I am using the wicket framework.
I have a requirement to send to the client browser several individual files (a zip file is not relevant).
I have added to my page an AJAXDownload class that extends AbstractAjaxBehavior - a solution for sending files to the client like this:
download = new AJAXDownload(){
#Override
protected IResourceStream getResourceStream(){
return new FileResourceStream(file){
#Override
public void close() throws IOException {
super.close();
file.delete();
}
};
}};
add(download);
At some other point in my code I am trying to initiate the download of several files to the client using an ajax request whilst looping through an arraylist of files and then each time triggering the AJAXDownload:
ArrayList<File> labelList = printLabels();
for(int i=0; i<labelList.size(); i++){
file = labelList.get(i);
//initiate the download
download.initiate(target);
}
However, it is only sending just one of these files to the client. I have checked and the files have definitely been created on the server side. But only one is of them is being sent to the client.
Can anyone give me an idea what I am doing wrong?
Thanks
You are doing everything correct!
I don't know how to solve your problem but I'll try to explain what happens so someone else could help:
The Ajax response has several entries like:
<evaluate>document.location=/some/path/to/a/file</evaluate>
wicket-ajax.js just loops over the evaluations and executes them. If there is one entry then everything is OK - you have the file downloaded. But if there are more then the browser receives several requests for changing its location in very short time. Apparently it drops all but one of them.
An obvious solution would be to use callbacks/promises - when a download finishes then trigger the next one. The problem is that there is no way how to receive a notification from the browser that such download finished. Or at least I don't know about it.
One can roll a solution based on timeouts (i.e. setTimeout) but it would be error prone.
I hope this information is sufficient for someone else to give you the solution!
Related
Does the native code of the VideoView give access to the received packets of the video before or after decoding it? I need to access these packets in order to transmit them to another device. The initial solution is to modify the Android native code. Other possible solutions that I found are to use GStreamer or FFmpeg libraries.
I need bit guidance in order to achieve that goal.
Assume the phone is rooted.
Short answer is no, not that I know of.
Long answer is that you haven't given enough detail. What data exactly do you need access to? Are you writing an application, or modifying your OS to do this to other applications?
The code that actually fetches a remote video is in MediaPlayer and is native. See the following method in MediaPlayer:
private void setDataSource(/* snip */) throws /* snip */ {
/* snip */
else if (scheme != null) {
// handle non-file sources
nativeSetDataSource(
MediaHTTPService.createHttpServiceBinderIfNecessary(path),
path,
keys,
values);
return;
}
/* snip */
Unfortunately for you, almost all of the relevant MediaPlayer code is native, and if not, it is private (so subclassing will not work here).
However, depending on what you need to do, you could possibly override VideoView method setVideoURI(Uri, Map<String, String>), which is public. Here you can grab the URI and then proxy it through your own web service, or something. This isn't quite what you were asking, though.
Or, you could possibly look into modifying the Surface that is drawn to by MediaPlayer. Most of the relevant code is still native though.
The final possibility that I'll mention (there are probably hundreds of possible approaches) would be to modify the MediaHTTPService class. This appears to be used by MediaPlayer, but I can't be sure because if it's used, it's used in native code.
This answer recommends finding the native code at androidxref.com
Edit:
As requested, here is a little more detail about what the "proxy server" solution might look like. I don't know the implementation details on Android.
Basically, when you get a URL to play in the VideoView, you pass it to your own server instead. Something like startProxyServer(videoUrl). This starts a server, which downloads and then re-hosts the video. To get this working locally, start a webserver listening on localhost. The server just downloads the video at videoUrl, saves it locally, and then hosts it at localhost:port/?video=${videoUrl}.
So in very high-level pseudo-code the server could look like.
public void startProxyServer(String videoUrl) {
int PORT = 28641; // random port
File f = downloadFile(videoUrl);
saveFile(f, '/path/to/server/storage');
startWebServer('localhost', PORT);
}
So now you give localhost:port/?video=${videoUrl} as url to the videoView instead. Also, now other videoView instances can download from that same localhost url.
To make it work with other phones, your server of course couldn't run on localhost.
Of course I've not implemented this, but it's just one solution I can think of.
i was trying to call the following web service from my android app, it hung then completed without returning the result:
web service:http://androidexample.com/media/webservice/JsonReturn.php
However when I clicked on the link, it worked fine - the json file displayed. yet it would not work in my app..
but now, it works fine now in my android app, perhaps it was temporarily down is what I am guessing. How can I know if a web service is up and running for an android app to consume ?
Typically, web services are designed to have a status page that can return status text or a HTTP return code to indicate service status.
If it doesn't have that, you can design a function to periodically do a very basic request with a known result to determine state. This is much better than doing a simple ping.
If it was down it would most likely show a HTML error page, which your app would try to parse, which would cause an error.
I had a similar issue, because I needed to know if the user was returning HTML or the correct JSON, to do this I created the ArrayList I was about to use outside of the try/catch of the parse area. You should do the same if you are using a string.
What I mean is, use:
ArrayList<Something> arrayList = new ArrayList<Something>();
String testString = ""; instead of String testString = null;
I was using only ArrayList<Something> arrayList; at one point which is incorrect. If the user then returns HTML, you won't get an error, the user will simply return an empty arraylist or empty string.
You can then plan for that and show some sort of error message. This way you only need one network request but you can still plan for getting the data back, and the server being down.
