【移動應用開發技術】用AsyncTask實現斷點續傳

在學習四大組件之一的service時，正好可以利用asyncTask和OKhttp來進行斷點續傳，并在手機的前臺顯示下載進度。

嘗試下載的是Oracle官網上的jdk1.7

在AS中使用OKhttp，只需要簡單的在app/build.gradle里加入一句就可以了，如下代碼，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

在該類里主要進行了文件是否存在，存在的話是否已經下載完成等判斷，還有利用OKhttp進行文件下載，最經典是是在文件寫入RandomAccessFile里時，判斷的當前狀態，如果是isPaused是true,表示點了暫停鍵，那么就要暫停下載等等判斷；還有使用asyncTask的方法，傳遞進度給前置通知顯示下載進度。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

原立鵬

on

2017/7/1.

*/

public

class

DownloadTask

extends

AsyncTask<String,Integer,Integer>

{

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

用來訪問指定的文件的

File

file=null;

try{

long

downloadLength=0;

//記錄已經下載的文件中長度

String

downloadUrl=params[0];

String

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

//獲取文件名

String

directory=

Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).getPath();

//獲取文件保存路徑

file=new

File(directory+fileName);

//創建文件

//如果文件存在

if

(file.exists()){

downloadLength=file.length();

//獲取已經存在的文件大小

}

long

contentLength=getContentLength(downloadUrl);

//獲取文件總大小

if

(contentLength==0){

return

TYPE_FAILED;

//已下載的文件異常，返回失敗

}else

if

(downloadLength==contentLength){

return

TYPE_SUCCESS;

//說明下載的文件和總長度一樣，返回成功

}

OkHttpClient

client=new

OkHttpClient();

Request

request=new

Request.Builder()

.header("RANGE","bytes="+downloadLength+"-")

//從下載之后的地方開始

.url(downloadUrl)

.build();

Response

response=client.newCall(request).execute();

if

(response!=null){

is=response.body().byteStream();

//獲取response中的輸入流

savedFile=new

RandomAccessFile(file,"rw");

//開始訪問指定的文件

savedFile.seek(downloadLength);

//跳過已經下載的文件長度

byte[]

b=new

byte[1024];

long

total=0;

int

len;

while

((len=is.read(b))!=-1){

//這個時候說明還沒有讀取到輸入流的最后

if

(isCanceld){

//說明取消了下載

return

TYPE_FAILED;

}else

if

(isPaused){

return

TYPE_PAUSED;

}else{

total+=len;

savedFile.write(b,0,len);

int

progress=

(int)

((total+downloadLength)*100/contentLength);

//計算下載的百分比

publishProgress(progress);

//調用onProgressUpdate()更新下載進度

}

}

response.body().close();

//關閉reponse

return

TYPE_SUCCESS;

//返回下載成功

}

}catch

(Exception

e){

e.printStackTrace();

}finally

{

try{

if

(is!=null){

is.close();

//關閉輸入流

}

if

(savedFile!=null){

savedFile.close();

//關閉查看文件

}

if

(isCanceld&&file!=null){

file.delete();

//如果點擊取消下載并且已經下載的文件存在，就刪除文件

}

}catch(Exception

e){

e.printStackTrace();

}

}

return

TYPE_FAILED;

}

/**

*

在doInBackground

里調用ublishProgress時調用此方法，更新UI進度

*

@param

values

*/

public

void

onProgressUpdate(Integer...

values){

int

progress=values[0];

//獲取傳過來的百分比值

if

(progress>lastProgress){

listener.onProgress(progress);

}

}

/**

*

當doInBackground

執行完成時，調用此方法

*

@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;

}

}

/**

*

按下暫停鍵時調用,暫停下載

*/

public

void

pausedDownload(){

isPaused=true;

}

public

void

canceledDownload(){

isCanceld=true;

}

/**

*

根據傳入的rul地址，獲取文件總長度

*

@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();

//獲取文件中長度

return

contentLength;

}

return

0;

}

}2、DownloadService.java

在這個里面，主要是根據Mainactivity里的指令，進行調用downloadTask類里的方法，以及調用前置通知，顯示進度。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;

//下載成功后，將前臺通知關閉，并創建一個下載成功的通告

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

主要是進行了開啟服務和綁定服務，對應按鈕的操作，以及運行時權限申請。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=

(DownloadServ