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Writing files inside an applet

Posted on 1998-05-08
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Last Modified: 2013-11-24
Okay, I'm wanting to create an applet that saves the information from the applee on to the host computer, or the web server that the applet is being posted on.  I know I can't write files or read files to the client but I should be able to read and write to the host computer.  I'm trying to implement something similar to a highscores table that saves information from an applet that lots of people will use, like a voting thing......
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Question by:GreenK
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8 Comments
 
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Expert Comment

by:hkp
ID: 1220842
I can imagine two ways to write files. One is to use the FTP protocol (this is long hair), and the other is to use the File() class. Here's a sample of the later, although I see trouble ahead from an applet (I assume, the c: drive is the webserver's):

// Create a file, if non-existent.
File f = new File("c:/","test.txt");
if ( f.exists() == false) {
try {
FileWriter fw = new FileWriter(f);
fw.write("123",0,3);
fw.flush();
fw.close();


}
catch (IOException e) {
e.printStackTrace();
};
}
f=null;


I hope this can get you on better ground.
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Expert Comment

by:gadio
ID: 1220843
GreenK, as far as I understand you want to do it from the client to the server, in java. What you should do is open a URL to the server to a location that you can write in, get the URLConnection, get an outputStream and write. The http server must enable the writing operation though.
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Expert Comment

by:DonReese
ID: 1220844
GreenK, consider opening a connection back to your webserver and post the information to a CGI-BIN that handles all the file work.
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Expert Comment

by:hkp
ID: 1220845
I think a good solution would require the use of CGI by means of a Java servlet, which handles the highscore table file updates and representations.

By using a URLConnection, you should be able to send parameters from your applet to the servlet via the URL.

If you don't have experience with Java servlets, this is a longer story. Look at http://java.sun.com/products/index.html and lookup the Servlet Development Kit, install it on the web server machine. Make your first servlet, and use the above code principles for writing to a file on the server.

:-)

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Author Comment

by:GreenK
ID: 1220846
Can't use new File because that accesses files on the client machine..and we can't write to that because it's an applet....

So I've created the perl cgi files to do all the file handling...

Now i'm trying to figure out how to pass the information to the perl file..
I've got it setup where a form can alter the data using the get method..

script.cgi?data1+data2+data3

So how do I pass that to perl using java stuff....


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Expert Comment

by:evijay
ID: 1220847
write a proxy server on the host from which the applet is originated.

A proxy server is another java program that listens at a known serversocket. Your applet can connect to the proxy server, send the data to it, and the proxy server inturn writes / reads the files onto the host harddisk.

check for a java telnet applet from site
http://www.first.gmd.de/persons/leo/java/Telnet/

This is a very good example of writing a proxy server to overcome the security restrictions of applets.



Vijay
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Author Comment

by:GreenK
ID: 1220848
The answer was rejected because your idea would only work if I was trying to write to the host computer and not the webserver computer that is hosting the applet.

This is going to be a game that keeps track of the highscores of everyone that plays....this file that they write to needs to be centrally located on the server.


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Accepted Solution

by:
evijay earned 50 total points
ID: 1220849
write a proxy server on the host from which the applet is originated.
A proxy server is another java program that listens at a known
serversocket. Your applet can connect to the proxy server, send the data
to it, and the proxy server inturn writes / reads the files onto the
host harddisk.
check for a java telnet applet from site
http://www.first.gmd.de/persons/leo/java/Telnet/
This is a very good example of writing a proxy server to overcome the
security restrictions of applets.
Vijay
0

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