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);
}
}
文章题目：用AsyncTask实现断点续传
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