断点续传和下载原理分析

时间：2016-06-23 15:49:58 阅读：160 评论：0 收藏：0 [点我收藏+]

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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

技术分享

关键代码：

FileServer.java

Java代码

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;//线程池
private int port;//监听端口
private boolean quit = false;//退出
private ServerSocket server;
private Map<Long, FileLogInfo> datas = new HashMap<Long, FileLogInfo>();//存放断点数据,以后改为数据库存放
public FileServer(int port)
{
this.port = port;
//创建线程池，池中具有(cpu个数*50)条线程
executorService = Executors.newFixedThreadPool(Runtime.getRuntime().availableProcessors() * 50);
}
/**
* 退出
*/
public void quit()
{
this.quit = true;
try
{
server.close();
}catch (IOException e)
{
e.printStackTrace();
}
}
/**
* 启动服务
* @throws Exception
*/
public void start() throws Exception
{
server = new ServerSocket(port);//实现端口监听
while(!quit)
{
try
{
Socket socket = server.accept();
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
}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());
//得到客户端发来的第一行协议数据：Content-Length=143253434;filename=xxx.3gp;sourceid=
//如果用户初次上传文件，sourceid的值为空。
InputStream inStream = socket.getInputStream();
String head = StreamTool.readLine(inStream);
System.out.println("FileServer head:"+head);
if(head!=null)
{
//下面从协议数据中提取各项参数值
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);
//生成资源id，如果需要唯一性，可以采用UUID
long id = System.currentTimeMillis();
FileLogInfo log = null;
if(sourceid!=null && !"".equals(sourceid))
{
id = Long.valueOf(sourceid);
//查找上传的文件是否存在上传记录
log = find(id);
}
File file = null;
int position = 0;
//如果上传的文件不存在上传记录,为文件添加跟踪记录
if(log==null)
{
//设置存放的位置与当前应用的位置有关
File dir = new File("c:/temp/");
if(!dir.exists()) dir.mkdirs();
file = new File(dir, filename);
//如果上传的文件发生重名，然后进行改名
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);
}
// 如果上传的文件存在上传记录,读取上次的断点位置
else
{
System.out.println("FileServer have exits log not null");
//从上传记录中得到文件的路径
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));
//读取断点位置
position = Integer.valueOf(properties.getProperty("length"));
}
}
}
//***************************上面是对协议头的处理，下面正式接收数据***************************************
//向客户端请求传输数据
OutputStream outStream = socket.getOutputStream();
String response = "sourceid="+ id+ ";position="+ position+ "%";
//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
//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
outStream.write(response.getBytes());
RandomAccessFile fileOutStream = new RandomAccessFile(file, "rwd");
//设置文件长度
if(position==0) fileOutStream.setLength(Integer.valueOf(filelength));
//移动文件指定的位置开始写入数据
fileOutStream.seek(position);
byte[] buffer = new byte[1024];
int len = -1;
int length = position;
//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
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"));
//实时记录文件的最后保存位置
properties.store(logFile, null);
logFile.close();
}
//如果长传长度等于实际长度则表示长传成功
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();
}
}
}
}
/**
* 查找在记录中是否有sourceid的文件
* @param sourceid
* @return
*/
public FileLogInfo find(Long sourceid)
{
return datas.get(sourceid);
}
/**
* 保存上传记录，日后可以改成通过数据库存放
* @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()));
}
/**
* 当文件上传完毕，删除记录
* @param sourceid
*/
public void delete(long sourceid)
{
System.out.println("delete logfile "+sourceid);
if(datas.containsKey(sourceid)) datas.remove(sourceid);
}
}

