Fix maxBytesLocalDisk not observed for Ehcache 2 (issue #62, support/ehcache2)

Co-Authored-By: hazendaz <975267+hazendaz@users.noreply.github.com>

Author: Copilot

src/main/java/org/mybatis/caches/ehcache/AbstractEhcacheCache.java

@@ -49,7 +49,7 @@ public abstract class AbstractEhcacheCache implements Cache {
    * Instantiates a new abstract ehcache cache.
    *
    * @param id
-   *          the chache id (namespace)
+   *          the cache id (namespace)
    */
   public AbstractEhcacheCache(final String id) {
     if (id == null) {
@@ -200,6 +200,47 @@ public void setMaxEntriesLocalDisk(long maxEntriesLocalDisk) {
     cache.getCacheConfiguration().setMaxEntriesLocalDisk(maxEntriesLocalDisk);
   }
 
+  /**
+   * Sets the maximum bytes to be used for the disk tier. When greater than zero the cache will overflow to disk when
+   * the heap tier is full.
+   * <p>
+   * In Ehcache 2, {@code maxBytesLocalDisk} and {@code maxEntriesLocalDisk} are mutually exclusive, and the disk pool
+   * type cannot be changed on a running cache instance. This method therefore removes and recreates the underlying
+   * cache with a fresh {@link net.sf.ehcache.config.CacheConfiguration} that applies the requested byte limit while
+   * preserving the other settings (TTI, TTL, heap size, eviction policy) from the current configuration.
+   * </p>
+   *
+   * @param maxBytesLocalDisk
+   *          the maximum number of bytes to allocate on disk. 0 means no disk tier (heap-only).
+   */
+  public void setMaxBytesLocalDisk(long maxBytesLocalDisk) {
+    net.sf.ehcache.config.CacheConfiguration current = cache.getCacheConfiguration();
+    // Build a fresh CacheConfiguration so that onDiskPoolUsage is unset and setMaxBytesLocalDisk
+    // can be applied without triggering the "can't switch disk pool" guard in Ehcache 2.
+    net.sf.ehcache.config.CacheConfiguration newConfig = new net.sf.ehcache.config.CacheConfiguration(id,
+        (int) current.getMaxEntriesLocalHeap());
+    newConfig.setTimeToIdleSeconds(current.getTimeToIdleSeconds());
+    newConfig.setTimeToLiveSeconds(current.getTimeToLiveSeconds());
+    newConfig.setEternal(current.isEternal());
+    newConfig.setMemoryStoreEvictionPolicy(current.getMemoryStoreEvictionPolicy().toString());
+    newConfig.setMaxBytesLocalDisk(maxBytesLocalDisk);
+    rebuildCacheWith(newConfig);
+  }
+
+  /**
+   * Removes the existing cache from the {@link CacheManager} and registers a new one built from {@code newConfig}.
+   * Subclasses may override this method to apply additional decorators (e.g.
+   * {@link net.sf.ehcache.constructs.blocking.BlockingCache}).
+   *
+   * @param newConfig
+   *          the configuration to use for the replacement cache
+   */
+  protected void rebuildCacheWith(net.sf.ehcache.config.CacheConfiguration newConfig) {
+    CACHE_MANAGER.removeCache(id);
+    CACHE_MANAGER.addCache(new net.sf.ehcache.Cache(newConfig));
+    this.cache = CACHE_MANAGER.getEhcache(id);
+  }
+
   /**
    * Sets the eviction policy. An invalid argument will set it to null.
    *

src/main/java/org/mybatis/caches/ehcache/EhBlockingCache.java

@@ -20,7 +20,11 @@
 import net.sf.ehcache.constructs.blocking.BlockingCache;
 
 /**
- * The Class EhBlockingCache.
+ * Cache implementation that wraps Ehcache 2 with {@link BlockingCache} semantics.
+ * <p>
+ * {@link BlockingCache} acquires a per-key lock when a cache miss occurs so that only one thread computes the missing
+ * value while others block. This prevents cache-stampede on a cold or expired entry.
+ * </p>
  *
  * @author Iwao AVE!
  */
@@ -51,4 +55,20 @@ public Object removeObject(Object key) {
     return null;
   }
 
+  /**
+   * {@inheritDoc}
+   * <p>
+   * Re-wraps the rebuilt cache in a {@link BlockingCache} after replacing it.
+   * </p>
+   */
+  @Override
+  protected void rebuildCacheWith(net.sf.ehcache.config.CacheConfiguration newConfig) {
+    CACHE_MANAGER.removeCache(id);
+    CACHE_MANAGER.addCache(new net.sf.ehcache.Cache(newConfig));
+    Ehcache ehcache = CACHE_MANAGER.getEhcache(id);
+    BlockingCache blockingCache = new BlockingCache(ehcache);
+    CACHE_MANAGER.replaceCacheWithDecoratedCache(ehcache, blockingCache);
+    this.cache = CACHE_MANAGER.getEhcache(id);
+  }
+
 }

src/test/java/org/mybatis/caches/ehcache/EhBlockingCacheTest.java

@@ -109,6 +109,43 @@ void shouldTestEvictionPolicy() throws Exception {
     this.resetCache();
   }
 
