dawndiy / jnigi

Golang Java JNI library

JNIGI

Java Native Interface Go Interface.

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

Docs: https://pkg.go.dev/tekao.net/jnigi

Pull Requests

Please make sure: go test works, add any doc comments for function signature changes.

v1

As of 2021-12-05 the master branch will be version 2. Packages that used JNIGI before this should update their go.mod to set v1 as the version. Or update their code to be compatible with version 2.

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.

Status

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

Changes

• 2022-07-29 Android support, see timob#55
• 2021-12-05 Version 2: New idiomatic API. Converter interfaces. Add docs.
• 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"
    "runtime"
)

func main() {
    if err := jnigi.LoadJVMLib(jnigi.AttemptToFindJVMLibPath()); err != nil {
        log.Fatal(err)
    }

    runtime.LockOSThread()
    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)
    }

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

    var goGreeting []byte
    err = greeting.CallMethod(env, "getBytes", &goGreeting)
    if err != nil {
        log.Fatal(err)
    }

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

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