I have been asked by someone to implement communication between a Java application and a Pascal application. I have very little knowledge of Pascal. Is it possible? If so, can someone provide some guidance? Currently I am clueless at this point.
Sure this is possible.
In case if you simply need to use a set of functions implemented on Pascal you can use JNI with the same way as C. I.e. create a DLL for Windows or shared library for UNIX using Pascal with the JNI specific function names.
You can use pas2jni instead of javac -h (or javah) or make your live even simple using JNA
If you are interesting with multi-process integration, i.e. you have one app written on Java and another app written on Pascal you can use SOAP or REST API.
To implementing SOAP on Pascal you can use
Web Service Toolkit
To implement REST on Pascal you can use
mORMot toolkit.
You can use
File system (cross file communications). i.e. you have one shared file which can be read/written by both apps
Network (SOAP/REST)
Is there a java api similar to RAPI? I want to be able to access files on the windows mobile device using a java desktop program.
Thanks.
You could use RAPI itself, and access it from Java using JNI or a wrapper like Swig
We were also looking for a similar API in Java but unfortunately none is available. I wrote my own RAPI wrapper using JNI and used that in my program.
The main problem with JNI is that any un-handled exceptions/faults cause the calling Java program to shutdown as well. Do keep that in mind when writing your wrapper. There are different approaches to safe guard these, the simplest and common approach is to write a standalone program written in .Net/C++ that communicates with the RAPI and your Java program communicates with that program using pipes/files etc. this way you also don't have to write a JNI wrapper :-)
We need to use a Java library from C++ code. An idea that I had is that if we could build a C++ client for Java RMI (ideally using some framework or wizard), than we could run the Java lib as a separate server. This seem cleaner than trying to run Java VM within a C++ application.
Alternatively, if you have any other idea on how to use Java from C++, I'd be glad to hear. We work on Linux.
thanks a lot,
David
RMI is intimately linked with the JVM (and Java serialisation), so that isn't reasonable. Not unless the C++ client includes a JVM.
CORBA is the obvious platform-independent equivalent. It is a bit design-by-committee and is now considered very untrendy. WS-/JAX-WS is kind of the modern equivalent with lots of XML, but may be considered a bad attempt at CORBA. REST is an attempt at a lightweight WS-, but see Joel's Stackoverflow DevDay rant on claimed "simplicity".
You could go old school and just shove byte over TCP/IP (or pipes). Or if local, just exec the C++ program. Or use a native interface: JNI built into the JRE, or JNA a nicer layer over the top.
Don't bother with RMI. If you're willing to take the step of making the Java application a separate server, have your C++ client communicate via JMS (Java Messaging Service). ActiveMQ is a free JMS message broker implementation that provides embedded services as well as C++ client libraries. The JMS protocol is dead simple to use (at least from Java). Its probably not as flexible as doing REST, but it would likely be an easier implementation.
JNI was the intended solution to the problem of C/C++ to Java integration. It's not difficult.
Message Queues are better for larger grained interactions, or remote interactions where the message queue is accessible over the network.
CORBA and RMI were also intended to be network access mechanisms.
From your description you don't want that. You want to consume a Java library in C++, and to do that, you use JNI.
How to start the JVM and invoke a Java method, from C++ (JDK doc)
I'm supporting a large system written in C++ and we now have a requirement for our application to talk with a third party system which only provides a JTAPI interface. It would appear that I am stuck writing a JTAPI proxy in Java that talks JTAPI on one side and some more language-neutral API on the other. However, this feels like it should be a solved problem and I don't want to unnecessarily re-invent the wheel. What is the best solution to interface to JTAPI from C++? Does such a proxy already exist, or perhaps is there a solution that does not require a Java layer?
This article shows a way to call Java objects from C++.
You can also think of embedding the JVM in your C++ program. This page talks about a possible way to do this. Also see: Embed Java code into your native apps
If your C++ system provides an API, then the easier approach is to write a Java program that wraps the C++ API (using JNI) and call the JTAPI library from there.
I have a really simple Java class that effectively decorates a Map with input validation, with the obvious void set() and String get() methods.
I'd like to be able to effectively call those methods and handle return values and exceptions from outside the JVM, but still on the same machine Update: the caller I have in mind is not another JVM; thanks #Dave Ray
My implementation considerations are typical
performance
ease of implementation and maintenance (simplicity?)
reliability
flexibility (i.e. can I call from a remote machine, etc.)
Is there a 'right way?' If not, what are my options, and what are the pro/cons for each?
(Stuff people have actually done and can provide real-life feedback on would be great!)
Ok. Here's another try now that I know the client is not Java. Since you want out-of-process access and possibly remote machine access, I don't think JNI is what you want since that's strictly in-process (and a total hassle). Here are some other options:
Raw Sockets : just set up a listener socket in Java and accept connections. When you get a connection read the request and send back a response. Almost every language can use sockets so this is a pretty universal solution. However, you'll have to define your own marshalling scheme, parsing, etc.
