Android AsyncTask实现下载文件功能

MainActivity

package com.example.asynctask;

import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.ProgressBar;
import android.widget.TextView;

import androidx.appcompat.app.AppCompatActivity;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URL;
import java.net.URLConnection;

public class MainActivity extends AppCompatActivity {

    public static final int progress = 0;
    public static final String APK_URL = "http://download.sj.qq.com/upload/connAssitantDownload/upload/MobileAssistant_1.apk";
    private ProgressBar progressBar;
    private Button button;
    private TextView textView;

    private static final String TAG = "MainActivity";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);


        progressBar = (ProgressBar) findViewById(R.id.progressBar);
        button = (Button) findViewById(R.id.button);
        textView = (TextView) findViewById(R.id.textView);
        progressBar.setProgress(progress);


        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                new Myasynctask().execute("imooc", "good");
            }
        });


    }


    public class Myasynctask extends AsyncTask<String, Integer, Boolean> {
        String path;

        /**
         * 开始调用
         */
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            textView.setText("下载中");
            button.setText("下载中");
            progressBar.setProgress(progress);

        }

        @Override
        protected void onProgressUpdate(Integer... values) {
            super.onProgressUpdate(values);
            progressBar.setProgress(values[0]);
            button.setText("下载中：" + values[0] + "%");
        }

        /**
         * 结束时调用
         *
         * @param aBoolean
         */
        @Override
        protected void onPostExecute(Boolean aBoolean) {
            super.onPostExecute(aBoolean);
            if (aBoolean) {
                textView.setText("下载完成:" + path);
                button.setText("点击下载");
            }
        }

        @Override
        protected Boolean doInBackground(String... strings) {
            try {
                URL url = new URL(APK_URL);
                URLConnection urlConnection = url.openConnection();

                InputStream inputStream = urlConnection.getInputStream();

                path = getExternalFilesDir(null).getPath() + "/" + "imooc.apk";
                File file = new File(path);

                if (file.exists()) {
                    file.delete();
                }

                //获取文件的总长度
                int contentLength = urlConnection.getContentLength();
                //获取输入流
                InputStream in = urlConnection.getInputStream();
                byte[] b = new byte[1024];
                int DownloadLength = 0; //用于保存实时下载长度
                int len = 0;
                OutputStream outputStream = new FileOutputStream(path);
                while ((len = in.read(b)) > -1) {
                    outputStream.write(b, 0, len);
                    DownloadLength += len;
                    publishProgress(DownloadLength * 100 / contentLength);
                }


            } catch (IOException e) {
                e.printStackTrace();
            }


            return true;
        }


    }
}

AndroidManifest.xml

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

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="20dp"
    android:orientation="vertical"
    tools:context=".MainActivity">


    <ProgressBar
        android:id="@+id/progressBar"
        style="?android:attr/progressBarStyleHorizontal"
        android:layout_width="match_parent"
        android:layout_height="20dp"/>

    <Button
        android:id="@+id/button"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="10dp"
        android:text="点击下载" />

    <TextView
        android:id="@+id/textView"
        android:layout_marginTop="10dp"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="准备下载" />
</LinearLayout>

扩展：多文件for循环下载 取消下载

private AsyncTask<String, Integer, Boolean> execute;
//主线程启动AsyncTask
execute = new Myasynctask().execute(APK_URL, APK_URL, APK_URL);

//通过按钮点击取消按钮 按钮监听下的代码
boolean flag = execute.cancel(true);
String str;
if (flag) {
    str = "取消成功";
}
else {
    str = "取消失败";
}
Toast.makeText(MainActivity.this, str , Toast.LENGTH_LONG).show();

//在doInBackground方法内就可以判断了
if(isCancelled()){
 return false;
}