\u5355\u4f8b\u6a21\u5f0f\u662f\u4e00\u79cd\u5e38\u89c1\u7684\u8bbe\u8ba1\u6a21\u5f0f\uff0c\u5982\u679c\u4e00\u4e2a\u7c7b\u53ea\u5e0c\u671b\u5b9e\u4f8b\u5316\u751f\u6210\u4e00\u4e2a\u5bf9\u8c61\uff0c\u90a3\u6211\u4eec\u5c31\u5e94\u4f7f\u7528\u5355\u4f8b\u6a21\u5f0f\u3002\u6bd4\u5982Servlet\u3001Spring\u4e2d\u7684Bean\u3001RunTime\u7b49\u7b49\u90fd\u5e94\u7528\u5230\u4e86\u5355\u4f8b\u6a21\u5f0f\u3002\u4f46\u4e00\u4e2a\u65b0\u624b\u5f80\u5f80\u4f1a\u5b58\u5728\u7684\u7591\u60d1\u662f\uff1a\u6211\u4eec\u4e3a\u4ec0\u4e48\u4e0d\u53ef\u4ee5\u5728\u4ee3\u7801\u4e2d\u53eanew\u4e00\u6b21\u8fd9\u4e2a\u5bf9\u8c61\uff0c\u5e76\u7ed9\u4e88\u5b83\u5168\u5c40\u53d8\u91cf\u7684\u4f5c\u7528\u57df\uff0c\u8ba9\u6240\u6709\u9700\u8981\u7528\u5230\u5b83\u7684\u53d8\u91cf\u5171\u4eab\u4f7f\u7528\u5b83\u5462\uff1f<\/p>\n
\u539f\u56e0\u662f\u8fd9\u79cd\u65b9\u5f0f\u4e0d\u5b89\u5168\u3002\u5982\u679c\u5728\u8fd9\u4e2a\u7c7b\u7684\u5b9a\u4e49\u4e2d\uff0c\u5b8c\u5168\u4e0d\u8bbe\u7f6e\u4efb\u4f55\u5b9e\u4f8b\u5316\u5bf9\u8c61\u76f8\u5173\u7684\u9650\u5236\u6761\u4ef6\uff0c\u90a3\u4e48\u4e00\u65e6\u5c06\u8be5\u7c7b\u6253\u6210jar\u5305\uff0c\u4f9b\u7ed9\u7b2c\u4e09\u65b9\u5ba2\u6237\u7aef\u8c03\u7528\u65f6\u5c31\u4f1a\u4ea7\u751f\u5b89\u5168\u95ee\u9898\uff0c\u5373\u53ef\u4ee5new\u51fa\u8d85\u8fc7\u4e00\u4e2a\u5b9e\u4f8b\u3002\u56e0\u4e3a\u5bf9\u4e8e\u5ba2\u6237\u7aef\u6765\u8bf4jar\u5305\u4e2d\u7684\u5185\u5bb9\u5b8c\u5168\u662f\u4e00\u4e2a\u9ed1\u76d2\uff0c\u5982\u679cjar\u5305\u4e2d\u8be5\u7c7b\u5bf9new\u7684\u6570\u91cf\u6ca1\u6709\u4f5c\u51fa\u9650\u5236\u5904\u7406\uff0c\u5ba2\u6237\u7aef\u5219\u53ef\u4ee5\u968f\u610fnew\u51fa>1\u4e2a\u7684\u5bf9\u8c61\u3002<\/p>\n
\u56e0\u6b64\u4e00\u4e2a\u7c7b\u8981\u60f3\u662f\u5355\u4f8b\uff0c\u4e0d\u80fd\u9760\u5ba2\u6237\u7aef\u751f\u6210\u5b9e\u4f8b\u53bb\u63a7\u5236\u552f\u4e00\u6027\uff0c\u800c\u8981\u4ece\u670d\u52a1\u7aef\u5bf9\u8fd9\u4e2a\u7c7b\u7684\u5b9a\u4e49\u8fdb\u884c\u552f\u4e00\u6027\u63a7\u5236\uff0c\u8fd9\u624d\u80fd\u4ece\u6839\u672c\u4e0a\u8fbe\u5230\u5355\u4f8b\u6548\u679c\u3002\u90a3\u4e48\u5982\u4f55\u53bb\u5b9a\u4e49\u5355\u4f8b\u7c7b\u5462\uff1f\u4e0b\u9762\u6211\u4eec\u5c31\u4ecb\u7ecd\u51e0\u79cd\u5e38\u7528\u5199\u6cd5\uff0c\u5e76\u6bd4\u8f83\u4ed6\u4eec\u4e4b\u95f4\u7684\u5f02\u540c\u548c\u4f7f\u7528\u573a\u666f\u3002<\/p>\n
\u6700\u7b80\u5355\u7c97\u66b4\u7684\u5199\u6cd5\u662f\u4e0b\u9762\u8fd9\u79cd\uff0c\u57fa\u672c\u7684\u5355\u4f8b\u6a21\u677f\u6709\u4e86\uff0c\u5ba2\u6237\u7aef\u53ea\u9700\u8c03\u7528\u9759\u6001\u65b9\u6cd5getInstance()\uff0c\u5e76\u5728\u5185\u90e8\u5224\u65adinstance\u662f\u5426\u5b9e\u4f8b\u5316\u8fc7\uff0c\u82e5\u5b9e\u4f8b\u5316\u8fc7\u5219\u8fd4\u56de\u4e4b\u524d\u7684\u90a3\u4e2a\u5bf9\u8c61\uff0c\u82e5\u672a\u5b9e\u4f8b\u5316\u8fc7\u5219\u73b0\u751f\u6210\u4e00\u4e2a\u65b0\u5bf9\u8c61\u8fd4\u56de\u3002<\/p>\n
