Fix KryoSerializer ThreadLocal ClassLoader leak in web containers

.mvn/extensions.xml

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <!--
 
-       Copyright 2015-2025 the original author or authors.
+       Copyright 2015-2026 the original author or authors.
 
        Licensed under the Apache License, Version 2.0 (the "License");
        you may not use this file except in compliance with the License.

.mvn/settings.xml

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <!--
 
-       Copyright 2015-2025 the original author or authors.
+       Copyright 2015-2026 the original author or authors.
 
        Licensed under the Apache License, Version 2.0 (the "License");
        you may not use this file except in compliance with the License.

format.xml

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <!--
 
-       Copyright 2015-2022 the original author or authors.
+       Copyright 2015-2026 the original author or authors.
 
        Licensed under the Apache License, Version 2.0 (the "License");
        you may not use this file except in compliance with the License.

pom.xml

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <!--
 
-       Copyright 2015-2025 the original author or authors.
+       Copyright 2015-2026 the original author or authors.
 
        Licensed under the Apache License, Version 2.0 (the "License");
        you may not use this file except in compliance with the License.

src/main/java/org/mybatis/caches/redis/DummyReadWriteLock.java

@@ -1,5 +1,5 @@
 /*
- *    Copyright 2015-2022 the original author or authors.
+ *    Copyright 2015-2026 the original author or authors.
  *
  *    Licensed under the Apache License, Version 2.0 (the "License");
  *    you may not use this file except in compliance with the License.

src/main/java/org/mybatis/caches/redis/JDKSerializer.java

@@ -1,5 +1,5 @@
 /*
- *    Copyright 2015-2023 the original author or authors.
+ *    Copyright 2015-2026 the original author or authors.
  *
  *    Licensed under the Apache License, Version 2.0 (the "License");
  *    you may not use this file except in compliance with the License.

src/main/java/org/mybatis/caches/redis/KryoSerializer.java

@@ -1,5 +1,5 @@
 /*
- *    Copyright 2015-2023 the original author or authors.
+ *    Copyright 2015-2026 the original author or authors.
  *
  *    Licensed under the Apache License, Version 2.0 (the "License");
  *    you may not use this file except in compliance with the License.
@@ -103,4 +103,22 @@ public Object unserialize(byte[] bytes) {
     }
   }
 
+  /**
+   * Removes the {@link Kryo} instance bound to the current thread, releasing the strong reference that would otherwise
+   * prevent the thread's context {@link ClassLoader} (e.g. Tomcat's {@code WebappClassLoader}) from being
+   * garbage-collected after an application redeployment.
+   * <p>
+   * In web-container environments the container reuses worker threads across redeployments. Without this call the
+   * reference chain <em>Container Thread → ThreadLocalMap → Kryo → Kryo.class → WebappClassLoader</em> keeps the loader
+   * (and all classes it loaded) alive in Metaspace until the JVM is restarted, eventually causing
+   * {@code OutOfMemoryError: Metaspace}.
+   * <p>
+   * Callers should invoke this method for every thread that has used the serializer, typically from a
+   * {@code ServletContextListener.contextDestroyed} callback.
+   */
+  @Override
+  public void reset() {
+    kryos.remove();
+  }
+
 }

src/main/java/org/mybatis/caches/redis/RedisCache.java

@@ -1,5 +1,5 @@
 /*
- *    Copyright 2015-2023 the original author or authors.
+ *    Copyright 2015-2026 the original author or authors.
  *
  *    Licensed under the Apache License, Version 2.0 (the "License");
  *    you may not use this file except in compliance with the License.

src/main/java/org/mybatis/caches/redis/RedisCallback.java

@@ -1,5 +1,5 @@
 /*
- *    Copyright 2015-2022 the original author or authors.
+ *    Copyright 2015-2026 the original author or authors.
  *
  *    Licensed under the Apache License, Version 2.0 (the "License");
  *    you may not use this file except in compliance with the License.

src/main/java/org/mybatis/caches/redis/RedisConfig.java

@@ -1,5 +1,5 @@
 /*
- *    Copyright 2015-2023 the original author or authors.
+ *    Copyright 2015-2026 the original author or authors.
  *
  *    Licensed under the Apache License, Version 2.0 (the "License");
  *    you may not use this file except in compliance with the License.

src/main/java/org/mybatis/caches/redis/RedisConfigurationBuilder.java

@@ -1,5 +1,5 @@
 /*
- *    Copyright 2015-2023 the original author or authors.
+ *    Copyright 2015-2026 the original author or authors.
  *
  *    Licensed under the Apache License, Version 2.0 (the "License");
  *    you may not use this file except in compliance with the License.

src/main/java/org/mybatis/caches/redis/Serializer.java

@@ -1,5 +1,5 @@
 /*
- *    Copyright 2015-2023 the original author or authors.
+ *    Copyright 2015-2026 the original author or authors.
  *
  *    Licensed under the Apache License, Version 2.0 (the "License");
  *    you may not use this file except in compliance with the License.
@@ -35,4 +35,16 @@ public interface Serializer {
    */
   Object unserialize(byte[] bytes);
 
+  /**
+   * Releases any thread-local resources held by this serializer for the current thread. Implementations that use
+   * {@link ThreadLocal} storage (e.g. {@link KryoSerializer}) should override this method to call
+   * {@link ThreadLocal#remove()} and prevent ClassLoader pinning / Metaspace leaks in web-container environments
+   * (Tomcat, etc.) where container threads are reused across redeployments. Callers (e.g. a
+   * {@code ServletContextListener}) should invoke this method for each thread that has used the serializer before the
+   * application is stopped.
+   */
+  default void reset() {
+    // no-op by default
+  }
+
 }

src/main/java/org/mybatis/caches/redis/package-info.java

@@ -1,5 +1,5 @@
 /*
- *    Copyright 2015-2022 the original author or authors.
+ *    Copyright 2015-2026 the original author or authors.
  *
  *    Licensed under the Apache License, Version 2.0 (the "License");
  *    you may not use this file except in compliance with the License.

src/site/site.xml

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <!--
 
-       Copyright 2015-2024 the original author or authors.
+       Copyright 2015-2026 the original author or authors.
 
