代码库/下载服务

摘自于第一行代码

1.定义一个回调接口，用于下载过程中各种状态的的监听和回调

void onProgress(int progress);

void onSuccess();

void onFailed();

void onPaused();

void onCanceled();

2.为了更方便在子线程中对UI进行操作，使用AsyncTask

    在doInBackground方法中，取出下载的URL地址，然后指定下载到SD卡的Download目录,若存在文件，则读取已下载的字节数，然后用getContentLength方法来验证下载文件的总长度，0则有问题，长度等于已下载文件长度，说明文件下载完成。

    用OkHttp发送网络请求，添加一个header，用于告知服务器从哪个字节开始下载

    接下来读取服务器响应的数据，使用java流程。

    判断用户有无暂定，取消的操作，然后调用publishProgress方法进行通知

OkHttpClient client=new OkHttpClient();
    Request request=new Request.Builder()
            .addHeader("Ranger","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); //跳过已下载的字节
        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);
                //计算已下载的百分比
                int progress=(int)((total+downloadedLength)*100/contentLength);
                publishProgress(progress);
            }
        }
        response.body().close();
        return TYPE_SUCCESS;
    }
}catch (IOException 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;

3.建立下载服务，并用NotificationManager的notify方法触发这个通知

4.在MainAc中绑定service

代码如下

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 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;
            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;
            stopForeground(true);
            Toast.makeText(DownloadService.this,"Paused",Toast.LENGTH_SHORT).show();
        }

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

        }
    };

    private DownloadBinder mBinder=new DownloadBinder();

    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("Download....",0));
                Toast.makeText(DownloadService.this,"Download.....",Toast.LENGTH_SHORT).show();
            }
        }

        public  void pauseDownload(){
            if (downloadTask!=null){
                downloadTask.pauseDownload();
            }
        }
        public void cancelDownload(){
            if (downloadTask!=null){
                downloadTask.cancelDownload();
            }else {
                    //取消下载时许将文件删除，并将通知关闭
                    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 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.setContentTitle(progress+"%");
            builder.setProgress(100,progress,false);
        }
        return builder.build();
    }

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


}

DownTask

import android.os.AsyncTask;
import android.os.Environment;

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 YRC on 2017/2/21.
 */

public class DownloadTask extends AsyncTask {

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

    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... strings) {
        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=strings[0];
            String fileName=downloadUrl.substring(downloadUrl.lastIndexOf("/"));
            String directory= Environment
                    .getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).getPath();
            file=new File(directory+fileName);
            if (file.exists()){
                downloadedLength=file.length();
            }
            long contentLength=getContentLength(downloadUrl);
            if (contentLength==0){
                return TYPE_FAILED;
            }else if (contentLength==downloadedLength){
                //已下载字节和文件总字节相等，说明已经下载完成了
                return TYPE_SUCCESS;
            }
            OkHttpClient client=new OkHttpClient();
            Request request=new Request.Builder()
                    .addHeader("Ranger","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); //跳过已下载的字节
                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);
                        //计算已下载的百分比
                        int progress=(int)((total+downloadedLength)*100/contentLength);
                        publishProgress(progress);
                    }
                }
                response.body().close();
                return TYPE_SUCCESS;
            }
        }catch (IOException 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_FAILED:
                listener.onFailed();
                break;
            case TYPE_PAUSED:
                listener.onPaused();
                break;
            case TYPE_CANCELED:
                listener.onCanceled();
                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();
            return contentLength;
        }
        return 0;
    }
}

MainAc

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;

public class MainActivity extends AppCompatActivity implements View.OnClickListener{
    private DownloadService.DownloadBinder downloadBinder;
    private ServiceConnection connection=new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName componentName, IBinder iBinder) {
            downloadBinder= (DownloadService.DownloadBinder) iBinder;
        }

        @Override
        public void onServiceDisconnected(ComponentName componentName) {

        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button startDownload= (Button) findViewById(R.id.start_download);
        Button pauseDownload= (Button) findViewById(R.id.pause_download);
        Button cancelDownload= (Button) findViewById(R.id.cancel_download);
        startDownload.setOnClickListener(this);
        pauseDownload.setOnClickListener(this);
        cancelDownload.setOnClickListener(this);
        Intent intent=new Intent(MainActivity.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 view) {
        if (downloadBinder==null){
            return;
        }
        switch (view.getId()){
            case R.id.start_download:
                String url="http://raw.githubusercontent.com/guolindev/eclipse/master/eclipse-inst-win64.exe";
                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:
        }
    }

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

DownloadListener

public  interface DownloadListener {

    void onProgress(int progress);

    void onSuccess();

    void onFailed();

    void onPaused();

    void onCanceled();


}