用AsyncTask实现断点续传

       在学习四大组件之一的service时，正好可以利用asyncTask 和OKhttp来进行断点续传，并在手机的前台显示下载进度。

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    尝试下载的是Oracle官网上的jdk1.7

    在AS中使用OKhttp，只需要简单的在app/build.gradle里加入一句就可以了，如下代码，就最后一行加入即可

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:3.8.1'
}

1、DownloadTask.java

    在该类里主要进行了文件是否存在，存在的话是否已经下载完成等判断，还有利用OKhttp进行文件下载，最经典是是在文件写入RandomAccessFile里时，判断的当前状态，如果是isPaused是true,表示点了暂停键，那么就要暂停下载等等判断；还有使用asyncTask的方法，传递进度给前置通知显示下载进度。

package com.yuanlp.servicebestproject;

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 原立鹏 on 2017/7/1.
 */

public class DownloadTask extends AsyncTask {
    private static final String TAG = "DownloadTask";

    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_CANCELD=3;

    private DownLoadListener listener;

    private boolean isCanceld=false;
    private boolean isPaused=false;
    private int lastProgress;

    public DownloadTask(DownLoadListener downloadListener){
        this.listener=downloadListener;
    }
    @Override
    protected Integer doInBackground(String... params) {
        InputStream is=null;
        RandomAccessFile savedFile=null;  //RandomAccessFile 用来访问指定的文件的
        File file=null;
        try{
            long downloadLength=0;  //记录已经下载的文件中长度
            String downloadUrl=params[0];
            String fileName=downloadUrl.substring(downloadUrl.lastIndexOf("/")); //获取文件名
            String directory= Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).getPath(); //获取文件保存路径
            file=new File(directory+fileName);  //创建文件

            //如果文件存在
            if (file.exists()){
                downloadLength=file.length();  //获取已经存在的文件大小
            }
            long contentLength=getContentLength(downloadUrl);  //获取文件总大小
            if (contentLength==0){
                return TYPE_FAILED;  //已下载的文件异常，返回失败
            }else if (downloadLength==contentLength){
                return TYPE_SUCCESS;  //说明下载的文件和总长度一样，返回成功
            }
            OkHttpClient client=new OkHttpClient();
            Request request=new Request.Builder()
                    .header("RANGE","bytes="+downloadLength+"-")  //从下载之后的地方开始
                    .url(downloadUrl)
                    .build();
            Response response=client.newCall(request).execute();
            if (response!=null){
                is=response.body().byteStream();  //获取response中的输入流
                savedFile=new RandomAccessFile(file,"rw");  //开始访问指定的文件
                savedFile.seek(downloadLength);  //跳过已经下载的文件长度
                byte[] b=new byte[1024];
                long total=0;
                int len;
                while ((len=is.read(b))!=-1){   //这个时候说明还没有读取到输入流的最后
                    if (isCanceld){  //说明取消了下载
                        return TYPE_FAILED;
                    }else if (isPaused){
                        return TYPE_PAUSED;
                    }else{
                        total+=len;
                        savedFile.write(b,0,len);
                        int progress= (int) ((total+downloadLength)*100/contentLength);  //计算下载的百分比
                        publishProgress(progress);  //调用onProgressUpdate()更新下载进度
                    }
                }
                response.body().close();  //关闭reponse
                return TYPE_SUCCESS;  //返回下载成功
            }

        }catch (Exception e){
            e.printStackTrace();
        }finally {
            try{
                if (is!=null){
                    is.close();  //关闭输入流
                }
                if (savedFile!=null){
                    savedFile.close();  //关闭查看文件
                }
                if (isCanceld&&file!=null){
                    file.delete();  //如果点击取消下载并且已经下载的文件存在，就删除文件
                }
            }catch(Exception e){
                e.printStackTrace();
            }
        }
        return TYPE_FAILED;
    }


    /**
     * 在doInBackground 里调用ublishProgress时调用此方法，更新UI进度
     * @param values
     */
    public void onProgressUpdate(Integer... values){
        int progress=values[0];  //获取传过来的百分比值
        if (progress>lastProgress){
            listener.onProgress(progress);
        }

    }

    /**
     * 当doInBackground 执行完成时，调用此方法
     * @param status
     */
    public void onPostExecute(Integer status){

        switch (status){
            case TYPE_SUCCESS:
                listener.onSuccess();
                break;
            case TYPE_FAILED:
                listener.onFailed();
                break;
            case TYPE_PAUSED:
                listener.onPause();
                break;
            case TYPE_CANCELD:
                listener.onCancled();
                break;
            default:
                break;
        }
    }