public class Singleton { \r\n private static Singleton instance; \r\n private Singleton (){} \r\n \r\n public static Singleton getInstance() { \r\n if (instance == null) { \r\n instance = new Singleton(); \r\n } \r\n return instance; \r\n } \r\n}<\/pre>\n\u53ef\u4ee5\u770b\u51fa\u8fd9\u79cd\u65b9\u5f0f\u662f\u61d2\u52a0\u8f7d\u7684\uff0c\u53ea\u6709\u5728\u7b2c\u4e00\u6b21\u4f7f\u7528\u5230\u8be5\u5355\u4f8b\u7684\u65f6\u5019\u624d\u4f1a\u751f\u6210\u5bf9\u8c61\u3002\u8fd9\u79cd\u5199\u6cd5\u5728\u5355\u7ebf\u7a0b\u573a\u666f\u4e0b\u6548\u7387\u5f88\u9ad8\uff0c\u4f46\u5728\u591a\u7ebf\u7a0b\u573a\u666f\u4e0b\u5f88\u663e\u7136\u662f\u975e\u7ebf\u7a0b\u5b89\u5168\u7684\uff0c\u6bd4\u5982\u8fd9\u4e2a\u60c5\u51b5\uff1a\u7ebf\u7a0bA\u6267\u884c\u5230if\u8bed\u53e5\u5757\u5185\u90e8\uff0c\u521a\u8981\u6267\u884cinstance = new Singleton();\u7684\u65f6\u5019\uff0c\u7ebf\u7a0bB\u62a2\u5360\u4e86CPU\u65f6\u95f4\u7247\u5e76\u4e14\u987a\u5229\u5730\u8fdb\u5165\u4e86if\u8bed\u53e5\u5757\u5185\u90e8\uff0c\u540c\u65f6\u751f\u6210\u4e86instance\u5bf9\u8c61\u8fd4\u56de\uff0c\u6b64\u65f6\u7ebf\u7a0bA\u518d\u7ee7\u7eed\u5f80\u4e0b\u6267\u884c\uff0c\u4fbf\u4f1a\u53c8\u751f\u6210\u4e00\u4e2a\u65b0\u5bf9\u8c61\u5e76\u8986\u76d6\u539f\u6765B\u751f\u6210\u7684\u90a3\u4e2a\u3002\u672c\u4f8b\u7ed9\u51fa\u7684\u8fd9\u4e2a\u5355\u4f8b\u5f88\u7b80\u5355\uff0c\u53ea\u662f\u4e2a\u793a\u4f8b\uff0c\u540e\u679c\u5e76\u4e0d\u4e25\u91cd\uff0c\u56e0\u4e3a\u5b83\u6ca1\u6709\u5305\u542b\u91cd\u8981\u7684\u6210\u5458\u53d8\u91cf\uff0c\u4f46\u5047\u8bbe\u5305\u542b\u4e86\u4e00\u4e9b\u6210\u5458\u53d8\u91cf\uff0c\u7ebf\u7a0bB\u5728\u8fd4\u56de\u5bf9\u8c61\u540e\uff0c\u5ba2\u6237\u7aef\u5411\u8fd9\u4e2a\u5355\u4f8b\u52a0\u5165\u4e86\u4e00\u4e9b\u5b9e\u9645\u7684\u914d\u7f6e\u53c2\u6570\uff0c\u90a3\u4e48\u7ebf\u7a0bA\u4e00\u8986\u76d6\u4e4b\u524d\u5bf9\u8c61\u4e2d\u7684\u53c2\u6570\u5c31\u6e05\u7a7a\u4e86\uff0c\u6574\u4e2a\u7a0b\u5e8f\u4e5f\u5c31\u4e00\u56e2\u4e71\u9ebb\u4e86\u3002<\/p>\n
2 \u7ebf\u7a0b\u5b89\u5168<\/h4>\n
\u90a3\u4e48\u5176\u5b9e\u53ea\u8981\u5bf9\u4e0a\u8ff0\u4ee3\u7801\u7a0d\u52a0\u6539\u8fdb\uff0c\u4fbf\u53ef\u4ee5\u5f97\u5230\u4e00\u79cd\u7ebf\u7a0b\u5b89\u5168\u7684\u5355\u4f8b\uff1a<\/p>\n
