Applet reading from http server ?

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Francisco Camarero - 11 Jul 2003 12:56 GMT

I am writing a very small Applet that reads some files via
http from different servers and reports some result.

I am using the usual code:

..
MyURL = new URL("http://www.somewhere.com/somepath/somefile");
InFile = new BufferedReader(new InputStreamReader(MyURL.openStream()));
inputLine = InFile.readLine();
..

But, when executing it with appletviewer I get exceptions:

java.security.AccessControlException: access denied (java.net.SocketPermission
www.somewhere.com resolve)

And from the Browser it doesn't work either.

I have read somewhere that this is normal... that because of
security, the applet can't read via http from other servers...

I have also read something about a workaround with servlets installed
on the servers I want to read from, but I don't control these servers,
so I can't install nothing there...

Any other solution or definitive negative ?

Thanks!

Fran.

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Ike - 11 Jul 2003 14:32 GMT

Use a test certificate -- go to java.sun.com and read how to create a test
certificate and use it to digitially sign. The other alternative, for you to
test locally, is to run it as an application. To do this, put a main() in
the applet, which instantiates the applet, as follows:

public class MyApplet extends Applet{

public boolean isAnApplet;

public class MyApplet(){
isAnApplet=true;
}

public static void main(String []args) {
MyApplet applet = new MyApplet ();
JFrame mainFrame = new JFrame(applet.getClass().getName());
applet.isAnApplet=false; //VITAL! this is a MyApplet class member
variable which you can use throughtout your code to tell you if you are
running in applet or application mode.
applet.init();
applet.start();
mainFrame.getContentPane().add(applet);
mainFrame.setSize(applet.windowsize); //width, height
mainFrame.setVisible(true);
mainFrame.addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent e) {
System.exit(0);
}
});
}
}

//now you can run it as an applet or an applicatrion. If you run as an
applet, to circumvent the security restrictions, digitally sign it - even
with a test certificate. -Ike

> I am writing a very small Applet that reads some files via
> http from different servers and reports some result.
[quoted text clipped - 26 lines]
>
> Fran.

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Francisco Camarero - 11 Jul 2003 16:47 GMT

I have tried the certificate solution:

javac HelloWorld.java
jar cvf HelloWorld.jar HelloWorld.class
jarsigner -keystore myKeystore HelloWorld.jar myself

and placed the jar and the html file in my web server.

See codes:

index.html:

<html>
<head>
</head>
<body>
<applet archive="HelloWorld.jar" code="HelloWorld.class" width=150
height=50></applet>
 
 
In the applet field above it should appear the text :
 
 
<html><head>
 
 
 
instead, you can see:
 
 
Empty Text
 
 
</body>
</html>

HelloWorld.java:

import java.applet.*;
import java.awt.*;
import java.net.*;
import java.net.*;
import java.io.*;

public class HelloWorld extends Applet {

//This causes the Browser to Redirect, and is not what we want...
//public void init() {
//
//AppletContext appletContext;
//URL my_url;
// try {
// my_url = new URL("http://www.yahoo.com");
// appletContext = getAppletContext();
// appletContext.showDocument(my_url);
// } catch (Exception e) {
// System.out.println("Exception!");
// }
//}

URL MyURL;
BufferedReader InFile;
String inputLine;

public void init() {
inputLine = "Empty Text";
try {
MyURL = new URL("http://www.yahoo.com");
InFile = new BufferedReader(new InputStreamReader(MyURL.openStream()));
inputLine = InFile.readLine();
} catch (Exception MyException) {
System.out.println(MyException);
}
}

public void paint(Graphics g) {
g.drawString(inputLine, 50,25);
}
}

When I browse that index.html file, I get the "Empty Text" string, and
not the first line of the www.yahoo.com server...

Am I doing something wrong?...

> Use a test certificate -- go to java.sun.com and read how to create a test
> certificate and use it to digitially sign. The other alternative, for you to
[quoted text clipped - 63 lines]
> >
> > Fran.

Signature

Francisco Camarero GSM: +41 764 5432 78
ETZ J86, Gloriastrasse 35 telephone: +41 1 632 76 50
CH-8092 Zurich telefax: +41 1 632 11 94
Switzerland e-mail: camarero@iis.ee.ethz.ch

Reply to this Message

Roedy Green - 12 Jul 2003 04:30 GMT

> MyURL = new URL("http://www.yahoo.com");

try running as an application first. then once it is working, flip to
applet and sign.

--
Canadian Mind Products, Roedy Green.
Coaching, problem solving, economical contract programming.
See http://mindprod.com/jgloss/jgloss.html for The Java Glossary.

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Ike - 12 Jul 2003 04:34 GMT

I dont think you can have an applet read from a server OTHER than the server
that it resides on. Unless your applet resides on http://www.yahoo.com I
dont think you can read from that -Ike

> I have tried the certificate solution:
>
[quoted text clipped - 148 lines]
> > >
> > > Fran.

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Francisco Camarero - 14 Jul 2003 10:40 GMT

So, I think that looks like a Definitive Negative answer to my problem...

Thanks anyway!

> I dont think you can have an applet read from a server OTHER than the server
> that it resides on. Unless your applet resides on http://www.yahoo.com I
> dont think you can read from that -Ike

Reply to this Message

Roedy Green - 12 Jul 2003 04:27 GMT

> MyURL = new URL("http://www.somewhere.com/somepath/somefile");

Unsigned applets are only permitted to read from the machine they were
loaded from.

See http://mindprod.com/jgloss/applet.html
http://mindprod.com/jgloss/signedapplet.html
http://mindprod.com/jgloss/javawebstart.html

--
Canadian Mind Products, Roedy Green.
Coaching, problem solving, economical contract programming.
See http://mindprod.com/jgloss/jgloss.html for The Java Glossary.

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Applet reading from http server ?

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