Android NDK get package signature

jobject getContext(JNIEnv *env) {
    jclass jAppAppGlobalsClass = env->FindClass("android/app/AppGlobals");

    jmethodID jGetInitialApplication = env->GetStaticMethodID(jAppAppGlobalsClass, "getInitialApplication",
                                                              "()Landroid/app/Application;");

    jobject jApplicationObject = env->CallStaticObjectMethod(jAppAppGlobalsClass, jGetInitialApplication);

    return jApplicationObject;
}

/**
 *
 * @param env - JNIEnv instance, shared to the whole application
 * @return
 */
const char *getSignature(JNIEnv *env) {
    jobject thiz = getContext(env);

    // Context
    jclass native_context = env->FindClass("android/content/Context");

    // Context#getPackageManager()
    jmethodID methodID_func = env->GetMethodID(native_context, "getPackageManager", "()Landroid/content/pm/PackageManager;");
    jobject package_manager = env->CallObjectMethod(thiz, methodID_func);
    jclass pm_clazz = env->GetObjectClass(package_manager);

    // PackageManager#getPackageInfo()
    jmethodID methodId_pm = env->GetMethodID(pm_clazz, "getPackageInfo", "(Ljava/lang/String;I)Landroid/content/pm/PackageInfo;");

    // Context#getPackageName()
    jmethodID methodID_packagename = env->GetMethodID(native_context, "getPackageName", "()Ljava/lang/String;");
    jstring name_str = static_cast<jstring>(env->CallObjectMethod(thiz, methodID_packagename));
    jobject package_info = env->CallObjectMethod(package_manager, methodId_pm, name_str, 64);
    jclass pi_clazz = env->GetObjectClass(package_info);

    // PackageInfo#signatures
    jfieldID fieldID_signatures = env->GetFieldID(pi_clazz, "signatures", "[Landroid/content/pm/Signature;");
    jobject signatur = env->GetObjectField(package_info, fieldID_signatures);
    jobjectArray signatures = reinterpret_cast<jobjectArray>(signatur);

    // PackageInfo#signatures[0]
    jobject signature = env->GetObjectArrayElement(signatures, 0);
    jclass s_clazz = env->GetObjectClass(signature);

    // PackageInfo#signatures[0].toCharString()
    jmethodID methodId_ts = env->GetMethodID(s_clazz, "toCharsString", "()Ljava/lang/String;");
    jstring ts = (jstring) env->CallObjectMethod(signature, methodId_ts);

    return env->GetStringUTFChars(ts, 0);
}

I am new to jni.. how to call this from a class of android?