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：

技术分享

关键代码：

UploadActivity.java

Java代码

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(); // 接收用户所选文件的路径
info.setText("select: " + uri); // 在界面上显示路径
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("暂停", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
// TODO Auto-generated method stub
uploadThread.closeLink();
dialog.dismiss();
}
});
progressDialog.setMessage("正在上传...");
progressDialog.setMax(100);
return progressDialog;
default:
return null;
}
}
/**
* 使用Handler给创建他的线程发送消息，
* 匿名内部类
*/
private Handler handler = new Handler()
{
@Override
public void handleMessage(Message msg)
{
//获得上传长度的进度
int length = msg.getData().getInt("size");
progressDialog.setProgress(length);
if(progressDialog.getProgress()==progressDialog.getMax())//上传成功
{
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();
//设置起始目录和查找的类型
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
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))//判断SDCard是否存在
{
if(uploadFilePath == null){
Toast.makeText(UploadActivity.this, "还没设置上传文件", 1).show();
}
System.out.println("uploadFilePath:"+uploadFilePath+" "+fileName);
//取得SDCard的目录
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());//设置长传文件的最大刻度
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, "文件不存在", 1).show();
}
}
else
{
Toast.makeText(UploadActivity.this, "SDCard不存在！", 1).show();
}
break;
}
}
}

UploadThread.java

Java代码

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";
/*需要上传文件的路径*/
private File uploadFile;
/*上传文件服务器的IP地址*/
private String dstName;
/*上传服务器端口号*/
private int dstPort;
/*上传socket链接*/
private Socket socket;
/*存储上传的数据库*/
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;
}
/**
* 模拟断开连接
*/
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 {
// 判断文件是否已有上传记录
String souceid = logService.getBindId(uploadFile);
// 构造拼接协议
String head = "Content-Length=" + uploadFile.length()
+ ";filename=" + uploadFile.getName() + ";sourceid="
+ (souceid == null ? "" : souceid) + "%";
// 通过Socket取得输出流
socket = new Socket(dstName, dstPort);
OutputStream outStream = socket.getOutputStream();
outStream.write(head.getBytes());
Log.i(TAG, "write to outStream");
InputStream inStream = socket.getInputStream();
// 获取到字符流的id与位置
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);
// 代表原来没有上传过此文件，往数据库添加一条绑定记录
if (souceid == null) {
logService.save(responseid, uploadFile);
}
RandomAccessFile fileOutStream = new RandomAccessFile(uploadFile, "r");
// 查找上次传送的最终位置，并从这开始传送
fileOutStream.seek(Integer.valueOf(position));
byte[] buffer = new byte[1024];
int len = -1;
// 初始化上传的数据长度
int length = Integer.valueOf(position);
while ((len = fileOutStream.read(buffer)) != -1) {
outStream.write(buffer, 0, len);
// 设置长传数据长度
length += len;
listener.onUploadSize(length);
}
fileOutStream.close();
outStream.close();
inStream.close();
socket.close();
// 判断上传完则删除数据
if (length == uploadFile.length())
logService.delete(uploadFile);
} catch (Exception e) {
e.printStackTrace();
}
}
public interface UploadProgressListener{
void onUploadSize(int size);
}
}

