前言
本示例来自郭霖第一行代码第二版，因为其中涉及到了一些书中没有讲到的知识点，所以想在这篇中整体记录一下。
（1）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
public interface DownloadListener {
void onProgress(int progress);
void onSuccess();
void onFail();
void onPaused();
void onCanceled();
}
（2）下载功能用AsyncTask来实现
public class DownloadTask extends AsyncTask{
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_CANCELED = 3;
private DownloadListener listener;
private boolean isCanceled = false;
private boolean isPaused = false;
private int lastProgress;
public DownloadTask(DownloadListener listener){
this.listener = listener;
}
@Override
protected Integer doInBackground(String... params) {
InputStream is = null;
RandomAccessFile saveFile = null;
File file = null;
try {
long downloadLength = 0;
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()){
downloadLength = file.length();
}
long contentLength = getContentLength(downloadUrl);
if(contentLength==0){
return TYPE_FAILED;
}else if(contentLength == downloadLength){
return TYPE_SUCCESS;
}
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="+downloadLength+"-")
.url(downloadUrl)
.build();
Response response = client.newCall(request).execute();
if(response != null){
is = response.body().byteStream();
saveFile = new RandomAccessFile(file,"rw");
saveFile.seek(downloadLength);//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;
}
saveFile.write(b,0,len);
//计算已经下载的百分比
int progress = (int)((total+downloadLength)*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 (IOException e) {
e.printStackTrace();
}
}
return TYPE_FAILED;
}
@Override
protected void onProgressUpdate(Integer... params) {
int progress = params[0];
if(progress>lastProgress){
listener.onProgress(progress);
lastProgress = progress;
}
}
@Override
protected void onPostExecute(Integer status) {
switch (status){
case TYPE_SUCCESS:
listener.onSuccess();
break;
case TYPE_FAILED:
listener.onFail();
break;
case TYPE_PAUSED:
listener.onPaused();
break;
case TYPE_CANCELED:
listener.onCanceled();
break;
default:
break;
}
}
public void pauseDownload(){
isPaused = true;
}
public void cancelDownload(){
isCanceled = true;
}
/**
* 获取待下载文件的总长度
* @param downloadUrl
* @return
* @throws IOException
*/
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;
}
}
（1）AsyncTask中的3个泛型参数，第一个指定为String，表示在执行AsyncTask的时候需要传入一个字符串参数给后台任务；第二个指定为Integer，表示使用整型数据来作为进度显示单位；第三个指定为Integer，则表示使用整形数据来反馈执行结果。
（2）RandomAccessFile可以查看（https://www.cnblogs.com/baoliyan/p/6225842.html）（https://www.cnblogs.com/zuochengsi-9/p/6485737.html）
（3）java获取文件大小可以参考（https://blog.csdn.net/chaijunkun/article/details/22387305）
（4）是时候弄清楚getExternalStorageDirectory()和getExternalFilesDir()的区别（https://blog.csdn.net/nugongahou110/article/details/48154859）
（3）为了保证DownloadTask可以一直在后台运行，创建一个下载的服务
public class DownloadService extends Service {
private DownloadTask downloadTask;
private String downloadUrl;
private DownloadBinder mBinder = new DownloadBinder();
private DownloadListener listener = new DownloadListener() {
@Override
public void onProgress(int progress) {
getNotificationManager().notify(1,getNotification("Downloading...",progress));
}
@Override
public void onSuccess() {
downloadTask = null;
//下载成功关闭前台服务通知，并创建一个下载成功的通知
stopForeground(true);
getNotificationManager().notify(1,getNotification("Download Success",-1));
Toast.makeText(DownloadService.this,"DownloadSuccess",Toast.LENGTH_SHORT).show();
}
@Override
public void onFail() {
downloadTask = null;
//下载失败关闭前台服务通知，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,"DownloadFailed",Toast.LENGTH_SHORT).show();
}
@Override
public void onPaused() {
downloadTask = null;
Toast.makeText(DownloadService.this,"DownloadPaused",Toast.LENGTH_SHORT).show();
}
@Override
public void onCanceled() {
downloadTask = null;
stopForeground(true);
Toast.makeText(DownloadService.this,"DownloadCancel",Toast.LENGTH_SHORT).show();
}
};
public DownloadService() {
}
@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);
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){
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(){
return (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
}
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,"007");
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();
}
}
（4）在activity中调用
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 startDownload = findViewById(R.id.start_download);
Button pauseDownload = findViewById(R.id.pause_download);
Button cancelDownload = findViewById(R.id.cancel_download);
startDownload.setOnClickListener(this);
pauseDownload.setOnClickListener(this);
cancelDownload.setOnClickListener(this);
Intent intent = new Intent(this,DownloadService.class);
bindService(intent,connection,BIND_AUTO_CREATE);
if(ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE)
!= PackageManager.PERMISSION_GRANTED){
ActivityCompat.requestPermissions(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.start_download:
// String url = "https://raw.githubusercontent.com/guolindev/eclipse/master/eclipse-inst-win64.exe";
String url = "http://dubapkg.cmcmcdn.com/duba/166/kinst_166_f13_k0063.exe";
downloadBinder.startDownload(url);
break;
case R.id.pause_download:
downloadBinder.pauseDownload();
break;
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){
Toast.makeText(this,"拒绝权限将无法使用程序",Toast.LENGTH_SHORT).show();
finish();
}
break;
default:
break;
}
}
@Override
protected void onDestroy() {
super.onDestroy();
unbindService(connection);
}
}