        Licensed under the Apache License, Version 2.0 (the "License");
        you may not use this file except in compliance with the License.

src/site/xdoc/index.xml.vm

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <!--
 
-       Copyright 2015-2022 the original author or authors.
+       Copyright 2015-2026 the original author or authors.
 
        Licensed under the Apache License, Version 2.0 (the "License");
        you may not use this file except in compliance with the License.

src/test/java/org/mybatis/caches/redis/RedisConfigurationBuilderTest.java

@@ -1,5 +1,5 @@
 /*
- *    Copyright 2015-2023 the original author or authors.
+ *    Copyright 2015-2026 the original author or authors.
  *
  *    Licensed under the Apache License, Version 2.0 (the "License");
  *    you may not use this file except in compliance with the License.

src/test/java/org/mybatis/caches/redis/RedisTestCase.java

@@ -1,5 +1,5 @@
 /*
- *    Copyright 2015-2023 the original author or authors.
+ *    Copyright 2015-2026 the original author or authors.
  *
  *    Licensed under the Apache License, Version 2.0 (the "License");
  *    you may not use this file except in compliance with the License.

src/test/java/org/mybatis/caches/redis/SerializerTestCase.java

@@ -1,5 +1,5 @@
 /*
- *    Copyright 2015-2023 the original author or authors.
+ *    Copyright 2015-2026 the original author or authors.
  *
  *    Licensed under the Apache License, Version 2.0 (the "License");
  *    you may not use this file except in compliance with the License.
@@ -148,4 +148,22 @@ void testSerializeCofig() {
     RedisConfig redisConfig = RedisConfigurationBuilder.getInstance().parseConfiguration();
     assertEquals(JDKSerializer.class, redisConfig.getSerializer().getClass());
   }
+
+  @Test
+  void testKryoResetClearsThreadLocal() throws InterruptedException {
+    // Verify that reset() removes the Kryo instance from the current thread's ThreadLocalMap.
+    // After reset(), a subsequent serialize call should still work (new Kryo is created on demand).
+    SimpleBeanStudentInfo rawSimpleBean = new SimpleBeanStudentInfo();
+
+    // Prime the ThreadLocal for this thread
+    kryoSerializer.serialize(rawSimpleBean);
+
+    // Reset should not throw and should clear the thread-local Kryo instance
+    kryoSerializer.reset();
+
+    // Serialization must still work correctly after reset (new Kryo created lazily)
+    byte[] serialBytes = kryoSerializer.serialize(rawSimpleBean);
+    SimpleBeanStudentInfo result = (SimpleBeanStudentInfo) kryoSerializer.unserialize(serialBytes);
+    assertEquals(rawSimpleBean, result);
+  }
 }

src/test/java/org/mybatis/caches/redis/SimpleBeanCourseInfo.java

@@ -1,5 +1,5 @@
 /*
- *    Copyright 2015-2022 the original author or authors.
+ *    Copyright 2015-2026 the original author or authors.
  *
  *    Licensed under the Apache License, Version 2.0 (the "License");
  *    you may not use this file except in compliance with the License.

src/test/java/org/mybatis/caches/redis/SimpleBeanStudentInfo.java

@@ -1,5 +1,5 @@
 /*
- *    Copyright 2015-2023 the original author or authors.
+ *    Copyright 2015-2026 the original author or authors.
  *
  *    Licensed under the Apache License, Version 2.0 (the "License");
  *    you may not use this file except in compliance with the License.

src/test/java/org/mybatis/caches/redis/sslconfig/TestHostnameVerifier.java

@@ -1,5 +1,5 @@
 /*
- *    Copyright 2015-2022 the original author or authors.
+ *    Copyright 2015-2026 the original author or authors.
  *
  *    Licensed under the Apache License, Version 2.0 (the "License");
  *    you may not use this file except in compliance with the License.

src/test/java/org/mybatis/caches/redis/sslconfig/TestSSLParameters.java

@@ -1,5 +1,5 @@
 /*
- *    Copyright 2015-2022 the original author or authors.
+ *    Copyright 2015-2026 the original author or authors.
  *
  *    Licensed under the Apache License, Version 2.0 (the "License");
  *    you may not use this file except in compliance with the License.

src/test/java/org/mybatis/caches/redis/sslconfig/TestSSLSocketFactory.java

@@ -1,5 +1,5 @@
 /*
- *    Copyright 2015-2022 the original author or authors.
+ *    Copyright 2015-2026 the original author or authors.
  *
  *    Licensed under the Apache License, Version 2.0 (the "License");
  *    you may not use this file except in compliance with the License.

src/test/resources/redis.properties

@@ -1,5 +1,5 @@
 #
-#    Copyright 2015-2022 the original author or authors.
+#    Copyright 2015-2026 the original author or authors.
 #
 #    Licensed under the Apache License, Version 2.0 (the "License");
 #    you may not use this file except in compliance with the License.

src/test/resources/test1.properties

@@ -1,5 +1,5 @@
 #
-#    Copyright 2015-2022 the original author or authors.
+#    Copyright 2015-2026 the original author or authors.
 #
 #    Licensed under the Apache License, Version 2.0 (the "License");
 #    you may not use this file except in compliance with the License.