android-go/examples/jni/jni_android.go

package main

/*
#cgo LDFLAGS: -landroid

#include <stdlib.h>
#include <jni.h>
#include <android/log.h>

static jobject gClassLoader;
static jmethodID gFindClassMethod;

void
SetLoader(JNIEnv* env, jobject context) {
	jclass cclass = (*env)->GetObjectClass(env, context);
	jmethodID gcl_id = (*env)->GetMethodID(env, cclass, "getClassLoader", "()Ljava/lang/ClassLoader;");
	jobject loader = (*env)->CallObjectMethod(env, context, gcl_id);
	gClassLoader = (*env)->NewGlobalRef(env, loader);
	jclass lclass = (*env)->GetObjectClass(env, loader);
	gFindClassMethod = (*env)->GetMethodID(env, lclass, "findClass", "(Ljava/lang/String;)Ljava/lang/Class;");
}

jclass
FindClass(JNIEnv* env, char* name) {
	jstring strClassName = (*env)->NewStringUTF(env, name);
	return (*env)->CallObjectMethod(env, gClassLoader, gFindClassMethod, strClassName);
}

JNIEXPORT jobject
CreateObject(JNIEnv* env, jclass cls) {
	jmethodID init = (*env)->GetMethodID(env, cls, "<init>", "()V");
	return (*env)->NewObject(env, cls, init);
}

void CallVoidMethod(JNIEnv *env, jobject obj, jmethodID methodID) {
	(*env)->CallVoidMethod(env, obj, methodID);
}

jint CallIntMethod(JNIEnv *env, jobject obj, jmethodID methodID) {
	return (*env)->CallIntMethod(env, obj, methodID);
}

jmethodID GetMethodID(JNIEnv *env, jclass clazz, const char *name, const char *sig) {
	return (*env)->GetMethodID(env, clazz, name, sig);
}

jint GetEnv(JavaVM *vm, JNIEnv **env, jint version) {
	return (*vm)->GetEnv(vm, (void **)env, version);
}

jint AttachCurrentThread(JavaVM *vm, JNIEnv **p_env, void *thr_args) {
	return (*vm)->AttachCurrentThread(vm, p_env, thr_args);
}

jint DetachCurrentThread(JavaVM *vm) {
	return (*vm)->DetachCurrentThread(vm);
}

*/
import "C"

import (
	"errors"
	"fmt"
	"log"
	"runtime"
	"unsafe"
)

var theJVM *C.JavaVM
type JNIEnv = C.JNIEnv

func SetJVM(jvm, context uintptr) {
	log.Print("set theJVM")
	theJVM = (*C.JavaVM)(unsafe.Pointer(jvm))
	log.Printf("theJVM = %d", uintptr(unsafe.Pointer(theJVM)))
	RunInJVM(func(env *C.JNIEnv) {
		C.SetLoader(env, (C.jobject)(context))
	})
}

func FindClass(env *C.JNIEnv, name string) C.jclass {
	cname := C.CString(name)
	defer C.free(unsafe.Pointer(cname))
	return C.FindClass((*C.JNIEnv)(env), cname)
}

func JniCallVoidMethod(env *C.JNIEnv, obj C.jobject, methodID C.jmethodID) {
	C.CallVoidMethod(env, obj, methodID)
}

func JniCallIntMethod(env *C.JNIEnv, obj C.jobject, methodID C.jmethodID) int {
	return (int)(C.CallIntMethod(env, obj, methodID))
}

func JniGetMethodID(env *C.JNIEnv, cls C.jclass, name, sig string) C.jmethodID {
	cname := C.CString(name)
	defer C.free(unsafe.Pointer(cname))
	csig := C.CString(sig)
	defer C.free(unsafe.Pointer(csig))
	return C.GetMethodID(env, cls, cname, csig)
}

func CreateObject(env *C.JNIEnv, cls C.jclass) C.jobject {
	return C.CreateObject(env, (C.jclass)(cls))
}

func RunInJVM(f func(env *C.JNIEnv)) {
	runtime.LockOSThread()
	defer runtime.UnlockOSThread()
	var env *C.JNIEnv
	var detach bool
	log.Printf("RunInJVM(): theJVM = %d", uintptr(unsafe.Pointer(theJVM)))
	if res := C.GetEnv(theJVM, &env, C.JNI_VERSION_1_6); res != C.JNI_OK {
		if res != C.JNI_EDETACHED {
			panic(fmt.Errorf("JNI GetEnv failed with error %d", res))
		}
		if C.AttachCurrentThread(theJVM, &env, nil) != C.JNI_OK {
			panic(errors.New("runInJVM: AttachCurrentThread failed"))
		}
		detach = true
	}

	if detach {
		defer func() {
			C.DetachCurrentThread(theJVM)
		}()
	}
	f(env)
}