基于AsyncTask进行异步下载(service后台服务执行并可查看下载进度)

本文章介绍使用AsyncTask异步下载，为了保证任务不被回收，使用service后台服务去执行下载任务，并用通知的方式查看下载进进度。

1.下载任务：

首先我们使用AsyncTask来完成下载任务。在doInBackground方法中编写逻辑。

我们首先确定保存路径，并查看是否存在需要下载的文件，如果存在了确定文件的长度。然后获取需要下载的文件长度，如果需要下载的文件长度是0，那么文件有问题返回错误，如果需要下载的文件长度和已经下载的长度一致说明已经存在，返回成功。然后是下载操作：需要注意的是添加了：.addHeader("RANGE", "bytes=" + downloadLength + "-" + contentLength)方法，意思是告诉服务器从哪里还是下载，截止到哪里。这是断点续传的关键一步。但是服务器需要配合，不然怎么操作都行从头开始。在后面就是保存下载的数据了，并计算进度，通过publishProgress(progress);方法把进度传出去。

在onProgressUpdate方法中，通过接口毁掉将更新进度。

在onPostExecute中将，通过接口毁掉跟新状态。

package com.example.mydownload;

import android.os.AsyncTask;
import android.os.Environment;
import android.util.Log;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.RandomAccessFile;

import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;

public class DownloadTask extends AsyncTask<String, Integer, Integer> {
    public static final int TYPE_SUCCESS = 0;
    public static final int TYPE_FAILED = 1;//失败
    public static final int TYPE_PAUSED = 2;
    public static final int TYPE_CANCELED = 3;
    private DownloadListener listener;
    private boolean isCancel = false;
    private boolean isPaused = false;
    private int lastProgress;

    public DownloadTask(DownloadListener listener) {
        this.listener = listener;
    }

    @Override
    protected Integer doInBackground(String... params) {
        InputStream is = null;
        File file = null;
        RandomAccessFile saveFile = null;
        try {
            //记录下载文件长度
            long downloadLength = 0;
            String dowmloadUrl = params[0];
            String fileName = dowmloadUrl.substring(dowmloadUrl.lastIndexOf("/"));
            //下载路径
            String directory = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).getPath();
            //如果文件存在 记录文件的长度
            file = new File(directory + fileName);
            if (file.exists()) {
                downloadLength = file.length();
            }

            //获取文件长度
            long contentLength = getContentLength(dowmloadUrl);
            if (contentLength == 0) {
                //文件总长度是0 说明有问题直接返回错误哦
                return TYPE_FAILED;
            } else if (contentLength <= downloadLength) {
                //已下载字节和文件总字节相同，说明下载完成。
                return TYPE_SUCCESS;
            }

            OkHttpClient client = new OkHttpClient();
            Request request = new Request.Builder()
                    //断点下载，从哪个字节开始下载 range
//                    .addHeader("RANGE", "bytes=" + downloadLength + "-")
                    .addHeader("RANGE", "bytes=" + downloadLength + "-" + contentLength)
                    .url(dowmloadUrl)
                    .build();
            Response response = client.newCall(request).execute();
            if (response != null) {
                is = response.body().byteStream();
                saveFile = new RandomAccessFile(file, "rw");
                saveFile.seek(downloadLength);//跳过已下载字节
                byte[] b = new byte[1024];
                int total = 0;
                int len;
                while ((len = is.read(b)) != -1) {
                    if (isCancel) {//取消加载任务    //中途有人点击取消
                        return TYPE_CANCELED;
                    } else if (isPaused) {  //中途有人点击暂停
                        return TYPE_PAUSED;
                    } else {
                        total += len;
                        saveFile.write(b, 0, len);
                        //计算下载的百分比
                        int progress = (int) ((total + downloadLength) * 100 / contentLength);

                        publishProgress(progress);
                    }
                }
                response.body().close();
                return TYPE_SUCCESS;
            }

