Load extensions with use of JShell ClassLoader

jjava-jupyter/src/main/java/org/dflib/jjava/jupyter/kernel/BaseKernel.java

@@ -547,10 +547,19 @@ protected void installDefaultExtensions() {
         installExtensionsFromClassLoader(getClass().getClassLoader());
     }
 
+    /**
+     * Returns the parent ClassLoader to use when loading extensions from classpath.
+     *
+     * @return the parent ClassLoader for extension loading
+     */
+    protected ClassLoader getParentClassLoader() {
+        return ClassLoader.getSystemClassLoader();
+    }
+
     /**
      * Locates, loads and initializes {@code Extension}s. Extension classes are discovered via {@link ServiceLoader}.
-     * It is passed a custom ClassLoader created internally based on a combination of system ClassLoader and the extra
-     * classpath specified as an argument.
+     * It is passed a custom ClassLoader created internally based on a combination of the parent ClassLoader
+     * (from {@link #getParentClassLoader()}) and the extra classpath specified as an argument.
      *
      * @param classpath one or more filesystem paths separated by {@link java.io.File#pathSeparator}.
      */
@@ -561,7 +570,8 @@ protected void installExtensionsFromClasspath(String classpath) {
                 .map(BaseKernel::pathToURL)
                 .toArray(URL[]::new);
 
-        try (URLClassLoader classLoader = URLClassLoader.newInstance(urls)) {
+        ClassLoader parentClassLoader = getParentClassLoader();
+        try (URLClassLoader classLoader = new URLClassLoader(urls, parentClassLoader)) {
             installExtensionsFromClassLoader(classLoader);
         } catch (IOException e) {
             throw new RuntimeException(e);

jjava-kernel/src/main/java/org/dflib/jjava/kernel/JavaKernel.java

@@ -347,6 +347,11 @@ public void interrupt() {
         this.evaluator.interrupt();
     }
 
+    @Override
+    protected ClassLoader getParentClassLoader() {
+        return evaluator.getJShellClassLoader();
+    }
+
     /**
      * @return a JShell instance used to evaluate Java code.
      */

jjava-kernel/src/main/java/org/dflib/jjava/kernel/execution/CodeEvaluator.java

@@ -177,7 +177,7 @@ private Object doEval(String code) {
      * Try to clean up information linked to a code snippet and the snippet itself
      */
     private void dropSnippet(Snippet snippet) {
-        JJavaExecutionControl execControl = execControlProvider.getRegisteredControlByID(this.execControlID);
+        JJavaExecutionControl execControl = execControlProvider.getRegisteredControlByID(execControlID);
         shell.drop(snippet);
         // snippet.classFullName() returns name of a wrapper class created for a snippet
         String className = snippetClassName(snippet);
@@ -272,4 +272,9 @@ public void interrupt() {
             execControl.interrupt();
         }
     }
+
+    public ClassLoader getJShellClassLoader() {
+        JJavaExecutionControl execControl = execControlProvider.getRegisteredControlByID(execControlID);
+        return execControl != null ? execControl.getJShellClassLoader() : null;
+    }
 }

jjava-kernel/src/main/java/org/dflib/jjava/kernel/execution/JJavaExecutionControl.java

@@ -179,6 +179,10 @@ void unloadClass(String className) {
         this.loaderDelegate.unloadClass(className);
     }
 
+    public ClassLoader getJShellClassLoader() {
+        return loaderDelegate.getClassLoader();
+    }
+
     @Override
     public String toString() {
         return "JJavaExecutionControl{" +

jjava-kernel/src/main/java/org/dflib/jjava/kernel/execution/JJavaLoaderDelegate.java

@@ -89,6 +89,10 @@ public void unloadClass(String name) {
         declaredClasses.remove(name);
     }
 
+    public ClassLoader getClassLoader() {
+        return classLoader;
+    }
+
     class BytecodeClassLoader extends URLClassLoader {
 
         public BytecodeClassLoader() {

jjava-kernel/src/test/java/org/dflib/jjava/kernel/JavaKernelExtensionsLifecycleTest.java

@@ -4,14 +4,14 @@
 import org.junit.jupiter.api.Test;
 
 import java.nio.file.Path;
+import java.util.List;
 
 import static org.junit.jupiter.api.Assertions.*;
-import static org.junit.jupiter.api.Assertions.assertEquals;
 
-public class JavaKernelExtensionsLifecycleTest {
+class JavaKernelExtensionsLifecycleTest {
 
     @Test
-    public void defaultExtensions() {
+    void defaultExtension() {
         assertNull(JavaNotebookStatics.kernel);
 
         JavaKernel kernel = JavaKernel.builder().name("TestKernel").build();
@@ -28,16 +28,16 @@ public void defaultExtensions() {
     }
 
     @Test
-    void extraClasspathExtensions() throws Exception {
-        Path jar = TestJarFactory.buildJar(
-                "java/",
-                "java/org/dflib/jjava/kernel/test/TestExtension.java",
-                "java/META-INF/services/org.dflib.jjava.jupyter.Extension"
+    void extraClasspathExtension() throws Exception {
+        Path extensionJar = TestJarFactory.buildJar(
+                "extensions/classpath/",
+                "extensions/classpath/org/dflib/jjava/kernel/test/ExtraClasspathExtension.java",
+                "extensions/classpath/META-INF/services/org.dflib.jjava.jupyter.Extension"
         );
 
-        String extraClasspath = PathsHandler.joinPaths(PathsHandler.resolveGlobs(jar.toAbsolutePath().toString()));
+        String extraClasspath = PathsHandler.joinPaths(List.of(extensionJar));
 
