终于写完了，但是感觉有时候不是太理解，书上有的说的很模糊，有时候甚至一带而过，不过这样也挺好的，能够锻炼一下自己的自学能力，对代码的理解能力。如果每段代码有大量的注释也不是很好，理解它的核心内容就可以了。
下面看看效果图：
DownloadTask.java
package com.example.lenovo.servicebestprectice;
import android.app.DownloadManager;
import android.os.AsyncTask;
import android.os.Environment;
import android.webkit.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 Lenovo on 2017/9/17.
*/
public class DownloadTask extends AsyncTask<String,Integer,Integer>{
public static final int TYPE_SUCCESS = 0;
public static final int TYPE_FAILED = 1;
public static final int TYPE_PAUSE = 2;
public static final int TYPE_CANCELED = 3;
private DownLoadListener listener;
private boolean isCanceled = false;
private boolean isPause = false;
private int lastProgress;
public DownloadTask(DownLoadListener listener){
this.listener = listener;
}
/*doInBackground方法 将在onPreExecute 方法执行后马上执行，该方法运行在后台线程中。
* 这里将主要负责执行那些很耗时的后台处理工作。可以调用 publishProgress方法来更新实时的任务进度。
* 该方法是抽象方法，子类必须实现。
* */
@Override
protected Integer doInBackground(String... params) {
InputStream is = null;
RandomAccessFile saveFile = null;
File file = null;
long downloadedLength = 0;//记录已下载的文件长度
String downloadUrl = params[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){
return TYPE_SUCCESS;
}
OkHttpClient client = new OkHttpClient();
Request request = new Request.Builder()
//断点下载，指定从哪个字节下载
.addHeader("RANGE","bytes = "+downloadedLength+"-")
.url(downloadUrl)
.build();
try {
Response response = client.newCall(request).execute();
if (response != null){
is = response.body().byteStream();
saveFile = new RandomAccessFile(file,"rw");
saveFile.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 (isPause){
return TYPE_PAUSE;
}else {
total+=len;
saveFile.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 (saveFile!=null){
saveFile.close();
}
if (isCanceled && file!=null){
file.delete();
}
}catch (Exception e){
e.printStackTrace();
}
}
return TYPE_FAILED;
}
/*
* onProgressUpdate(Progress…),在publishProgress方法被调用后，
* UI 线程将调用这个方法从而在界面上展示任务的进展情况，例如通过一个进度条进行展示。
* */
@Override
protected void onProgressUpdate(Integer... values) {
int progress = values[0];
if (progress > lastProgress){
listener.onProgress(progress);
lastProgress = progress;
}
}
/*
* 在doInBackground 执行完成后，onPostExecute 方法将被UI 线程调用，
* 后台的计算结果将通过该方法传递到UI 线程，并且在界面上展示给用户.
* */
@Override
protected void onPostExecute(Integer status) {
switch (status){
case TYPE_SUCCESS:
listener.onSuccess();
break;
case TYPE_FAILED:
listener.onFailed();
break;
case TYPE_PAUSE:
listener.onPause();
break;
case TYPE_CANCELED:
listener.onCanceled();
break;
default:
break;
}
}
public void pauseDownload(){
isPause = true;
}
public void cancelDownload(){
isCanceled = true;
}
private long getContentLength(String downloadUrl){
OkHttpClient client = new OkHttpClient();
Request request = new Request.Builder()
.url(downloadUrl)
.build();
try {
Response response = client.newCall(request).execute();
if (response!=null && response.isSuccessful()){
long contentlength = response.body().contentLength();
response.close();
return contentlength;
}
} catch (IOException e) {
e.printStackTrace();
}
return 0;
}
}
DownloadService.java
package com.example.lenovo.servicebestprectice;
import android.app.Notification;
import android.app.NotificationManager;
import android.app.PendingIntent;
import android.app.Service;
import android.content.Intent;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Binder;
import android.os.Environment;
import android.os.IBinder;
import android.support.v7.app.NotificationCompat;
import android.webkit.DownloadListener;
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 profress) {
getNotificationManager().notify(1,getNotification("Downloading...",profress));
}
@Override
public void onSuccess() {
downloadTask = null;
//下载成功前将前台服务通知关闭，并创建一个下载成功的通知
stopForeground(true);
//触发getNotification通知
getNotificationManager().notify(1,getNotification("Download success",-1));
Toast.makeText(DownloadService.this, "Download Success", Toast.LENGTH_SHORT).show();
}
@Override
public void onFailed() {
downloadTask = null;
//下载失败前将前台服务通知关闭，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;
}
class DownloadBinder extends Binder{
public void startDownload(String url){
if (downloadTask == null){
downloadUrl = url;
downloadTask = new DownloadTask(listener);
downloadTask.execute(downloadUrl);
//为了让下载服务成为一个前台服务，我们还调用了startForeground()
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){
//取消下载时需要将文件删除，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 NotificationManager getNotificationManager(){
//获取通知管理器
return (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
}
//用于显示下载进度的通知
private Notification getNotification(String title,int progress){
Intent intent = new Intent(this,MainActivity.class);
// 创建一个PendingIntent，和Intent类似,不同的是由于不是马上调用，
// 需要在下拉状态条出发的activity，所以采用的是PendingIntent,
// 即点击Notification跳转启动到哪个Activity
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+"%");
//第一个参数通知最大参数，
//第二个参数传入通知的当前进度
//第三个参数表示是否使用模糊的进度条
builder.setProgress(100,progress,false);
}
return builder.build();
}
}
MainActivity.java
package com.example.lenovo.servicebestprectice;
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 Button mBtnstartDownload,mBtnPauseDownload,mBtnCanceDownload;
private ServiceConnection connection = new ServiceConnection() {
@Override
public void onServiceConnected(ComponentName componentName, IBinder service) {
downloadBinder = (DownloadService.DownloadBinder) service;
}
@Override
public void onServiceDisconnected(ComponentName componentName) {
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mBtnstartDownload = (Button) findViewById(R.id.btn_start_download);
mBtnPauseDownload = (Button) findViewById(R.id.btn_pause_download);
mBtnCanceDownload = (Button) findViewById(R.id.btn_cancel_download);
mBtnstartDownload.setOnClickListener(this);
mBtnPauseDownload.setOnClickListener(this);
mBtnCanceDownload.setOnClickListener(this);
Intent intent = new Intent(this,DownloadService.class);
startService(intent);//启动服务
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.btn_start_download:
String url = "https://raw.githubusercontent.com/guolindev/eclipse/master/eclipse-inst-win64.exe";
downloadBinder.startDownload(url);
break;
case R.id.btn_pause_download:
downloadBinder.pauseDownload();
break;
case R.id.btn_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, "拒绝权限无法使用程序", Toast.LENGTH_SHORT).show();
finish();
}
break;
default:
}
}
@Override
protected void onDestroy() {
super.onDestroy();
unbindService(connection);
}
}
DownLoadListener.java
package com.example.lenovo.servicebestprectice;
/**
* Created by Lenovo on 2017/9/17.
*/
public interface DownLoadListener {
void onProgress(int profress);
void onSuccess();
void onFailed();
void onPause();
void onCanceled();
}
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
>
<Button
android:id="@+id/btn_start_download"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Start Download"
android:textAllCaps="false"
/>
<Button
android:id="@+id/btn_pause_download"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Pause Download"
android:textAllCaps="false"
/>
<Button
android:id="@+id/btn_cancel_download"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Cancel Download"
android:textAllCaps="false"
/>
</LinearLayout>