Using a Java library in an iOS project

Steps:

Create an XCode project
Create a Java file
Convert the Java file into a native library
Include the native library in the XCode project

Create an XCode project

Open XCode
File -> New -> Project
Choose iOS - App
Select SwiftUI for the interface and Swift as Language.
A default project will be generated.
Make sure you can run that default project on a connected phone.

Create a Java file

Outside the XCode project, create a directory, e.g. staticjava
In that directory, create a directory hello
Copy the HelloStaticLib.java file to the hello directory
Download GraalVM from here and install locally in what you call GRAALVM_HOME, e.g. /opt/graalvm-jdk-23+23.1
Compile HelloStaticLib: javac -p /opt/graalvm-jdk-23+23.1/Contents/Home/jmods --add-modules org.graalvm.nativeimage hello/HelloStaticLib.java

Convert the java code into a native lib

Download C-header defintions from mycapcache.zip. Unpack into e.g. /tmp/mycapcache

Run native-image, e.g.

/bin/native-image \
-Ddebug.jdk.graal.jvmciConfigCheck=warn \
-Djdk.internal.lambda.eagerlyInitialize=false \
--no-server  \
-H:+SharedLibrary \
-H:+ExitAfterRelocatableImageWrite \
-H:TempDirectory=/tmp/out \
-Dsvm.targetName=iOS -Dsvm.targetArch=arm64 -H:+UseCAPCache -H:CAPCacheDir=/tmp/mycapcache \
-H:CompilerBackend=lir -Dsvm.platform=org.graalvm.nativeimage.Platform\$IOS_AARCH64 \
-cp . hello.HelloStaticLib

The resulting objectfile is in /tmp/out/SVM-.... /hello.hellostaticlib.a, and generated headerfiles (graal_isolate.h and hello.hellostaticlib.h) are in the current working directory.
Create a static lib from that objectfile:ar rsc libmyapp.a /tmp/out/SVM-.../hello.hellostaticlib.o



Include the native library in the XCode project

Modify the ContentView.swift to include some java calls by
overwriting it with this one.
Create a C-header file in the Swift project (nothing java specific):

Create a new C Bridging header file (File -> New -> File -> Header File) and name it myapp-Bridging-Header.h.
In project settings (click on your project in the Project Navigator, then select your target), go to the "Build Settings" tab.
Search for "Objective-C Bridging Header".
Set the path to the bridging header file you just created, relative to your project’s root.

copy the graal_isolate.h header to your project.
Modify the bridging header file to include that file, e.g. add #include "yourProject/graal_isolate.h"
Add the exported java functions from your java file to the bridging header, e.g.
extern int javaSum(void* thread, int a, int b);
extern int javaDiff(void* thread, int a, int b);

copy the hello.hellostaticlib.a to your project
Download the JDK libs from here and add it to your project
Download the JVM libs from here and add it to your project
In Project settings, Build Phases, add those 3 libs to Link Binary with Libraries, and also add libz.tbd there.


Build and run!