fix(core): resolve dependencies and change classes across classloader…

core/flamingock-core/src/main/java/io/flamingock/internal/core/change/loaded/CodeLoadedChangeBuilder.java

@@ -30,8 +30,11 @@
 
 import java.lang.reflect.Constructor;
 import java.lang.reflect.Method;
+import java.util.Arrays;
+import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Optional;
+import java.util.Set;
 
 public class CodeLoadedChangeBuilder implements LoadedChangeBuilder<CodeLoadedChange> {
 
@@ -229,13 +232,31 @@ private void setRecoveryFromClass(Class<?> sourceClass) {
         }
     }
 
+    // Tried in order: the thread's context classloader is what frameworks like Spring Boot DevTools
+    // point at the "live" app classes (e.g. its RestartClassLoader), so it must win when present.
+    // This class's own loader is the pre-existing fallback, kept for environments (CLI, plain Java)
+    // where no context classloader is set. The system loader is a last resort.
     private Class<?> getClassForName(String clazzName) {
-        try {
-            return Class.forName(clazzName);
-        }
-        catch (ClassNotFoundException e) {
-            throw new RuntimeException(e);
+        ClassNotFoundException lastException = null;
+        for (ClassLoader candidate : candidateClassLoaders()) {
+            if (candidate == null) {
+                continue;
+            }
+            try {
+                return Class.forName(clazzName, true, candidate);
+            } catch (ClassNotFoundException e) {
+                lastException = e;
+            }
         }
+        throw new RuntimeException(lastException);
+    }
+
+    private Set<ClassLoader> candidateClassLoaders() {
+        return new LinkedHashSet<>(Arrays.asList(
+                Thread.currentThread().getContextClassLoader(),
+                getClass().getClassLoader(),
+                ClassLoader.getSystemClassLoader()
+        ));
     }
 
     private Constructor<?> getConstructorFromPreview(CodePreviewChange preview) {

core/flamingock-core/src/main/java/io/flamingock/internal/core/context/SimpleContext.java

@@ -18,6 +18,8 @@
 import io.flamingock.internal.common.core.context.Context;
 import io.flamingock.internal.common.core.context.Dependency;
 import io.flamingock.internal.util.Property;
+import io.flamingock.internal.util.log.FlamingockLoggerFactory;
+import org.slf4j.Logger;
 
 import java.io.File;
 import java.net.InetAddress;
@@ -46,6 +48,8 @@
 
 public class SimpleContext extends AbstractSimpleContextResolver implements Context {
 
+    private static final Logger logger = FlamingockLoggerFactory.getLogger("SimpleContext");
+
     private final Map<String, Dependency> dependenciesByName;
     private final Map<Class<?>, Dependency> dependenciesByExactType;
 
@@ -64,9 +68,23 @@ protected Optional<Dependency> getByType(Class<?> type) {
         Optional<Dependency> dependencyByExactClass = Optional.ofNullable(dependenciesByExactType.get(type));
         if (dependencyByExactClass.isPresent()) {
             return dependencyByExactClass;
-        } else {
-            return getFirstAssignableDependency(type);
         }
+        Optional<Dependency> assignableDependency = getFirstAssignableDependency(type);
+        if (assignableDependency.isPresent()) {
+            return assignableDependency;
+        }
+        // Fallback for types with the same fully-qualified name loaded by different classloaders
+        // (e.g. Spring Boot DevTools' restart classloader), where Class<?> identity/assignability
+        // checks above never match even though it's logically the same application type.
+        Optional<Dependency> sameNameDependency = getFirstSameNameDependency(type);
+        if (sameNameDependency.isPresent()) {
+            logger.warn("Dependency[{}] resolved by class name across a classloader boundary " +
+                            "(requested type and registered type share the name but are different Class instances). " +
+                            "This usually happens under a hot-reload classloader (e.g. Spring Boot DevTools). " +
+                            "If this is unexpected, check for duplicate classes on the classpath.",
+                    type.getName());
+        }
+        return sameNameDependency;
     }
 
     private Optional<Dependency> getFirstAssignableDependency(Class<?> type) {
@@ -76,6 +94,13 @@ private Optional<Dependency> getFirstAssignableDependency(Class<?> type) {
                 .findFirst();
     }
 
+    private Optional<Dependency> getFirstSameNameDependency(Class<?> type) {
+        return dependenciesByExactType.entrySet().stream()
+                .filter(entry -> type.getName().equals(entry.getKey().getName()))
+                .map(Map.Entry::getValue)
+                .findFirst();
+    }
+
     @Override
     public void addDependency(Dependency dependency) {
         if (!dependency.isDefaultNamed()) {

core/flamingock-core/src/test/java/io/flamingock/internal/core/context/ClassloaderMismatchReproTest.java

