本篇文章为大家展示了怎么在Android应用中实现一个HTTP多线程下载功能，内容简明扼要并且容易理解，绝对能使你眼前一亮，通过这篇文章的详细介绍希望你能有所收获。
多线程断点需要的功能
多线程下载，
支持断点。
使用多线程的好处：使用多线程下载会提升文件下载的速度。
多线程下载文件的过程是：
(1)首先获得下载文件的长度，然后设置本地文件的长度。
HttpURLConnection.getContentLength();//获取下载文件的长度 RandomAccessFile file = new RandomAccessFile("QQWubiSetup.exe","rwd"); file.setLength(filesize);//设置本地文件的长度(2)根据文件长度和线程数计算每条线程下载的数据长度和下载位置。
如：文件的长度为6M，线程数为3，那么，每条线程下载的数据长度为2M，每条线程开始下载的位置如下图所示。
例如10M大小，使用3个线程来下载，
线程下载的数据长度 (10%3 == 0 ？ 10/3:10/3+1) ,第1，2个线程下载长度是4M，第三个线程下载长度为2M
下载开始位置：线程id*每条线程下载的数据长度 = ?
下载结束位置：（线程id+1）*每条线程下载的数据长度-1=?
(3)使用Http的Range头字段指定每条线程从文件的什么位置开始下载，下载到什么位置为止，
如：指定从文件的2M位置开始下载，下载到位置(4M-1byte)为止
HttpURLConnection.setRequestProperty("Range", "bytes=2097152-4194303");(4)保存文件，使用RandomAccessFile类指定每条线程从本地文件的什么位置开始写入数据。
RandomAccessFile threadfile = new RandomAccessFile("QQWubiSetup.exe ","rwd");threadfile.seek(2097152);//从文件的什么位置开始写入数据MainActivity中代码:
package com.android.downloader;import java.io.File;import com.android.network.DownloadProgressListener;import com.android.network.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 MainActivity extends Activity { private EditText downloadpathText; private TextView resultView; private ProgressBar progressBar; 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(MainActivity.this, R.string.success, 1).show(); } break; case -1: Toast.makeText(MainActivity.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.path); progressBar = (ProgressBar) this.findViewById(R.id.downloadbar); resultView = (TextView) this.findViewById(R.id.resultView); Button button = (Button) this.findViewById(R.id.button); button.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { // TODO Auto-generated method stub String path = downloadpathText.getText().toString(); System.out.println(Environment.getExternalStorageState()+"------"+Environment.MEDIA_MOUNTED); if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){ download(path, Environment.getExternalStorageDirectory()); }else{ Toast.makeText(MainActivity.this, R.string.sdcarderror, 1).show(); } } }); } private void download(final String path, final File savedir) { new Thread(new Runnable() { @Override public void run() { FileDownloader loader = new FileDownloader(MainActivity.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(); }}DBOpenHelper中代码：
package com.android.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 = "down.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中代码：
package com.android.service;import java.util.HashMap;import java.util.Map;import android.content.Context;import android.database.Cursor;import android.database.sqlite.SQLiteDatabase;public class FileService { private DBOpenHelper openHelper; public FileService(Context context) { openHelper = new DBOpenHelper(context); } 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; } 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(); } 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(); } public void delete(String path){ SQLiteDatabase db = openHelper.getWritableDatabase(); db.execSQL("delete from filedownlog where downpath=?", new Object[]{path}); db.close(); }}DownloadProgressListener中代码：
package com.android.network;public interface DownloadProgressListener { public void onDownloadSize(int size);}FileDownloader中代码：
package com.android.network;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.android.service.FileService;import android.content.Context;import android.util.Log;public class FileDownloader { private static final String TAG = "FileDownloader"; private Context context; private FileService fileService; private int downloadSize = 0; private int fileSize = 0; private DownloadThread[] threads; private File saveFile; private Map<Integer, Integer> data = new ConcurrentHashMap<Integer, Integer>(); private int block; private String downloadUrl; public int getThreadSize() { return threads.length; } public int getFileSize() { return fileSize; } protected synchronized void append(int size) { downloadSize += size; } protected synchronized void update(int threadId, int pos) { this.data.put(threadId, pos); this.fileService.update(this.downloadUrl, this.data); } 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, * 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; } 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; } 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; } 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 中代码:
package com.android.network;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; 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, * public boolean isFinish() { return finish; } public long getDownLength() { return downLength; }}上述内容就是怎么在Android应用中实现一个HTTP多线程下载功能，你们学到知识或技能了吗？如果还想学到更多技能或者丰富自己的知识储备，欢迎关注编程网行业资讯频道。
