Android下载示例

Android下载示例

菜鸟一只，写点文章，保证自己学到的东西不会忘记

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添加OkHttp依赖

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
        exclude group: 'com.android.support', module: 'support-annotations'
    })
    compile 'com.android.support:appcompat-v7:25.3.1'
    compile 'com.android.support.constraint:constraint-layout:1.0.2'
    testCompile 'junit:junit:4.12'
    compile 'com.squareup.okhttp3:okhttp:3.4.1'
}

网络功能采用OkHttp来实现

定义回调接口

public interface DownloadListener {

    void onProgress(int progress);

    void onSuccess();

    void onFailed();

    void onPause();

    void onCanceled();

}

一共定义5个回调方法，onProgress()方法用于通知当前的下载进度，onSuccess()方法用于通知下载完成事件，onFailed()用于通知下载失败事件，onPause()用于通知下载暂停事件，onCanceled()用于通知下载取消事件。

编写下载功能

通过AsyncTask来实现下载功能

package com.slience.downloaddemo.downloadtask;

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

import com.slience.downloaddemo.downloadinterface.DownloadListener;

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;

/**
 * Created by Slience on 2017/10/20.
 */

public class DownloadTask extends AsyncTask {

    public static final int TYPE_SUCCESS = 0;
    public static final int TYPE_FAILED = 1;
    public static final int TYPE_PAUSED = 2;
    public static final int TYPE_CANCELED = 3;

    public static final String TAG = "DownloadTask";

    private DownloadListener listener;

    private boolean isCanceled = false;

    private boolean isPaused = false;

    private int lastProgress;

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

    @Override
    protected Integer doInBackground(String... params) {

        InputStream is = null;
        RandomAccessFile savedFile = null;
        File file = null;
        try {
            long downloadedLength = 0;          //记录已下载的文件长度
            String downloadUrl = params[0];

            Log.i(TAG , "DownloadUrl = " + downloadUrl);

            String fileName = downloadUrl.substring(downloadUrl.lastIndexOf("/"));

            Log.i(TAG , "FileName = " + fileName);

            String dirctory = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).getPath();

            Log.i(TAG , "Dirctory = " + dirctory);

            file = new File(dirctory + fileName);
            if(file.exists()){
                downloadedLength = file.length();
            }

            long contentLength = getContentLength(downloadUrl);

            Log.i(TAG , "ContentLength = " + contentLength);

            if(contentLength == 0){
                return TYPE_FAILED;
            }else if(contentLength == downloadedLength){
                return TYPE_SUCCESS;
            }

            OkHttpClient client = new OkHttpClient();
            Request request = new Request.Builder()
                    .addHeader("RANGE" , "bytes = " + downloadedLength + "-")
                    .url(downloadUrl)
                    .build();
            Response response = client.newCall(request).execute();
            if(response != null){
                is = response.body().byteStream();
                savedFile = new RandomAccessFile(file , "rw");
                savedFile.seek(downloadedLength);
                byte[] b = new byte[1024];
                int total = 0;
                int len;
                while((len = is.read(b)) != -1){
                    if(isCanceled){
                        return TYPE_CANCELED;
                    }else if(isPaused){
                        return TYPE_PAUSED;
                    }else{
                        total += len;
                        savedFile.write(b , 0 , len);
                        //计算下载百分比
                        int progress = (int)((total + downloadedLength) * 100 / contentLength);
                        publishProgress(progress);
                    }
                }
                response.body().close();
                return TYPE_SUCCESS;
            }
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            try {
                if(is != null){
                    is.close();
                }
                if(savedFile != null){
                    savedFile.close();
                }
                if(isCanceled && file != null){
                    file.delete();
                }
            }catch (Exception e){
                e.printStackTrace();
            }
        }

        return TYPE_FAILED;
    }

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

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

                break;
        }
    }

    public void pauseDownload(){
        isPaused = true;
    }

    public void cancelDownload(){
        isCanceled = true;
    }

    private long getContentLength(String downloadUrl) throws IOException{
        OkHttpClient client = new OkHttpClient();
        Request request = new Request.Builder()
                .url(downloadUrl)
                .build();
        Response response = client.newCall(request).execute();
        if(response != null && response.isSuccessful()){
            long contentLength = response.body().contentLength();
            response.close();
            Log.i(TAG , "response is not null");
            return contentLength;
        }else{
            Log.i(TAG , "response is null");
        }

        return 0;
    }
}

AsyncTask三个泛型参数，第一个String类型参数表示在执行AsyncTask的时候需要传入一个字符串参数给后台任务，第二个int类型参数表示用整数来作为进度显示单位，第三个int类型参数用来反馈执行结果

