Java(tm) Communications API FAQ
Thanks for the positive feedback on the Java(tm) communications API.
Since we cannot reply individually, we have compiled an FAQ to help
communicate with our customers/users.
Q: Will it be part of the JDK?
A: The Java communications API will be a Java Standard Extension, it will
not be part of the core JDK.
Q: My application does not find any ports when it enumerates available ports.
Q: BlackBox gives me a message that says "No serial ports found!"
A: In order for the Java communications API to find ports the file
javax.comm.properties must be in the correct place. The preferred location
is in <jdk>/lib. See the installation instructions for alternate locations
and further information.
Q: The port enumeration reports more/less ports that actually exist on my
computer.
A: This is due to platform limitations. For Windows 95 and Windows 98 the
Java communications API will always enumerate the serial ports
COMM 1 though COMM 4 and the parallel ports LPT1 and LPT2. For Windows NT
the Java communications API will enumerate the serial ports entered in the
Registry and the parallel port LPT1 and LPT2. Attempting to open a port
that does not exist will result in a PortInUseException being thrown.
For Solaris the Java communications API enumerates both the actual port
names and the aliases to the ports.
Q: Can I load my own CommPort drivers, or am I limited to the provided
Serial/Parallel drivers?
A: As a result of feedback, we have added this functionality.
IMPORTANT: Use the Solaris implementation's comm.jar as a
framework. The win32 implementation is closely tied to its native
library. See the CommDriver javadocs for details.
Q: Is there a linux version of the Java communications API?
A: We do not provide a linux implementation. But Kevin Hester
has written Java communications API drivers for linux and uses our CommPort
driver loading scheme to load his own gnu.io.RXTXCommDriver class. He gave
us permission to disclose his web page:
http://www.interstice.com/kevinh/linuxcomm.html
Q: I would like to port the Java communications API to my favorite platform.
Can you give me the source code to the reference implementations to help
me out?
A: Sun will not be releasing the source code to reference implementations.
Successful porting efforts are underway without the reference implementation
source code (see previous answer).
Q: Will there be support for USB, Firewire or ISDN? How about higher level
protocols such as X/Y/Z-modem or Kermit?
A: We are investigating adding support for other low-level communication
protocols. But higher-level protocols such as X/Y/Z-modem or Kermit are
outside of the focus of the Java communications API.
Q: How many listeners are allowed per instance of CommPort?
A: Currently the Java communications API supports one. Therefore,
Parallel/SerialPort.removeEventListener() doesn't take any arguments.
Q: How does the CommPortIdentifier class relate to CommPort?
A: There is a one-to-one correspondence between a CommPortIdentifier
object and a CommPort object. CommPortIdentifier provides
functionality for discovering comm ports at init time, opening comm
ports and managing ownership change events. The static method
CommPortIdentifier.getPortIdentifier(String portName) returns a
CommPortIdentifier instance with portName, while getPortIdentifiers()
returns an enumeration of CommPortIdentifier objects that represent
all the available ports.
Q: Can my app make direct reads from a port and also receive event
notification on the same port?
A: Yes. Event notification is done with the lightweight JDK 1.1 event
model. No data from the port is delivered with event notification. You
will read from the port using CommPort.getInputStream().read().
Q: Can I use the Java communications API in applets?
A: Yes in signed applets, but no in unsigned applets (most cases). Since we
do not allow unsigned applets access to any communications port under the
JDK1.1 security model, you can not use the Java communications API with
unsigned applets. We do plan to be compliant to JDK1.2 security model in
later releases, which might allow trusted applet access to ports.
Q: I've edited my javax.comm.properties file and now my application cannot
find any ports.
A: The javax.comm.properties file is not intended to be edited by users. If
you are having problems after editing the file, we suggest that you
reinstall the file.
Q: I've downloaded and installed the Java communications API. Now I have a
great idea about an application that will use it. Can you tell me how to
do the following...
A: The Java communications API team can not provide product support. We suggest
that you use the Java Developer Connection(tm) (JDC). There are several
avenues available in the JDC for getting answers to questions about how to
use the Java communications API, including discussion groups with other
developers. You must register to use the JDC, but there is no charge for
registration.
The URL for the JDC is:
http://developer.java.sun.com
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