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49_多线程断点下载的实现&界面的更新
发布时间：2021-02-28 16:42:37编辑：雪饮阅读（）
上一篇我们了解了子线程更新ui的具体实现，接下来就继续回到上上篇中我们还没有完善的ui更新，来实现这个多线程断点下载最后的下载进度等的ui更新。
import androidx.appcompat.app.AppCompatActivity;
import android.annotation.SuppressLint;
import android.annotation.TargetApi;
import android.os.Build;
import android.os.Bundle;
import android.os.Environment;
import android.os.Handler;
import android.os.Message;
import android.os.StrictMode;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;
public class MainActivity extends AppCompatActivity implements View.OnClickListener {
private ProgressBar pb;
private Button bt;
private TextView tv;
private EditText et;
//是否下载完成的标记位，下载完成后不继续监听ui更新
boolean flag = true;
//是否点击暂停按钮的标志位
boolean stopflag = false;
private Handler handler = new Handler() {
@Override
public void handleMessage(Message msg) {
//设置最新下载进度
pb.setProgress(total);
int max = pb.getMax();
System.out.println("本次获得max:"+max+"本次获得total:"+total);
if (total >= max) {
total = max;
flag = false;
}
//获取百分比
//对于大文件这里就会导致虽然是做乘法，且都是正整数，但结果因为超出int范围而导致溢出成负数的情况
long bigNum=(long)total * 100;
int result = (int)(bigNum/ max);
System.out.println("total * 100:"+total * 100);
System.out.println("bigNum:"+bigNum);
tv.setText("当前进度 :" + result + "%");
super.handleMessage(msg);
}
};
int total = 0;
@Override
protected void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
pb = (ProgressBar) this.findViewById(R.id.pb);
bt = this.findViewById(R.id.bt);
tv = (TextView) this.findViewById(R.id.tv_process);
et = this.findViewById(R.id.et);
bt.setOnClickListener(this);
}
@TargetApi(Build.VERSION_CODES.GINGERBREAD)
@SuppressLint("NewApi")
@Override
public void onClick(View v) {
StrictMode.ThreadPolicy policy=new StrictMode.ThreadPolicy.Builder().permitAll().build();
StrictMode.setThreadPolicy(policy);
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);
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", Toast.LENGTH_LONG).show();
return;
}
try {
URL url = new URL(path);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("GET");
conn.setConnectTimeout(5000);
int code = conn.getResponseCode();
if (code == 200) {
int len = conn.getContentLength();
//建立到sdcard根目录吧
RandomAccessFile file = new RandomAccessFile(
Environment.getExternalStorageDirectory() + File.separator+Util.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", Toast.LENGTH_LONG).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(Environment.getExternalStorageDirectory() + File.separator + 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;
}
}
}
System.out.println("线程" + threadid + "实际正在下载 " + "开始位置 : "
+ startposition + "结束位置 " + endpositon);
// "Range", "bytes=2097152-4194303")
conn.setRequestProperty("Range", "bytes=" + startposition + "-"
+ endpositon);
conn.setRequestMethod("GET");
conn.setConnectTimeout(5000);
InputStream is = conn.getInputStream();
RandomAccessFile file = new RandomAccessFile(Environment.getExternalStorageDirectory() + File.separator
+ Util.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) {
//接受暂停下载的信号
if (stopflag) {
return;
}
file.write(buffer, 0, len);
synchronized (MainActivity.this) {
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();
}
}
}
class Util{
public static String getFilenName(String path) {
int start = path.lastIndexOf("/") + 1;
return path.substring(start, path.length());
}
}
最后就是部署测试啦
<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:layout_width="fill_parent"
android:layout_height="wrap_content"
android:hint="@string/hint"
android:text="http://192.168.43.71:8080/javaweb/output.mp4"
android:id="@+id/et"
/>
<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:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="@string/download"
android:id="@+id/bt"
/>
</LinearLayout>
关键字词：多线程,界面更新