public class Singleton { \r\n private static Singleton instance; \r\n private Singleton (){} \r\n public static synchronized Singleton getInstance() { \r\n if (instance == null) { \r\n instance = new Singleton(); \r\n } \r\n return instance; \r\n } \r\n}<\/pre>\n\u5bf9\u5355\u4f8b\u83b7\u53d6\u65b9\u6cd5\u4f53\u52a0\u4e0asynchronized\u5173\u952e\u5b57\u5373\u53ef\u4fdd\u8bc1\u540c\u4e00\u65f6\u523b\u8fdb\u5165getInstance()\u7684\u53ea\u6709\u4e00\u4e2a\u7ebf\u7a0b\uff0c\u5c3d\u7ba1\u5982\u679c\u6709\u7ebf\u7a0b\u62a2\u5360\u4e86CPU\u65f6\u95f4\u7247\uff0c\u7531\u4e8e\u5b83\u6ca1\u6709\u5355\u4f8b\u7c7b\u7684\u9501\uff0c\u56e0\u6b64\u4f1a\u963b\u585e\u7b49\u5f85\uff0c\u7136\u540e\u4ea4\u7531\u6709\u9501\u7684\u90a3\u4e2a\u7ebf\u7a0b\u5904\u7406\u5b8c\u6bd5\u540e\uff0c\u518d\u8fdb\u884c\u6267\u884c\uff0c\u8fd9\u6837\u5c31\u4fdd\u8bc1\u4e86\u7ebf\u7a0b\u5b89\u5168\u3002\u4f46\u8be5\u65b9\u6cd5\u4e5f\u6709\u5f0a\u7aef\uff0c\u90a3\u5c31\u662f\u6548\u7387\u5f88\u4f4e\uff0c\u56e0\u4e3a\u5176\u5b9e\u53ea\u8981\u7b2c\u4e00\u6b21\u751f\u6210\u4e86\u5355\u4f8b\u5bf9\u8c61\uff0c\u90a3\u4e48\u4e4b\u540e\u6240\u6709\u5bf9\u8c61\u8bbf\u95ee\u8be5\u5355\u4f8b\uff0c\u90fd\u4e0d\u9700\u8981\u52a0\u9501\u5c31\u53ef\u4ee5\u76f4\u63a5return instance\u4e86\uff0c\u800c\u52a0\u9501\u662f\u975e\u5e38\u8017\u8d39\u65f6\u95f4\u7684\uff0c\u56e0\u6b64\u505a\u4e86\u5f88\u591a\u65e0\u7528\u529f\u3002<\/p>\n
\u997f\u6c49\u5f0f\u5199\u6cd5<\/h3>\n
\u6240\u8c13\u997f\u6c49\uff0c\u5c31\u662f\u5728\u4e0d\u9700\u8981\u5403\u996d\u7684\u65f6\u5019\u4e5f\u5403\u996d\u3002\u5728\u5355\u4f8b\u6a21\u5f0f\u4e2d\u7684\u542b\u4e49\u5c31\u662f\uff0c\u5728\u4e0d\u9700\u8981\u5355\u4f8b\u7684\u65f6\u5019\u4e5f\u53bb\u751f\u6210\u5355\u4f8b\u5148\u50a8\u5907\u5728\u90a3\u91cc\u3002\u90a3\u4e48\u5f88\u81ea\u7136\u60f3\u5230\u7684\u65b9\u5f0f\u5c31\u662f\u5229\u7528JVM\u7684classloader\u673a\u5236\uff0c\u5728\u7c7b\u88c5\u8f7d\u7684\u65f6\u5019\u5c31\u5b9e\u4f8b\u5316\uff0c\u5982\u4e0b\u9762\u4ee3\u7801\u6240\u793a\uff1a<\/p>\n
public class Singleton { \r\n private static Singleton instance = new Singleton(); \r\n private Singleton (){} \r\n public static Singleton getInstance() { \r\n return instance; \r\n } \r\n}<\/pre>\n\u8fd9\u79cd\u65b9\u5f0f\u7b80\u5355\u53c8\u5b89\u5168\uff0c\u4f46\u663e\u7136\u6ca1\u6709\u8fbe\u5230\u6309\u9700\u53d6\u7528\u7684\u6548\u679c\uff0c\u5982\u679c\u8fd9\u4e2a\u5355\u4f8b\u975e\u5e38\u7684\u5e9e\u5927\u8017\u8d39\u5185\u5b58\u7a7a\u95f4\uff0c\u90a3\u4e48\u52bf\u5fc5\u4f1a\u5bf9\u7cfb\u7edf\u8fd0\u884c\u9020\u6210\u4e0d\u5c0f\u7684\u538b\u529b\u3002<\/p>\n
\u9759\u6001\u5185\u90e8\u7c7b\u5199\u6cd5<\/h3>\n