        } catch (Exception e) {

        } finally {


            try {
                if (is != null)
                    is.close();
                if (saveFile != null)
                    saveFile.close();
                if (isCancel && file != null)
                    file.delete();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return TYPE_FAILED;
    }


    @Override
    protected void onProgressUpdate(Integer... values) {
        int progress = values[0];
        if (progress > lastProgress) {
            listener.onProgess(progress);
            lastProgress = progress;
        }
    }

    @Override
    protected void onPostExecute(Integer integer) {
        switch (integer) {
            case TYPE_SUCCESS:
                listener.onSuccess();
                break;
            case TYPE_FAILED:
                listener.onFailed();
                break;
            case TYPE_PAUSED:
                listener.onPaused();
                break;
            case TYPE_CANCELED:
                listener.onCanceled();
                break;
        }
    }

    public void pauseDownload() {
        isPaused = true;
    }

    public void cancelDownlag() {
        isCancel = true;
    }

    private long getContentLength(String dowmloadUrl) throws IOException {
        OkHttpClient client = new OkHttpClient();
        Request request = new Request.Builder()
                .url(dowmloadUrl)
                .build();
        Response response = client.newCall(request).execute();
        if (response != null && response.isSuccessful()) {
            long contentLength = response.body().contentLength();
            response.close();
            return contentLength;
        }
        return 0;

    }
} 

2.开启服务

为了避免下载任务在执行中被回收，我们采用使用服务区下载。通过DownloadBinder区开启异步下载。并在service中实现接口回调。

package com.example.mydownload;

import android.app.Notification;
import android.app.NotificationManager;
import android.app.PendingIntent;
import android.app.Service;
import android.content.Intent;
import android.database.sqlite.SQLiteDoneException;
import android.graphics.BitmapFactory;
import android.os.Binder;
import android.os.Environment;
import android.os.IBinder;
import android.widget.Toast;

import androidx.core.app.NotificationCompat;

import java.io.File;

public class DownloadService extends Service {
    private DownloadTask downloadTask;
    private String downloadUrl;
    private DownloadListener listener = new DownloadListener() {
        @Override
        public void onProgess(int progress) {
            getNotificationManager().notify(1, getNotification("Downloading...", progress));
        }

        @Override
        public void onSuccess() {
            downloadTask = null;
            //下载成功通知前台关闭通知，并创建下一个通知
            stopForeground(true);
            getNotificationManager().notify(1, getNotification("Download Success", -1));
            Toast.makeText(DownloadService.this, "Download Success", Toast.LENGTH_SHORT).show();

        }

        @Override
        public void onFailed() {
            downloadTask = null;
            //下载失败时将前台服务关闭，并创建下一个失败通知
            stopForeground(true);
            getNotificationManager().notify(1, getNotification("Download Failed", -1));
            Toast.makeText(DownloadService.this, "Download Failed", Toast.LENGTH_SHORT).show();

        }

        @Override
        public void onPaused() {
            downloadTask = null;
            Toast.makeText(DownloadService.this, "Download Paused", Toast.LENGTH_SHORT).show();

        }

        @Override
        public void onCanceled() {
            downloadTask = null;
            stopForeground(true);
            Toast.makeText(DownloadService.this, "Download Canceled", Toast.LENGTH_SHORT).show();

        }
    };

    public DownloadService() {
    }


    private DownloadBinder mBinder = new DownloadBinder();

    @Override
    public IBinder onBind(Intent intent) {
        return mBinder;
    }

    class DownloadBinder extends Binder {
        public void startDownload(String url) {
            if (downloadTask == null) {
                downloadUrl = url;
                downloadTask = new DownloadTask(listener);
                downloadTask.execute(downloadUrl);
                startForeground(1, getNotification("下载...", 0));
                Toast.makeText(DownloadService.this, "Downloading...", Toast.LENGTH_SHORT).show();
            }
        }

        public void pausedDownload() {
            if (downloadTask != null) {
                downloadTask.pauseDownload();
            }
        }

