I have a DLL file mostly written in vb.net
It will take 2 parameters.
I am suppose to make use of this DLL in my java code and pass required 2 parameters.
How should I go about it?
Use JNI, Load your dll and call native functions
See
Examples
In Java there's basically two good options for this: (in order of recommendation)
If your DLL has C function headers (rather than C++ decorations), you should use JNA. It has a simple, declarative syntax and only requires writing some Java.
Write JNI bindings for your DLL (there'll be some Java and some C++ code involved).
Related
I am new to native code programming in java. i have client dll where they have exposed apis and also given api document.I want to use them in java.
I have written some code to load native library using system.loadLibrary and declared few native methods and able to call them successfully.
But they have some callback methods as well and few data structures that needs to be passed. I have written simlar classes in Java seeing their api. But it is not working.
i am confused about JNI or JNa uses. do I need to use them and create any header files as I already native methods are implmented.
i suppose jni to be used only when we need to develop some part of code in other language like c c++.
Creating header files and then implementing and creating dll. But thats already with me.
Whats the way to easily write those typedef in java??
and is my understanding correct that i dont need jni or jna for this?
I have existing cpp files from a project which I would like to use it for my application which is in Java. I cannot change the cpp files. How can I call the functions from Java?
I'm working in Windows 10 using JavaFX for my application. I've seen some articles about JNI but none seem to solve my issue.
If JNI or swig is not desired or seems too low level,
A really blunt approach is to wrap the .cpp in c/c++ program and built an .exe that dumps to stdout/file. Then execute that in java via an external shell command.
Another good alternative is
Apache thrift
This basicly handles everything and goes everywhere so to speak (works by auto-generating code to target languages) and it is one I usually recommend in RPC situations. However there could be more setup cost involved (in the end, depends on your actual needs) - also since you need to host the .cpp in a service, in your case, locally.
If you package your library inside a shared object or a dll, you can also use JNA: https://github.com/java-native-access/jna or https://github.com/java-native-access/jna/blob/master/www/GettingStarted.md
For example, you already have mapping to Windows API.
Another example is a mapping of mediainfo in Java: https://github.com/andersonkyle/mediainfo-java-api/blob/master/src/main/java/org/apothem/mediainfo/api/MediaInfo.java
Note that, as far as I understand it, this is based on JNI: it simplify the process since you mostly have to only declare interface on Java side and call appropriate method.
I am developing a Java application in which I need to call some C++ functions (from Google Talk library libjingle) . The objective is to run it all on Google App Engine (which only supports Python or Java).
How can I do this?
You need to define native methods in your java code for whatever you want to be implemented in C++ and directly access your native code. Then you run javah on your code and it will generate the C header files for you and you'll need to provide C++ implementations.
The native methods you can call from your Java code like any other methods and still they'll have their implementation written in C++ and talking to whatever other native library directly.
You then need to set the java.library.path system property to include the shared C/C++ libraries that you require: the google library and your own JNI implementation library would be required in this case.
If the library has C bindings through a DLL/SO, I usually prefer writing wrappers in Java using Java Native Access (JNA) rather than writing the bindings in C/C++ using the Java Native Interface (JNI). The former is easier to manipulate as the JNI access to Java objects is a real pain in the neck. However, it's not as obvious to wrap C++ classes using that API.
You might also want to look into the Simplified Wrapper and Interface Generator (SWIG) for automating part of this process!
You can't run native code on App Engine - only JRE code. If there's no avoiding the native code, you'll need to run this part of your app on another system, and call it from your App Engine app - or use the built-in XMPP API, in this case.
I have some dll files(not custom and not written by me) and I need to use the functions, that are c/c++ written, in these files in my java project. I googled and read many examples about JNI but they were all about writing your own program and dll and then reaching them. Also I don't think dllexport exists in these dlls, so dllimport/dllexport method is not available I guess.
How can I reach these functions?
Thanks in advance..
I'm sure, you looked at the JNI Tutorial at oracle already. I had a quick look at the part, where a native function is implemented and a dll is compiled and I don't think, that special conditions have to be met.
I'd give it a try with a single, easy function from that dll:
Write a simple class with just main method that uses one of the native methods (with easy parameters to have an easy start)
Generate the header file and
run the test application
If the dll is not 'jni compliant' (whatever that means), you'll know by then and then you probably know that you have to recompile the native code.
I have a .dll that was provided, and I need to interface with it using java.
Do I have to rewrite the C to use the JNI types provided in jni.h? as seen in java sun's jni example.
Otherwise, How do i declare the native function my java function to pass and receive pointers?
thanks
You may find JNA useful
"JNA provides Java programs easy access to native shared libraries (DLLs on Windows) without writing anything but Java code—no JNI or native code is required. This functionality is comparable to Windows' Platform/Invoke and Python's ctypes. Access is dynamic at runtime without code generation."
In a way, yes.
Most of the time you would just write a small "wrapper" dll with functions that would do the type conversions and delegate to the corresponding functions in the "real" DLL.
You can rewrite the C code of course, but it's not uncommon to write a wrapper (technically, using the Facade or Bridge pattern) for the C code. You write code that matches your expectations in the Java, and have that code call your existing C code.