-        String extInstalledProp = "ext.installs:org.dflib.jjava.kernel.test.TestExtension";
+        String extInstalledProp = "ext.installs:org.dflib.jjava.kernel.test.ExtraClasspathExtension";
         System.clearProperty(extInstalledProp);
 
         JavaKernel kernel = JavaKernel
@@ -62,4 +62,63 @@ void extraClasspathExtensions() throws Exception {
         assertNull(System.getProperty(extInstalledProp));
     }
 
+    @Test
+    void evalExtension() throws Exception {
+        Path extensionJar = TestJarFactory.buildJar(
+                "extensions/eval/",
+                "extensions/eval/org/dflib/jjava/kernel/test/EvalExtension.java",
+                "extensions/eval/META-INF/services/org.dflib.jjava.jupyter.Extension"
+        );
+
+        String extraClasspath = PathsHandler.joinPaths(List.of(extensionJar));
+
+        JavaKernel kernel = JavaKernel
+                .builder()
+                .name("TestKernel")
+                .build();
+        try {
+            kernel.onStartup();
+            kernel.addToClasspath(extraClasspath);
+
+            Object installed = kernel.evalRaw("evalExtensionInstalled");
+            assertEquals(true, installed, "EvalExtension should have been installed");
+
+            Object result = kernel.evalRaw("evalValue");
+            assertEquals("Test message", result.toString(), "eval() call was not successful");
+        } finally {
+            kernel.onShutdown(false);
+        }
+    }
+
+    @Test
+    void libraryExtension() throws Exception {
+        Path libraryJar = TestJarFactory.buildJar(
+                "extensions/library/",
+                "extensions/library/org/dflib/jjava/kernel/test/TestLibraryClass.java"
+        );
+        Path extensionJar = TestJarFactory.buildJar(
+                "extensions/library/",
+                "extensions/library/org/dflib/jjava/kernel/test/ExternalLibraryExtension.java",
+                "extensions/library/META-INF/services/org.dflib.jjava.jupyter.Extension"
+        );
+
+        String extraClasspath = PathsHandler.joinPaths(List.of(libraryJar, extensionJar));
+
+        JavaKernel kernel = JavaKernel
+                .builder()
+                .name("TestKernel")
+                .build();
+        try {
+            kernel.onStartup();
+            kernel.addToClasspath(extraClasspath);
+
+            Object installed = kernel.evalRaw("externalLibraryExtensionInstalled");
+            assertEquals(true, installed, "ExternalLibraryExtension should have been installed");
+
+            Object result = kernel.evalRaw("externalLibraryValue");
+            assertEquals("Test message", result.toString(), "Library class method call was not successful");
+        } finally {
+            kernel.onShutdown(false);
+        }
+    }
 }

jjava-kernel/src/test/resources/extensions/classpath/META-INF/services/org.dflib.jjava.jupyter.Extension

@@ -0,0 +1 @@
+org.dflib.jjava.kernel.test.ExtraClasspathExtension

jjava-kernel/src/test/resources/java/org/dflib/jjava/kernel/test/TestExtension.java → jjava-kernel/src/test/resources/extensions/classpath/org/dflib/jjava/kernel/test/ExtraClasspathExtension.java

@@ -2,9 +2,8 @@
 
 import org.dflib.jjava.jupyter.Extension;
 import org.dflib.jjava.jupyter.kernel.BaseKernel;
-import org.dflib.jjava.kernel.JavaNotebookStatics;
 
-public class TestExtension implements Extension {
+public class ExtraClasspathExtension implements Extension {
 
     @Override
     public void install(BaseKernel kernel) {

jjava-kernel/src/test/resources/extensions/eval/META-INF/services/org.dflib.jjava.jupyter.Extension

@@ -0,0 +1 @@
+org.dflib.jjava.kernel.test.EvalExtension

jjava-kernel/src/test/resources/extensions/eval/org/dflib/jjava/kernel/test/EvalExtension.java

@@ -0,0 +1,13 @@
+package org.dflib.jjava.kernel.test;
+
+import org.dflib.jjava.jupyter.Extension;
+import org.dflib.jjava.jupyter.kernel.BaseKernel;
+
+public class EvalExtension implements Extension {
+
+    @Override
+    public void install(BaseKernel kernel) {
+        kernel.eval("var evalValue = \"Test message\";");
+        kernel.eval("var evalExtensionInstalled = true;");
+    }
+}

jjava-kernel/src/test/resources/extensions/library/META-INF/services/org.dflib.jjava.jupyter.Extension

@@ -0,0 +1 @@
+org.dflib.jjava.kernel.test.ExternalLibraryExtension

jjava-kernel/src/test/resources/extensions/library/org/dflib/jjava/kernel/test/ExternalLibraryExtension.java

@@ -0,0 +1,21 @@
+package org.dflib.jjava.kernel.test;
+
+import org.dflib.jjava.jupyter.Extension;
+import org.dflib.jjava.jupyter.kernel.BaseKernel;
+
+public class ExternalLibraryExtension implements Extension {
+
+    @Override
+    public void install(BaseKernel kernel) {
+        Object value;
+        try {
+            Class<?> libClass = Class.forName("org.dflib.jjava.kernel.test.TestLibraryClass");
+            value = libClass.getMethod("getMessage").invoke(null);
+        } catch (ReflectiveOperationException e) {
+            throw new RuntimeException(e);
+        }
+
+        kernel.eval("var externalLibraryValue = \"" + value + "\";");
+        kernel.eval("var externalLibraryExtensionInstalled = true;");
+    }
+}

jjava-kernel/src/test/resources/extensions/library/org/dflib/jjava/kernel/test/TestLibraryClass.java

@@ -0,0 +1,8 @@
+package org.dflib.jjava.kernel.test;
+
+public class TestLibraryClass {
+
+    public static String getMessage() {
+        return "Test message";
+    }
+}