Minimum changes for Android support

Package.swift

@@ -362,7 +362,7 @@ let package = Package(
       name: "CSwiftJavaJNI",
       swiftSettings: [
         .swiftLanguageMode(.v5),
-        .unsafeFlags(["-I\(javaIncludePath)", "-I\(javaPlatformIncludePath)"])
+        .unsafeFlags(["-I\(javaIncludePath)", "-I\(javaPlatformIncludePath)"], .when(platforms: [.macOS, .linux, .windows]))
       ]
     ),
 

Sources/CSwiftJavaJNI/AndroidSupport.cpp

@@ -0,0 +1,98 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2025 Apple Inc. and the Swift.org project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of Swift.org project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+#ifdef __ANDROID__
+
+#include <CSwiftJavaJNI.h>
+#include <android/log.h>
+#include <dlfcn.h>
+
+// these are not exported by the Android SDK
+
+extern "C" {
+  using JavaRuntime_GetDefaultJavaVMInitArgs_fn = jint (*)(void *vm_args);
+  using JavaRuntime_CreateJavaVM_fn = jint (*)(JavaVM **, JNIEnv **, void *);
+  using JavaRuntime_GetCreatedJavaVMs_fn = jint (*)(JavaVM **, jsize, jsize *);
+}
+
+static JavaRuntime_GetDefaultJavaVMInitArgs_fn
+    JavaRuntime_GetDefaultJavaVMInitArgs;
+static JavaRuntime_CreateJavaVM_fn JavaRuntime_CreateJavaVM;
+static JavaRuntime_GetCreatedJavaVMs_fn JavaRuntime_GetCreatedJavaVMs;
+
+static void *JavaRuntime_dlhandle;
+
+__attribute__((constructor)) static void JavaRuntime_init(void) {
+  JavaRuntime_dlhandle = dlopen("libnativehelper.so", RTLD_NOW | RTLD_LOCAL);
+  if (JavaRuntime_dlhandle == nullptr) {
+    __android_log_print(ANDROID_LOG_FATAL, "JavaRuntime",
+                        "failed to open libnativehelper.so: %s", dlerror());
+    return;
+  }
+
+  JavaRuntime_GetDefaultJavaVMInitArgs =
+      reinterpret_cast<JavaRuntime_GetDefaultJavaVMInitArgs_fn>(
+          dlsym(JavaRuntime_dlhandle, "JNI_GetDefaultJavaVMInitArgs"));
+  if (JavaRuntime_GetDefaultJavaVMInitArgs == nullptr)
+    __android_log_print(ANDROID_LOG_FATAL, "JavaRuntime",
+                        "JNI_GetDefaultJavaVMInitArgs not found: %s",
+                        dlerror());
+
+  JavaRuntime_CreateJavaVM = reinterpret_cast<JavaRuntime_CreateJavaVM_fn>(
+      dlsym(JavaRuntime_dlhandle, "JNI_CreateJavaVM"));
+  if (JavaRuntime_CreateJavaVM == nullptr)
+    __android_log_print(ANDROID_LOG_FATAL, "JavaRuntime",
+                        "JNI_CreateJavaVM not found: %s", dlerror());
+
+  JavaRuntime_GetCreatedJavaVMs =
+      reinterpret_cast<JavaRuntime_GetCreatedJavaVMs_fn>(
+          dlsym(JavaRuntime_dlhandle, "JNI_GetCreatedJavaVMs"));
+  if (JavaRuntime_GetCreatedJavaVMs == nullptr)
+    __android_log_print(ANDROID_LOG_FATAL, "JavaRuntime",
+                        "JNI_GetCreatedJavaVMs not found: %s", dlerror());
+}
+
+__attribute__((destructor)) static void JavaRuntime_deinit(void) {
+  if (JavaRuntime_dlhandle) {
+    dlclose(JavaRuntime_dlhandle);
+    JavaRuntime_dlhandle = nullptr;
+  }
+
+  JavaRuntime_GetDefaultJavaVMInitArgs = nullptr;
+  JavaRuntime_CreateJavaVM = nullptr;
+  JavaRuntime_GetCreatedJavaVMs = nullptr;
+}
+
+jint JNI_GetDefaultJavaVMInitArgs(void *vm_args) {
+  if (JavaRuntime_GetDefaultJavaVMInitArgs == nullptr)
+    return JNI_ERR;
+
+  return (*JavaRuntime_GetDefaultJavaVMInitArgs)(vm_args);
+}
+
+jint JNI_CreateJavaVM(JavaVM **vm, JNIEnv **env, void *vm_args) {
+  if (JavaRuntime_CreateJavaVM == nullptr)
+    return JNI_ERR;
+
+  return (*JavaRuntime_CreateJavaVM)(vm, env, vm_args);
+}
+
+jint JNI_GetCreatedJavaVMs(JavaVM **vmBuf, jsize bufLen, jsize *nVMs) {
+  if (JavaRuntime_GetCreatedJavaVMs == nullptr)
+    return JNI_ERR;
+
+  return (*JavaRuntime_GetCreatedJavaVMs)(vmBuf, bufLen, nVMs);
+}
+
+#endif