Java IDL FAQ
This is a document that attempts to answer many of the questions
you may have about using Java IDL technology.
Errors
Features
Compatibility/Interoperability
General
Errors
The most common reason for this error when running
HelloServer (and also HelloClient) from the Java IDL tutorial is
that HelloServer is not in the classpath. For more
information on setting the classpath variable, see Setting the class path.
The second most common reason occurs when a space is added
between quotation marks in the following line of code:
NameComponent nc = new NameComponent("Hello", "");
There should be no spaces between the quotation marks. Without
spaces, this value is passed as a null. With a space between the
quotations, a space character is passed.
My existing programs aren't running using this release. Are
there any compatibility issues that could affect this?
Information on compatibility between J2SE 1.4.x and J2SE 5.0 can
be found in CORBA Compatibility
Information - J2SE 5.0.
Why can't I connect using IOR's from a Linux server when the
IOR contains 127.0.0.0 as the host address?
On Red Hat Linux installations
InetAddress.getLocalHost() may return an
InetAddress corresponding to the loopback address
(127.0.0.1). This arises because the default installation creates
an association in /etc/hosts between the hostname of the
machine and the loopback address. To ensure that
InetAddress.getLocalHost() returns the actual host
address, update the /etc/hosts file or the name service
configuration file (/etc/nsswitch.conf) to query dns or
nis before searching hosts.
The most recent versions of the standard (OMG) minor
code exceptions can be found on the OMG Web site at http://www.omg.org/.
Some of the most common Sun minor code exceptions are the
following:
COMM_FAILURE/201. vmcid: SUN minor code: 201 literally means "CONNECT_FAILURE". This may be caused by a java.net.SocketException, usually one of BindException, ConnectException, or NoRouteToHostException.
Some things to verify are:
Is a naming service running? If not, start the ORBD naming
service as described in the document Starting and Stopping
ORBD.
Are the -ORBInitialHost and
-ORBInitialPort values being set correctly for the
naming service? If you are uncertain about what the settings should
be, read the document Starting and Stopping
ORBD.
Are the client and server applications aware of the port number
(and machine name, if applicable) where the Naming Service is
running? Read Starting and Stopping
ORBD for more information on how to do this.
COMM_FAILURE/208. vmcid: SUN minor code:
208 literally means "CONNECTION ABORT", which generally means
the connection has been dropped.
COMM_FAILURE/209. vmcid: SUN minor code:
209 literally means "CREATE_LISTENER_FAILED": Unable to
create the listener thread on the specific port. Either the post is
taken or there was an error creating the daemon thread. This
generally indicates that the port on which you are trying to run
the naming service is in use by another process. If you are running
on Solaris, you could discover whether or not something is running
on this port using the following terminal prompt command:
netstat | grep port_number
OBJECT_NOT_EXIST/204. vmcid: SUN minor
code: 204 literally means "SERVANT_NOT_FOUND". It is only
thrown in one place:
corba.INSSubcontract.getINSReference.
MARSHAL/217. vmcid: SUN minor code:
217 means that your client tried to send either a
wchar or wstring in GIOP 1.0, which is
not legal in the spec.
MARSHAL/202. vmcid: SUN minor code:
202 means that the code is attempting to marshal an object
that derives from org.omg.CORBA.Object, but that
particular instance has never been connected to an ORB. When using
the POA, you need to register the object with the POA first. If you
need more information on how to register an object with the POA,
refer to Portable Object Adapter (POA) or the
Getting Started with Java™ IDL
tutorial.
BAD_PARAM/201. vmcid: SUN minor code:
201 literally means "NULL_PARAM". This exception often occurs
because a Java null was given to a write
method such as write_string,
write_octet_array, etc. You cannot return a Java
null as the result of a Java method.
org.omg.CORBA.INTERNAL. vmcid: SUN minor
code: 208 means Unable to determine local hostname using
InetAddress.getLocalHost().getHostName().
