Android通过HTTP协议实现断点续传下载实例

整理文档，搜刮出一个Android通过HTTP协议实现断点续传下载的代码，稍微整理精简一下做下分享。

FileDownloader.java                                                                                                                

package cn.itcast.net.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 cn.itcast.service.FileService;

import android.content.Context;
import android.util.Log;
/**
* 文件下载器
* FileDownloader loader = new FileDownloader(context, "http://browse.babasport.com/ejb3/ActivePort.exe",
       new File("D:\\androidsoft\\test"), 2);
   loader.getFileSize();//得到文件总大小
   try {
     loader.download(new DownloadProgressListener(){
       public void onDownloadSize(int size) {
         print("已经下载："+ size);
       }      
     });
   } catch (Exception e) {
     e.printStackTrace();
   }
*/
public class FileDownloader {
 private static final String TAG = "FileDownloader";
 private Context context;
 private FileService fileService;  
 /* 已下载文件长度 */
 private int downloadSize = 0;
 /* 原始文件长度 */
 private int fileSize = 0;
 /* 线程数 */
 private DownloadThread[] 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 synchronized void update(int threadId, int pos) {
   this.data.put(threadId, pos);
   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 FileDownloader(Context context, String downloadUrl, File fileSaveDir, int threadNum) {
   try {
     this.context = context;
     this.downloadUrl = downloadUrl;
     fileService = new FileService(this.context);
     URL url = new URL(this.downloadUrl);
     if(!fileSaveDir.exists()) fileSaveDir.mkdirs();
     this.threads = new DownloadThread[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 ");

String filename = getFileName(conn);//获取文件名称
       this.saveFile = new File(fileSaveDir, filename);//构建保存文件
       Map<Integer, Integer> logdata = fileService.getData(downloadUrl);//获取下载记录
       if(logdata.size()>0){//如果存在下载记录
         for(Map.Entry<Integer, Integer> entry : logdata.entrySet())
           data.put(entry.getKey(), entry.getValue());//把各条线程已经下载的数据长度放入data中
       }
       if(this.data.size()==this.threads.length){//下面计算所有线程已经下载的数据长度
         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);
       }
       //计算每条线程下载的数据长度
       this.block = (this.fileSize ％ this.threads.length)==0? this.fileSize / this.threads.length : this.fileSize / this.threads.length + 1;
     }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);
   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);
       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(DownloadProgressListener 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();
       for (int i = 0; i < this.threads.length; i++) {
         this.data.put(i+1, 0);//初始化每条线程已经下载的数据长度为0
       }
     }
     for (int i = 0; i < this.threads.length; i++) {//开启线程进行下载
       int downLength = this.data.get(i+1);
       if(downLength < this.block && this.downloadSize<this.fileSize){//判断线程是否已经完成下载,否则继续下载  
         this.threads[i] = new DownloadThread(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) {// 循环判断所有线程是否完成下载
       Thread.sleep(900);
       notFinish = false;//假定全部线程下载完成
       for (int i = 0; i < this.threads.length; i++){
         if (this.threads[i] != null && !this.threads[i].isFinish()) {//如果发现线程未完成下载
           notFinish = true;//设置标志为下载没有完成
           if(this.threads[i].getDownLength() == -1){//如果下载失败,再重新下载
             this.threads[i] = new DownloadThread(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);//通知目前已经下载完成的数据长度
     }
     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());
   }
 }

private static void print(String msg){
   Log.i(TAG, msg);
 }
}

DownloadThread.Java

package cn.itcast.net.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;

public class DownloadThread extends Thread {
 private static final String TAG = "DownloadThread";
 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 FileDownloader downloader;

public DownloadThread(FileDownloader 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.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;
 }
}

DownloadProgressListener.java

package cn.itcast.net.download;

public interface DownloadProgressListener {
 public void onDownloadSize(int size);
}

DBOpenHelper.java

package cn.itcast.service;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class DBOpenHelper extends SQLiteOpenHelper {
 private static final String DBNAME = "itcast.db";
 private static final int VERSION = 1;

public DBOpenHelper(Context context) {
   super(context, DBNAME, null, VERSION);
 }

@Override
 public void onCreate(SQLiteDatabase db) {
   db.execSQL("CREATE TABLE IF NOT EXISTS filedownlog (id integer primary key autoincrement, downpath varchar(100), threadid INTEGER, downlength INTEGER)");
 }

@Override
 public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
   db.execSQL("DROP TABLE IF EXISTS filedownlog");
   onCreate(db);
 }

