{"id":1443,"date":"2026-05-17T17:58:24","date_gmt":"2026-05-17T09:58:24","guid":{"rendered":"https:\/\/yunyanglib.cn\/?p=1443"},"modified":"2026-05-17T17:58:25","modified_gmt":"2026-05-17T09:58:25","slug":"%e3%80%90java%e3%80%91weakhashmap%e8%af%a6%e8%a7%a3%ef%bc%9a%e5%8e%9f%e7%90%86%e3%80%81%e5%ae%9e%e7%8e%b0%e4%b8%8e%e5%ae%9e%e6%88%98","status":"publish","type":"post","link":"https:\/\/yunyanglib.cn\/?p=1443","title":{"rendered":"\u3010Java\u3011WeakHashMap\u8be6\u89e3\uff1a\u539f\u7406\u3001\u5b9e\u73b0\u4e0e\u5b9e\u6218"},"content":{"rendered":"\n

\u5927\u5bb6\u597d\uff0c\u6211\u662f\u4e91\u626c\uff5e \u4eca\u5929\u60f3\u548c\u5927\u5bb6\u6df1\u5165\u804a\u804a Java \u96c6\u5408\u6846\u67b6\u4e2d\u4e00\u4e2a\u7279\u6b8a\u7684\u5b58\u5728 \u2014\u2014WeakHashMap\u3002\u5b83\u548c\u6211\u4eec\u5e38\u7528\u7684 HashMap \u957f\u5f97\u5f88\u50cf\uff0c\u4f46\u9aa8\u5b50\u91cc\u85cf\u7740 \u201c\u81ea\u52a8\u56de\u6536\u201d \u7684\u9ed1\u79d1\u6280\uff0c\u5728\u7f13\u5b58\u8bbe\u8ba1\u3001\u4e34\u65f6\u6570\u636e\u5b58\u50a8\u7b49\u573a\u666f\u4e2d\u7279\u522b\u5b9e\u7528\u3002\u8fd9\u7bc7\u6587\u7ae0\u4f1a\u4ece\u539f\u7406\u5230\u4ee3\u7801\uff0c\u5e26\u5927\u5bb6\u5f7b\u5e95\u641e\u61c2 WeakHashMap\uff01<\/p>\n\n\n\n

\u4e00\u3001\u5148\u641e\u61c2\uff1aWeakHashMap \u548c HashMap \u7684\u6838\u5fc3\u533a\u522b<\/h2>\n\n\n\n

\u6211\u4eec\u5e73\u65f6\u7528\u7684 HashMap\uff0ckey \u662f\u5f3a\u5f15\u7528<\/strong>\u2014\u2014 \u53ea\u8981 HashMap \u672c\u8eab\u4e0d\u88ab\u56de\u6536\uff0ckey \u548c\u5bf9\u5e94\u7684 value \u5c31\u4f1a\u4e00\u76f4\u5360\u7740\u5185\u5b58\u3002\u800c WeakHashMap \u7684\u5173\u952e\u7279\u6027\u662f\uff1akey \u662f\u5f31\u5f15\u7528\uff0c\u4e0d\u4f1a\u963b\u6b62\u5783\u573e\u56de\u6536\uff08GC\uff09<\/strong>\u3002<\/p>\n\n\n\n

\u7b80\u5355\u8bf4\uff1a\u5f53 WeakHashMap \u7684 key \u4e0d\u518d\u88ab\u5176\u4ed6\u5f3a\u5f15\u7528\u6307\u5411\u65f6\uff0c\u4e0b\u4e00\u6b21 GC \u5c31\u4f1a\u56de\u6536\u8fd9\u4e2a key\uff0c\u800c WeakHashMap \u4f1a\u81ea\u52a8\u5220\u9664\u5bf9\u5e94\u7684 key-value \u5bf9\uff0c\u907f\u514d\u5185\u5b58\u6cc4\u6f0f\u3002<\/p>\n\n\n\n

\u4e8c\u3001Java \u56db\u79cd\u5f15\u7528\u7c7b\u578b\uff08\u57fa\u7840\u5fc5\u5907\uff09<\/h2>\n\n\n\n

\u8981\u7406\u89e3 WeakHashMap\uff0c\u5fc5\u987b\u5148\u6e05\u695a Java \u7684\u56db\u79cd\u5f15\u7528\u7c7b\u578b\uff0c\u8fd9\u662f\u5b83\u7684\u6838\u5fc3\u5e95\u5c42\u652f\u6491\uff1a<\/p>\n\n\n\n