\u4e0b\u9762\u8fd9\u79cd\u65b9\u5f0f\u662f\u300aEffective Java\u300b\u4e2d\u63a8\u8350\u7684\uff0c\u5b83\u7684\u4e3b\u8981\u601d\u60f3\u662f\u91c7\u7528\u9759\u6001\u5185\u90e8\u7c7b\u8fbe\u5230\u61d2\u6c49\u5f0f\u52a0\u8f7d\u7684\u6548\u679c\uff0c\u5229\u7528\u4e86\u4e00\u4e2a\u7c7b\u4e2d\u7684\u5185\u90e8\u7c7b\u662f\u5ef6\u65f6\u52a0\u8f7d\u7684\u8fd9\u4e00\u70b9\u53bb\u5b9e\u73b0\uff0c\u5982\u4e0b\u6240\u793a\uff1a<\/p>\n
public class Singleton { \r\n private static class SingletonHolder { \r\n private static final Singleton INSTANCE = new Singleton(); \r\n } \r\n private Singleton (){} \r\n public static final Singleton getInstance() { \r\n return SingletonHolder.INSTANCE; \r\n } \r\n}<\/pre>\n\u8fd9\u79cd\u65b9\u5f0f\u4e0e\u4e0a\u9762\u7684\u65b9\u5f0f\u4e0d\u540c\uff0c\u997f\u6c49\u5f0f\u52a0\u8f7d\u53ea\u8981Singleton\u7c7b\u52a0\u8f7d\u4e86\uff0c\u90a3\u4e48instance\u5c31\u4f1a\u88ab\u5b9e\u4f8b\u5316\uff0c\u800c\u8fd9\u79cd\u65b9\u5f0fSingleton\u7c7b\u52a0\u8f7d\u4e86instance\u4e5f\u4e0d\u4f1a\u5b9e\u4f8b\u5316\uff0c\u53ea\u6709\u5728\u663e\u5f0f\u5730\u901a\u8fc7getInstance()\u83b7\u53d6\u5b9e\u4f8b\u65f6\uff0c\u624d\u4f1a\u8fdb\u4e00\u6b65\u88c5\u5728SingletonHolder\u7c7b\uff0c\u5e76\u521d\u59cb\u5316\u5176\u9759\u6001\u53d8\u91cf\uff0c\u8fd4\u56deSingleton\u7684\u5b9e\u4f8b\u3002<\/p>\n
\u679a\u4e3e\u7c7b\u5199\u6cd5<\/h3>\n
\u4e0b\u9762\u4ecb\u7ecd\u7684\u8fd9\u79cd\u5199\u6cd5\u662fEffective Java\u4f5c\u8005Josh Bloch \u63d0\u5021\u7684\u65b9\u5f0f\uff0c\u5b83\u4e0d\u4ec5\u80fd\u907f\u514d\u591a\u7ebf\u7a0b\u540c\u6b65\u95ee\u9898\uff0c\u800c\u4e14\u8fd8\u80fd\u9632\u6b62\u53cd\u5e8f\u5217\u5316\u91cd\u65b0\u521b\u5efa\u65b0\u7684\u5bf9\u8c61\uff0c\u53ef\u8c13\u662f\u5f88\u575a\u5f3a\u7684\u58c1\u5792\u554a\uff0c\u4e0d\u8fc7\u5728\u5b9e\u9645\u5de5\u4f5c\u4e2d\uff0c\u5176\u5b9e\u5f88\u5c11\u770b\u89c1\u6709\u4eba\u8fd9\u4e48\u5199\u8fc7\uff1a<\/p>\n
public enum Singleton {\r\n INSTANCE;\r\n private Resource instance;\r\n Singleton() {\r\n instance = new Resource();\r\n }\r\n public Resource getInstance() {\r\n return instance;\r\n }\r\n}<\/pre>\n\u53cc\u91cd\u6821\u9a8c\u9501\u5199\u6cd5<\/h3>\n
\u8fd9\u79cd\u5199\u6cd5\u4fe1\u606f\u91cf\u770b\u8d77\u6765\u5c31\u5f88\u5927\uff0c\u867d\u7136\u6211\u4eec\u4e0d\u4e00\u5b9a\u4f7f\u7528\u5b83\uff0c\u4f46\u5b83\u6240\u8574\u542b\u7684\u601d\u60f3\u8fd8\u662f\u975e\u5e38\u503c\u5f97\u5b66\u4e60\u7684\uff1a<\/p>\n
