How can I run Java Codes in Qt/C++ without QAndroidExtras?

[Ibrahim]

Hi; I'm using Qt 5.7 on Ubuntu 16.04, my Java version is Oracle Java 8. I have got a Java class, it's here:

package com.pack;

import android.content.Context;
import android.widget.Toast;

public class AndroidClass
{
  public static void runToast(Context context)
  {
    Toast.makeText(context, "Hello World!", Toast.LENGTH_LONG).show();
  }
}

I can running this class with QAndroidExtras like this:

QtAndroid::runOnAndroidThread([]
{
  QAndroidJniObject::callStaticMethod<void>("com/pack/AndroidClass",
                                            "runToast",
                                            "(Landroid/content/Context;)V",
                                            QtAndroid::androidActivity().object());
});

But I need to use this Java class with pure JNI (jni.h). I have to choose pure Jni, because I want to use my JNI code both Qt / C++ and C++Builder / FireMonkey. If I choose QAndroidExtras, I can see mismatch and QAndroidExtras license is LGPL license. So, I have to use pure JNI. I wrote a C++ code with pure JNI on Qt, it's here:

QtAndroid::runOnAndroidThread([]
{
    JavaVM* jvm;
    JNIEnv* env;
    JavaVMInitArgs jvm_args;
    JavaVMOption options[1];

    options[0].optionString = "-Djava.class.path=android/src";
    jvm_args.version = JNI_VERSION_1_8;
    jvm_args.options = options;
    jvm_args.nOptions = 1;
    jvm_args.ignoreUnrecognized = JNI_TRUE;

    jint res = JNI_CreateJavaVM(&jvm, (void**)&env, &jvm_args);
    if (res < 0)
    {
      qDebug() << "Cannot create JVM!\n";
      exit(1);
    }

    jclass class_ = env->FindClass("com/pack/AndroidClass");
    if (class_ == 0)
    {
      qDebug() << "Class not found!\n";
      exit(1);
    }

    jmethodID method_id = env->GetStaticMethodID(class_, "runToast", "(Landroid/content/Context;)V");
    if (method_id == 0)
    {
      qDebug() << "runToast() method not found!\n";
      exit(1);
    }

    env->CallStaticVoidMethod(class_, method_id, QtAndroid::androidActivity().object());
});

But when I ran this project on Android, I get the errors:

Whereas I included the necessary commands in the .pro file:

android: {
    QT += androidextras
    INCLUDEPATH += /usr/lib/jvm/java-8-oracle/include
    INCLUDEPATH += /usr/lib/jvm/java-8-oracle/include/linux
    LIBS += -L/usr/lib/jvm/java-8-oracle/jre/lib/amd64/server/ -ljvm
}

How can I run Java codes in Qt with pure JNI for Qt?
Also does Qt runs with JavaVM (JNI_CreateJavaVM) on Android? So, I have to create a new JavaVM with pure JNI? Thanks.

[jsulm]

@Ibrahim Are you using 64bit Qt and compiler? I guess the JDK is 32bit and you're trying to use its lib in a 64bit application. Both must be either 32bit or 64bit, but not a mix.

[Ibrahim]

@jsulm thanks, I'm using 64Bit Oracle Java 8. When I compiled code for Desktop 64bit, it is successfuly. But when I compiled code for Android ARMv7 or x86, it gets like the image. (undefined reference to JNI_CreateJavaVM etc.).

[jsulm]

@Ibrahim So, you're trying to use a library which is built for x86_64 for an ARM build? This is not going to work.

[Ibrahim]

@jsulm I found this answer: Link. He said: "you cannot create JavaVM on Android, your app is already running inside a JVM." Well, how can I find running JavaVM for Qt Android app? Also how can I use JavaVM of Qt Android app with pure Jni? I found this: JavaVM *QAndroidJniEnvironment::javaVM(). But I need to add -Djava.class.path=/Java/Sources/Path with options.optionString, because I set my path.
Thanks.

[jsulm]

@Ibrahim Qt apps are not running in an Java VM as they are native applications written in C++.
I don't know whether it is possible to somehow use a Java VM from a Qt app on Android, maybe somebody else knows.

[Ibrahim]

@jsulm said in How can I run Java Codes in Qt/C++ without QAndroidExtras?:

Qt apps are not running in an Java VM as they are native applications written in C++.

I know it, but we can calling / running Android SDK with Java code, I think Java codes are running on JavaVM. Otherwise how do run calling Java codes in Qt with QAndroidExtras?

[Ibrahim]

I found new jni.h and libjvm.so positions:
jni.h positions:

/usr/lib/jvm/java-8-oracle/include/jni.h

Android/Sdk/ndk-bundle/platforms/android-*/arch-arm/usr/include/jni.h

android-studio/jre/include/jni.h

libjvm.so positions:

/home/username/android-studio/jre/jre/lib/amd64/server/libjvm.so

/usr/lib/jvm/java-8-oracle/jre/lib/amd64/server/libjvm.so

Also I updated my .pro file like this:

#.pro File

# FOR ANDROID:
android: {
    QT += androidextras
    INCLUDEPATH += /home/username/Android/Sdk/ndk-bundle/platforms/android-19/arch-arm/usr/include/
}

# FOR LINUX-G++ (DESKTOP):
linux-g++: {
    INCLUDEPATH += /usr/lib/jvm/java-8-oracle/include
    INCLUDEPATH += /usr/lib/jvm/java-8-oracle/include/linux
    LIBS += -L/usr/lib/jvm/java-8-oracle/jre/lib/amd64/server/ -ljvm
}

But I get this error: JNI_CreateJavaVM was not declared in this scope.
Which should I use jni.h and libjvm.so files for Android ARMv7?

[jsulm]

@Ibrahim I think /home/username/android-studio/jre is the JRE used by AndroidStudio itself (which is a Java application) - it is NOT for the target device!
amd64 means it is for X86_64 and not ARM.
You cannot use it on most Android devices.
Is there libjvm.so in Android/Sdk/ndk-bundle/platforms/ ...?
You really should ask in an Android developer forum or mailing list as your problem is not Qt related.

[Ibrahim]

@jsulm thanks. I used this command: locate "libjvm.so" in terminal, and I see 2 libjvm.so positions. There is not libjvm.so in android-19/include.
I asked question in Android NDK google+ page. Do you know a platform for this question?