    /**
     * 按下暂停键时调用,暂停下载
     */
    public void pausedDownload(){
        isPaused=true;

    }

    public void canceledDownload(){

        isCanceld=true;
    }


    /**
     * 根据传入的rul地址，获取文件总长度
     * @param url
     * @return
     */
    public long getContentLength(String url) throws IOException {
        OkHttpClient client=new OkHttpClient();
        Request request=new Request.Builder()
                .url(url)
                .build();
        Response reponse=client.newCall(request).execute();
        if (reponse!=null&&reponse.isSuccessful()){  //成功返回reponse
            long contentLength=reponse.body().contentLength();  //获取文件中长度
            return contentLength;

        }
            return 0;
    }
}

2、DownloadService.java

    在这个里面，主要是根据Mainactivity里的指令，进行调用downloadTask类里的方法，以及调用前置通知，显示进度。

package com.yuanlp.servicebestproject;

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 static final String TAG = "DownloadService";
    private DownloadTask downloadTask;
    private String downloadUrl;

    public DownloadService() {
    }

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

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

        @Override
        public void onSuccess() {
            downloadTask=null;
            //下载成功后，将前台通知关闭，并创建一个下载成功的通告
            stopForeground(true);

            getNotifactionManager().notify(1,getNotification("Download Success",-1));
            Toast.makeText(DownloadService.this,"Download Success",Toast.LENGTH_SHORT).show();
        }

        @Override
        public void onFailed() {
            downloadTask=null;
            stopForeground(true);
            getNotifactionManager().notify(1,getNotification("Down Failed",-1));
            Toast.makeText(DownloadService.this,"Down Failed",Toast.LENGTH_SHORT).show();

        }

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

        }

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

        }
    };

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

            }
        }

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

        public void cancelDownload(){
            if (downloadTask==null){
                downloadTask.canceledDownload();
            }else{
                if (downloadUrl!=null){
                    String filename=downloadUrl.substring(downloadUrl.lastIndexOf("/"));
                    String directory= Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).getPath();
                    File file=new File(directory);
                    if (file.exists()){
                        file.delete();
                    }
                    getNotifactionManager().cancel(1);
                    stopForeground(true);
                    Toast.makeText(DownloadService.this,"Canceled",Toast.LENGTH_SHORT).show();
                }
            }

        }
    }

    private NotificationManager getNotifactionManager(){
        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();
    }


}

3、MainActivity.java

    主要是进行了开启服务和绑定服务，对应按钮的操作，以及运行时权限申请。

package com.yuanlp.servicebestproject;

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.support.v4.app.ActivityCompat;
import android.support.v4.content.ContextCompat;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {
    private static final String TAG = "MainActivity";

    private DownloadService.DownloadBinder mDownloadBinder;
    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Intent intent=new Intent(this,DownloadService.class);
        startService(intent);
        bindService(intent,conn,BIND_AUTO_CREATE);

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

        @Override
        public void onServiceDisconnected(ComponentName name) {

        }
    };

    /**
     * 点击开始下载
     * @paam view
     */
    public void startService(View view){
        Toast.makeText(this,"点击下载",Toast.LENGTH_SHORT).show();
        if (mDownloadBinder==null){
            return;
        }
        String url="http://download.java.net/java/jdk9/archive/176/binaries/jdk-9+176_windows-x86_bin.exe";
        mDownloadBinder.startDownload(url);
    }

    public void pauseService(View view){
        if (mDownloadBinder==null){
            return;
        }
        mDownloadBinder.pauseDownload();
    }

    public void cancelSerivce(View view){
        if (mDownloadBinder==null){
            return;
        }
        mDownloadBinder.cancelDownload();
    }

    public void onRequestPermissiosResult(int requestCode,String[] permissions,int[] grantResult){
        switch (requestCode){
            case 1:
                if (grantResult.length>0&&grantResult[0]!=PackageManager.PERMISSION_GRANTED){
                    Toast.makeText(this,"拒绝授权将无法使用程序",Toast.LENGTH_SHORT).show();
                    finish();
                }
                break;
            default:
        }
    }

    public void onDestroy(){
        super.onDestroy();
        unbindService(conn);
    }
}

本文名称：用AsyncTask实现断点续传
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