The ORB uses
InetAddress.getLocalHost().getHostName() to create a
reference to the name service for looking for and/or binding
references. It also uses
InetAddress.getLocalHost().getHostName() on the server
side to create remote object references (i.e., IORs) that contain
the name/port of the server (rather than a dotted-decimal/port
pair).
To avoid the call to getHostName, you can set the
following properties (refer to Starting and Stopping
ORBD if you are not sure how to do this):
Set com.sun.CORBA.ORBServerHost to the DNS name or
dotted-decimal address of the server if the ORB is acting as a
server.
Set com.sun.CORBA.ORBInitialHost to the DNS name
or dotted-decimal address of the name server.
NOTE: These properties are proprietary and are subject
to deletion or change.
The longer version of this question was as follows:
My server code needs multiple JAR files in the
classpath. When I register my server using the
servertool, and try to specify the classpath, I get
the syntax of the register command. I assume my
command line is exceeding the limit.
How do I specify a really long classpath while registering the
server in the servertool?
The servertool does accept multiple JAR files,
however, there is currently a bug with the length of the command
line buffer in servertool. Read more about the
servertool wrapper bug, 4482166.
The workaround is to call the ServerTool class to
start the server, rather than starting the server from within
servertool, such as:
${JAVA_HOME}/bin/java com.sun.corba.se.internal.Activation.ServerTool
-ORBInitialPort ${ORB_INITIAL_PORT} -cmd register -server
sample.MyServer -classpath jar1:jar2:jar3 -applicationName sample
Please note that the name of the servertool
class may change in future releases.
If the naming service fails to startup on Linux,
include the following lines in the /etc/hosts file:
<Local Host IP Address> localhost
<Local Host IP Address> <HostName>
where <Local Host IP Address> is the IP address
where the naming service (tnameserv,
orbd) is started.
Features
What is the thread model
supported by the CORBA implementation in this release?
The Java CORBA ORB shipped in Java SE is
multi-threaded. On the server side, we have a thread pool such that
each incoming request is handled by a separate thread. If all the
pool's threads are in use when a new request comes in, a new thread
is created and added to the pool. The thread is returned to the
pool after the request is finished.
The Java CORBA ORB is threaded to allow scalability and
concurrent request processing. The SINGLE_THREAD option for the POA
threading policy is not supported.
The threading model for the Java CORBA ORB is implicit:
the user does not set the thread policy for the ORB. There are no
external, user-level APIs exposed for controlling the threading
model or the number of threads.
Does
Java IDL contain notification/event services? an Interface
Repository?
No, it does not. If you need one of these services, you
can implement one, you can purchase one off the shelf, or you can
search for one freely available to start things off with. You can
plug-in 3rd party services such as these to the ORB using INS
technology.
How can I run the Hello World
example on two machines?
You need to use the -ORBInitialHost <Host Name
where Name Service is Launched> option when starting the
client and/or server (whichever is not running on the same machine
as the name server). This way the client and server know where to
find the Name Service. An example can be found at Java IDL: The "Hello World"
Example on Two Machines.
Is Java IDL
technology compliant with CORBA specifications?
For compliance information for CORBA technology shipped
with J2SE 5.0, read the CORBA compliance statement at Official Specifications for CORBA support in J2SE 5.0.
Compatibility/Interoperability
With which CORBA
specifications does J2SE 5.0 comply?
See Official Specifications for CORBA
support in J2SE 5.0.
How can I specify
a different ORB?
To use an ORB other than the Java CORBA ORB in your
application, you can set the org.omg.CORBA.ORBClass
property to the ORB of your choice. For example, use code as shown
in the example to explicitly set the ORB to the ORB-implementation
you would prefer to use:
public class MyApp {
public static void main( String args[] ) {
Properties properties = System.getProperties();
properties.put( "org.omg.CORBA.ORBClass",
"<com.other_company.package.ORB>" );
try {
ORB orb = ORB.init( args, properties);
...
