├── cscalljava.csproj
├── Makefile
├── MyTest.java
├── README.md
├── init.cs
└── wraper.cpp


/cscalljava.csproj:
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1 | <Project Sdk="Microsoft.NET.Sdk">
2 | 
3 |   <PropertyGroup>
4 |     <OutputType>Exe</OutputType>
5 |     <TargetFramework>netcoreapp2.0</TargetFramework>
6 |   </PropertyGroup>
7 | </Project>
8 | 


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/Makefile:
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1 | wraper.so:wraper.cpp 
2 | 	g++ -shared -o wraper.so  -L/usr/lib/jvm/java-1.9.0-openjdk-amd64/lib/amd64/server  -I/usr/lib/jvm/java-9-openjdk-amd64/include -I/usr/lib/jvm/java-9-openjdk-amd64/include/linux/  ./wraper.cpp -fPIC -ljvm
3 | 	export LD_LIBRARY_PATH=/usr/lib/jvm/java-1.9.0-openjdk-amd64/lib/amd64/server 
4 | 


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/MyTest.java:
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 1 | public class MyTest {
 2 |      private static int magic_counter=777;
 3 | 
 4 |      public static void sayHi() {   // <=== We will call this
 5 |          System.out.println("Hello, World from java");
 6 |          System.out.println(magic_counter);
 7 |      }
 8 |      public static int Square(int n){
 9 |         return n*n;
10 |      }
11 | }
12 | 


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/README.md:
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 1 | # CSharpCallJava
 2 | C#  invoke Java via C++ as a wraper. 
 3 | 
 4 | C# invoke C++ via P/invoke. C++ starts a JVM to run the Java code.
 5 | 
 6 | C# code should be compiled in .NET core 2.0 
 7 | 
 8 | You should edit the Makefile to set the Path of Java SDK
 9 | export LD_LIBRARY_PATH=/usr/lib/jvm/java-1.9.0-openjdk-amd64/lib/amd64/server 
10 | or add it into your enviroment
11 | # Compile:
12 | javac MyTest.java
13 | 
14 | make
15 | 
16 | dotnet build
17 | 


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/init.cs:
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 1 | using System;
 2 | using System.Runtime.InteropServices;
 3 | namespace invoke
 4 | {
 5 |     class Program
 6 |     {
 7 |         [DllImport("libc.so.6")]
 8 |          private static extern int getpid();
 9 | 		 // You should edit the path of you .so lib
10 |         [DllImport("./wraper.so",EntryPoint="Invokejava")]
11 |          private static extern int Invokejava(string message);
12 | 
13 |         static void Main(string[] args)
14 |         {
15 |          int pid= getpid();
16 |          Console.WriteLine(pid);
17 |             Console.WriteLine("Hello World!");
18 |             int status= Invokejava("Hi C# to cpp");
19 |             Console.WriteLine(status);
20 |     
21 |         }
22 |     }
23 | }
24 | 


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/wraper.cpp:
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 1 | #include <jni.h>
 2 | #include <iostream>
 3 | #include <cstdio>
 4 | using namespace std;
 5 | extern "C"{
 6 | int Invokejava(const char*  message)
 7 | {
 8 |        JavaVM *jvm;                      // Pointer to the JVM (Java Virtual Machine)
 9 |        JNIEnv *env;                      // Pointer to native interface
10 |            //================== prepare loading of Java VM ============================
11 |        JavaVMInitArgs vm_args;                        // Initialization arguments
12 |        JavaVMOption* options = new JavaVMOption[1];   // JVM invocation options
13 |        options[0].optionString = "-Djava.class.path=.";   // where to find java .class
14 |        vm_args.version = JNI_VERSION_1_6;             // minimum Java version
15 |        vm_args.nOptions = 1;                          // number of options
16 |        vm_args.options = options;
17 |        vm_args.ignoreUnrecognized = false;     // invalid options make the JVM init fail
18 |            //=============== load and initialize Java VM and JNI interface =============
19 |        jint rc = JNI_CreateJavaVM(&jvm, (void**)&env, &vm_args);  // YES !!
20 |        delete options;    // we then no longer need the initialisation options.
21 |        if (rc != JNI_OK) {
22 |               // TO DO: error processing...
23 |              cin.get();
24 |              exit(EXIT_FAILURE);
25 |        }
26 |           //=============== Display JVM version =======================================
27 |        cout << "JVM load succeeded: Version ";
28 |        jint ver = env->GetVersion();
29 |        cout << ((ver>>16)&0x0f) << "."<<(ver&0x0f) << endl;
30 |         jclass cls2 = env->FindClass("MyTest");
31 |         if(cls2== nullptr){
32 |         cerr<<"ERROR : class not find";
33 |         }
34 |         else{
35 |            printf("%s",message);
36 |             cout<<"Class MyTest found"<<endl;
37 |             jmethodID mid= env->GetStaticMethodID(cls2,"sayHi","()V");
38 |             if(mid==nullptr)
39 |                 cerr<<"ERROR : method void sayHi() not found!"<<endl;
40 |             else{
41 |             env->CallStaticVoidMethod(cls2,mid);
42 |             }
43 |         }
44 |        jmethodID mid2 = env->GetStaticMethodID(cls2,"Square","(I)I");
45 |         if(mid2==nullptr){
46 |         cerr<<"ERROR: method Square(int) not find!"<<endl;
47 |         }
48 |         else{
49 |             int i;
50 |             cout<<"input a number"<<endl;
51 |             cin>>i;
52 |             cout<<"get Square return = "<< env->CallStaticIntMethod(cls2,mid2,(jint)i);
53 |             cout<<endl;
54 |         }
55 |        // TO DO: add the code that will use JVM <============  (see next steps)
56 | 
57 |        jvm->DestroyJavaVM();
58 |        cin.get();
59 |        return 0;
60 | }
61 | }
62 | 


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