Add warning and bump up version.

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "jsoniq"
-version = "0.1.0a9"
+version = "0.1.0a10"
 description = "Python edition of RumbleDB, a JSONiq engine"
 requires-python = ">=3.11"
 dependencies = [

src/jsoniq/session.py

@@ -1,5 +1,9 @@
 from pyspark.sql import SparkSession
 from .sequence import SequenceOfItems
+import sys
+import platform
+import os
+import re
 import importlib.resources as pkg_resources
 
 with pkg_resources.path("jsoniq.jars", "rumbledb-1.24.0.jar") as jar_path:
@@ -19,6 +23,39 @@ def __init__(self, spark_session: SparkSession):
 
     class Builder:
         def __init__(self):
+
+            java_version = os.popen("java -version 2>&1").read()
+            if "version" in java_version:
+                match = re.search(r'version "(\d+\.\d+)', java_version)
+                if match:
+                    version = match.group(1)
+                    if not (version.startswith("17.") or version.startswith("21.")):
+                        sys.stderr.write("**************************************************************************\n")
+                        sys.stderr.write("[Error] RumbleDB builds on top of pyspark 4, which requires Java 17 or 21.\n")
+                        sys.stderr.write(f"Your Java version: {version}\n")
+                        sys.stderr.write("**************************************************************************\n")
+                        sys.stderr.write("\n")
+                        sys.stderr.write("What should you do?\n")
+                        sys.stderr.write("\n")
+                        sys.stderr.write("If you do NOT have Java 17 or 21 installed, you can download Java 17 or 21 for example from https://adoptium.net/\n")
+                        sys.stderr.write("\n")
+                        sys.stderr.write("Quick command for macOS: brew install --cask temurin17    or    brew install --cask temurin21\n")
+                        sys.stderr.write("Quick command for Ubuntu: apt-get install temurin-17-jdk    or    apt-get install temurin-21-jdk\n")
+                        sys.stderr.write("Quick command for Windows 11: winget install EclipseAdoptium.Temurin.17.JDK   or.   winget install EclipseAdoptium.Temurin.21.JDK\n")
+                        sys.stderr.write("\n")
+                        sys.stderr.write(
+                            "If you DO have Java 17 or 21, but the wrong version appears above, then it means you need to set your JAVA_HOME environment variable properly to point to Java 17 or 21.\n"
+                        )
+                        sys.stderr.write("\n")
+                        sys.stderr.write("For macOS, try: export JAVA_HOME=$(/usr/libexec/java_home -v 17)    or    export JAVA_HOME=$(/usr/libexec/java_home -v 21)\n");
+                        sys.stderr.write("\n")
+                        sys.stderr.write("For Ubuntu, find the paths to installed versions with this command: update-alternatives --config java\n  then: export JAVA_HOME=...your desired path...\n")
+                        sys.stderr.write("\n")
+                        sys.stderr.write("For Windows 11: look for the default Java path with 'which java' and/or look for alternate installed versions in Program Files. Then: setx /m JAVA_HOME \"...your desired path here...\"\n")
+                        sys.exit(43)
+            else:
+                sys.stderr.write("[Error] Could not determine Java version. Please ensure Java is installed and JAVA_HOME is properly set.\n")
+                sys.exit(43)
             self._sparkbuilder = SparkSession.builder.config("spark.jars", jar_path_str)
 
         def getOrCreate(self):