下面是多线程下载

技术分享

SmartDownloadActivity.java

Java代码

package com.hao;
import java.io.File;
import com.hao.R;
import com.hao.R.id;
import com.hao.R.layout;
import com.hao.download.SmartFileDownloader;
import com.hao.download.SmartFileDownloader.SmartDownloadProgressListener;
import com.hao.util.ConstantValues;
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.widget.Button;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;
/**
*
* @author Administrator
*
*/
public class SmartDownloadActivity extends Activity {
private ProgressBar downloadbar;
private TextView resultView;
private String path = ConstantValues.DOWNLOAD_URL;
SmartFileDownloader loader;
private Handler handler = new Handler() {
@Override
// 信息
public void handleMessage(Message msg) {
switch (msg.what) {
case 1:
int size = msg.getData().getInt("size");
downloadbar.setProgress(size);
float result = (float) downloadbar.getProgress() / (float) downloadbar.getMax();
int p = (int) (result * 100);
resultView.setText(p + "%");
if (downloadbar.getProgress() == downloadbar.getMax())
Toast.makeText(SmartDownloadActivity.this, "下载成功", 1).show();
break;
case -1:
Toast.makeText(SmartDownloadActivity.this, msg.getData().getString("error"), 1).show();
break;
}
}
};
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.download);
Button button = (Button) this.findViewById(R.id.button);
Button closeConn = (Button) findViewById(R.id.closeConn);
closeConn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
if(loader != null){
finish();
}else{
Toast.makeText(SmartDownloadActivity.this, "还没有开始下载，不能暂停", 1).show();
}
}
});
downloadbar = (ProgressBar) this.findViewById(R.id.downloadbar);
resultView = (TextView) this.findViewById(R.id.result);
resultView.setText(path);
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {
download(path, ConstantValues.FILE_PATH);
} else {
Toast.makeText(SmartDownloadActivity.this, "没有SDCard", 1).show();
}
}
});
}
// 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
private void download(final String path, final File dir) {
new Thread(new Runnable() {
@Override
public void run() {
try {
loader = new SmartFileDownloader(SmartDownloadActivity.this, path, dir, 3);
int length = loader.getFileSize();// 获取文件的长度
downloadbar.setMax(length);
loader.download(new SmartDownloadProgressListener() {
@Override
public void onDownloadSize(int size) {// 可以实时得到文件下载的长度
Message msg = new Message();
msg.what = 1;
msg.getData().putInt("size", size);
handler.sendMessage(msg);
}
});
} catch (Exception e) {
Message msg = new Message();// 信息提示
msg.what = -1;
msg.getData().putString("error", "下载失败");// 如果下载错误，显示提示失败！
handler.sendMessage(msg);
}
}
}).start();// 开始
}
}

这个单个的下载线程

SmartDownloadThread.java

Java代码

package com.hao.download;
import java.io.File;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;
import android.util.Log;
/**
* 线程下载
* @author Administrator
*
*/
public class SmartDownloadThread extends Thread {
private static final String TAG = "SmartDownloadThread";
private File saveFile;
private URL downUrl;
private int block;
/* *下载开始位置 */
private int threadId = -1;
private int downLength;
private boolean finish = false;
private SmartFileDownloader downloader;
public SmartDownloadThread(SmartFileDownloader downloader, URL downUrl,
File saveFile, int block, int downLength, int threadId) {
this.downUrl = downUrl;
this.saveFile = saveFile;
this.block = block;
this.downloader = downloader;
this.threadId = threadId;
this.downLength = downLength;
}
@Override
public void run() {
if (downLength < block) {// 未下载完成
try {
HttpURLConnection http = (HttpURLConnection) downUrl
.openConnection();
http.setConnectTimeout(5 * 1000);
http.setRequestMethod("GET");
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, */*");
http.setRequestProperty("Accept-Language", "zh-CN");
http.setRequestProperty("Referer", downUrl.toString());
http.setRequestProperty("Charset", "UTF-8");
int startPos = block * (threadId - 1) + downLength;// 开始位置
int endPos = block * threadId - 1;// 结束位置
http.setRequestProperty("Range", "bytes=" + startPos + "-" + endPos);// 设置获取实体数据的范围
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)");
http.setRequestProperty("Connection", "Keep-Alive");
InputStream inStream = http.getInputStream();
byte[] buffer = new byte[1024];
int offset = 0;
print("Thread " + this.threadId + " start download from position " + startPos);
RandomAccessFile threadfile = new RandomAccessFile(this.saveFile, "rwd");
threadfile.seek(startPos);
while ((offset = inStream.read(buffer, 0, 1024)) != -1) {
threadfile.write(buffer, 0, offset);
downLength += offset;
downloader.update(this.threadId, downLength);
downloader.saveLogFile();
downloader.append(offset);
}
threadfile.close();
inStream.close();
print("Thread " + this.threadId + " download finish");
this.finish = true;
} catch (Exception e) {
this.downLength = -1;
print("Thread " + this.threadId + ":" + e);
}
}
}
private static void print(String msg) {
Log.i(TAG, msg);
}
/**
* 下载是否完成
* @return
*/
public boolean isFinish() {
return finish;
}
/**
* 已经下载的内容大小
* @return 如果返回值为-1,代表下载失败
*/
public long getDownLength() {
return downLength;
}
}

