JNIGI

Java Native Interface Golang Interface.

A package to access Java from Golang code. Can be used from a Golang executable or shared library. This allows for Golang to initiate the JVM or Java to start a Golang runtime respectively.

Compile

The CGO_CFLAGS needs to be set to add the JNI C header files. The compilevars.sh script will do this.

# put this in your build script
source <gopath>/src/tekao.net/jnigi/compilevars.sh <root path of jdk>

On Windows you can use compilevars.bat in the same way (but you don't need source at the begining).

Finding JVM at Runtime

Use the LoadJVMLib(jvmLibPath string) error function to load the shared library at run time. There is a function AttemptToFindJVMLibPath() string to help to find the library path.

Notes

Signals

The JVM calls sigaction, Golang requires that SA_ONSTACK flag be passed. Without this Golang will not be able to print the exception information eg. type, stack trace, line number. On Linux a solution is using LD_PRELOAD with a library that intercepts sigaction and adds the flag. (Code that does this: https://gist.github.com/timob/5d3032b54ed6ba2dc6de34b245c556c7)

Status

Has been used in Golang (many versions since 1.6) executable multi threaded applications on Linux / Windows.
Tests for main functions tests are present.
Documentation needed.

Changes

2020-12-09 Add go.mod file, updated import path to tekao.net/jnigi.
2020-08-21 Add ExceptionHandler interface for handling Java exceptions. Add 3 general handlers DescribeExceptionHandler (default), ThrowableToStringExceptionHandler and ThrowableErrorExceptionHandler.
2020-08-11 Add DestroyJavaVM support, JNI_VERSION_1_8 const
2019-05-29 Better multiplatform support, dynamic loading of JVM library.
2016-08-01 Initial version.

Example

package main

import (
    "fmt"
    "tekao.net/jnigi"
    "log"
)

func main() {
    if err := jnigi.LoadJVMLib(jnigi.AttemptToFindJVMLibPath()); err != nil {
        log.Fatal(err)
    }
    jvm, env, err := jnigi.CreateJVM(jnigi.NewJVMInitArgs(false, true, jnigi.DEFAULT_VERSION, []string{"-Xcheck:jni"}))
    if err != nil {
        log.Fatal(err)
    }

    hello, err := env.NewObject("java/lang/String", []byte("Hello "))
    if err != nil {
        log.Fatal(err)
    }

    world, err := env.NewObject("java/lang/String", []byte("World!"))
    if err != nil {
        log.Fatal(err)
    }

    v, err := hello.CallMethod(env, "concat", jnigi.ObjectType("java/lang/String"), world)
    if err != nil {
        log.Fatal(err)
    }
    greeting := v.(*jnigi.ObjectRef)

    v, err = greeting.CallMethod(env, "getBytes", jnigi.Byte|jnigi.Array)
    if err != nil {
        log.Fatal(err)
    }
    goGreeting := string(v.([]byte))

    // Prints "Hello World!"
    fmt.Printf("%s", goGreeting)

    if err := jvm.Destroy(); err != nil {
        log.Fatal(err)
    }
}

janmejay/jnigi