\u5f15\u7528\u7c7b\u578b<\/th>\u7279\u70b9<\/th>\u9002\u7528\u573a\u666f<\/th><\/tr><\/thead>
\u5f3a\u5f15\u7528\uff08\u9ed8\u8ba4\uff09<\/td>\u53ea\u8981\u53ef\u8fbe\uff0c\u7edd\u4e0d\u56de\u6536<\/td>\u666e\u901a\u5bf9\u8c61\u5b58\u50a8\uff08\u5982 HashMap \u7684 key\uff09<\/td><\/tr>
\u8f6f\u5f15\u7528\uff08SoftRef\uff09<\/td>\u5185\u5b58\u4e0d\u8db3\u65f6\u624d\u56de\u6536<\/td>\u7f13\u5b58\uff08\u5982\u56fe\u7247\u7f13\u5b58\uff09<\/td><\/tr>
\u5f31\u5f15\u7528\uff08WeakRef\uff09<\/td>\u4e0b\u4e00\u6b21 GC \u5fc5\u5b9a\u56de\u6536<\/td>WeakHashMap \u7684 key<\/td><\/tr>
\u865a\u5f15\u7528\uff08PhantomRef\uff09<\/td>\u65e0\u6cd5\u83b7\u53d6\u5bf9\u8c61\uff0c\u4ec5\u7528\u4e8e\u76d1\u542c\u56de\u6536\u4e8b\u4ef6<\/td>\u8d44\u6e90\u91ca\u653e\u76d1\u542c<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

WeakHashMap \u6b63\u662f\u5229\u7528\u4e86\u5f31\u5f15\u7528<\/strong>\u7684\u7279\u6027\uff0c\u8ba9 key \u53ef\u4ee5\u88ab\u81ea\u52a8\u56de\u6536\u3002<\/p>\n\n\n\n

\u4e09\u3001WeakHashMap \u7684\u5e95\u5c42\u5b9e\u73b0\u539f\u7406<\/h2>\n\n\n\n

1. Entry \u7ee7\u627f WeakReference<\/h3>\n\n\n\n

WeakHashMap \u7684\u5185\u90e8\u7c7b Entry \u5e76\u6ca1\u6709\u76f4\u63a5\u6301\u6709 key \u7684\u5f3a\u5f15\u7528\uff0c\u800c\u662f\u7ee7\u627f\u4e86 WeakReference\uff0c\u5c06 key \u4f5c\u4e3a\u5f31\u5f15\u7528\u7684\u76ee\u6807\u5bf9\u8c61\uff1a<\/p>\n\n\n\n