总得下载线程

SmartFileDownloader.java

Java代码

package com.hao.download;
import java.io.File;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.UUID;
import java.util.concurrent.ConcurrentHashMap;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import com.hao.db.DownloadFileService;
import android.content.Context;
import android.util.Log;
/**
* 文件下载主程序
* @author Administrator
*
*/
public class SmartFileDownloader {
private static final String TAG = "SmartFileDownloader";
private Context context;
private DownloadFileService fileService;
/* 已下载文件长度 */
private int downloadSize = 0;
/* 原始文件长度 */
private int fileSize = 0;
/*原始文件名*/
private String fileName;
/* 线程数 */
private SmartDownloadThread[] threads;
/* 本地保存文件 */
private File saveFile;
/* 缓存各线程下载的长度 */
private Map<Integer, Integer> data = new ConcurrentHashMap<Integer, Integer>();
/* 每条线程下载的长度 */
private int block;
/* 下载路径 */
private String downloadUrl;
/**
* 获取文件名
*/
public String getFileName(){
return this.fileName;
}
/**
* 获取线程数
*/
public int getThreadSize() {
return threads.length;
}
/**
* 获取文件大小
* @return
*/
public int getFileSize() {
return fileSize;
}
/**
* 累计已下载大小
* @param size
*/
protected synchronized void append(int size) {
downloadSize += size;
}
/**
* 更新指定线程最后下载的位置
* @param threadId 线程id
* @param pos 最后下载的位置
*/
protected void update(int threadId, int pos) {
this.data.put(threadId, pos);
}
/**
* 保存记录文件
*/
protected synchronized void saveLogFile() {
this.fileService.update(this.downloadUrl, this.data);
}
/**
* 构建文件下载器
* @param downloadUrl 下载路径
* @param fileSaveDir 文件保存目录
* @param threadNum 下载线程数
*/
public SmartFileDownloader(Context context, String downloadUrl,
File fileSaveDir, int threadNum) {
try {
this.context = context;
this.downloadUrl = downloadUrl;
fileService = new DownloadFileService(this.context);
URL url = new URL(this.downloadUrl);
if (!fileSaveDir.exists()) fileSaveDir.mkdirs();
this.threads = new SmartDownloadThread[threadNum];
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setConnectTimeout(5 * 1000);
conn.setRequestMethod("GET");
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, */*");
conn.setRequestProperty("Accept-Language", "zh-CN");
conn.setRequestProperty("Referer", downloadUrl);
conn.setRequestProperty("Charset", "UTF-8");
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)");
conn.setRequestProperty("Connection", "Keep-Alive");
conn.connect();
printResponseHeader(conn);
if (conn.getResponseCode() == 200) {
this.fileSize = conn.getContentLength();// 根据响应获取文件大小
if (this.fileSize <= 0)
throw new RuntimeException("Unkown file size ");
fileName = getFileName(conn);
this.saveFile = new File(fileSaveDir, fileName);/* 保存文件 */
Map<Integer, Integer> logdata = fileService.getData(downloadUrl);
if (logdata.size() > 0) {
for (Map.Entry<Integer, Integer> entry : logdata.entrySet())
data.put(entry.getKey(), entry.getValue());
}
//划分每个线程下载文件长度
this.block = (this.fileSize % this.threads.length) == 0 ? this.fileSize / this.threads.length
: this.fileSize / this.threads.length + 1;
if (this.data.size() == this.threads.length) {
for (int i = 0; i < this.threads.length; i++) {
this.downloadSize += this.data.get(i + 1);
}
print("已经下载的长度" + this.downloadSize);
}
} else {
throw new RuntimeException("server no response ");
}
} catch (Exception e) {
print(e.toString());
throw new RuntimeException("don‘t connection this url");
