How can I call a Go function from Java using the Java native interface?

Question

It is possible to call C methods through the JNA interface in Java. How can I reach the same functionality with Go?

package main

import "fmt"

import "C"

//export Add
func Add(x, y int) int {
    fmt.Printf("Go says: adding %v and %v\n", x, y)
    return x + y
}

Answer 1

After review of the documentation about Go Shared Libraries:

It is possible to integrate the call of Go functions from Java Spring Batch. Below is a short example:

Go function:

package main

import "fmt"

import "C"

//export Add
func Add(x, y int) int {
    fmt.Printf("Go says: adding %v and %v\n", x, y)
    return x + y
}

After that, execute the command to generate the binary files:

go build -buildmode=c-shared -o bin/lib-cqm-transformer.so src/cqm_transformer.go

This generates the binary files:

ls -la bin/
total 2860
drwxrwxr-x 2 dmotta dmotta    4096 abr 23 01:13 .
drwxrwxr-x 5 dmotta dmotta    4096 abr 23 00:35 ..
-rw-r--r-- 1 root   root      1558 abr 23 01:13 lib-cqm-transformer.h
-rw-r--r-- 1 root   root   2915112 abr 23 01:13 lib-cqm-transformer.so

Finally, create the JNA class:

package com.XX.XX.batch.engine.transformer;

import com.sun.jna.Library;
import com.sun.jna.Native;

public class GoEngineTransformerTest {
  static GoCqmTransformer GO_CQM_TRANSFORMER;
  static {
    String os = System.getProperty("os.name").toLowerCase();
    String libExtension;
    if (os.contains("mac os")) {
      libExtension = "dylib";
    } else if (os.contains("windows")) {
      libExtension = "dll";
    } else {
      libExtension = "so";
    }

    String pwd = System.getProperty("user.dir");
    String lib = pwd + "/golang/bin/lib-cqm-transformer." + libExtension;
    GO_CQM_TRANSFORMER = (GoCqmTransformer) Native.loadLibrary(lib, GoCqmTransformer.class);
  }

  public interface GoCqmTransformer extends Library {
    long Add(long x, long y);
  }

  public static void main(String[] args) {
    System.out.println("Java says: about to call Go ..");
    long total = GO_CQM_TRANSFORMER.Add(30, 12);
    System.out.println("Java says: result is " + total);
  }
}

After that, execute from the main Java class. Results:

Java HotSpot(TM) 64-Bit Server VM warning: You have loaded library /tmp/jna1412558273325390219.tmp which might have disabled stack guard. The VM will try to fix the stack guard now.
It's highly recommended that you fix the library with 'execstack -c <libfile>', or link it with '-z noexecstack'.
Java says: about to call Go ..
Go says: adding 30 and 12
Java says: result is 42