\/\/ WeakHashMap \u5185\u90e8 Entry \u6e90\u7801\u7b80\u5316\nprivate static class Entry<K,V> extends WeakReference<Object> implements Map.Entry<K,V> {\n    V value;\n    final int hash;\n    Entry<K,V> next;\n\n    \/\/ key \u88ab\u5305\u88c5\u6210\u5f31\u5f15\u7528\uff0c\u4f20\u5165\u5f15\u7528\u961f\u5217\n    Entry(Object key, V value,\n              ReferenceQueue<Object> queue,\n              int hash, Entry<K,V> next) {\n        super(key, queue); \/\/ \u8c03\u7528 WeakReference \u6784\u9020\u5668\uff0ckey \u6210\u4e3a\u5f31\u5f15\u7528\n        this.value = value;\n        this.hash = hash;\n        this.next = next;\n    }\n\n    \/\/ ... \u5176\u4ed6\u65b9\u6cd5\n}\n<\/code><\/pre>\n\n\n\n
\u8fd9\u91cc\u7684\u5173\u952e\u662f super(key, queue)<\/code>\uff1a\u5c06 key \u4ea4\u7ed9 WeakReference \u7ba1\u7406\uff0c\u540c\u65f6\u5173\u8054\u4e00\u4e2a\u5f15\u7528\u961f\u5217\uff08ReferenceQueue\uff09<\/strong>\u3002<\/p>\n\n\n\n
2. \u5f15\u7528\u961f\u5217\u7684\u4f5c\u7528<\/h3>\n\n\n\n
\u5f53 key \u88ab GC \u6807\u8bb0\u4e3a\u5783\u573e\u540e\uff0c\u4f1a\u88ab\u52a0\u5165\u5230\u8fd9\u4e2a\u5f15\u7528\u961f\u5217\u4e2d\u3002WeakHashMap \u5728\u6267\u884c put()<\/code>\u3001get()<\/code>\u3001size()<\/code> \u7b49\u65b9\u6cd5\u65f6\uff0c\u4f1a\u5148\u68c0\u67e5\u5f15\u7528\u961f\u5217\uff0c\u628a\u5df2\u7ecf\u5931\u6548\u7684 Entry\uff08key \u5df2\u88ab\u56de\u6536\uff09\u4ece\u54c8\u5e0c\u8868\u4e2d\u5220\u9664 \u2014\u2014 \u8fd9\u5c31\u662f \u201c\u81ea\u52a8\u6e05\u7406\u201d \u7684\u6838\u5fc3\u3002<\/p>\n\n\n\n
\u56db\u3001\u4ee3\u7801\u5b9e\u6218\uff1a\u9a8c\u8bc1 WeakHashMap \u7684\u7279\u6027<\/h2>\n\n\n\n
\u5149\u8bf4\u4e0d\u7ec3\u5047\u628a\u5f0f\uff0c\u6211\u4eec\u7528\u4ee3\u7801\u9a8c\u8bc1 WeakHashMap \u7684 key \u56de\u6536\u673a\u5236\uff1a<\/p>\n\n\n\n
\u793a\u4f8b 1\uff1akey \u65e0\u5f3a\u5f15\u7528\u65f6\u81ea\u52a8\u56de\u6536<\/h3>\n\n\n\n
import java.util.WeakHashMap;\n\npublic class WeakHashMapTest {\n    public static void main(String[] args) {\n        \/\/ 1. \u521b\u5efa WeakHashMap\n        WeakHashMap<String, String> weakMap = new WeakHashMap<>();\n\n        \/\/ 2. key \u662f\u4e34\u65f6\u5bf9\u8c61\uff0c\u65e0\u5176\u4ed6\u5f3a\u5f15\u7528\n        String key = new String(\"\u4e91\u626c\u7684key\");\n        weakMap.put(key, \"WeakHashMap \u6d4b\u8bd5\u503c\");\n\n        \/\/ 3. \u6253\u5370\u6b64\u65f6\u7684 map \u5185\u5bb9\uff08\u6709\u503c\uff09\n        System.out.println(\"GC\u524d\uff1a\" + weakMap); \/\/ \u8f93\u51fa\uff1a{\u4e91\u626c\u7684key=WeakHashMap \u6d4b\u8bd5\u503c}\n\n        \/\/ 4. \u79fb\u9664 key \u7684\u5f3a\u5f15\u7528\uff08\u5173\u952e\uff01\uff09\n        key = null;\n\n        \/\/ 5. \u624b\u52a8\u89e6\u53d1 GC\n        System.gc();\n        \/\/ \u6682\u505c\u4e00\u4e0b\uff0c\u8ba9 GC \u5b8c\u6210\n        try {\n            Thread.sleep(1000);\n        } catch (InterruptedException e) {\n            e.printStackTrace();\n        }\n\n        \/\/ 6. \u518d\u6b21\u6253\u5370 map\uff08key \u5df2\u88ab\u56de\u6536\uff0cEntry \u88ab\u81ea\u52a8\u5220\u9664\uff09\n        System.out.println(\"GC\u540e\uff1a\" + weakMap); \/\/ \u8f93\u51fa\uff1a{}\n    }\n}\n<\/code><\/pre>\n\n\n\n
\u8fd0\u884c\u7ed3\u679c<\/strong>\uff1a<\/p>\n\n\n\n
GC\u524d\uff1a{\u4e91\u626c\u7684key=WeakHashMap \u6d4b\u8bd5\u503c}\nGC\u540e\uff1a{}\n<\/code><\/pre>\n\n\n\n
\u7ed3\u8bba<\/strong>\uff1a\u5f53 key \u6ca1\u6709\u5f3a\u5f15\u7528\u65f6\uff0cGC \u4f1a\u56de\u6536 key\uff0cWeakHashMap \u81ea\u52a8\u5220\u9664\u5bf9\u5e94\u7684 Entry\u3002<\/p>\n\n\n\n
\u793a\u4f8b 2\uff1akey \u6709\u5f3a\u5f15\u7528\u65f6\u4e0d\u56de\u6536<\/h3>\n\n\n\n
