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：
?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=?
Activity代码
public class MainActivity extends AppCompatActivity implements View.OnClickListener {
@SuppressLint("HandlerLeak")
public static Handler handler = new Handler() {
@Override
public void handleMessage(Message msg) {
super.handleMessage(msg);
int size = msg.getData().getInt("size");
// progressbar.setProgress();
float temp = (float) size / (float)progressbar.getMax();
int progress = (int) (temp * 100);
if (progress == 100) {
Log.e("TAG", "handleMessage: " + "下载完成");
}
tv_result.setText("下载进度：" + progress + "%");
}
};
private EditText ed;
private Button btn_download;
private static ProgressBar progressbar;
private static TextView tv_result;
private String urlstring;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
initView();
}
private void initView() {
ed = (EditText) findViewById(R.id.ed);
btn_download = (Button) findViewById(R.id.btn_download);
progressbar = (ProgressBar) findViewById(R.id.progressbar);
tv_result = (TextView) findViewById(R.id.tv_result);
btn_download.setOnClickListener(this);
}
@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.btn_download:
submit();
download();
break;
}
}
//下载文件
private void download() {
//获取sd卡路径
String path = Environment.getExternalStorageDirectory() + "/morethreaddownload/";
File file = new File(path);
if (!file.exists()) {
// 如果文件目录不存在，就创建此文件夹
file.mkdir();
}
// 指定下载的大文件的名称
String filename = "fulin.apk";
// 要下载的文件路径
String filepath = path + filename;
// 线程的数量
int threadcount = 5;
// 开启子线程下载文件（获取文件的长度）
DownLoadTask task = new DownLoadTask(progressbar,urlstring,filepath,threadcount);
task.start();
}
private void submit() {
//输入框中用户输入的网络路径
urlstring = ed.getText().toString().trim();
if (TextUtils.isEmpty(urlstring)) {
Toast.makeText(this, "edString不能为空", Toast.LENGTH_SHORT).show();
return;
}
}
}
DownLoadTask类
public class DownLoadTask extends Thread {
// 网路文件的下载地址
private String downloadUrl;
// 保存文件的路径
private String filePath;
// 线程的数量
private int threadcount;
// 进度条
private ProgressBar progressBar;
// 文件的大小
public static int filesize;
// 每个线程的下载量
private int blockSize;
//构造方法
public DownLoadTask(ProgressBar progressBar, String downloadUrl, String filePath, int threadcount) {
this.progressBar=progressBar;
this.downloadUrl = downloadUrl;
this.filePath = filePath;
this.threadcount = threadcount;
}
@Override
public void run() {
super.run();
// 线程数组
FileDownloadThread[] threads = new FileDownloadThread[threadcount];
try {
URL url = new URL(downloadUrl);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.connect();
if (conn.getResponseCode() == 200) {
// 读取下载文件的总长度
filesize = conn.getContentLength();
if (filesize <= 0) {
Log.e(TAG, "run: " + "读取文件失败");
return;
}
// 设置progressbar的最大值
progressBar.setMax(filesize);
//
// 计算每条线程下载的数据长度
blockSize = filesize % threadcount == 0 ? filesize / threadcount : filesize / threadcount + 1;
//sd卡里边指定的保存网络端下载下来的文件
File file = new File(filePath);
// 启动每个线程，分别下载所分配的长度
for (int i = 0; i < threadcount; i++) {
threads[i] = new FileDownloadThread(file,url,(i+1),blockSize);
threads[i].setName("Thread：" + i);
threads[i].start();
}
//是否下载完成
boolean isfinished = false;
// 下载的总长度
int downloadAllsize = 0;
while (!isfinished) {
isfinished = true;
downloadAllsize = 0;
for (int i = 0; i < threadcount; i++) {
downloadAllsize += threads[i].getDownloadlenght();
if (!threads[i].isCompleted()) {
isfinished = false;
}
}
// 通知handler去更新
Message message = new Message();
message.getData().putInt("size", downloadAllsize);
MainActivity.handler.sendMessage(message);
Thread.sleep(1000);
}
Log.e(TAG, "run:下载的总大小： "+ downloadAllsize);
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
class FileDownloadThread extends Thread {
/**
* 文件保存路径
*/
private File file;
/**
* 文件下载路径 (文件网址)
*/
private URL downloadUrl;
/**
* 当前下载线程ID
*/
private int threadId;
/**
* 线程下载数据长度
*/
private int blockSize;
private int downloadlenght;
private boolean isCompleted;
public FileDownloadThread(File file, URL downloadUrl, int threadId, int blockSize) {
this.file = file;
this.downloadUrl = downloadUrl;
this.threadId = threadId;
this.blockSize = blockSize;
}
@Override
public void run() {
super.run();
BufferedInputStream bis=null;
RandomAccessFile raf=null;
try {
HttpURLConnection conn = (HttpURLConnection) downloadUrl.openConnection();
conn.setAllowUserInteraction(true);
// 开始的位置
int startpos=blockSize*(threadId-1);
int endpos=blockSize*threadId-1;
// 设置当前线程下载的开始点和结束点
conn.setRequestProperty("Range","bytes="+startpos+"-"+endpos);
byte[] buffer=new byte[1024];
bis=new BufferedInputStream(conn.getInputStream());
raf=new RandomAccessFile(file,"rwd");
raf.seek(startpos);
int len=0;
while((len=bis.read(buffer,0,1024))!=-1){
raf.write(buffer,0,len);
downloadlenght+=len;
}
isCompleted=true;
} catch (IOException e) {
e.printStackTrace();
}
}
//每个线程下载的数据长度
public int getDownloadlenght() {
return downloadlenght;
}
//返回线程是否下载完成
public boolean isCompleted() {
return isCompleted;
}
}
FileDownloadThread类
class FileDownloadThread extends Thread {
/**
* 文件保存路径
*/
private File file;
/**
* 文件下载路径 (文件网址)
*/
private URL downloadUrl;
/**
* 当前下载线程ID
*/
private int threadId;
/**
* 线程下载数据长度
*/
private int blockSize;
private int downloadlenght;
private boolean isCompleted;
public FileDownloadThread(File file, URL downloadUrl, int threadId, int blockSize) {
this.file = file;
this.downloadUrl = downloadUrl;
this.threadId = threadId;
this.blockSize = blockSize;
}
@Override
public void run() {
super.run();
BufferedInputStream bis=null;
RandomAccessFile raf=null;
try {
HttpURLConnection conn = (HttpURLConnection) downloadUrl.openConnection();
conn.setAllowUserInteraction(true);
// 开始的位置
int startpos=blockSize*(threadId-1);
int endpos=blockSize*threadId-1;
// 设置当前线程下载的开始点和结束点
conn.setRequestProperty("Range","bytes="+startpos+"-"+endpos);
byte[] buffer=new byte[1024];
bis=new BufferedInputStream(conn.getInputStream());
raf=new RandomAccessFile(file,"rwd");
raf.seek(startpos);
int len=0;
while((len=bis.read(buffer,0,1024))!=-1){
raf.write(buffer,0,len);
downloadlenght+=len;
}
isCompleted=true;
} catch (IOException e) {
e.printStackTrace();
}
}
//每个线程下载的数据长度
public int getDownloadlenght() {
return downloadlenght;
}
//返回线程是否下载完成
public boolean isCompleted() {
return isCompleted;
}
}
详细配置信息可以参考我写的这篇文章：http://blog.ncmem.com/wordpress/2019/08/28/net%e6%96%87%e4%bb%b6%e6%89%b9%e9%87%8f%e4%b8%8b%e8%bd%bd/