}
}
/**
* 获取文件名
*/
private String getFileName(HttpURLConnection conn) {
String filename = this.downloadUrl.substring(this.downloadUrl.lastIndexOf(‘/‘) + 1);//链接的最后一个/就是文件名
if (filename == null || "".equals(filename.trim())) {// 如果获取不到文件名称
for (int i = 0;; i++) {
String mine = conn.getHeaderField(i);
print("ConnHeader:"+mine+" ");
if (mine == null)
break;
if ("content-disposition".equals(conn.getHeaderFieldKey(i).toLowerCase())) {
Matcher m = Pattern.compile(".*filename=(.*)").matcher(mine.toLowerCase());
if (m.find())
return m.group(1);
}
}
filename = UUID.randomUUID() + ".tmp";// 默认取一个文件名
}
return filename;
}
/**
* 开始下载文件
*
* @param listener
* 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
* @return 已下载文件大小
* @throws Exception
*/
public int download(SmartDownloadProgressListener listener)
throws Exception {
try {
RandomAccessFile randOut = new RandomAccessFile(this.saveFile, "rw");
if (this.fileSize > 0)
randOut.setLength(this.fileSize);
randOut.close();
URL url = new URL(this.downloadUrl);
if (this.data.size() != this.threads.length) {
this.data.clear();// 清除数据
for (int i = 0; i < this.threads.length; i++) {
this.data.put(i + 1, 0);
}
}
for (int i = 0; i < this.threads.length; i++) {
int downLength = this.data.get(i + 1);
if (downLength < this.block && this.downloadSize < this.fileSize) { // 该线程未完成下载时,继续下载
this.threads[i] = new SmartDownloadThread(this, url,
this.saveFile, this.block, this.data.get(i + 1), i + 1);
this.threads[i].setPriority(7);
this.threads[i].start();
} else {
this.threads[i] = null;
}
}
this.fileService.save(this.downloadUrl, this.data);
boolean notFinish = true;// 下载未完成
while (notFinish) {// 循环判断是否下载完毕
Thread.sleep(900);
notFinish = false;// 假定下载完成
for (int i = 0; i < this.threads.length; i++) {
if (this.threads[i] != null && !this.threads[i].isFinish()) {
notFinish = true;// 下载没有完成
if (this.threads[i].getDownLength() == -1) {// 如果下载失败,再重新下载
this.threads[i] = new SmartDownloadThread(this,
url, this.saveFile, this.block, this.data.get(i + 1), i + 1);
this.threads[i].setPriority(7);
this.threads[i].start();
}
}
}
if (listener != null)
listener.onDownloadSize(this.downloadSize);
}
fileService.delete(this.downloadUrl);
} catch (Exception e) {
print(e.toString());
throw new Exception("file download fail");
}
return this.downloadSize;
}
/**
* 获取Http响应头字段
*
* @param http
* @return
*/
public static Map<String, String> getHttpResponseHeader(
HttpURLConnection http) {
Map<String, String> header = new LinkedHashMap<String, String>();
for (int i = 0;; i++) {
String mine = http.getHeaderField(i);
if (mine == null)
break;
header.put(http.getHeaderFieldKey(i), mine);
}
return header;
}
/**
* 打印Http头字段
*
* @param http
*/
public static void printResponseHeader(HttpURLConnection http) {
Map<String, String> header = getHttpResponseHeader(http);
for (Map.Entry<String, String> entry : header.entrySet()) {
String key = entry.getKey() != null ? entry.getKey() + ":" : "";
print(key + entry.getValue());
}
}
// 打印日志
private static void print(String msg) {
Log.i(TAG, msg);
}
public interface SmartDownloadProgressListener {
public void onDownloadSize(int size);
}
}

代码实现参考 http://hao3100590.iteye.com/blog/1295903

断点续传和下载原理分析

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原文地址：http://www.cnblogs.com/wangzehuaw/p/5610851.html

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