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MainActivity.javapackage com.example.mydownpre;import java.io.File;import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.IOException;import java.io.InputStream;import java.io.OutputStream;import java.io.RandomAccessFile;import java.net.MalformedURLException;import java.net.URL;import java.net.URLConnection;import android.app.Activity;import android.os.Bundle;import android.os.Environment;import android.os.Handler;import android.os.Message;import android.util.Log;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;import android.widget.ProgressBar;import android.widget.TextView;import android.widget.Toast;import androidx.appcompat.app.AppCompatActivity;//MainActivity extends AppCompatActivitypublic class MainActivity extends AppCompatActivity {
       /** Called when the activity is first created. */    private static final String Path="http://192.168.43.8/song/Csaprs-NarkomanPavlik.mp3";    private ProgressBar progressBar;    private TextView textView;    private Button button;    private int FileLength;    private int DownedFileLength=0;    private InputStream inputStream;    private URLConnection connection;    private OutputStream outputStream;    @Override    public void onCreate(Bundle savedInstanceState) {
           super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        progressBar=(ProgressBar) findViewById(R.id.progress);        textView=(TextView) findViewById(R.id.text);        button=(Button) findViewById(R.id.button);        button.setOnClickListener(new ButtonListener());    }    class ButtonListener implements OnClickListener{
           @Override        public void onClick(View v) {
               DownedFileLength=0;            // TODO Auto-generated method stub            Thread thread=new Thread(){
                   public void run(){
                       try {
                           DownFile(Path);                    } catch (Exception e) {
                           // TODO: handle exception                    }                }            };            thread.start();        }    }    private Handler handler=new Handler()    {
           public void handleMessage(Message msg)        {
               if (!Thread.currentThread().isInterrupted()) {
                   switch (msg.what) {
                       case 0:                        progressBar.setMax(FileLength);                        Log.i("文件长度----------->", progressBar.getMax()+"");                        break;                    case 1:                        progressBar.setProgress(DownedFileLength);                        int x=DownedFileLength*100/FileLength;                        textView.setText(x+"%");                        break;                    case 2:                        Toast.makeText(getApplicationContext(), "下载完成", Toast.LENGTH_LONG).show();                        break;                    default:                        break;                }            }        }    };    private void DownFile(String urlString)    {
           /*         * 连接到服务器         */        try {
               URL url=new URL(urlString);            connection=url.openConnection();            if (connection.getReadTimeout()==5) {
                   Log.i("---------->", "当前网络有问题");                // return;            }            inputStream=connection.getInputStream();        } catch (MalformedURLException e1) {
               // TODO Auto-generated catch block            e1.printStackTrace();        } catch (IOException e) {
               // TODO Auto-generated catch block            e.printStackTrace();        }        /*         * 文件的保存路径和和文件名其中Nobody.mp3是在手机SD卡上要保存的路径，如果不存在则新建         */        String savePAth=Environment.getExternalStorageDirectory()+"/DownFile";        File file1=new File(savePAth);        if (!file1.exists()) {
               file1.mkdir();        }        String savePathString=Environment.getExternalStorageDirectory()+"/DownFile/"+"DJ.mp3";        File file =new File(savePathString);        if (!file.exists()) {
               try {
                   file.createNewFile();            } catch (IOException e) {
                   // TODO Auto-generated catch block                e.printStackTrace();            }        }        /*         * 向SD卡中写入文件,用Handle传递线程         */        Message message=new Message();        try {
               outputStream=new FileOutputStream(file);            byte [] buffer=new byte[1024*4];            FileLength=connection.getContentLength();            message.what=0;            handler.sendMessage(message);            while (DownedFileLength
   
    ", DownedFileLength+"");                Message message1=new Message();                message1.what=1;                handler.sendMessage(message1);            }            Message message2=new Message();            message2.what=2;            handler.sendMessage(message2);        } catch (FileNotFoundException e) {
               // TODO Auto-generated catch block            e.printStackTrace();        } catch (IOException e) {
               // TODO Auto-generated catch block            e.printStackTrace();        }    }}第二步  activity-main.xml
    
        
         
         
     
    第三步：权限   
        
        
            android:usesCleartextTraffic="true"
   

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