本篇文章主要介绍以下几个知识点：
- 服务的实践应用。
图片来源于网络
10.5 服务的最佳实践——完整版的下载示例
本节来综合运用一下，实现一个在服务中经常使用到的功能——下载。效果如下：
下载示例效果
首先添加网络请求依赖库：
compile 'com.squareup.okhttp3:okhttp:3.5.0'
接下来需要定义一个回调接口，用于对下载过程中的各种状态进行监听和回调，新建 DownloadListener 接口：
/**
* Function：回调接口，对下载过程中的各种状态进行监听和回调
* Author：kxwon on 2017/1/22 19:09
* Email：kxwonder@163.com
*/
public interface DownloadListener {
void onProgress(int progress); // 下载进度
void onSuccess(); // 下载成功
void onFailed(); // 下载失败
void onPaused(); // 下载暂停
void onCanceled(); // 下载取消
}
回调接口定义好后，下面就开始编写下载功能了，这里用 AsyncTask 来实现，新建一个 DownloadTask 继承自 AsyncTask：
public class DownloadTask extends AsyncTask<String,Integer,Integer>{
public static final int TYPE_SUCCESS = 0; // 下载成功
public static final int TYPE_FAILED = 1; // 下载失败
public static final int TYPE_PAUSED = 2; // 下载暂停
public static final int TYPE_CANCELED = 3; // 下载取消
private DownloadListener listener;
private boolean isCanceled = false;
private boolean isPaused = false;
private int lastProgress;//上一次的下载进度
public DownloadTask(DownloadListener listener){
this.listener = listener;
}
/**
* 用于在后台执行具体的下载逻辑
* @param params
* @return
*/
@Override
protected Integer doInBackground(String... params) {
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 = params[0];//获取到下载的URL地址
String fileName = downloadUrl.substring(downloadUrl.lastIndexOf("/"));//下载的文件名
String directory = Environment.getExternalStoragePublicDirectory
(Environment.DIRECTORY_DOWNLOADS).getPath();//将文件下载到指定目录
file = new File(directory + fileName);
if (file.exists()){
downloadedLength = file.length();
}
long contentLength = getContentLength(downloadUrl);//获取待下载文件的总长度
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;
}
// 发送网络请求，从网络读取数据写入到本地，直到文件下载完
OkHttpClient client = new OkHttpClient();
Request request = new Request.Builder()
// 断点下载，指定从哪个字节开始下载
.addHeader("RANGE","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);//通知当前的下载进度
}
}
response.body().close();
return TYPE_SUCCESS;
}
}catch (Exception 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;
}
/**
* 用于在界面上更新当前的下载速度
* @param values
*/
@Override
protected void onProgressUpdate(Integer... values) {
int progress = values[0];//当前的下载进度
if (progress > lastProgress){
listener.onProgress(progress);//通知下载进度更新
lastProgress = progress;
}
}
/**
* 用于通知最终的下载结果
* @param integer
*/
@Override
protected void onPostExecute(Integer integer) {
switch (integer){
case TYPE_SUCCESS:
listener.onSuccess();//下载成功
break;
case TYPE_FAILED:
listener.onFailed();//下载失败
break;
case TYPE_PAUSED:
listener.onPaused();//下载暂停
break;
case TYPE_CANCELED:
listener.onCanceled();//下载取消
break;
default:
break;
}
}
/**
* 暂停
*/
public void pauseDownload(){
isPaused = true;
}
/**
* 取消
*/
public void cancelDownload(){
isCanceled = true;
}
/**
* 获取待下载文件的总长度
* @param downloadUrl
* @return
*/
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;
}
}
以上就把具体的下载功能完成了，下面为了保证 DownloadTask 可以一直在后台运行，还需创建一个下载的服务。新建 DownloadService 如下：
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;
// 下载成功时将前台服务通知关闭，并创建一个下载成功的通知
stopForeground(true);
getNotificationManager().notify(1,getNotification("Download Success",-1));
ToastUtils.showShort("下载成功");
}
@Override
public void onFailed() {
downloadTask = null;
// 下载失败时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));
ToastUtils.showShort("下载失败");
}
@Override
public void onPaused() {
downloadTask = null;
