android 多任务断点下载 DEMO

package com.icss.service; import java.io.File; import java.io.InputStream; import java.io.RandomAccessFile; import java.net.HttpURLConnection; import java.net.URL; import java.util.ArrayList; import java.util.List; import com.icss.dao.Dao; import com.icss.entity.DownloadInfo; import com.icss.entity.LoadInfo; import android.content.Context; import android.os.Handler; import android.os.Message; import android.util.Log; public class Downloader { private String urlstr;// 下载的地址 private String localfile;// 保存路径 private int threadcount;// 线程数 private Handler mHandler;// 消息处理器 private Dao dao;// 工具类 private int fileSize;// 所要下载的文件的大小 private List<DownloadInfo> infos;// 存放下载信息类的集合 private static final int INIT = 1;// 定义三种下载的状态：初始化状态，正在下载状态，暂停状态 private static final int DOWNLOADING = 2; private static final int PAUSE = 3; private int state = INIT; public Downloader(String urlstr, String localfile, int threadcount, Context context, Handler mHandler) { this.urlstr = urlstr; this.localfile = localfile; this.threadcount = threadcount; this.mHandler = mHandler; dao = new Dao(context); } /** * 判断是否正在下载 */ public boolean isdownloading() { return state == DOWNLOADING; } /** * 得到downloader里的信息 首先进行判断是否是第一次下载，如果是第一次就要进行初始化，并将下载器的信息保存到数据库中 * 如果不是第一次下载，那就要从数据库中读出之前下载的信息（起始位置，结束为止，文件大小等），并将下载信息返回给下载器 */ public LoadInfo getDownloaderInfors() { if (isFirst(urlstr)) { init(); int range = fileSize / threadcount; infos = new ArrayList<DownloadInfo>(); for (int i = 0; i < threadcount - 1; i++) { DownloadInfo info = new DownloadInfo(i, i * range, (i + 1) * range - 1, 0, urlstr); infos.add(info); } DownloadInfo info = new DownloadInfo(threadcount - 1, (threadcount - 1) * range, fileSize - 1, 0, urlstr); infos.add(info); // 保存infos中的数据到数据库 dao.saveInfos(infos); // 创建一个LoadInfo对象记载下载器的具体信息 LoadInfo loadInfo = new LoadInfo(fileSize, 0, urlstr); return loadInfo; } else { // 得到数据库中已有的urlstr的下载器的具体信息 infos = dao.getInfos(urlstr); Log.v("TAG", "not isFirst size=" + infos.size()); int size = 0; int compeleteSize = 0; for (DownloadInfo info : infos) { compeleteSize += info.getCompeleteSize(); size += info.getEndPos() - info.getStartPos() + 1; } return new LoadInfo(size, compeleteSize, urlstr); } } /** */ private void init() { try { URL url = new URL(urlstr); HttpURLConnection connection = (HttpURLConnection) url .openConnection(); connection.setConnectTimeout(5000); connection.setRequestMethod("GET"); fileSize = connection.getContentLength(); File file = new File(localfile); if (!file.exists()) { file.createNewFile(); } // 本地访问文件 RandomAccessFile accessFile = new RandomAccessFile(file, "rwd"); accessFile.setLength(fileSize); accessFile.close(); connection.disconnect(); } catch (Exception e) { e.printStackTrace(); } } /** * 判断是否是第一次 下载 */ private boolean isFirst(String urlstr) { return dao.isHasInfors(urlstr); } /** * 114 * 利用线程开始下载数据 115 */ public void download() { if (infos != null) { if (state == DOWNLOADING) return; state = DOWNLOADING; for (DownloadInfo info : infos) { new MyThread(info.getThreadId(), info.getStartPos(), info.getEndPos(), info.getCompeleteSize(), info.getUrl()).start(); } } } public class MyThread extends Thread { private int threadId; private int startPos; private int endPos; private int compeleteSize; private String urlstr; public MyThread(int threadId, int startPos, int endPos, int compeleteSize, String urlstr) { this.threadId = threadId; this.startPos = startPos; this.endPos = endPos; this.compeleteSize = compeleteSize; this.urlstr = urlstr; } @Override public void run() { HttpURLConnection connection = null; RandomAccessFile randomAccessFile = null; InputStream is = null; try { URL url = new URL(urlstr); connection = (HttpURLConnection) url.openConnection(); connection.setConnectTimeout(5000); connection.setRequestMethod("GET"); // 设置范围，格式为Range：bytes x-y; connection.setRequestProperty("Range", "bytes=" + (startPos + compeleteSize) + "-" + endPos); randomAccessFile = new RandomAccessFile(localfile, "rwd"); randomAccessFile.seek(startPos + compeleteSize); // 将要下载的文件写到保存在保存路径下的文件中 is = connection.getInputStream(); byte[] buffer = new byte[4096]; int length = -1; while ((length = is.read(buffer)) != -1) { randomAccessFile.write(buffer, 0, length); compeleteSize += length; // 更新数据库中的下载信息 dao.updataInfos(threadId, compeleteSize, urlstr); // 用消息将下载信息传给进度条，对进度条进行更新 Message message = Message.obtain(); message.what = 1; message.obj = urlstr; message.arg1 = length; mHandler.sendMessage(message); if (state == PAUSE) { return; } } } catch (Exception e) { e.printStackTrace(); } finally { try { is.close(); randomAccessFile.close(); connection.disconnect(); dao.closeDb(); } catch (Exception e) { e.printStackTrace(); } } } } // 删除数据库中urlstr对应的下载器信息 public void delete(String urlstr) { dao.delete(urlstr); } // 设置暂停 public void pause() { state = PAUSE; } // 重置下载状态 public void reset() { state = INIT; } }