实现原理
(1)首先获得下载文件的长度，然后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：
（网上找的图）
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=?
之前练习时的一个demo，不多说了，直接上代码吧，有关断点续传，需要使用数据库，不再加了，网上有很多成熟的项目可以直接用。
实例
mainapp：
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package com.amos.app; import java.io.file; import java.io.ioexception; import java.net.malformedurlexception; import java.net.url; import java.net.urlconnection; import com.amos.download.r; import android.annotation.suppresslint; import android.app.activity; 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.progressbar; import android.widget.textview; import android.widget.toast; /** * @author yangxiaolong * @2014-5-6 */public class mainapp extends activity implements onclicklistener { private static final string tag = mainapp.class.getsimplename(); /** 显示下载进度textview */private textview mmessageview; /** 显示下载进度progressbar */private progressbar mprogressbar; @overrideprotected void oncreate(bundle savedinstancestate) { super.oncreate(savedinstancestate); setcontentview(r.layout.progress_activity); findviewbyid(r.id.download_btn).setonclicklistener(this); mmessageview = (textview) findviewbyid(r.id.download_message); mprogressbar = (progressbar) findviewbyid(r.id.download_progress); } @overridepublic void onclick(view v) { if (v.getid() == r.id.download_btn) { dodownload(); } } /** * 使用handler更新ui界面信息 */@suppresslint("handlerleak") handler mhandler = new handler() { @overridepublic void handlemessage(message msg) { mprogressbar.setprogress(msg.getdata().getint("size")); float temp = (float) mprogressbar.getprogress() / (float) mprogressbar.getmax(); int progress = (int) (temp * 100); if (progress == 100) { toast.maketext(mainapp.this, "下载完成！", toast.length_long).show(); } mmessageview.settext("下载进度:" + progress + " %"); } }; /** * 下载准备工作，获取sd卡路径、开启线程 */private void dodownload() { // 获取sd卡路径 string path = environment.getexternalstoragedirectory() + "/amosdownload/"; file file = new file(path); // 如果sd卡目录不存在创建 if (!file.exists()) { file.mkdir(); } // 设置progressbar初始化 mprogressbar.setprogress(0); // 简单起见，我先把url和文件名称写死，其实这些都可以通过httpheader获取到 string downloadurl = "http://gdown.baidu.com/data/wisegame/91319a5a1dfae322/baidu_16785426.apk"; string filename = "baidu_16785426.apk"; int threadnum = 5; string filepath = path + filename; log.d(tag, "download file path:" + filepath); downloadtask task = new downloadtask(downloadurl, threadnum, filepath); task.start(); } /** * 多线程文件下载 * * @author yangxiaolong * @2014-8-7 */class downloadtask extends thread { private string downloadurl;// 下载链接地址 private int threadnum;// 开启的线程数 private string filepath;// 保存文件路径地址 private int blocksize;// 每一个线程的下载量 public downloadtask(string downloadurl, int threadnum, string fileptah) { this.downloadurl = downloadurl; this.threadnum = threadnum; this.filepath = fileptah; } @overridepublic void run() { filedownloadthread[] threads = new filedownloadthread[threadnum]; try { url url = new url(downloadurl); log.d(tag, "download file http path:" + downloadurl); urlconnection conn = url.openconnection(); // 读取下载文件总大小 int filesize = conn.getcontentlength(); if (filesize <= 0) { system.out.println("读取文件失败"); return; } // 设置progressbar最大的长度为文件size mprogressbar.setmax(filesize); // 计算每条线程下载的数据长度 blocksize = (filesize % threadnum) == 0 ? filesize / threadnum : filesize / threadnum + 1; log.d(tag, "filesize:" + filesize + " blocksize:"); file file = new file(filepath); for (int i = 0; i < threads.length; i++) { // 启动线程，分别下载每个线程需要下载的部分 threads[i] = new filedownloadthread(url, file, blocksize, (i + 1)); threads[i].setname("thread:" + i); threads[i].start(); } boolean isfinished = false; int downloadedallsize = 0; while (!isfinished) { isfinished = true; // 当前所有线程下载总量 downloadedallsize = 0; for (int i = 0; i < threads.length; i++) { downloadedallsize += threads[i].getdownloadlength(); if (!threads[i].iscompleted()) { isfinished = false; } } // 通知handler去更新视图组件 message msg = new message(); msg.getdata().putint("size", downloadedallsize); mhandler.sendmessage(msg); // log.d(tag, "current downloadsize:" + downloadedallsize); thread.sleep(1000);// 休息1秒后再读取下载进度 } log.d(tag, " all of downloadsize:" + downloadedallsize); } catch (malformedurlexception e) { e.printstacktrace(); } catch (ioexception e) { e.printstacktrace(); } catch (interruptedexception e) { e.printstacktrace(); } } } } |
filedownloadthread:
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package com.amos.app; import java.io.bufferedinputstream; import java.io.file; import java.io.ioexception; import java.io.randomaccessfile; import java.net.url; import java.net.urlconnection; import android.util.log; /** * 文件下载类 * * @author yangxiaolong * @2014-5-6 */public class filedownloadthread extends thread { private static final string tag = filedownloadthread.class.getsimplename(); /** 当前下载是否完成 */private boolean iscompleted = false; /** 当前下载文件长度 */private int downloadlength = 0; /** 文件保存路径 */private file file; /** 文件下载路径 */private url downloadurl; /** 当前下载线程id */private int threadid; /** 线程下载数据长度 */private int blocksize; /** * * @param url:文件下载地址 * @param file:文件保存路径 * @param blocksize:下载数据长度 * @param threadid:线程id */public filedownloadthread(url downloadurl, file file, int blocksize, int threadid) { this.downloadurl = downloadurl; this.file = file; this.threadid = threadid; this.blocksize = blocksize; } @overridepublic void run() { bufferedinputstream bis = null; randomaccessfile raf = null; try { urlconnection conn = downloadurl.openconnection(); conn.setallowuserinteraction(true); int startpos = blocksize * (threadid - 1);//开始位置 int endpos = blocksize * threadid - 1;//结束位置 //设置当前线程下载的起点、终点 conn.setrequestproperty("range", "bytes=" + startpos + "-" + endpos); system.out.println(thread.currentthread().getname() + " bytes="+ startpos + "-" + endpos); byte[] buffer = new byte[1024]; bis = new bufferedinputstream(conn.getinputstream()); raf = new randomaccessfile(file, "rwd"); raf.seek(startpos); int len; while ((len = bis.read(buffer, 0, 1024)) != -1) { raf.write(buffer, 0, len); downloadlength += len; } iscompleted = true; log.d(tag, "current thread task has finished,all size:"+ downloadlength); } catch (ioexception e) { e.printstacktrace(); } finally { if (bis != null) { try { bis.close(); } catch (ioexception e) { e.printstacktrace(); } } if (raf != null) { try { raf.close(); } catch (ioexception e) { e.printstacktrace(); } } } } /** * 线程文件是否下载完毕 */public boolean iscompleted() { return iscompleted; } /** * 线程下载文件长度 */public int getdownloadlength() { return downloadlength; } } |
效果图：
log控制台：
可以看到文件总大小、我们创建的5个线程每个负责下载的区间
sd卡：
关于android实现网络多线程文件下载小编就给大家介绍这么多，希望对大家有所帮助！同时也非常感谢大家一直以来对服务器之家网站的支持！