Check the vendor's documentation for information on setting
properties specific to their ORB implementation.
How can I test whether
my JDK ORB Client can communicate with another company's ORB
implementation?
This ORB has been tested as part of the J2EE certification
process, however, it has not been tested with all vendor's
standalone CORBA ORBs.
If INS is supported in the other vendor's service, then, try
this. Convert the Interoperable Object References (see Java ID: Interoperable Naming Service Example)
on the other vendor's ORB server to a string using the
ORB.object_to_string() method using INS. Write that string
to a file.
Do you have any examples that use a CORBA client and an EJB
server application?
A developer guide that includes an example application with a
C++ client and an Enterprise JavaBeans component can be found on
the Web site at: Enterprise
JavaBeans™ Components and CORBA Clients: A Developer's Guide.
How do I connect to a 3rd-party Naming Service from Sun's
ORB?
The recommended way is to use the Java IDL: Interoperable Naming Service (INS) Example,
if this option is supported by the 3rd-party Naming Service.
To use the Sun ORB with another vendor's Naming Service,
- Start the 3rd-party name server on Host <H> and Port.
<P>
- Pass the following argument to ORB.init():
-ORBInitRef NameService=corbaloc:iiop:1.2@:/NameService
When you do orb.resolve_initial_references( "NameService"
), you should be able to connect to 3rd-party Name Service. If
you are still not able to connect, try these troubleshooting
hints:
- Verify that the 3rd-party Name Service supports INS.
- Verify that the host and port information is accurate.
- Verify that the 3rd-party Name Service has been started
successfully.
- Verify that the 3rd-party Name Service supports GIOP 1.2. If
not, refer to the Name Server's documentation for the correct the
GIOP version, and modify the corbaloc: URL
accordingly.
- Determine if the 3rd-party Name Service has a different object
key it uses to contact NameService. If so, refer to the
Name Server's documentation.
Can I use the Java IDL
ORB with a C++ CORBA server? (interoperability)
The Java IDL ORB is an ORB completely written using
Java technology. The idlj compiler generates code that
follows the conventions defined in the IDL to Java Language
Mapping Specification. The Java ORB does not provide a
compiler that generates code in any languages other than the Java
platform. If you want to test interoperability between the Java ORB
and an ORB written in another language (such as C++), you will need
to find an ORB written in that language and a compiler that
conforms to the specific language mapping. Language mapping
specifications are available from the Object Management Group Web
site at http://www.omg.org/. A
user who wants to use the Java platform on one side and C++ on the
other will only share the IDL. You will have to use your C++ ORB's
tools to generate the stubs and skeletons for use with the C++ ORB,
but you don't have to change the IDL at all. To find a vendor that
provides a CORBA ORB and a language mapping compiler in the
language you are working with, search the Web for "C++ CORBA ORB",
or equivalent.
A developer guide that includes an example application with a
C++ client and an Enterprise JavaBeans component can be found on
the Web site at: Enterprise
JavaBeans™ Components and CORBA Clients: A Developer's Guide.
Although it is true that ORBs written in different
languages should be able to talk to each other, we haven't tested
the interoperability of the Java ORB with other vendor's
ORBs.
General
Should I use Java
IDL or Java RMI-IIOP technology?
This is a fundamental question and it's important to understand
the distinction between these two ways of integrating the Java
programming language with CORBA.
Java IDL technology is for CORBA programmers who want to program
in the Java programming language based on interfaces defined in
CORBA Interface Definition Language (IDL). This is "business as
usual" CORBA programming, supporting Java in exactly the same way
as other languages like C++ or COBOL.
Java Remote Method Invocation
over Internet Inter-ORB Protocol ("RMI-IIOP") technology is for
Java programmers who want to program to the Java Remote Method
Invocation ("Java RMI") interfaces, but use IIOP as the underlying
transport. RMI-IIOP provides interoperability with other CORBA
objects implemented in various languages - but only if all the
remote interfaces are originally defined as Java RMI interfaces. It
is of particular interest to programmers using Enterprise
JavaBeans™ (EJB™) technology, since the EJB remote object model
is based on Java RMI technology.
