Android loading may fallback to standard JVM (#9)

* Android loading may fallback to standard JVM

* Java code must target JVM 1.8 in order to be compatible Android.

Co-authored-by: Salomon BRYS <salomon@kodein.net>

jni/android/src/main/java/fr/acinq/secp256k1/jni/NativeSecp256k1AndroidLoader.kt

@@ -0,0 +1,31 @@
+package fr.acinq.secp256k1.jni
+
+import android.util.Log
+import fr.acinq.secp256k1.Secp256k1
+import fr.acinq.secp256k1.NativeSecp256k1
+import java.util.*
+
+public object NativeSecp256k1AndroidLoader {
+
+    @JvmStatic
+    @Synchronized
+    @Throws(Exception::class)
+    fun load(): Secp256k1 {
+        try {
+            System.loadLibrary("secp256k1-jni")
+            return NativeSecp256k1
+        } catch (ex: UnsatisfiedLinkError) {
+            // Purposefully not using Android Log
+            println("Could not load Android Secp256k1. Trying to extract JVM platform specific version.")
+            try {
+                val cls = Class.forName("fr.acinq.secp256k1.jni.NativeSecp256k1JvmLoader")
+                val load = cls.getMethod("load")
+                return load.invoke(null) as Secp256k1
+            } catch (_: ClassNotFoundException) {
+                throw ex
+            }
+
+        }
+    }
+
+}

jni/android/src/main/kotlin/fr/acinq/secp256k1/jni/NativeSecp256k1Loader.kt

@@ -1,16 +0,0 @@
-package fr.acinq.secp256k1.jni
-
-import fr.acinq.secp256k1.Secp256k1
-import fr.acinq.secp256k1.NativeSecp256k1
-
-public object NativeSecp256k1Loader {
-
-    @JvmStatic
-    @Synchronized
-    @Throws(Exception::class)
-    fun load(): Secp256k1 {
-        System.loadLibrary("secp256k1-jni")
-        return NativeSecp256k1
-    }
-
-}