        public void cancelDownload() {
            if (downloadTask != null) {
                downloadTask.cancelDownlag();
            } else {
                if (downloadUrl != null) {
                    //取消下载时 需要将文件删除，并将通知关闭
                    String fileName = downloadUrl.substring(downloadUrl.lastIndexOf("/"));
                    //下载路径
                    String directory = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).getPath();
                    File file = new File(directory + fileName);
                    //如果文件存在 记录文件的长度
                    if (file.exists()) {
                        file.delete();
                    }
                    getNotificationManager().cancel(1);
                    stopForeground(true);
                    Toast.makeText(DownloadService.this, "Cancel", Toast.LENGTH_SHORT).show();

                }
            }
        }

    }

    private NotificationManager getNotificationManager() {
        return (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
    }

    private Notification getNotification(String title, int progress) {
        Intent intent = new Intent(this, MainActivity.class);
        PendingIntent pi = PendingIntent.getActivity(this, 0, intent, 0);
        NotificationCompat.Builder builder = new NotificationCompat.Builder(this);
        builder.setSmallIcon(R.mipmap.ic_launcher);
        builder.setLargeIcon(BitmapFactory.decodeResource(getResources(), R.mipmap.ic_launcher));
        builder.setContentIntent(pi);
        builder.setContentTitle(title);
        if (progress > 0) {
            //当progress >0 或 =0 的时候才需要显示现在进度
            builder.setContentText(progress + "%");
            builder.setProgress(100, progress, false);

        }
        return builder.build();
    }
} 

3.接口

public interface DownloadListener {
    void onProgess(int progress);

    void onSuccess();

    void onFailed();

    void onPaused();

    void onCanceled();
} 

4.调用：

package com.example.mydownload;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.ActivityCompat;
import androidx.core.content.ContextCompat;

import android.Manifest;
import android.content.ComponentName;
import android.content.Intent;
import android.content.ServiceConnection;
import android.content.pm.PackageManager;
import android.os.Bundle;
import android.os.IBinder;
import android.os.health.PackageHealthStats;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {
    private DownloadService.DownloadBinder downloadBinder;
    private ServiceConnection connection = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {
            downloadBinder = (DownloadService.DownloadBinder) service;
        }

        @Override
        public void onServiceDisconnected(ComponentName name) {

        }
    };
    private Intent intent;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button start = findViewById(R.id.start);
        Button pause = findViewById(R.id.pause);
        Button cancle = findViewById(R.id.cancle);

        intent = new Intent(this, DownloadService.class);
        startService(intent);//启动服务
        bindService(intent, connection, BIND_EXTERNAL_SERVICE);//绑定服务
        if (ContextCompat.checkSelfPermission(MainActivity.this, Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
            ActivityCompat.requestPermissions(MainActivity.this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, 1);
        }

        start.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String s = "http://mirrors.neusoft.edu.cn/eclipse/oomph/epp/2020-06/R/eclipse-inst-win64.exe";
                downloadBinder.startDownload(s);
            }
        });
        pause.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                downloadBinder.pausedDownload();
            }
        });
        cancle.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                downloadBinder.cancelDownload();
            }
        });


    }

    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        switch (requestCode) {
            case 1:
                if (grantResults.length > 0 && grantResults[0] != PackageManager.PERMISSION_GRANTED) {
                    Toast.makeText(this, "请开启权限", Toast.LENGTH_SHORT).show();
                    finish();
                }
                break;
        }
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        stopService(intent);
        unbindService(connection);
    }
} 

5.对应的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:orientation="vertical"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/start"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="下载" />

    <Button
        android:id="@+id/pause"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="暂停" />

    <Button
        android:id="@+id/cancle"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="取消" />

</LinearLayout>

6.权限：

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

转发表明出处：https://blog.csdn.net/qq_35698774/article/details/107729677

点击下载源码

android互助群：

感谢：郭霖的《第一行代码 第二版》

本文地址：https://blog.csdn.net/qq_35698774/article/details/107729677