Where can I download the
idltojava compiler?
The idltojava compiler is no longer available for
download. We highly recommend that you use the latest version of
the IDL-to-Java compiler, idlj.
To get the latest version of the IDL-to-Java compiler, download
the latest version of the Java™
Platform, Standard Edition (Java SE). When Java SE is
installed, idlj will be located in the bin
directory.
Other troubleshooting information related to idltojava
is located in the Java IDL
FAQ for J2SE v.1.3.
What are my options for
developing CORBA applications using Java technology?
CORBA technology as part of the Java 2 platform
consists of an Object Request Broker
(ORB) written in the Java language (with a small bit of native
code), the RMI programming model, and
the IDL programming
model.
The "magic" that gives us the cross-language,
cross-vendor interoperability is the Internet InterORB Protocol, or
IIOP. IIOP can be a transport protocol for distributed applications
written in either IDL or Java RMI. IIOP allows distributed objects
to conform to OMG's CORBA specification.
When using the IDL programming model, the interface is
everything! It defines the points of entry that can be called from
a remote process, such as the types of arguments the called
procedure will accept, or the value/output parameter of information
returned. Using IDL, the programmer can make the entry points and
datatypes that pass between communicating processes act like a
standard language.
CORBA is a language-neutral system in which the
argument values or return values are limited to what can be
represented in the involved implementation languages. In CORBA,
object orientation is limited only to objects that can be passed by
reference (the object code itself cannot be passed from
machine-to-machine) or are predefined in the overall framework.
Passed and returned types must be those declared in the
interface.
With RMI, the IDL and the implementation language are
the same thing, so you don't have to worry about mapping from one
to the other. Language-level objects (the code itself) can be
passed from one process to the next. Values can be returned by
their actual type, not the declared type. Or, you can compile the
interfaces to generate IIOP-compliant stubs and skeletons to talk
to objects written on other machines in other CORBA-compliant
languages.
What is the difference
between Java IDL and Java RMI-IIOP?
This is a fundamental question and it's important to
understand the distinction between these two ways of integrating
the Java programming language with CORBA.
Java IDL is for CORBA programmers who want to program
in the Java programming language based on interfaces defined in
CORBA Interface Definition Language (IDL). This is "business
as usual" CORBA programming, supporting the Java language in
exactly the same way as other languages like C++ or
COBOL.
Java RMI-IIOP (Remote Method Invocation over Internet
Inter-ORB Protocol) is for developers who want to use the Java
programming language to program to the Java RMI interfaces, but use
IIOP as the underlying transport. Java RMI-IIOP provides
interoperability with other CORBA objects implemented in various
languages - but only if all the remote interfaces are originally
defined as Java RMI interfaces. It is of particular interest to
programmers using Enterprise JavaBeans (EJB), since the remote
object model for EJB's is RMI-based.
There are several scenarios that will define how you
will want to create distributed CORBA applications. Here are some
of them:
-
Java IDL - If you have been developing CORBA
applications using IDL for some time, you will probably want to
stay in this environment. Create the interfaces using IDL, and
define the client and server applications using the Java
programming language to take advantage of its portability, its
highly productive implementation environment, and its very robust
platform.
-
RMI-JRMP - If all of your applications are written in
the Java programming language, you will probably want to use Java
RMI technology to enable communication between Java objects on
different virtual machines and different physical machines. Using
Java RMI without its IIOP option leverages its strengths of code
portability, security, and garbage collection.
-
Java RMI-IIOP - If you are writing most of your new
applications using the Java programming language, but need to
maintain legacy applications written in other programming languages
as well, you will probably want to use Java RMI with its IIOP
compiler option.
For more information on product limitations, read
Limitations.
The most recent versions of standard tag allocation
files can be found at the OMG Web site: http://www.omg.org/.