ToastUtils.showShort("下载暂停");
}
@Override
public void onCanceled() {
downloadTask = null;
stopForeground(true);
ToastUtils.showShort("下载取消");
}
};
public DownloadService() {
}
private DownloadBinder mBinder = new DownloadBinder();
class DownloadBinder extends Binder{
/**
* 开始下载
* @param url
*/
public void startDownload(String url){
if (downloadTask == null){
downloadUrl = url;
downloadTask = new DownloadTask(listener);
downloadTask.execute(downloadUrl);
startForeground(1,getNotification("Downloading ...",0));
ToastUtils.showShort("Downloading ...");
}
}
/**
* 暂停下载
*/
public void pauseDownload(){
if (downloadTask != null){
downloadTask.pauseDownload();;
}
}
/**
* 取消下载
*/
public void cancelDownload(){
if (downloadTask != null){
downloadTask.cancelDownload();
}else {
if (downloadUrl != null){
// 取消下载时需要将文件删除，并且通知关闭
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();
}
}
}
}
}
@Override
public IBinder onBind(Intent intent) {
return mBinder;
}
private NotificationManager getNotificationManager(){
return (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
}
/**
* 构建通知方法
*/
private Notification getNotification(String title,int progress){
Intent intent = new Intent(this,DownloadActivity.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){
// 当progress大于或等于0时才需要显示下载进度
builder.setContentText(progress + "%");
// 三个参数：通知的最大进度、通知的当前进度、是否使用模糊进度条
builder.setProgress(100,progress,false);
}
return builder.build();
}
}
现在下载的服务已实现，后端的工作基本完成，接下来就开始编写前端的部分。在布局中放置3个按钮，分别用于开始下载、暂停下载、取消下载，如下：
public class DownloadActivity extends AppCompatActivity implements View.OnClickListener {
private DownloadService.DownloadBinder downloadBinder;
private ServiceConnection connection = new ServiceConnection() {
@Override
public void onServiceConnected(ComponentName name, IBinder service) {
downloadBinder = (DownloadService.DownloadBinder) service;
}
@Override
public void onServiceDisconnected(ComponentName name) {
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_download);
Button start_download = (Button) findViewById(R.id.start_download);
Button pause_download = (Button) findViewById(R.id.pause_download);
Button cancel_download = (Button) findViewById(R.id.cancel_download);
start_download.setOnClickListener(this);
pause_download.setOnClickListener(this);
cancel_download.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(DownloadActivity.this, android.Manifest.
permission.WRITE_EXTERNAL_STORAGE)!= PackageManager.PERMISSION_GRANTED){
ActivityCompat.requestPermissions(DownloadActivity.this,new
String[]{android.Manifest.permission.WRITE_EXTERNAL_STORAGE},1);
}
}
@Override
public void onClick(View v) {
if (downloadBinder == null){
return;
}
switch (v.getId()){
// 开始下载
case R.id.start_download:
String url = "https://raw.githubusercontent.com/guolindev/eclipse/" +
"master/eclipse-inst-win64.exe";
downloadBinder.startDownload(url);
break;
// 暂停下载
case R.id.pause_download:
downloadBinder.pauseDownload();
break;
// 取消下载
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){
ToastUtils.showShort("拒绝权限将无法使用程序");
finish();
}
break;
default:
}
}
@Override
protected void onDestroy() {
super.onDestroy();
unbindService(connection);//解绑服务
}
}
最后，别忘了声明权限：
<!-- 访问SD卡权限 -->
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<!-- 访问网络权限 -->
<uses-permission android:name="android.permission.INTERNET" />
以上，就是整个的下载示例。
本篇文章就介绍到这。
