Solved

Using javax.comm in Java 1.2 applets

Posted on 2000-03-12
4
374 Views
Last Modified: 2008-03-04
I am trying to get access to a PC's serial ports from a signed Java applet, using the Java 1.2.2 plug-in for IE5 and the Java Comms API v2.0. I have copied the win32com.dll, comm.jar and properties file to the appropriate places for the right runtime environment on the client PC, and granted all permissions to applets signed by me. In the applet, I use getCommPortIdentifiers to get an enumerator, then use this to obtain all available serial ports. However, when the applet is loaded, the following error is reported when I execute the hasMoreElements() method of the enumerator:
"Caught java.lang.NullPointerException: name can't be null while loading driver com.sun.comm.Win32Driver"

The same code works fine when run as an application. The security setup is definitely having an effect, since I also try to read from a local file - this fails as expected when the applet is unsigned (and the comm port stuff raises a different seurity-related error, too) but succeeds when the applet is signed. Perhaps I have missed something else though.

If anyone has any ideas on how to proceed, I would be glad to hear them.

Many thanks,
Chris
0
Comment
Question by:chrisgresty
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 2
  • 2
4 Comments
 
LVL 16

Accepted Solution

by:
heyhey_ earned 75 total points
ID: 2611362
it seems that JavaComm can't configure itself.

the only thing I can suggest is to decompile the JavaComm classes and add some additional logging.

you can find the code that prints the error message inside javax.comm.CommPortIdentifier.java

try
{
    CommDriver commdriver = (CommDriver)Class.forName(s1).newInstance();
    commdriver.initialize();
}
catch(Throwable throwable)
{
    System.err.println("Caught " + throwable + " while loading driver " + s1);
}

the real problem is somewhere inside com.sun.comm.Win32Driver
0
 

Author Comment

by:chrisgresty
ID: 2612215
Thanks heyhey_, you pointed me in the right direction. There is a problem during the static initialisation of CommPortIdentifier. During this, the following lines are executed:

loadDriver(s1);
propfilename = new String(s1);

(s1 is the javax.comm.properties file)

As part of the driver initialisation started by loadDriver, the addPortName() method is called. If there is a security manager being used, it checks the delete permission on propfilename. Which hasn't been initialised yet. Whoops.

So initialisation fails whenever you use javax.comm with a security manager.

Switching the two lines around solves this problem. I can't see any negative implications of this yet...
0
 

Author Comment

by:chrisgresty
ID: 2615237
Heyhey_'s comments gave me a handle on the problem, and led me to find the right answer - thanks!
0
 
LVL 16

Expert Comment

by:heyhey_
ID: 2615709
thank you :)
0

Featured Post

Salesforce Made Easy to Use

On-screen guidance at the moment of need enables you & your employees to focus on the core, you can now boost your adoption rates swiftly and simply with one easy tool.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Java functions are among the best things for programmers to work with as Java sites can be very easy to read and prepare. Java especially simplifies many processes in the coding industry as it helps integrate many forms of technology and different d…
Basic understanding on "OO- Object Orientation" is needed for designing a logical solution to solve a problem. Basic OOAD is a prerequisite for a coder to ensure that they follow the basic design of OO. This would help developers to understand the b…
Video by: Michael
Viewers learn about how to reduce the potential repetitiveness of coding in main by developing methods to perform specific tasks for their program. Additionally, objects are introduced for the purpose of learning how to call methods in Java. Define …
This tutorial will introduce the viewer to VisualVM for the Java platform application. This video explains an example program and covers the Overview, Monitor, and Heap Dump tabs.
Suggested Courses

734 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question