Android实现网络多线程文件下载

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：

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;
@override
protected 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);
}
@override
public 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() {
@override
public 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;
}
@override
public 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:

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;
}
@override
public 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！