\u5982\u679c key \u8fd8\u6709\u5176\u4ed6\u5f3a\u5f15\u7528\uff0c\u5373\u4f7f\u653e\u5165 WeakHashMap\uff0c\u4e5f\u4e0d\u4f1a\u88ab\u56de\u6536\uff1a<\/p>\n\n\n\n
public class WeakHashMapStrongRefTest {\n    public static void main(String[] args) {\n        WeakHashMap<String, String> weakMap = new WeakHashMap<>();\n        \/\/ \u5f3a\u5f15\u7528\u6301\u6709 key\n        String strongKey = new String(\"\u5f3a\u5f15\u7528key\");\n        weakMap.put(strongKey, \"\u4e0d\u4f1a\u88ab\u56de\u6536\u7684\u503c\");\n\n        \/\/ \u89e6\u53d1 GC\n        System.gc();\n        try {\n            Thread.sleep(1000);\n        } catch (InterruptedException e) {\n            e.printStackTrace();\n        }\n\n        \/\/ key \u6709\u5f3a\u5f15\u7528\uff0c\u4e0d\u4f1a\u88ab\u56de\u6536\n        System.out.println(\"\u6709\u5f3a\u5f15\u7528\u65f6\uff1a\" + weakMap); \/\/ \u8f93\u51fa\uff1a{\u5f3a\u5f15\u7528key=\u4e0d\u4f1a\u88ab\u56de\u6536\u7684\u503c}\n\n        \/\/ \u79fb\u9664\u5f3a\u5f15\u7528\n        strongKey = null;\n        System.gc();\n        try {\n            Thread.sleep(1000);\n        } catch (InterruptedException e) {\n            e.printStackTrace();\n        }\n\n        \/\/ \u6b64\u65f6 key \u88ab\u56de\u6536\n        System.out.println(\"\u79fb\u9664\u5f3a\u5f15\u7528\u540e\uff1a\" + weakMap); \/\/ \u8f93\u51fa\uff1a{}\n    }\n}\n<\/code><\/pre>\n\n\n\n
\u4e94\u3001WeakHashMap \u5982\u4f55\u6e05\u7406\u5931\u6548 Entry\uff1f<\/h2>\n\n\n\n
\u5f88\u591a\u4eba\u4f1a\u7591\u60d1\uff1akey \u88ab GC \u56de\u6536\u540e\uff0cWeakHashMap \u662f\u600e\u4e48\u77e5\u9053\u8981\u5220\u9664\u5bf9\u5e94\u7684 Entry \u7684\uff1f<\/p>\n\n\n\n
\u7b54\u6848\u662f\uff1a\u4e3b\u52a8\u8f6e\u8be2 + \u5f15\u7528\u961f\u5217<\/strong>\u3002WeakHashMap \u5e76\u6ca1\u6709\u4f9d\u8d56 Java \u7684 \u201c\u5bf9\u8c61\u56de\u6536\u901a\u77e5\u201d\uff08\u56e0\u4e3a Java \u6ca1\u6709\u53ef\u9760\u7684\u56de\u8c03\u673a\u5236\uff09\uff0c\u800c\u662f\u5728\u6bcf\u6b21\u8c03\u7528 put()<\/code>\u3001get()<\/code>\u3001size()<\/code>\u3001isEmpty()<\/code> \u7b49\u65b9\u6cd5\u65f6\uff0c\u90fd\u4f1a\u5148\u6267\u884c expungeStaleEntries()<\/code> \u65b9\u6cd5\uff0c\u904d\u5386\u5f15\u7528\u961f\u5217\uff0c\u5220\u9664\u6240\u6709\u5931\u6548\u7684 Entry\uff1a<\/p>\n\n\n\n
\/\/ WeakHashMap \u6838\u5fc3\u6e05\u7406\u65b9\u6cd5\uff08\u7b80\u5316\u7248\uff09\nprivate void expungeStaleEntries() {\n    Entry e;\n    \/\/ \u904d\u5386\u5f15\u7528\u961f\u5217\uff0c\u53d6\u51fa\u6240\u6709\u5df2\u56de\u6536 key \u5bf9\u5e94\u7684 Entry\n    while ((e = (Entry.poll()) != null) {\n        int hash = e.hash;\n        int index = indexFor(hash, table.length);\n\n        \/\/ \u4ece\u54c8\u5e0c\u8868\u4e2d\u5220\u9664\u8be5 Entry\uff08\u94fe\u8868\u64cd\u4f5c\uff09\n        Entry> prev = table[index];\n        Entry p = prev;\n        while (p != null) {\n            Entry> next = p.next;\n            if (p == e) {\n                if (prev == e)\n                    table[index] = next;\n                else\n                    prev.next = next;\n                e.value = null; \/\/ \u91ca\u653e value \u7684\u5f15\u7528\uff0c\u5e2e\u52a9 GC\n                size--;\n                break;\n            }\n            prev = p;\n            p = next;\n        }\n    }\n}\n<\/code><\/pre>\n\n\n\n
\u8fd9\u5c31\u662f\u4e3a\u4ec0\u4e48\u6211\u4eec\u5728\u793a\u4f8b\u4e2d\u89e6\u53d1 GC \u540e\uff0cWeakHashMap \u4f1a\u81ea\u52a8\u6e05\u7a7a \u2014\u2014 \u4e0b\u6b21\u8c03\u7528 toString()<\/code>\uff08\u95f4\u63a5\u8c03\u7528 size()<\/code>\uff09\u65f6\uff0c\u4f1a\u89e6\u53d1\u6e05\u7406\u903b\u8f91\u3002<\/p>\n\n\n\n
\u516d\u3001\u4f7f\u7528\u573a\u666f\u4e0e\u6ce8\u610f\u4e8b\u9879<\/h2>\n\n\n\n
1. \u9002\u5408\u573a\u666f<\/h3>\n\n\n\n