public class Singleton { \r\n private static Singleton instance; \r\n private Singleton (){} \r\n public static Singleton getInstance() { \r\n if (instance == null) { \r\n synchronized (Singleton.class) { \r\n if (instance == null) { \r\n instance = new Singleton(); \r\n } \r\n } \r\n } \r\n return instance; \r\n } \r\n}<\/pre>\n\u4ed4\u7ec6\u5206\u6790\u4e00\u4e0b\u8fd9\u79cd\u5199\u6cd5\u7684\u597d\u5904\uff1a\u9996\u5148\u8fd8\u662f\u5224\u65ad\u5355\u4f8b\u662f\u5426\u5b58\u5728\uff0c\u5982\u679c\u5b58\u5728\u5c31\u76f4\u63a5\u8fd4\u56de\u3002\u7ee7\u7eed\u5f80\u4e0b\u770b\u5c31\u4f1a\u53d1\u73b0\uff1asynchronized\u7c7b\u9501\u5e76\u6ca1\u6709\u52a0\u5728\u65b9\u6cd5\u4f53\u4e0a\uff0c\u800c\u662f\u7f29\u51cf\u5230\u4e86\u7b2c\u4e00\u91cdif\u5224\u7a7a\u8bed\u53e5\u5185\u90e8\uff0c\u5f88\u663e\u7136\u8fd9\u6837\u7f29\u51cf\u9501\u533a\u7684\u65b9\u5f0f\u8f83\u597d\u5730\u907f\u514d\u4e86\u201c\u5355\u4f8b\u5bf9\u8c61\u751f\u6210\u540e\u518d\u8bbf\u95ee\u65f6\u76f2\u76ee\u52a0\u9501\u9020\u6210\u7684\u6548\u7387\u5f71\u54cd\u201d\u3002\u90a3\u4e48\u518d\u5f80\u4e0b\u770b\u53c8\u51fa\u73b0\u4e86\u7b2c\u4e8c\u91cdif\u5224\u7a7a\u8bed\u53e5\uff0c\u5b83\u548c\u7b2c\u4e00\u6b21\u5224\u65ad\u6709\u4ec0\u4e48\u533a\u522b\u5462\uff1f\u5176\u5b9e\u7b2c\u4e00\u6b21\u5224\u65ad\u53ea\u662f\u4e3a\u4e86\u5224\u65ad\u5bf9\u8c61\u662f\u5426\u751f\u6210\u8fc7\uff0c\u5982\u679c\u751f\u6210\u4e86\u5c31\u76f4\u63a5return\uff1b\u800c\u7b2c\u4e8c\u6b21\u5224\u65ad\u662f\u4e3a\u4e86\u9632\u6b62\u91cd\u590d\u751f\u6210\u5bf9\u8c61\u7528\u7684\uff0c\u56e0\u4e3a\u5f88\u53ef\u80fd\u591a\u4e2a\u7ebf\u7a0b\u90fd\u5728\u7b49\u7740Singleton.class\u8fd9\u628a\u7c7b\u9501\uff0c\u4e00\u65e6\u8fdb\u5165\u540c\u6b65\u5757\u4fbf\u4f1a\u91cd\u590d\u751f\u6210\u5e76\u8986\u76d6instance\u5b9e\u4f8b\u3002<\/p>\n
\u7136\u800c\u4e0a\u8ff0\u4ee3\u7801\u867d\u7136\u770b\u4f3c\u5df2\u7ecf\u975e\u5e38\u5b8c\u7f8e\u4e86\uff0c\u4f46\u8fd8\u662f\u6709\u7455\u75b5\uff0c\u4e3b\u8981\u5728\u4e8e\uff1ainstance = new Singleton();\u8fd9\u53e5\uff0c\u56e0\u4e3a\u8fd9\u53e5\u8d4b\u503c\u8bed\u53e5\u5e76\u975e\u539f\u5b50\u64cd\u4f5c\uff0c\u5728JVM\u4e2d\u5b83\u662f\u7531\u5982\u4e0b3\u6b65\u539f\u5b50\u64cd\u4f5c\u7ec4\u5408\u800c\u6210\u7684\uff1a<\/p>\n
\n- \u4e3ainstance\u5206\u914d\u4e00\u7247\u5b64\u7acb\u7684\u5185\u5b58\u7a7a\u95f4<\/li>\n
- \u8c03\u7528Singleton\u7684\u6784\u9020\u51fd\u6570\u6765\u521d\u59cb\u5316\u6210\u5458\u53d8\u91cf<\/li>\n
- \u5c06instance\u5f15\u7528\u6307\u54111\u4e2d\u5206\u914d\u7684\u5185\u5b58\u7a7a\u95f4<\/li>\n<\/ol>\n
