33、多线程断点下载的实现&界面的更新

 <?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >

<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="@string/down_load" />

<EditText
android:id="@+id/et"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:hint="@string/hint"
android:text="http://192.168.1.247:8080/youdao.exe" />

<ProgressBar
android:id="@+id/pb"
style="?android:attr/progressBarStyleHorizontal"
android:layout_width="fill_parent"
android:layout_height="wrap_content" />

<TextView
android:id="@+id/tv_process"
android:layout_width="fill_parent"
android:layout_height="wrap_content" />

<Button
android:id="@+id/bt"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="@string/download" />

</LinearLayout>

 /**
* 49_多线程断点下载的实现&界面的更新 DEMO
* @author dr
*
*/
public class DemoActivity extends Activity implements OnClickListener {

private ProgressBar pb;
private Button bt;
private TextView tv;
private EditText et;
boolean flag = true;
boolean stopflag = false;
int total = 0;

private Handler handler = new Handler() {

@Override
public void handleMessage(Message msg) {
pb.setProgress(total);
// 文件总长度
int max = pb.getMax();
// total和max都是从0开始的。
if (total >= (max - 1)) {
total = max;
flag = false;
}
int result = total * 100 / max;
tv.setText("当前进度 :" + result + "%");

super.handleMessage(msg);
}
};

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
pb = (ProgressBar) this.findViewById(R.id.pb);
bt = (Button) this.findViewById(R.id.bt);
tv = (TextView) this.findViewById(R.id.tv_process);
et = (EditText) this.findViewById(R.id.et);
bt.setOnClickListener(this);

}

@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.bt:
// 创建一个子线程 定期的更新ui
if ("开始下载".equals(bt.getText().toString())) {
bt.setText("暂停");
stopflag = false; // 开始下载
} else {
bt.setText("开始下载");
stopflag = true;
}
new Thread() {
@Override
public void run() {
super.run();
while (flag) {
try {
sleep(1000);
// 如果total > = 文件长度
Message msg = new Message();
handler.sendMessage(msg);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}.start();

// 开始执行下载的操作
String path = et.getText().toString().trim();
if ("".equals(path)) {
Toast.makeText(this, "路径不能为空", 1).show();
return;
}
try {
URL url = new URL(path);
HttpURLConnection conn = (HttpURLConnection) url
.openConnection();
conn.setRequestMethod("GET");
conn.setConnectTimeout(5000);
conn.setRequestProperty("User-Agent",
"Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1)");
int code = conn.getResponseCode();
if (code == 200) {
int len = conn.getContentLength();
RandomAccessFile file = new RandomAccessFile("/mnt/sdcard/"
+ getFilenName(path), "rwd");
// 1.设置本地文件大小跟服务器的文件大小一致
file.setLength(len);
// 设置进度条的最大值
pb.setMax(len);

// 2 .假设开启3 个线程
int threadnumber = 3;
int blocksize = len / threadnumber;
/**
* 线程1 0~ blocksize 线程2 1*bolocksize ~ 2*blocksize 线程3
* 2*blocksize ~ 文件末尾
*/
for (int i = 0; i < threadnumber; i++) {
int startposition = i * blocksize;
int endpositon = (i + 1) * blocksize;
if (i == (threadnumber - 1)) {
// 最后一个线程
endpositon = len;
}

DownLoadTask task = new DownLoadTask(i, path,
startposition, endpositon);
task.start();
}

}
} catch (Exception e) {
Toast.makeText(this, "下载出现异常", 0).show();
e.printStackTrace();
}

break;
}

}

class DownLoadTask extends Thread {

int threadid;
String filepath;
int startposition;
int endpositon;

public DownLoadTask(int threadid, String filepath, int startposition,
int endpositon) {
this.threadid = threadid;
this.filepath = filepath;
this.startposition = startposition;
this.endpositon = endpositon;

}

@Override
public void run() {
try {
File postionfile = new File("/mnt/sdcard/" + threadid + ".txt");
URL url = new URL(filepath);
HttpURLConnection conn = (HttpURLConnection) url
.openConnection();
System.out.println("线程" + threadid + "正在下载 " + "开始位置 : "
+ startposition + "结束位置 " + endpositon);

if (postionfile.exists()) {
FileInputStream fis = new FileInputStream(postionfile);
byte[] result = StreamTool.getBytes(fis);
String str = new String(result);
if (!"".equals(str)) {
int newstartposition = Integer.parseInt(str);
if (newstartposition > startposition) {
startposition = newstartposition;
}
}
}

// "Range", "bytes=2097152-4194303")
conn.setRequestProperty("Range", "bytes=" + startposition + "-"
+ endpositon);
conn.setRequestMethod("GET");
conn.setConnectTimeout(5000);
conn.setRequestProperty("User-Agent",
"Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1)");
InputStream is = conn.getInputStream();
RandomAccessFile file = new RandomAccessFile("/mnt/sdcard/"
+ getFilenName(filepath), "rwd");
// 设置 数据从文件哪个位置开始写
file.seek(startposition);
byte[] buffer = new byte[1024];
int len = 0;
// 代表当前读到的服务器数据的位置 ,同时这个值已经存储的文件的位置
int currentPostion = startposition;
// 创建一个文件对象 ,记录当前某个文件的下载位置

while ((len = is.read(buffer)) != -1) {
if (stopflag) {   // 暂停下载
return;
}
file.write(buffer, 0, len);

synchronized (DemoActivity.this) { // 同步当前的
total += len;
}

currentPostion += len;
// 需要把currentPostion 信息给持久化到存储设备
String position = currentPostion + "";
FileOutputStream fos = new FileOutputStream(postionfile);
fos.write(position.getBytes());
fos.flush();
fos.close();
}

file.close();
System.out.println("线程" + threadid + "下载完毕");
// 当线程下载完毕后 把文件删除掉
if (postionfile.exists()) {
postionfile.delete();
}
} catch (Exception e) {
e.printStackTrace();
}
super.run();
}
}

public String getFilenName(String path) {
int start = path.lastIndexOf("/") + 1;
return path.substring(start, path.length());
}
}

 public class StreamTool {
/**
* 把一个inputstream里面的内容转化成一个byte[]
*/
public static byte[] getBytes(InputStream is) throws Exception{
ByteArrayOutputStream bos = new ByteArrayOutputStream();
byte[] buffer = new byte[1024];
int len = 0;
while((len = is.read(buffer))!=-1){
bos.write(buffer, 0, len);
}
is.close();
bos.flush();
byte[] result = bos.toByteArray();
System.out.println(new String(result));
return  result;
}
}

     <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.INTERNET"/>