remram44/java-cpp-example

Example of using C++ classes from Java. Showcases SWIG, JNA and JNI

Example of using C++ code from Java

This repository contains three separate examples of calling a simple C++ library from Java code.

The example library doesn't do anything but contains a class, MyClass, forcing us to support C++ (and not just plain C).

CMake is used to build this, since locating the dependencies got outside the range of my make-fu. The project is supposed to be portable to all major platforms.

Three different wrappers are used, documented below. Each one achieves the same goal, which is using this C++ class from Java code.

SWIG

This needs the SWIG tool: http://www.swig.org/

SWIG parses the C++ header file and generates both the C++ JNI code and the Java native and helper classes.

JNA

JNA allows Java code to use C dynamic libraries directly. Because our library is in fact C++, a small wrapper is included that wraps it as C code.

You will need the JNA jar to run this: https://github.com/java-native-access/jna

JNI

This examples uses JNI directly, without auto-generation. The MyClass class in Java code just declares its methods as being "native", they are provided by the dynamic library.

java-cpp-example's Issues

jna invokation problem

https://github.com/remram44/java-cpp-example/blob/master/java-jna/java/src/edu/nyu/cpptest/cpplib/MyClass.java

[root@SzfyTestServer backup]# java -Djna.debug_load=true -classpath .:jna-5.5.0.jar MyClass
Feb 12, 2020 11:33:56 AM com.sun.jna.Native extractFromResourcePath
INFO: Looking in classpath from sun.misc.Launcher$AppClassLoader@4e0e2f2a for /com/sun/jna/linux-x86-64/libjnidispatch.so
Feb 12, 2020 11:33:56 AM com.sun.jna.Native extractFromResourcePath
INFO: Found library resource at jar:file:/opt/backup/jna-5.5.0.jar!/com/sun/jna/linux-x86-64/libjnidispatch.so
Feb 12, 2020 11:33:56 AM com.sun.jna.Native extractFromResourcePath
INFO: Extracting library to /root/.cache/JNA/temp/jna15688228076106253.tmp
Feb 12, 2020 11:33:56 AM com.sun.jna.NativeLibrary loadLibrary
INFO: Looking for library '/root/cpp_test/java-cpp-example-master/cpplib/build/libcpplib.so'
Feb 12, 2020 11:33:56 AM com.sun.jna.NativeLibrary loadLibrary
INFO: Adding paths from jna.library.path: null
Feb 12, 2020 11:33:56 AM com.sun.jna.NativeLibrary loadLibrary
INFO: Trying /root/cpp_test/java-cpp-example-master/cpplib/build/libcpplib.so
Feb 12, 2020 11:33:56 AM com.sun.jna.NativeLibrary loadLibrary
INFO: Found library '/root/cpp_test/java-cpp-example-master/cpplib/build/libcpplib.so' at /root/cpp_test/java-cpp-example-master/cpplib/build/libcpplib.so
Exception in thread "main" java.lang.UnsatisfiedLinkError: Error looking up function 'MyClass': /root/cpp_test/java-cpp-example-master/cpplib/build/libcpplib.so: undefined symbol: MyClass
        at com.sun.jna.Function.<init>(Function.java:252)
        at com.sun.jna.NativeLibrary.getFunction(NativeLibrary.java:594)
        at com.sun.jna.NativeLibrary.getFunction(NativeLibrary.java:570)
        at com.sun.jna.NativeLibrary.getFunction(NativeLibrary.java:556)
        at com.sun.jna.Library$Handler.invoke(Library.java:243)
        at com.sun.proxy.$Proxy0.MyClass(Unknown Source)
        at MyClass.<init>(MyClass.java:23)
        at MyClass.main(MyClass.java:35)

when i test this demo it throw the exception, i wonder if 「cpplib_shared」 is casual, or can i use another name?

the second problem is if 「MyClass_」prefix is necessary?

How to run the executable

Hi, I have successfully compiled the project through cmake and make (without making any changes to the code). I can't figure out where the executable is being generated and how do I run the executable?

From some other JNI tutorials, I learned this
java -Djava.library.path=. <executable-name>
But I get the class not found error in this case

Thanks!

miss jna jar files

cmake error
how to resolve it?

How to generate cpplib DLL in Windows environment?