Android-多线程断点下载

权限：

<span style="font-family:KaiTi_GB2312;font-size:18px;"> <uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/></span>

MainActivity.java
<span style="font-family:KaiTi_GB2312;font-size:18px;">public class MainActivity extends Activity {

static int ThreadCount = 3;
static int finishedThread = 0;

int currentProgress;
String fileName = "kugou.exe";
//确定下载地址
String path = "http://192.168.47.38:8080/mytest/" + fileName;
private ProgressBar pb;
TextView tv;

Handler handler = new Handler(){
public void handleMessage(android.os.Message msg) {
//把变量改成long，在long下运算

// tv.setText((long)pb.getProgress() * 100 / pb.getMax() + "%");
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
pb = (ProgressBar) findViewById(R.id.pb);
tv = (TextView) findViewById(R.id.tv);
}

public void click(View v){
Thread t = new Thread(){
@Override
public void run() {
//发送get请求，请求这个地址的资源
try {
//URL路径
URL url = new URL(path);
//获取连接
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
//请求方式
conn.setRequestMethod("GET");
//连接超时
conn.setConnectTimeout(5000);
//读取超时
conn.setReadTimeout(5000);
//判断连接是否成功
if(conn.getResponseCode() == 200){
//拿到所请求资源文件的长度
int length = conn.getContentLength();
//设置进度条的最大值就是原文件的总长度
pb.setMax(length);
File file = new File(Environment.getExternalStorageDirectory(), fileName);
//生成临时文件
RandomAccessFile raf = new RandomAccessFile(file, "rwd");
//设置临时文件的大小
raf.setLength(length);
raf.close();
//计算出每个线程应该下载多少字节
int size = length / ThreadCount;

for (int i = 0; i < ThreadCount; i++) {
//计算线程下载的开始位置和结束位置
int startIndex = i * size;
int endIndex = (i + 1) * size - 1;
//如果是最后一个线程，那么结束位置写死
if(i == ThreadCount - 1){
endIndex = length - 1;
}
// System.out.println("线程" + i + "的下载区间是：" + startIndex + "---" + endIndex);
new DownLoadThread(startIndex, endIndex, i).start();
}
}
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
};
t.start();
}

class DownLoadThread extends Thread{
int startIndex;
int endIndex;
int threadId;

public DownLoadThread(int startIndex, int endIndex, int threadId) {
super();
this.startIndex = startIndex;
this.endIndex = endIndex;
this.threadId = threadId;
}

@Override
public void run() {
//再次发送http请求，下载原文件
try {
File progressFile = new File(Environment.getExternalStorageDirectory(), threadId + ".txt");
//判断进度临时文件是否存在
if(progressFile.exists()){
FileInputStream fis = new FileInputStream(progressFile);
BufferedReader br = new BufferedReader(new InputStreamReader(fis));
//从进度临时文件中读取出上一次下载的总进度，然后与原本的开始位置相加，得到新的开始位置
int lastProgress = Integer.parseInt(br.readLine());
startIndex += lastProgress;
//把上次下载的进度显示至进度条
currentProgress += lastProgress;
pb.setProgress(currentProgress);
//发送消息，让主线程刷新文本进度
handler.sendEmptyMessage(1);
fis.close();
}
System.out.println("线程" + threadId + "的下载区间是：" + startIndex + "---" + endIndex);
HttpURLConnection conn;
URL url = new URL(path);
conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("GET");
conn.setConnectTimeout(5000);
conn.setReadTimeout(5000);
//设置本次http请求所请求的数据的区间
conn.setRequestProperty("Range", "bytes=" + startIndex + "-" + endIndex);

//请求部分数据，相应码是206
if(conn.getResponseCode() == 206){
//流里此时只有1/3原文件的数据
InputStream is = conn.getInputStream();
byte[] b = new byte[1024];
int len = 0;
int total = 0;
//拿到临时文件的输出流
File file = new File(Environment.getExternalStorageDirectory(), fileName);
RandomAccessFile raf = new RandomAccessFile(file, "rwd");
//把文件的写入位置移动至startIndex
raf.seek(startIndex);
while((len = is.read(b)) != -1){
//每次读取流里数据之后，同步把数据写入临时文件
raf.write(b, 0, len);
total += len;
System.out.println("线程" + threadId + "下载了" + total);
//每次读取流里数据之后，把本次读取的数据的长度显示至进度条
currentProgress += len;
pb.setProgress(currentProgress);
//发送消息，让主线程刷新文本进度
handler.sendEmptyMessage(1);
//生成一个专门用来记录下载进度的临时文件
RandomAccessFile progressRaf = new RandomAccessFile(progressFile, "rwd");
//每次读取流里数据之后，同步把当前线程下载的总进度写入进度临时文件中
progressRaf.write((total + "").getBytes());
progressRaf.close();
}
System.out.println("线程" + threadId + "------------下载完毕-----------");
raf.close();

finishedThread++;
synchronized (path) {
if(finishedThread == ThreadCount){
for (int i = 0; i < ThreadCount; i++) {
File f = new File(Environment.getExternalStorageDirectory(), i + ".txt");
f.delete();
}
finishedThread = 0;
}
}
}
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}

}</span>