\u4f46\u662f\u5728 JVM \u7684\u5373\u65f6\u7f16\u8bd1\u5668\u4e2d\u5b58\u5728\u6307\u4ee4\u91cd\u6392\u5e8f\u7684\u4f18\u5316\u3002\u5373\u4e0a\u8ff0\u7ec4\u5408\u5e76\u4e0d\u4e00\u5b9a\u662f\u6309\u71671-2-3\u7684\u987a\u5e8f\u6267\u884c\u7684\uff0c\u4e5f\u53ef\u80fd\u662f1-3-2\uff0c\u90a3\u4e48\u4e00\u65e63\u5148\u4e8e2\u6267\u884c\u5b8c\uff0c\u90a3\u4e48instance\u5c31\u5df2\u7ecf\u6307\u5411\u4e86\u4e00\u7247\u5e76\u672a\u521d\u59cb\u5316\u53c2\u6570\u7684\u7a7a\u95f4\u4e86\uff0c\u6b64\u65f6\u7ebf\u7a0bB\u5982\u679c\u5728\u6b63\u8981\u6267\u884c\u7b2c\u4e00\u91cdif\u5224\u7a7a\u8bed\u53e5\u65f6\u62a2\u5360\u5230\u4e86CPU\u65f6\u95f4\u7247\uff08\u6ce8\u610f\uff1a\u7ebf\u7a0bA\u5f53\u524d\u6301\u6709\u7c7b\u9501\u5e76\u4e0d\u610f\u5473\u7740\u7ebf\u7a0bB\u4e0d\u80fd\u62a2\u5360CPU\u65f6\u95f4\u7247\u53bb\u6267\u884c\uff0c\u5c3d\u7ba1\u7ebf\u7a0bB\u5728\u7ebf\u7a0bA\u672a\u5728\u540c\u6b65\u5757\u4e2d\u6267\u884c\u5b8c\u4e4b\u524d\u662f\u65e0\u6cd5\u83b7\u5f97\u7c7b\u9501\uff0c\u4f46\u8bd5\u63a2\u7684\u6743\u5229\u8fd8\u662f\u6709\u7684\uff01\uff09\uff0c\u90a3\u4e48\u5f88\u81ea\u7136instance\u4e0d\u4e3a\u7a7a\uff0c\u5c31\u4f1a\u9a6c\u4e0areturn instance\uff0c\u800c\u8fd9\u4e2ainstance\u7684\u6210\u5458\u53c2\u6570\u90fd\u662f\u7a7a\u503c\uff0c\u662f\u4e2a\u65e0\u6cd5\u4f7f\u7528\u7684\u5f02\u5e38\u5355\u4f8b\u3002<\/p>\n
\u800c\u89e3\u51b3\u8fd9\u4e2a\u95ee\u9898\u6700\u597d\u7684\u529e\u6cd5\u5c31\u662f\u4f7f\u7528volatile\u5173\u952e\u5b57\uff0c\u5c31\u50cf\u4e0b\u9762\u8fd9\u6837\uff1a<\/p>\n
public class Singleton { \r\n private static volatile Singleton instance; \r\n private Singleton (){} \r\n public static Singleton getInstance() { \r\n if (instance == null) { \r\n synchronized (Singleton.class) { \r\n if (instance == null) { \r\n instance = new Singleton(); \r\n } \r\n } \r\n } \r\n return instance; \r\n } \r\n}<\/pre>\nvolatile\u5173\u952e\u5b57\u6700\u51fa\u540d\u7684\u7684\u4f18\u52bf\u5c31\u662f\u5176\u53ef\u89c1\u6027\uff0c\u6bd4\u5982\u591a\u4e2a\u7ebf\u7a0b\u90fd\u8981\u5bf9\u4e00\u4e2a\u5171\u4eab\u53d8\u91cf\u8fdb\u884c\u8bfb\u3001\u5199\u64cd\u4f5c\uff0c\u8fd9\u4e2a\u65f6\u5019\u5c3d\u7ba1\u5bf9\u5199\u64cd\u4f5c\u7684\u540c\u6b65\u5757\u52a0\u4e86\u9501\uff0c\u4e5f\u4e0d\u80fd\u4fdd\u8bc1\u5728\u7ebf\u7a0bA\u4fee\u6539\u4e86\u8be5\u53d8\u91cf\u540e\uff0c\u7ebf\u7a0bB\u5c31\u80fd\u9a6c\u4e0a\u8bfb\u5230\u4fee\u6539\u540e\u7684\u53d8\u91cf\u503c\uff0c\u800c\u5f88\u53ef\u80fd\u8bfb\u5230\u7684\u8fd8\u662f\u5b83\u4e4b\u524d\u7684\u503c\uff01\u8fd9\u662f\u56e0\u4e3a\u6bcf\u4e2a\u7ebf\u7a0b\u90fd\u6709\u4e2a\u5de5\u4f5c\u5185\u5b58\uff0c\u7ebf\u7a0b\u5efa\u7acb\u7684\u65f6\u5019\uff0c\u4f1a\u4e8b\u5148\u628a\u5171\u4eab\u53d8\u91cf\u4fdd\u5b58\u4e00\u4e2a\u526f\u672c\u5728\u5de5\u4f5c\u5185\u5b58\u4e2d\uff0c\u5bf9\u5171\u4eab\u53d8\u91cf\u7684\u4fee\u6539\u5148\u53d