Compiling JNI C++ Native Code with x86_64-w64-mingw32-g++

Question

I want to compile and run a simple Hello World program that declares and calls a native print method (defined in C++) from Java.

HelloCPP.java

class HelloCPP{
    private native void print();
    public static void main(String [] args){
        new HelloCPP().print();
    }
    static{
        System.loadLibrary("HelloCPP");
    } 
}

HelloCPP.cpp

#include <jni.h>
#include<iostream>
#include "HelloCPP.h" 
using namespace std;

extern "C" 
JNIEXPORT void JNICALL Java_HelloCPP_print(JNIEnv *env, jobject obj){
    cout << "Hello World from C++!" << endl;
    return; 
}

In the command prompt I run the following:

javac HelloCPP.java
javah -jni HelloCPP
86_64-w64-mingw32-g++ -c -I"C:\Java\jdk1.8.0_171\include" -I"C:\Java\jdk1.8.0_171\include\win32" HelloCPP.cpp
x86_64-w64-mingw32-g++ -shared -o HelloCPP.dll HelloCPP.o
java -Djava.library.path=. HelloCPP

Then the infamous DLL linking/loading error

Exception in thread "main" java.lang.UnsatisfiedLinkError:<"MyProjectDirectory">\HelloCPP.dll: Can't find dependent libraries at java.lang.ClassLoader$NativeLibrary.load(Native Method) at java.lang.ClassLoader.loadLibrary0(ClassLoader.java:1941) at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1857) at java.lang.Runtime.loadLibrary0(Runtime.java:870) at java.lang.System.loadLibrary(System.java:1122) at HelloCPP.(HelloCPP.java:8)

Attempted Solutions

java -Djava.library.path=. HelloCPP is supposed to check the current project directory which is where the dll is built and should link fine
Tried copying the dll into a another folder and adding that folder directory to the path system environment variable
Used the Dependency Walker and noticed HelloCPP.dll is looking for libstdc++-6.dll and other dlls
Tried copying these drivers into the same directory and then it causes a chain reaction looking for additional dlls
Tried adding commands like -static-libstdc++

Additional Notes

I can run this exact program with the native method in C and using x86_64-w64-mingw32-gcc, the DLL is found, linked, loaded and program runs fine
x86_64-w64-mingw32-g++ was downloaded through Cygwin
Switched to x86_64-w64-mingw32-g++ because I was having the same issue as Cygwin compilation error Problematic frame: # C [cygwin1.dll+0xd6d47] using JNI when using g++
Currently using Sublime text editor to write my Java and C++ files, then compiling through command prompt
If anyone can recommend me a good IDE to use for dev with JNI that would be great
First time posting hopefully did not miss anything important, have spent much time going through already asked questions

Cygwin is a layer for linux (?) programs. This lay mey not used by windows programs like java. Use a native windows compiler for the JNI part. — Konrad
@Konrad I thought Cygwin is a set of tools that essentially give a Linux like environment for Windows. Do not believe the compiler I am using is restricted to Linux, as I have been able to compile other non JNI C/C++ sources without issue — Richard S
What version of Java are you using? If it's a 64 bit version you can't load a 32 bit library with it. Afaik the compiler you're using always produces 32 bit binaries. — Jorn Vernee
@JornVernee Thank you. I had followed some other resource to supposedly check whether the DLL that was being built was 64bit. Switching to MinGW-W64 compiler has solved the issue for me. sourceforge.net/projects/mingw-w64/files/… in case anyone needs it — Richard S

Praveena Reddy Praveena Reddy · Accepted Answer · 2019-07-29T14:53:52

Java Code: helloworld.java

class helloworld{
    public native void hello();

    static {
            System.loadLibrary("hello");
    }
    public static void main(String args[]){
            new Helloworld().hello();
    }
}

cpp code: hello.cpp

#include<iostream>
#include "helloworld.h"
using namespace std;
JNIEXPORT void JNICALL Java_helloworld_hello(JNIEnv *env, jobject obj)
{
    cout<<"Hello World";

    return;
}

Commands

javac -h . helloworld.java
g++ -I /usr/lib/jvm/java-8-oracle/include/ -I /usr/lib/jvm/java-8-oracle/include/linux/ hello.cpp -shared -o libhello.so -fPIC
java -Djava.library.path=. helloworld

Compiling JNI C++ Native Code with x86_64-w64-mingw32-g++

1 Answers