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Index › Programming Questions & Help › Programs › Reading data from URL: problem in applet
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Reading data from URL: problem in applet (Read 1237 times)
sala
Reading data from URL: problem in applet
May 25th, 2006, 5:00pm  
Hi all

I have the following problem: I am using processing to visualize data from the web, using a standard java URL reader to get the data.

When I export this as an application, everything works fine. When I export it as an applet, however, I don't seem to get any data from the web.

For example, I can run Daniel Shiffmans Google News reader (http://itp.nyu.edu/~dts204/a2z/thread/) without problem as an application, but when I export it as an applet, all I get is a gray, empty canvas.

I first though that there was an issue with my networks settings, but since I can view Daniels' applet on his website without any problems, this seems not to be the case. I tried to put the exported applet on my own webserver (http://www.aharef.info/static/applet/), but again, no luck.

Has anyone ever encountered such a problem? Any help / hint would be  greatly appreciated!

Best regards
Sala
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fjen
Re: Reading data from URL: problem in applet
Reply #1 - May 25th, 2006, 7:08pm  
sala,

this is a known problem with applets. by default they are only allowed to read data from the server they are coming from. see the exception that your applet raises:

java.security.AccessControlException: access denied (java.net.SocketPermission itp.nyu.edu resolve)

so .. to get this working you should either sign your applet, or even better use php to fetch the data from the other server like:

applet -> php -> other server -> php -> applet

i don't have an example at hand, but since this is something people run into quite often i'm sure you will find one by searching the forum ( try "PHP" ) ...

best,
F
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sala
Re: Reading data from URL: problem in applet
Reply #2 - May 25th, 2006, 8:54pm  
Fijen,

Thanks for your response. I'll check that.

Anyways, I'm still curious why it works on Shiffman's site. I dont assume he uses a certifcate.
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fjen
Re: Reading data from URL: problem in applet
Reply #3 - May 25th, 2006, 9:24pm  
no. the problem is that the applet is not allowed to read from any other servers than it came from. so your applet can read from your server / domain ... shiffman reads from his server, so that's ok. but your applet can't read from his.

F
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sala
Re: Reading data from URL: problem in applet
Reply #4 - May 26th, 2006, 2:05pm  
fjen,

thanks again. I have now managed the php part, works fine. However, now I am having another difficulty. Two, to be precise:

It works fine on firefox, but nothing on safari

Even stranger, if I check it online at another computer, it gives me some java errors of classes missing. I thought they are all in the jar that the export function creates?

Puh, I am having a hard time figuring this out.

I wrote this app to create networks of any HTML DOM (see http://www.aharef.info/2006/05/websites_as_graphs.htm for screenshots), it works fine in processing, but I just dont get it running on a webserver Sad
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jkriss
Re: Reading data from URL: problem in applet
Reply #5 - May 26th, 2006, 2:31pm  
Sounds to me like a Java version problem.  Which classes are missing?  If the Java plugin version is 1.1, for example, you'll get class not found errors for all Collections other than Vector (ArrayList, HashMap, etc.).
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sala
Re: Reading data from URL: problem in applet
Reply #6 - May 26th, 2006, 2:43pm  
org.w3c.dom.Node is missing
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sala
Re: Reading data from URL: problem in applet
Reply #7 - May 28th, 2006, 6:57pm  
Ok, I just wanted to say I got it up and running: http://www.aharef.info/static/htmlgraph/
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Markavian
Re: Reading data from URL: problem in applet
Reply #8 - May 28th, 2006, 8:14pm  
Heres my derived 'web browser' version:
http://mkv25.net/applets/mkv_htmlgraph/getDataFromURL.php?url=http://www.aharef.info
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