fix code

hutool-cache/src/main/java/cn/hutool/cache/impl/WeakCache.java

@@ -1,7 +1,12 @@
 package cn.hutool.cache.impl;
 
+import cn.hutool.cache.CacheListener;
+import cn.hutool.core.lang.Opt;
+import cn.hutool.core.lang.mutable.Mutable;
 import cn.hutool.core.map.WeakConcurrentMap;
 
+import java.lang.ref.Reference;
+
 /**
  * 弱引用缓存<br>
  * 对于一个给定的键，其映射的存在并不阻止垃圾回收器对该键的丢弃，这就使该键成为可终止的，被终止，然后被回收。<br>
@@ -24,4 +29,15 @@ public class WeakCache<K, V> extends TimedCache<K, V>{
 	public WeakCache(long timeout) {
 		super(timeout, new WeakConcurrentMap<>());
 	}
+
+	@Override
+	public WeakCache<K, V> setListener(CacheListener<K, V> listener) {
+		super.setListener(listener);
+
+		final WeakConcurrentMap<Mutable<K>, CacheObj<K, V>> map = (WeakConcurrentMap<Mutable<K>, CacheObj<K, V>>) this.cacheMap;
+		// WeakKey回收之后，key对应的值已经是null了，因此此处的key也为null
+		map.setPurgeListener((key, value)-> listener.onRemove(Opt.ofNullable(key).map(Reference::get).map(Mutable::get).get(), value.getValue()));
+
+		return this;
+	}
 }

hutool-cache/src/test/java/cn/hutool/cache/WeakCacheTest.java

@@ -26,11 +26,13 @@ public class WeakCacheTest {
 	@Ignore
 	public void removeByGcTest(){
 		// https://gitee.com/dromara/hutool/issues/I51O7M
-		// 经过GC，
 		WeakCache<String, String> cache = new WeakCache<>(-1);
 		cache.put("a", "1");
 		cache.put("b", "2");
+
+		// 监听
 		Assert.assertEquals(2, cache.size());
+		cache.setListener(Console::log);
 
 		// GC测试
 		int i=0;