XML-RPC : this isn't as hip these days, but it's simple and effective. There are Java libraries as well as libraries in most other languages.
CORBA : as mentioned above, CORBA is an option, but it's pretty complicated and experts are getting harder to come by.
Web Server : set up an embedded web server in your app and handle reqests. I've heard good things about Jetty or you can use the one provided with Java. I've used the latter successfully to server KML files to Google Earth from a simulation written in Java. Most other languages have libraries for making HTTP requests. How you encode the data (XML, text, etc) is up to you.
Web Services : This would be more complicated I think, but you could use JAX-WS to expose you objects as web services. NetBeans has pretty nice tools for building Web Services, but this may be overkill.
Will you be calling from another JVM-based system, or is the client language arbitrary? If you're calling from another JVM, one of the simplest approaches is to expose your object as an MBean through JMX. The canonical Hello World MBean is shown here. The pros are:
Really easy to implement
Really easy to call from other JVMs
Support for remote machines
jconsole allows you to manually test your MBean without writing a client
Cons:
Client has to be on a JVM (I think)
Not great for more complicated data structures and interactions. For example, I don't think an MBean can return a reference to another MBean. It will serialize and return a copy.
Since your callers are not Java apps and you're already foreseeing networked callers, RMI-IIOP (CORBA) might be an option. Though it's definitely not easy to implement, it has the advantage of being a widely-recognized standard.
Since your caller is not JVM-based, this is a question of inter-process communication with JVM. The options I have in mind are:
Communicate over a socket: make your JVM listen to incoming connections and caller send commands
Communicate using shared files (caller writes to file, JVM polls and updates)
Using JNI, start JVM inside a callers process and then use RMI/MBeans to communicate with the first ("server") JVM. Caller will have access to results using JNI
Option 3 IMO is the most "Java" way of doing this, and is the most complex/error-prone.
Option 2 is ugly but simple
Option 1 is moderately easy (java part) and otherwise ok.
For ease of use, I would use Spring Remoting. If you are already using Spring in your project, that's a no brainer. If you arent ... well you should have a look anyway.
Spring provides an abstraction that allow you to switch remoting protocols easily. It supports the most widely deployed protocols (SOAP, Hessian, Burlap, RMI, ...). If you are calling from non Java code, Hessian has support in a number of other languages, is known to be more efficient than SOAP and easier than CORBA.
Beanshell is a shell-like java interpreter that can be exposed over a network socket. Basically you do this from java:
i = new bsh.Interpreter();
i.set( "myapp", this ); // Provide a reference to your app
i.eval("server(7000)");
and then you do this from anywhere else:
telnet localhost 7001
myapp.someMethod();
This little utility does remote java invocations much more easily than JNI or RMI ever has.
For more, start at: http://www.beanshell.org/manual/remotemode.html
JNI (Java Native Interface) allows access to java code from C or C++.
I have an Inno Setup script (installing a Java program) which calls some Java methods to perform some operations or check some conditions.
I (actually my predecessor) just instanciate java.exe on each call. Which is, obviously, costly, although not critical in my case (and the Windows cache kicks in, I suppose).
An alternative is to use some inter-language communication/messaging, your Java program acting as a server. Corba comes to mind, as it is language agnostic. But a bit heavy, perhaps. You can use sockets. RPC is another buzzword too, but I haven't much experience in the field.
What you want is the Java Native Interface (JNI), despite the difficulties that it may present. There is no other equivalent technology that will be as easy to implement.
As mentioned in the comments for the preceding answer, the JNI is optimized for calling native code from Java, but it can also be used for the reverse with a little work. In your native code you'll need to implement the JNI entry point--something like SetMapPointer()--then call that function from the Java code once the Map is built. The implementation of SetMapPointer() should save the Java object pointer someplace accessible, then the native code can invoke Java methods on it as needed.
You'll need to make sure that this happens in the right order (i.e. the native code doesn't try to access the Map before it's been built and passed to native code), but that shouldn't be an especially hard problem.
Another alternative to consider if the other process will be on the same machine and the OS is POSIX-compliant (not Windows) is Named Pipes.
The outside process writes the operations, as strings or some other agreed-upon byte encoding, to the named pipe while the Java application is reading from the pipe, parsing up the incoming operations and executing them against your object.
This is the same strategy that you would use for socket connections, just instead of a SocketInputStream you'd be reading from a FileInputStream that is attached to a named pipe.
An alternative to CORBA is ICE, unless the licence is a problem (it's GPL, but you can also buy a commercial licence).
It has pretty much all the benefits of CORBA, but ZeroC, the vendor, provides bindings for many different languages. CORBA vendors tend to only provide one or two language bindings, and then you start finding compatibility problems.
The documentation is also excellent. I wouldn't have said it was particularly easy to pick up, but probably easier than CORBA.
Otherwise, another option I don't think has been mentioned is the new middleware/RPC framework developed by Cisco, now donated to Apache, called Etch. It's still pretty new though, and documentation is sparse.