public UploadThread(Context context, File uploadFile, final String dstName,final int dstPort){
this.uploadFile = uploadFile;
this.dstName = dstName;
this.dstPort = dstPort;
logService = new UploadLogService(context);
}
public void setListener(UploadProgressListener listener) {
this.listener = listener;
}
/**
* 模擬斷開連線
*/
public void closeLink(){
try{
if(socket != null) socket.close();
}catch(IOException e){
e.printStackTrace();
Log.e(TAG, "close socket fail");
}
}
@Override
public void run() {
// TODO Auto-generated method stub
try {
// 判斷檔案是否已有上傳記錄
String souceid = logService.getBindId(uploadFile);
// 構造拼接協議
String head = "Content-Length=" + uploadFile.length()
+ ";filename=" + uploadFile.getName() + ";sourceid="
+ (souceid == null ? "" : souceid) + "%";
// 通過Socket取得輸出流
socket = new Socket(dstName, dstPort);
OutputStream outStream = socket.getOutputStream();
outStream.write(head.getBytes());
Log.i(TAG, "write to outStream");
InputStream inStream = socket.getInputStream();
// 獲取到字元流的id與位置
String response = StreamTool.readLine(inStream);
Log.i(TAG, "response:" + response);
String[] items = response.split(";");
String responseid = items[0].substring(items[0].indexOf("=") + 1);
String position = items[1].substring(items[1].indexOf("=") + 1);
// 代表原來沒有上傳過此檔案，往資料庫新增一條繫結記錄
if (souceid == null) {
logService.save(responseid, uploadFile);
}
RandomAccessFile fileOutStream = new RandomAccessFile(uploadFile, "r");
// 查詢上次傳送的最終位置，並從這開始傳送
fileOutStream.seek(Integer.valueOf(position));
byte[] buffer = new byte[1024];
int len = -1;
// 初始化上傳的資料長度
int length = Integer.valueOf(position);
while ((len = fileOutStream.read(buffer)) != -1) {
outStream.write(buffer, 0, len);
// 設定長傳資料長度
length += len;
listener.onUploadSize(length);
}
fileOutStream.close();
outStream.close();
inStream.close();
socket.close();
// 判斷上傳完則刪除資料
if (length == uploadFile.length())
logService.delete(uploadFile);
&

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