让我们看一下代码的实现方法。

- package com.smart.db;
 - 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
 getData(String path){ - SQLiteDatabase db = openHelper.getReadableDatabase();
 - Cursor cursor = db.rawQuery("select threadid, downlength from SmartFileDownlog where downpath=?", new String[]{path});
 - Map
 data = new HashMap (); - 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
 map){//int threadid, int position - SQLiteDatabase db = openHelper.getWritableDatabase();
 - db.beginTransaction();
 - try{
 - for(Map.Entry
 entry : map.entrySet()){ - db.execSQL("insert into SmartFileDownlog(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
 map){ - SQLiteDatabase db = openHelper.getWritableDatabase();
 - db.beginTransaction();
 - try{
 - for(Map.Entry
 entry : map.entrySet()){ - db.execSQL("update SmartFileDownlog 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 SmartFileDownlog where downpath=?", new Object[]{path});
 - db.close();
 - }
 - }
 - package com.smart.impl;
 - 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 android.content.Context;
 - import android.util.Log;
 - import com.smart.db.FileService;
 - /**
 - * 文件下载器
 - * @author lihuoming@sohu.com
 - */
 - public class SmartFileDownloader {
 - private static final String TAG = "SmartFileDownloader";
 - 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 SmartDownloadThread[] threads;
 - /* 本地保存文件 */
 - private File saveFile;
 - /* 缓存各线程下载的长度*/
 - private Map
 data = new ConcurrentHashMap (); - /* 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 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 FileService(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 ");
 - String filename = getFileName(conn);
 - this.saveFile = new File(fileSaveDir, filename);/* 保存文件 */
 - Map
 logdata = fileService.getData(downloadUrl); - if(logdata.size()>0){
 - for(Map.Entry
 entry : logdata.entrySet()) - data.put(entry.getKey(), entry.getValue());
 - }
 - 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);
 - 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(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.threads = new SmartDownloadThread(this, url, this.saveFile, this.block, this.data.get(i+1), i+1);
 - this.threads.setPriority(7);
 - this.threads.start();
 - }else{
 - this.threads = 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 != null && !this.threads.isFinish()) {
 - notFinish = true;//下载没有完成
 - if(this.threads.getDownLength() == -1){//如果下载失败,再重新下载
 - this.threads = new SmartDownloadThread(this, url, this.saveFile, this.block, this.data.get(i+1), i+1);
 - this.threads.setPriority(7);
 - this.threads.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
 getHttpResponseHeader(HttpURLConnection http) { - Map
 header = new LinkedHashMap (); - 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
 header = getHttpResponseHeader(http); - for(Map.Entry
 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);
 - }
 - }
 - package com.smart.impl;
 - 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 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;
 - }
 - }
 - package com.smart.activoty.download;
 - import java.io.File;
 - 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;
 - import com.smart.impl.SmartDownloadProgressListener;
 - import com.smart.impl.SmartFileDownloader;
 - public class SmartDownloadActivity extends Activity {
 - private ProgressBar downloadbar;
 - private EditText pathText;
 - private TextView resultView;
 - 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, R.string.success, 1).show();
 - break;
 - case -1:
 - Toast.makeText(SmartDownloadActivity.this, R.string.error, 1).show();
 - break;
 - }
 - }
 - };
 - @Override
 - public void onCreate(Bundle savedInstanceState) {
 - super.onCreate(savedInstanceState);
 - setContentView(R.layout.main);
 - Button button = (Button)this.findViewById(R.id.button);
 - downloadbar = (ProgressBar)this.findViewById(R.id.downloadbar);
 - pathText = (EditText)this.findViewById(R.id.path);
 - resultView = (TextView)this.findViewById(R.id.result);
 - button.setOnClickListener(new View.OnClickListener() {
 - @Override
 - public void onClick(View v) {
 - String path = pathText.getText().toString();
 - if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
 - File dir = Environment.getExternalStorageDirectory();//文件保存目录
 - download(path, dir);
 - }else{
 - Toast.makeText(SmartDownloadActivity.this, R.string.sdcarderror, 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 {
 - SmartFileDownloader 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
 - }
 - }
 
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