1\u751f\u5728\u5de5\u4f5c\u5185\u5b58\uff0c\u518d\u5c06\u5176\u56de\u5199\u81f3\u5171\u4eab\u53d8\u91cf\u771f\u6b63\u6240\u5728\u7684\u4e3b\u5185\u5b58\u4e2d\u3002\u56e0\u6b64\u4e00\u65e6\u7ebf\u7a0bB\u6ca1\u5728\u53d8\u91cf\u56de\u5199\u5230\u4e3b\u5185\u5b58\u4e4b\u540e\u8bbf\u95ee\uff0c\u53d6\u5230\u7684\u5c31\u662f\u4e4b\u524d\u7684\u503c\uff01\u800c\u53ea\u8981\u52a0\u4e0avolatile\u5173\u952e\u5b57\uff0c\u8bfb\u5199\u64cd\u4f5c\u90fd\u5c06\u76f4\u63a5\u53d1\u751f\u5728\u4e3b\u5185\u5b58\uff0c\u8fd9\u6837\u5c31\u80fd\u4fdd\u8bc1\u6b63\u786e\u6027\u4e86\u3002<\/p>\n
\u4f46\u53ef\u89c1\u6027\u5e76\u4e0d\u610f\u5473\u7740\u540c\u6b65\u6027\uff08\u8fd9\u91cc\u591a\u8bf4\u4e00\u70b9\u4e0e\u672c\u6587\u65e0\u5173\u7684\u5185\u5bb9\uff0c\u56e0\u4e3a\u5b83\u7684\u786e\u633a\u91cd\u8981\uff09\uff0c\u6bd4\u5982\u73b0\u5728i\u662f\u4e2a\u88abvolatile\u4fee\u9970\u7684\u5171\u4eab\u53d8\u91cf\uff0c\u7136\u540e\u8981\u6267\u884ci++\u8fd9\u79cd\u975e\u539f\u5b50\u7684\u64cd\u4f5c\uff1a<\/p>\n
\n- \u4ece\u4e3b\u5185\u5b58\u8bfb\u53d6i\u7684\u503c<\/li>\n
- \u6267\u884ci+1\u64cd\u4f5c\u5f97\u5230\u7ed3\u679c<\/li>\n
- \u5c06\u7ed3\u679c\u56de\u5199\u81f3\u4e3b\u5b58\u4e2d\u7684i<\/li>\n<\/ol>\n
\u5047\u5982\u7ebf\u7a0bA\u5728\u4f9d\u6b21\u6267\u884c\u5b8c1-2\u6b65\u540e\uff0c\u7ebf\u7a0bB\u62a2\u5360\u4e86CPU\u65f6\u95f4\u7247\uff0c\u5e76\u5bf9i\u7684\u503c\u8fdb\u884c\u4e86\u4fee\u6539\uff0c\u7531\u4e8evolatile\u7684\u53ef\u89c1\u6027\uff0ci\u5728\u4e3b\u5185\u5b58\u7684\u503c\u5f88\u5feb\u5f97\u5230\u6539\u53d8\uff0c\u800c\u7ebf\u7a0bA\u73b0\u5728\u5f97\u5230CPU\u65f6\u95f4\u7247\u7ee7\u7eed\u6267\u884c\u7b2c3\u6b65\u5c06i\u56de\u5199\u81f3\u4e3b\u5b58\uff0c\u90a3\u4e48\u5f88\u663e\u7136\u521a\u624d\u7ebf\u7a0bB\u4fee\u6539\u7684i\u7684\u503c\u5c31\u88ab\u8986\u76d6\u4e86\uff0c\u8fd9\u5c31\u5bfc\u81f4\u4e86\u7ebf\u7a0b\u4e0d\u5b89\u5168\u3002\u56e0\u6b64\u540c\u6b65\u6027\u8fd8\u662f\u9700\u8981\u4f9d\u9760sychronized\u6216AtomicXXX\u5305\u88c5\u7c7b\u6765\u4fdd\u8bc1\u3002<\/p>\n
\u626f\u5f97\u6709\u70b9\u8fdc\u4e86\uff0c\u56de\u5230\u672c\u6587\uff0cvolatile\u7684\u53ef\u89c1\u6027\u7684\u786e\u5f88\u597d\u5f88\u5f3a\u5927\uff0c\u4f46\u8fd9\u5e76\u4e0d\u662f\u8fd9\u4e2a\u5355\u4f8b\u5199\u6cd5\u8981\u7528\u5230\u5b83\u7684\u539f\u56e0\uff0c\u5b83\u7684\u53e6\u4e00\u4e2a\u7279\u6027\u624d\u662f\u6839\u672c\u539f\u56e0\uff1a\u7981\u6b62\u6307\u4ee4\u91cd\u6392\u5e8f\u4f18\u5316\u3002\u5373instance = new