创建下载服务

package com.slience.downloaddemo.downloadservice;

import android.app.Notification;
import android.app.NotificationManager;
import android.app.PendingIntent;
import android.app.Service;
import android.content.Intent;
import android.graphics.BitmapFactory;
import android.os.Binder;
import android.os.Environment;
import android.os.IBinder;
import android.support.v4.app.NotificationCompat;
import android.widget.Toast;

import com.slience.downloaddemo.MainActivity;
import com.slience.downloaddemo.R;
import com.slience.downloaddemo.downloadinterface.DownloadListener;
import com.slience.downloaddemo.downloadtask.DownloadTask;

import java.io.File;

public class DownloadService extends Service {

    private DownloadTask downloadTask;

    private String downloadUrl;

    private DownloadListener listener = new DownloadListener() {
        @Override
        public void onProgress(int progress) {
            getNotificationManager().notify(1,getNotification("Downloading..." , progress));
        }

        @Override
        public void onSuccess() {
            downloadTask = null;
            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;
            //下载失败将前台服务关闭，并创建一个下载失败的通知
            stopForeground(true);
            getNotificationManager().notify(1,getNotification("Download Failed" , -1));
            Toast.makeText(DownloadService.this , "Download Failed" , Toast.LENGTH_SHORT).show();
        }

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

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

    public DownloadService() {
    }

    private DownloadBinder mBinder = new DownloadBinder();

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

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

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

        public void cancelDownload(){
            if(downloadTask != null){
                downloadTask.cancelDownload();
            }else{
                if(downloadUrl != null){
                    String fileName = downloadUrl.substring(downloadUrl.lastIndexOf("/"));
                    String directory = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).getPath();
                    File file = new File(directory + fileName);
                    if(file.exists()){
                        file.delete();
                    }
                    getNotificationManager().cancel(1);
                    stopForeground(true);
                    Toast.makeText(DownloadService.this , "Canceled" , 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){
            builder.setContentText(progress + "%");
            builder.setProgress(100 , progress , false);
        }
        return builder.build();
    }
}

getNotificationManager()方法用来调用NotificationManager的notify()方法，触发通知不停的更新当前的下载进度
DownloadBinder中提供了startDownload()，pauseDownload()，cancelDownload()三个方法，分别用于开始下载，暂停下载，和取消下载

MainActivity

package com.slience.downloaddemo;

import android.Manifest;
import android.content.ComponentName;
import android.content.Intent;
import android.content.ServiceConnection;
import android.content.pm.PackageManager;
import android.os.IBinder;
import android.support.annotation.NonNull;
import android.support.v4.app.ActivityCompat;
import android.support.v4.content.ContextCompat;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

import com.slience.downloaddemo.downloadservice.DownloadService;

public class MainActivity extends AppCompatActivity implements View.OnClickListener{

    private DownloadService.DownloadBinder downloadBinder;
    private Button startDwonload , pauseDownload , cancelDownload;

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

        @Override
        public void onServiceDisconnected(ComponentName name) {

        }
    };

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

        startDwonload = (Button)findViewById(R.id.start_download);
        pauseDownload = (Button)findViewById(R.id.pause_download);
        cancelDownload = (Button)findViewById(R.id.cancel_download);
        startDwonload.setOnClickListener(this);
        pauseDownload.setOnClickListener(this);
        cancelDownload.setOnClickListener(this);

        Intent intent = new Intent(this , DownloadService.class);
        startService(intent);
        bindService(intent , connection , BIND_AUTO_CREATE);        //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);
        }
    }

    @Override
    public void onClick(View v) {
        if(downloadBinder == null){
            return;
        }
        switch (v.getId()){
            case R.id.start_download:
                String url = "http://imtt.dd.qq.com/16891/FDC777ED452DD64653166EDFBF9273D4.apk";
                downloadBinder.startDownload(url);
                break;
            case R.id.pause_download:
                downloadBinder.pauseDownload();
                break;
            case R.id.cancel_download:
                downloadBinder.cancelDownload();
                break;
            default:

                break;
        }
    }

    @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 , "拒绝权限将无法使用程序" , Toast.LENGTH_SHORT).show();
                    finish();
                }
                break;
            default:

                break;
        }
    }

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

由于程序使用了网络和调用SD卡的功能，需要在Manifest中添加INTERNET和WRITE_EXTERNAL_STORAGE这两个权限

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