我们学习了连接网络与服务器后不只是仅仅上一些网页，与服务器进行交流。我们还可以从网上下载文件(Download)
文件的下载分为多种：
1.单线程下载
2.多线程下载
3.多线程断点续传
单线程下载
首先我们来看单线程下载：
文件的下载需要时间的，所以文件的Download属于耗时操作，故而不能将它放在UI主线程中，也是需要Handler或者异步线程(AsyncTask)
本次为AsyncTask
1.首先显示连接服务器。
2.通过GetContentLength获取要下载的文件的长度。
3.得到输入流，用来读取文件。
4.创建文件名
5.通过FileOutputStream(file)向创建的文件中写入下载的文件
6.UI主线程调用异步线程
/**
* 单线程下载的线程
class DownLoadSingleTask extends AsyncTask<String,Integer,String>{
@Override
protected String doInBackground(String... params) {
try {
URL url = new URL("http://192.168.***.**:8080/HTTpTest_Servelet/music/SetMeFree.mp3");
URLConnection connection = url.openConnection();
int length =connection.getContentLength();//获取内容的长度
InputStream is = connection.getInputStream();
File file = new File(Environment.getExternalStorageDirectory(),"Set Me Free.mp3");//创建文件夹
if (!file.exists()){
file.createNewFile();
FileOutputStream fos = new FileOutputStream(file);
byte[] array = new byte[1024];//缓存区，用于缓存读取的数据
int i = is.read(array);
int sum = 0;
while (i!=-1){
fos.write(array);
sum += i;
publishProgress(length,sum);
i = is.read(array);
fos.flush();
fos.close();
is.close();
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
return null;
}
在UI主线程中调用AsyncTask
case R.id.button_download_single:
DownLoadSingleTask task = new DownLoadSingleTask();
task.execute();
break;
多线程下载
有时文件较大，用一个线程下载文件时会消耗很多时间，通过多线程能够缩短文件下载的时间。
多线程的工作流程：（三线程的）
多线程下载：用for循环创建多个线程
打开网络连接—>得到数据长度—>长度除以线程数—>写入文件
connection.setRequestProperty(“Range”, “bytes=” + start + “-” + end);//设置头信息的，比如格式，UA等，不设置自然有默认的，一般的请求倒不需要去设置，可以去看看android里的DefaultHttpClient里也有设置头信息的
RandomAccessFile (文件路径，”rw”)
seek(start) 之后再写文件
1.主线程调一个线程为了用来连接网络(服务器)
2.单独写一个线程，用来多线程下载。主要有文件地址url，每个线程下载的起始位置start，每个线程下载的末尾位置end，下载后的文件File
/**
* 多线程下载的线程
* Created by Went_Gone on 2015/9/12.
public class MulitDownloadThread extends Thread{
private int start;
private int end;
private String urlPath;
private File file;
private int sum;
public int getSum() {
return sum;
public MulitDownloadThread( int start, int end, String urlPath, File file) {
this.start = start;
this.end = end;
this.urlPath = urlPath;
this.file = file;
@Override
public void run() {
try {
URL url = new URL(urlPath);
URLConnection connection = url.openConnection();
connection.setAllowUserInteraction(true);
connection.setRequestProperty("Range", "bytes=" + start + "-" + end);//设置头信息的，比如格式，UA等，不设置自然有默认的，一般的请求倒不需要去设置，可以去看看android里的DefaultHttpClient里也有设置头信息的
InputStream is = connection.getInputStream();
RandomAccessFile raf = new RandomAccessFile(file.getAbsolutePath(),"rw");//随机访问文件的读写，第一个参数是文件的路径
raf.seek(start);
byte[] array = new byte[1024];
int index = is.read(array);
while (index!=-1){
raf.write(array,0,index);
sum+=index;
index = is.read(array);
Log.d("Mulit",this.getName()+" "+sum+"");//用来检验是不是多线程下载
raf.close();
is.close();
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
在Activity中。
/**
* 多线程下载
private void MulitDownload() {
new Thread(new Runnable() {
@Override
public void run() {
try {
String urlPath = "http://192.168.***.*:8080/HTTpTest_Servelet/music/SetMeFree.mp3";
// String urlPath = "http://img1.cache.netease.com/catchpic/6/6C/6C1F6740B3ECD7CC23C9E70B0C04B6C0.jpg";
// String urlPath = "http://p.gdown.baidu.com/a7171b404c2b222af1cb5a3eca249e36e4ffb41e33c741e8fee67227b09cfd84cf4d133189ea79f032759a367b6d3dda9658d02aae07f2b8dc82b1c2c1169460e528cbd7742a45f9e7fe69eb61959bf3e9e537b5cb5f221b49366ca7af9d625ec9b0d991e96240723ddbfad0177b32ae8ab3c4903216bf582093102d7e6c0d3e78658f3a92c078ffe4dc7ed9e29a20192eba2f785430ca3b4c7b695578dd010ad7fcc6499ee3cfa2bed4d0ba07edaa1097957a4a96ee7e397976dc6060f9902ee34f85506a484274";
URL url = new URL(urlPath);
URLConnection connection = url.openConnection();
length =connection.getContentLength();//获取内容的长度
File file = new File(Environment.getExternalStorageDirectory(),"Set Me Free aa.mp3");
// File file = new File(Environment.getExternalStorageDirectory(),"tanyan.jpg");
// File file = new File(Environment.getExternalStorageDirectory(),"QQyinyue.apk");
if (!file.exists()){
file.createNewFile();
MulitDownloadThread[] threads = new MulitDownloadThread[3];//用于管理下载线程
for (int i = 0;i<3;i++) {
MulitDownloadThread thread = null;
if (i==2){
thread = new MulitDownloadThread(length / 3 * 2, length, urlPath, file);
}else {
thread = new MulitDownloadThread(length / 3 * i, length / 3 * (i + 1)-1, urlPath, file);
thread.start();
threads[i] = thread;
boolean isFinish = true;
int sum = 0;
while (isFinish){
for (MulitDownloadThread thread:threads) {
sum += thread.getSum();
Message msg = handler.obtainMessage();
msg.what = MULITE;
msg.arg1 = sum;
handler.sendMessage(msg);
if (sum==length){
isFinish = false;
Thread.sleep(200);
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
}).start();
}
UI主线程中不能使用其他线程控制View，这里用Handler
private Handler handler = new Handler(){
@Override
public void handleMessage(Message msg) {
switch (msg.what){
case MULITE:
mProgressBar.setProgress((int) (msg.arg1*100.0/length));
break;