@@ -0,0 +1,110 @@
+/*
+ * Copyright 2023 Flamingock (https://www.flamingock.io)
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package io.flamingock.internal.core.context;
+
+import io.flamingock.internal.common.core.context.Dependency;
+import org.junit.jupiter.api.Test;
+
+import java.io.InputStream;
+import java.net.URL;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+/**
+ * Reproduces https://github.com/flamingock/flamingock-java/issues/951
+ * <p>
+ * Simulates what Spring Boot DevTools' RestartClassLoader does: the same
+ * fully-qualified class is loaded twice by two different classloaders,
+ * producing two distinct {@code Class<?>} instances with the same name.
+ * SimpleContext keys its dependency map by exact {@code Class<?>} identity,
+ * so a dependency registered under one loader's Class instance is not found
+ * when looked up with the other loader's Class instance.
+ */
+class ClassloaderMismatchReproTest {
+
+    private static final String TARGET_CLASS = "io.flamingock.internal.core.context.repro.MigrationConfiguration";
+
+    @Test
+    void dependencyRegisteredUnderOneClassloaderIsNotFoundUnderAnother() throws Exception {
+        ClassLoader appLoader = ClassloaderMismatchReproTest.class.getClassLoader();
+        Class<?> typeFromRegistration = loadIsolated(appLoader).loadClass(TARGET_CLASS);
+        Class<?> typeFromLookup = loadIsolated(appLoader).loadClass(TARGET_CLASS);
+
+        assertFalse(typeFromRegistration.equals(typeFromLookup),
+                "precondition: the two loaders must produce distinct Class instances");
+
+        SimpleContext context = new SimpleContext();
+        Object instance = typeFromRegistration.getConstructor(String.class)
+                .newInstance("some-config");
+        context.addDependency(new Dependency(typeFromRegistration, instance));
+
+        boolean found = context.getDependency(typeFromLookup).isPresent();
+
+        assertTrue(found, "dependency should be found by name across classloader boundaries");
+    }
+
+    private static IsolatedClassLoader loadIsolated(ClassLoader parent) {
+        return new IsolatedClassLoader(parent);
+    }
+
+    /** Loads only classes under the repro package in isolation; delegates everything else to parent. */
+    private static class IsolatedClassLoader extends ClassLoader {
+        private final ClassLoader resourceLoader;
+
+        IsolatedClassLoader(ClassLoader resourceLoader) {
+            super(null);
+            this.resourceLoader = resourceLoader;
+        }
+
+        @Override
+        protected Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException {
+            if (name.equals(TARGET_CLASS)) {
+                synchronized (getClassLoadingLock(name)) {
+                    Class<?> loaded = findLoadedClass(name);
+                    if (loaded == null) {
+                        String path = name.replace('.', '/') + ".class";
+                        try (InputStream is = resourceLoader.getResourceAsStream(path)) {
+                            if (is == null) {
+                                throw new ClassNotFoundException(name);
+                            }
+                            java.io.ByteArrayOutputStream baos = new java.io.ByteArrayOutputStream();
+                            byte[] buf = new byte[4096];
+                            int n;
+                            while ((n = is.read(buf)) != -1) {
+                                baos.write(buf, 0, n);
+                            }
+                            byte[] bytes = baos.toByteArray();
+                            loaded = defineClass(name, bytes, 0, bytes.length);
+                        } catch (Exception e) {
+                            throw new ClassNotFoundException(name, e);
+                        }
+                    }
+                    if (resolve) {
+                        resolveClass(loaded);
+                    }
+                    return loaded;
+                }
+            }
+            return Class.forName(name, resolve, resourceLoader);
+        }
+
+        @Override
+        public URL getResource(String name) {
+            return resourceLoader.getResource(name);
+        }
+    }
+}

core/flamingock-core/src/test/java/io/flamingock/internal/core/context/repro/MigrationConfiguration.java

@@ -0,0 +1,28 @@
+/*
+ * Copyright 2023 Flamingock (https://www.flamingock.io)
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package io.flamingock.internal.core.context.repro;
+
+public class MigrationConfiguration {
+    private final String configCollection;
+
+    public MigrationConfiguration(String configCollection) {
+        this.configCollection = configCollection;
+    }
+
+    public String getConfigCollection() {
+        return configCollection;
+    }
+}