Singleton();\u4e2d\u5bf9instance\u7684\u8bfb\u64cd\u4f5c\u5fc5\u987b\u8981\u7b491-2-3\u62161-3-2\u5199\u64cd\u4f5c\u6267\u884c\u5b8c\u6210\u540e\u624d\u80fd\u8fdb\u884c\uff0c\u4ece\u300c\u5148\u884c\u53d1\u751f\u539f\u5219\u300d\u7684\u89d2\u5ea6\u7406\u89e3\u7684\u8bdd\uff0c\u5c31\u662f\u5bf9\u4e8e\u4e00\u4e2a volatile \u53d8\u91cf\u7684\u5199\u64cd\u4f5c\u90fd\u5148\u884c\u53d1\u751f\u4e8e\u540e\u9762\u5bf9\u8fd9\u4e2a\u53d8\u91cf\u7684\u8bfb\u64cd\u4f5c\uff08\u8fd9\u91cc\u7684\u201c\u540e\u9762\u201d\u662f\u65f6\u95f4\u4e0a\u7684\u5148\u540e\u987a\u5e8f\uff09\u3002<\/p>\n
\u7ed3\u8bed<\/h3>\n
\u4e0a\u8ff0\u7ed9\u51fa\u4e86\u591a\u79cd\u5355\u4f8b\u5199\u6cd5\uff0c\u5176\u5b9e\u5c31\u4e00\u822c\u4f7f\u7528\u800c\u8a00\uff0c\u901a\u5e38\u91c7\u7528\u997f\u6c49\u5f0f\u5199\u6cd5\uff0c\u56e0\u4e3a\u5229\u7528JVM\u672c\u8eab\u7684\u673a\u5236\u4fdd\u8bc1\u4e86\u7ebf\u7a0b\u5b89\u5168\uff0c\u53ea\u8981\u751f\u6210\u8be5\u5355\u4f8b\u4e0d\u662f\u7279\u522b\u8017\u8d39\u8d44\u6e90\u7684\u8bdd\uff0c\u5927\u591a\u6570\u60c5\u51b5\u5747\u4f18\u5148\u8003\u8651\u5b83\u3002\u800c\u5982\u679c\u662f\u9047\u5230\u8981\u6ee1\u8db3\u61d2\u52a0\u8f7d\u7684\u60c5\u51b5\u7684\u8bdd\uff0c\u901a\u5e38\u91c7\u7528\u9759\u6001\u5185\u90e8\u7c7b\u5199\u6cd5\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"
\u5f15\u8a00 \u5355\u4f8b\u6a21\u5f0f\u662f\u4e00\u79cd\u5e38\u89c1\u7684\u8bbe\u8ba1\u6a21\u5f0f\uff0c\u5982\u679c\u4e00\u4e2a\u7c7b\u53ea\u5e0c\u671b\u5b9e\u4f8b\u5316\u751f\u6210\u4e00\u4e2a\u5bf9\u8c61\uff0c\u90a3\u6211\u4eec\u5c31\u5e94\u4f7f\u7528\u5355\u4f8b\u6a21\u5f0f\u3002\u6bd4\u5982Servl […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[42,49],"tags":[],"_links":{"self":[{"href":"http:\/\/yaochenkun.site\/index.php\/wp-json\/wp\/v2\/posts\/1915"}],"collection":[{"href":"http:\/\/yaochenkun.site\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/yaochenkun.site\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/yaochenkun.site\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/yaochenkun.site\/index.php\/wp-json\/wp\/v2\/comments?post=1915"}],"version-history":[{"count":6,"href":"http:\/\/yaochenkun.site\/index.php\/wp-json\/wp\/v2\/posts\/1915\/revisions"}],"predecessor-version":[{"id":1922,"href":"http:\/\/yaochenkun.site\/index.php\/wp-json\/wp\/v2\/posts\/1915\/revisions\/1922"}],"wp:attachment":[{"href":"http:\/\/yaochenkun.site\/index.php\/wp-json\/wp\/v2\/media?parent=1915"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/yaochenkun.site\/index.php\/wp-json\/wp\/v2\/categories?post=1915"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/yaochenkun.site\/index.php\/wp-json\/wp\/v2\/tags?post=1915"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}