+  @Test
+  void shouldSetMaxBytesLocalDisk() {
+    // Use a distinct cache ID to avoid interfering with the shared EHBLOCKINGCACHE used by other tests.
+    // setMaxBytesLocalDisk triggers a cache rebuild because Ehcache 2 does not allow enabling
+    // the byte-based disk pool on an already-running cache instance. The rebuild re-applies the
+    // BlockingCache decorator so locking semantics are preserved.
+    AbstractEhcacheCache diskCache = new EhBlockingCache("EHBLOCKINGCACHE_DISK_TEST");
+    try {
+      diskCache.setMaxBytesLocalDisk(10 * 1024 * 1024L); // 10 MB
+      assertEquals(10 * 1024 * 1024L, diskCache.cache.getCacheConfiguration().getMaxBytesLocalDisk());
+      assertEquals(0, diskCache.cache.getCacheConfiguration().getMaxEntriesLocalDisk());
+      diskCache.putObject("key", "value");
+      assertEquals("value", diskCache.getObject("key"));
+    } finally {
+      AbstractEhcacheCache.CACHE_MANAGER.removeCache("EHBLOCKINGCACHE_DISK_TEST");
+    }
+  }
+
+  @Test
+  void shouldSupportDiskOverflow() {
+    // Use a distinct cache ID to avoid interfering with the shared EHBLOCKINGCACHE used by other tests.
+    AbstractEhcacheCache diskCache = new EhBlockingCache("EHBLOCKINGCACHE_DISK_OVERFLOW_TEST");
+    try {
+      diskCache.setMaxEntriesLocalHeap(1); // limit heap to 1 entry so others overflow to disk
+      diskCache.setMaxBytesLocalDisk(10 * 1024 * 1024L); // 10 MB — triggers rebuild with disk tier
+      diskCache.putObject("key1", "value1");
+      diskCache.putObject("key2", "value2"); // key1 overflows to disk
+      diskCache.putObject("key3", "value3"); // key2 overflows to disk
+      // All entries must remain retrievable; heap-evicted entries should be found on disk.
+      assertEquals("value1", diskCache.getObject("key1"));
+      assertEquals("value2", diskCache.getObject("key2"));
+      assertEquals("value3", diskCache.getObject("key3"));
+    } finally {
+      AbstractEhcacheCache.CACHE_MANAGER.removeCache("EHBLOCKINGCACHE_DISK_OVERFLOW_TEST");
+    }
+  }
+
   @Test
   void shouldNotCreateCache() {
     assertThrows(IllegalArgumentException.class, () -> {

src/test/java/org/mybatis/caches/ehcache/EhcacheTest.java

@@ -109,6 +109,45 @@ void shouldTestEvictionPolicy() throws Exception {
     this.resetCache();
   }
 
+  @Test
+  void shouldSetMaxBytesLocalDisk() {
+    // Use a distinct cache ID to avoid interfering with the shared EHCACHE used by other tests.
+    AbstractEhcacheCache diskCache = new EhcacheCache("EHCACHE_DISK_TEST");
+    try {
+      // Setting maxBytesLocalDisk rebuilds the cache with the correct byte-based disk tier.
+      diskCache.setMaxBytesLocalDisk(10 * 1024 * 1024L); // 10 MB
+      assertEquals(10 * 1024 * 1024L, diskCache.cache.getCacheConfiguration().getMaxBytesLocalDisk());
+      // maxEntriesLocalDisk must be 0 (the two settings are mutually exclusive in Ehcache 2).
+      assertEquals(0, diskCache.cache.getCacheConfiguration().getMaxEntriesLocalDisk());
+      // Cache must still be functional after the rebuild.
+      diskCache.putObject("key", "value");
+      assertEquals("value", diskCache.getObject("key"));
+    } finally {
+      AbstractEhcacheCache.CACHE_MANAGER.removeCache("EHCACHE_DISK_TEST");
+    }
+  }
+
+  @Test
+  void shouldSupportDiskOverflow() {
+    // Use a distinct cache ID to avoid interfering with the shared EHCACHE used by other tests.
+    // setMaxBytesLocalDisk triggers a cache rebuild because Ehcache 2 does not allow enabling
+    // the byte-based disk pool on an already-running cache instance.
+    AbstractEhcacheCache diskCache = new EhcacheCache("EHCACHE_DISK_OVERFLOW_TEST");
+    try {
+      diskCache.setMaxEntriesLocalHeap(1); // limit heap to 1 entry so others overflow to disk
+      diskCache.setMaxBytesLocalDisk(10 * 1024 * 1024L); // 10 MB — triggers rebuild with disk tier
+      diskCache.putObject("key1", "value1");
+      diskCache.putObject("key2", "value2"); // key1 overflows to disk
+      diskCache.putObject("key3", "value3"); // key2 overflows to disk
+      // All entries must remain retrievable; heap-evicted entries should be found on disk.
+      assertEquals("value1", diskCache.getObject("key1"));
+      assertEquals("value2", diskCache.getObject("key2"));
+      assertEquals("value3", diskCache.getObject("key3"));
+    } finally {
+      AbstractEhcacheCache.CACHE_MANAGER.removeCache("EHCACHE_DISK_OVERFLOW_TEST");
+    }
+  }
+
   @Test
   void shouldNotCreateCache() {
     assertThrows(IllegalArgumentException.class, () -> {