I'm making a web application for blackberry and I really need the current URL
In the description of documentUrl, it says
This method will return the URL of the currently loaded page of this BrowserField Instance
My code is:
_bf2.requestContent("google.com";);
add(_bf2);
Global.c = _bf2.getDocumentUrl();
Global.be=new BasicEditField("URL: "+Global.c,Global.c);
add(Global.be);
and the weird thing is that www.google.com gets loaded in the BrowserField and the documentUrl returns null.
This is my current code:
BrowserField _bf2 = new BrowserField();
MYBrowserFieldListener _listener = new MYBrowserFieldListener();
_bf2.requestContent("google.com";);
_bf2.addListener(_listener);
String url=_bf2.getDocumentUrl();
Global.be=new BasicEditField("URL: "+url,url);
add(Global.be);
add(_bf2);
I changed it to
final BrowserField _bf2 = new BrowserField();
_bf2.requestContent("google.com";);
//_bf2.addListener(listener);
Global.be=new BasicEditField("URL: "+Global.c,Global.c);
add(Global.be);
add(_bf2);
_bf2.addListener(new BrowserFieldListener(){
public void documentLoaded(BrowserField _bf2, Document document) throws Exception {
Global.c=_bf2.getDocumentUrl();
}
});
But it still returns null. Can someone please tell me how to fix this? Thanks in advance!
I would say that Arhimed has answered your question. An HTTP request is a very time consuming process (from a CPU perspective) and will block until the server responds. I suspect that RIM programmers have coded the requestContent() method as per their own recommendations and are fetching the web content on a separate thread. So, requestContent() will return immediately, when you call getDocumentUrl() it is still null since the fetch thread has probably not even connected to the server at this point.
You will need to implement a BrowserFieldListener and listen for documentLoaded().
I am writing a phoneGap plugin to allow multitouch on android devices (hoping to get this included in phonegap/callback eventually)
Event delegation is taking ~200ms using the plugin success callback and ~50ms with the WebView.loadUrl('javascript:somecodehere()') call
Unfortunately loadUrl has the side-effect of flickering the soft keyboard which isn't acceptable for a general solution.
Phonegap's Plugin.success uses an internal web server and an XmlHttpRequest object to send data, this method is way too slow.
Is there any 3rd method of sending javascript to the web browser? (or even sending a poke to the javascript engine to cause an event to happen, so that event could check a custom jsInterface object)
Take a look at addJavascriptInterface in the WebView class. It sounds more like what you are looking for.
In you plugin try calling:
this.ctx.sendJavascript(statement);
Not quite as fast as loadUrl but it may be a bit faster than returning a PluginResult.
You could roll your own stripped down message queue with a java object that is basically an arraylist and an accessor, then use addJavascriptInterface to bind it into the javascript context and inject a javascript polling loop that uses setTimeout to call the accessor method of your queue. Whenever you have javascript to execute, just add it to your arraylist. I'm not sure how it would perform, but perhaps it's worth a try?
class JSQueue {
private ArrayList<String> messages;
public String getMessage() {
String message = "";
if(messages.size() >0) {
message = messages.remove(0);
}
return message;
}
public void addMessage(String message) {
messages.add(message);
}
}
JSQueue jsq = new JSQueue();
dc.appMobiCanvas.hiddenView.addJavascriptInterface(jsq, "jsq");
dc.appMobiCanvas.hiddenView.loadUrl("javascript:(function checkJSQ(){eval(jsq.getMessage());setTimeout(checkJSQ, 50);}})();");
//add messages via jsq.addMessage();
It seems we have developed something similar
https://github.com/Philzen/webview-multitouch-polyfill
However, i have never experienced the issue you're describing before, but maybe you would like to test on your device or maybe contribute your expertise to the project. It has already been suggested on the Cordova (Phonegap) Roadmap, so we'll happy about every user and/or contributor to help this cause!
As I talk about befor I'm using to jQuery to refresh / update a webcam image.
This works just fine if you wanna update the image every 5th or 10sec.
But when your gonna do a stream with 10-15fps it gets into problems with most browsers
it seems. The problem seem to be that it sends a request befor the first one was done.
Is there a way to wait for the first request to be done befor sending a new update request for the webcam image? Because to me it seems to stack up requests if there is alittle delay on the server with the image.
Sorry if I did explain it alittle bad but... I'm norwegian and blode. Not the best combination. :)
Webcam Image is a single url
ex. http://www.ohoynothere.com/image.jpg
Old code I use.
$(document).ready(function() {
setInterval('updateCamera()',3000);
});
function updateCamera() {
$('.online2').each(function() {
var url = $(this).attr('src').split('&')[0];
$(this).attr('src', url + '&rand=' + new Date().getTime());
})
}
Definitely!
It sounds like your best bet would be to use the jQuery.ajax() method ( http://api.jquery.com/jQuery.ajax/ ) or .get() method to chain your requests. Basically, you want a JavaScript function that does a request for the image using the .ajax() call. In the response handler, simply call the function again:
function getMyImage() {
jQuery.get(image_url, function(response) {
jQuery('#img-name').attr('src', response);
getMyImage();
});
}
Whenever getMyImage successfully returns the image's src value from the webcam, it will immediately go out and try to retrieve a new image, but not before the previous one is loaded.
If I haven't understood what you're trying to do, please let me know. It would be helpful to know more about how the webcam image is retrieved (i.e. is it the same image src returned every time, etc.).