fix: use context class loader, then parent in GIZMO (#2284)

Co-authored-by: Jan Willem Keizer <janwillemkeizer@gmail.com>
Co-authored-by: Lukáš Petrovický <lukas@timefold.ai>

Author: 3 people

core/src/main/java/ai/timefold/solver/core/config/solver/SolverConfig.java

@@ -203,6 +203,7 @@ public final class SolverConfig extends AbstractConfig<SolverConfig> {
     @XmlTransient
     private Clock clock = null;
     @XmlTransient
+    @Deprecated(since = "2.1.0", forRemoval = true)
     private ClassLoader classLoader = null;
 
     // Warning: all fields are null (and not defaulted) because they can be inherited
@@ -263,6 +264,10 @@ public SolverConfig(@NonNull Clock clock) {
         this.clock = Objects.requireNonNull(clock);
     }
 
+    /**
+     * @deprecated does not have any effect.
+     */
+    @Deprecated(since = "2.1.0", forRemoval = true)
     public SolverConfig(@Nullable ClassLoader classLoader) {
         this.classLoader = classLoader;
     }
@@ -294,10 +299,18 @@ public void setClock(@Nullable Clock clock) {
         this.clock = clock;
     }
 
+    /**
+     * @deprecated does not have any effect.
+     */
+    @Deprecated(since = "2.1.0", forRemoval = true)
     public @Nullable ClassLoader getClassLoader() {
         return classLoader;
     }
 
+    /**
+     * @deprecated does not have any effect.
+     */
+    @Deprecated(since = "2.1.0", forRemoval = true)
     public void setClassLoader(@Nullable ClassLoader classLoader) {
         this.classLoader = classLoader;
     }
@@ -501,6 +514,10 @@ public void setMonitoringConfig(@Nullable MonitoringConfig monitoringConfig) {
         return this;
     }
 
+    /**
+     * @deprecated does not have any effect.
+     */
+    @Deprecated(since = "2.1.0", forRemoval = true)
     public @NonNull SolverConfig withClassLoader(@NonNull ClassLoader classLoader) {
         this.setClassLoader(classLoader);
         return this;

core/src/main/java/ai/timefold/solver/core/impl/domain/common/accessor/gizmo/GizmoClassLoader.java

@@ -44,6 +44,42 @@ public String getName() {
         return "Timefold Solver Gizmo ClassLoader";
     }
 
+    @Nullable
+    private Class<?> loadClassFrom(@Nullable ClassLoader otherClassLoader, String name) {
+        if (otherClassLoader == null || otherClassLoader == this) {
+            return null;
+        }
+        try {
+            return otherClassLoader.loadClass(name);
+        } catch (ClassNotFoundException ignored) {
+            return null;
+        }
+    }
+
+    @Override
+    public Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException {
+        synchronized (getClassLoadingLock(name)) {
+            var loadedClass = findLoadedClass(name);
+            if (loadedClass == null) {
+                if (hasBytecodeFor(name)) {
+                    loadedClass = findClass(name);
+                } else {
+                    var contextClassLoader = Thread.currentThread().getContextClassLoader();
+
+                    // First context, then parent
+                    loadedClass = loadClassFrom(contextClassLoader, name);
+                    if (loadedClass == null) {
+                        loadedClass = super.loadClass(name, false);
+                    }
+                }
+            }
+            if (resolve) {
+                resolveClass(loadedClass);
+            }
+            return loadedClass;
+        }
+    }
+
     @Override
     public Class<?> findClass(String name) throws ClassNotFoundException {
         var byteCode = getBytecodeFor(name);

core/src/test/java/ai/timefold/solver/core/impl/solver/DefaultSolverTest.java

@@ -78,6 +78,7 @@
 import ai.timefold.solver.core.testdomain.TestdataEntity;
 import ai.timefold.solver.core.testdomain.TestdataSolution;
 import ai.timefold.solver.core.testdomain.TestdataValue;
+import ai.timefold.solver.core.testdomain.classloader.TestdataSeparateClassLoaderDomain;
 import ai.timefold.solver.core.testdomain.list.TestdataListEntity;
 import ai.timefold.solver.core.testdomain.list.TestdataListSolution;
 import ai.timefold.solver.core.testdomain.list.TestdataListValue;
@@ -1775,6 +1776,26 @@ private void solveListVarEntityRangeModel(MoveSelectorConfig<?> moveSelectionCon
         assertThat(bestEntity3.getValueList()).doesNotContain(value1, value2, value3);
     }
 
+    @Test
+    void solveCustomClassLoader() {
+        // Spring DevTools redefine existing classes, with their updated definitions replacing
+        // existing instances, and their updated definition are only available from the Thread's Context ClassLoader.
+        // This test verify the Context ClassLoader definition is used instead of the one from the parent ClassLoader.
+        var solverConfig = PlannerTestUtils.buildSolverConfig(TestdataSeparateClassLoaderDomain.getTestdataSolutionClass(),
+                TestdataSeparateClassLoaderDomain.getTestdataEntityClass());
+        var originalClassLoader = Thread.currentThread().getContextClassLoader();
+        try {
+            Thread.currentThread().setContextClassLoader(TestdataSeparateClassLoaderDomain.getClassLoader());
+            var solution = TestdataSeparateClassLoaderDomain.generateSolution();
+
+            solution = PlannerTestUtils.solveAssertingEvents(solverConfig, solution,
+                    BestScoreChangedEvent.constructionHeuristic(SimpleScore.ZERO, 0));
+            assertThat(solution).isNotNull();
+        } finally {
+            Thread.currentThread().setContextClassLoader(originalClassLoader);
+        }
+    }
+
     @Test
     void solveListVarEntityRangeModelWithTreeSet() {
         var solverConfig = new SolverConfig()