}

FileService.java

package cn.itcast.service;

import java.util.HashMap;
import java.util.Map;

import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
/**
* 业务bean
*
*/
public class FileService {
 private DBOpenHelper openHelper;

public FileService(Context context) {
   openHelper = new DBOpenHelper(context);
 }
 /**
  * 获取每条线程已经下载的文件长度
  * @param path
  * @return
  */
 public Map<Integer, Integer> getData(String path){
   SQLiteDatabase db = openHelper.getReadableDatabase();
   Cursor cursor = db.rawQuery("select threadid, downlength from filedownlog where downpath=?", new String[]{path});
   Map<Integer, Integer> data = new HashMap<Integer, Integer>();
   while(cursor.moveToNext()){
     data.put(cursor.getInt(0), cursor.getInt(1));
   }
   cursor.close();
   db.close();
   return data;
 }
 /**
  * 保存每条线程已经下载的文件长度
  * @param path
  * @param map
  */
 public void save(String path, Map<Integer, Integer> map){//int threadid, int position
   SQLiteDatabase db = openHelper.getWritableDatabase();
   db.beginTransaction();
   try{
     for(Map.Entry<Integer, Integer> entry : map.entrySet()){
       db.execSQL("insert into filedownlog(downpath, threadid, downlength) values(?,?,?)",
           new Object[]{path, entry.getKey(), entry.getValue()});
     }
     db.setTransactionSuccessful();
   }finally{
     db.endTransaction();
   }
   db.close();
 }
 /**
  * 实时更新每条线程已经下载的文件长度
  * @param path
  * @param map
  */
 public void update(String path, Map<Integer, Integer> map){
   SQLiteDatabase db = openHelper.getWritableDatabase();
   db.beginTransaction();
   try{
     for(Map.Entry<Integer, Integer> entry : map.entrySet()){
       db.execSQL("update filedownlog set downlength=? where downpath=? and threadid=?",
           new Object[]{entry.getValue(), path, entry.getKey()});
     }
     db.setTransactionSuccessful();
   }finally{
     db.endTransaction();
   }
   db.close();
 }
 /**
  * 当文件下载完成后，删除对应的下载记录
  * @param path
  */
 public void delete(String path){
   SQLiteDatabase db = openHelper.getWritableDatabase();
   db.execSQL("delete from filedownlog where downpath=?", new Object[]{path});
   db.close();
 }

}

DownloadActivity.java

package cn.itcast.download;

import java.io.File;

import cn.itcast.net.download.DownloadProgressListener;
import cn.itcast.net.download.FileDownloader;

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.EditText;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;

public class DownloadActivity extends Activity {
 private EditText downloadpathText;
 private TextView resultView;
 private ProgressBar progressBar;
 //当Handler被创建会关联到创建它的当前线程的消息队列，该类用于往消息队列发送消息
 //消息队列中的消息由当前线程内部进行处理
 private Handler handler = new Handler(){

@Override
   public void handleMessage(Message msg) {      
     switch (msg.what) {
     case 1:        
       progressBar.setProgress(msg.getData().getInt("size"));
       float num = (float)progressBar.getProgress()/(float)progressBar.getMax();
       int result = (int)(num*100);
       resultView.setText(result+ "％");
       if(progressBar.getProgress()==progressBar.getMax()){
         Toast.makeText(DownloadActivity.this, R.string.success, 1).show();
       }
       break;

case -1:
       Toast.makeText(DownloadActivity.this, R.string.error, 1).show();
       break;
     }
   }
 };

@Override
 public void onCreate(Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
   setContentView(R.layout.main);

downloadpathText = (EditText) this.findViewById(R.id.downloadpath);
   progressBar = (ProgressBar) this.findViewById(R.id.downloadbar);
   resultView = (TextView) this.findViewById(R.id.result);
   Button button = (Button) this.findViewById(R.id.button);
   button.setOnClickListener(new View.OnClickListener() {      
     @Override
     public void onClick(View v) {
       String path = downloadpathText.getText().toString();
       if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
         download(path, Environment.getExternalStorageDirectory());
       }else{
         Toast.makeText(DownloadActivity.this, R.string.sdcarderror, 1).show();
       }

}
   });
 }
 //主线程(UI线程)
 //业务逻辑正确，但是该程序运行的时候有问题
 //对于显示控件的界面更新只是由UI线程负责，如果是在非UI线程更新控件的属性值，更新后的显示界面不会反映到屏幕上
 private void download(final String path, final File savedir) {
   new Thread(new Runnable() {      
     @Override
     public void run() {
       FileDownloader loader = new FileDownloader(DownloadActivity.this, path, savedir, 3);
       progressBar.setMax(loader.getFileSize());//设置进度条的最大刻度为文件的长度
       try {
         loader.download(new DownloadProgressListener() {
           @Override
           public void onDownloadSize(int size) {//实时获知文件已经下载的数据长度
             Message msg = new Message();
             msg.what = 1;
             msg.getData().putInt("size", size);
             handler.sendMessage(msg);//发送消息
           }
         });
       } catch (Exception e) {
         handler.obtainMessage(-1).sendToTarget();
       }
     }
   }).start();
 }
}

demo下载：MulThreadDownload_jb51.rar

来源：http://blog.csdn.net/jaycee110905/article/details/8592372