{"id":18335,"date":"2025-07-05T21:33:04","date_gmt":"2025-07-05T13:33:04","guid":{"rendered":"https:\/\/92it.top\/?p=18335"},"modified":"2025-07-05T21:33:04","modified_gmt":"2025-07-05T13:33:04","slug":"java-optional%ef%bc%9a%e4%bc%98%e9%9b%85%e5%a4%84%e7%90%86%e7%a9%ba%e5%80%bc%e7%9a%84%e6%9c%80%e4%bd%b3%e5%ae%9e%e8%b7%b5","status":"publish","type":"post","link":"https:\/\/92it.top\/?p=18335","title":{"rendered":"Java Optional\uff1a\u4f18\u96c5\u5904\u7406\u7a7a\u503c\u7684\u6700\u4f73\u5b9e\u8df5"},"content":{"rendered":"\n

\u8f6c\u8f7d\uff1aJava Optional\uff1a\u4f18\u96c5\u5904\u7406\u7a7a\u503c\u7684\u6700\u4f73\u5b9e\u8df5<\/a><\/p>\n\n\n\n

\u4f60\u662f\u5426\u7ecf\u5e38\u9047\u5230 NullPointerException\uff1f\u662f\u5426\u538c\u5026\u4e86\u5199\u5927\u91cf\u7684 null \u68c0\u67e5\uff1f\u4eca\u5929\uff0c\u8ba9\u6211\u4eec\u4e00\u8d77\u63a2\u7d22 Java Optional\uff0c\u8fd9\u4e2a\u8ba9\u7a7a\u503c\u5904\u7406\u66f4\u4f18\u96c5\u3001\u66f4\u5b89\u5168\u7684\u5de5\u5177\u3002<\/p>\n\n\n\n

\u4e00\u3001Optional \u662f\u4ec0\u4e48\uff1f<\/strong><\/p>\n\n\n\n

\n\n\n\n

Optional \u662f Java 8 \u5f15\u5165\u7684\u4e00\u4e2a\u5bb9\u5668\u7c7b\uff0c\u7528\u4e8e\u8868\u793a\u4e00\u4e2a\u503c\u53ef\u80fd\u5b58\u5728\u6216\u4e0d\u5b58\u5728\u3002\u5b83\u53ef\u4ee5\u5e2e\u52a9\u6211\u4eec\u907f\u514d\u7a7a\u6307\u9488\u5f02\u5e38\uff0c\u4f7f\u4ee3\u7801\u66f4\u52a0\u5065\u58ee\u548c\u4f18\u96c5\u3002<\/p>\n\n\n\n

\u5728\u4f20\u7edf\u7684 Java \u7f16\u7a0b\u4e2d\uff0c\u6211\u4eec\u7ecf\u5e38\u9700\u8981\u5199\u5927\u91cf\u7684 null \u68c0\u67e5\u4ee3\u7801\uff0c\u8fd9\u4e0d\u4ec5\u4f7f\u4ee3\u7801\u53d8\u5f97\u5197\u957f\uff0c\u800c\u4e14\u5bb9\u6613\u51fa\u9519\u3002Optional \u63d0\u4f9b\u4e86\u4e00\u79cd\u66f4\u4f18\u96c5\u7684\u65b9\u5f0f\u6765\u5904\u7406\u53ef\u80fd\u4e3a\u7a7a\u7684\u503c\uff0c\u4f7f\u4ee3\u7801\u66f4\u52a0\u6e05\u6670\u548c\u53ef\u7ef4\u62a4\u3002<\/p>\n\n\n\n

\/\/ \u4f20\u7edf\u65b9\u5f0f\npublic String getUserName(User user) {\n    if (user != null) {\n        return user.getName();\n    }\n    return null;\n}\n\n\/\/ Optional \u65b9\u5f0f\npublic Optional<String> getUserName(User user) {\n    return Optional.ofNullable(user)\n        .map(User::getName);\n}<\/pre>\n\n\n\n
\u3000<\/p>\n\n\n\n
\u4e8c\u3001Optional \u7684\u521b\u5efa\u65b9\u5f0f<\/strong><\/p>\n\n\n\n
\n\n\n\n
Optional \u63d0\u4f9b\u4e86\u591a\u79cd\u521b\u5efa\u65b9\u5f0f\uff0c\u6bcf\u79cd\u65b9\u5f0f\u90fd\u6709\u5176\u7279\u5b9a\u7684\u4f7f\u7528\u573a\u666f\u3002\u9009\u62e9\u5408\u9002\u7684\u521b\u5efa\u65b9\u5f0f\u53ef\u4ee5\u8ba9\u4ee3\u7801\u66f4\u52a0\u6e05\u6670\u548c\u9ad8\u6548\u3002<\/p>\n\n\n\n
1. \u521b\u5efa\u5305\u542b\u503c\u7684 Optional<\/p>\n\n\n\n
\u5f53\u786e\u5b9a\u503c\u4e0d\u4e3a\u7a7a\u65f6\uff0c\u4f7f\u7528 Optional.of() \u521b\u5efa Optional\u3002\u5982\u679c\u4f20\u5165 null\uff0c\u4f1a\u629b\u51fa NullPointerException\u3002\u5f53\u503c\u53ef\u80fd\u4e3a\u7a7a\u65f6\uff0c\u4f7f\u7528 Optional.ofNullable() \u521b\u5efa Optional\u3002<\/p>\n\n\n\n
\/\/ \u521b\u5efa\u4e00\u4e2a\u5305\u542b\u975e\u7a7a\u503c\u7684 Optional\nOptional<String> optional = Optional.of(\"Hello\");\n\n\/\/ \u521b\u5efa\u4e00\u4e2a\u53ef\u80fd\u4e3a\u7a7a\u7684 Optional\nOptional<String> nullable = Optional.ofNullable(null);<\/pre>\n\n\n\n
\u3000<\/p>\n\n\n\n
2. \u521b\u5efa\u7a7a Optional<\/p>\n\n\n\n
\u5f53\u9700\u8981\u8868\u793a\u4e00\u4e2a\u660e\u786e\u4e0d\u5b58\u5728\u7684\u503c\u65f6\uff0c\u4f7f\u7528 Optional.empty() \u521b\u5efa\u7a7a\u7684 Optional\u3002\u8fd9\u79cd\u65b9\u5f0f\u6bd4\u8fd4\u56de null \u66f4\u52a0\u660e\u786e\u548c\u7c7b\u578b\u5b89\u5168\u3002<\/p>\n\n\n\n
\/\/ \u521b\u5efa\u4e00\u4e2a\u7a7a\u7684 Optional\nOptional<String> empty = Optional.empty();<\/pre>\n\n\n\n
\u3000<\/p>\n\n\n\n
3. \u4ece\u96c6\u5408\u521b\u5efa Optional<\/p>\n\n\n\n
\u5728\u5904\u7406\u96c6\u5408\u65f6\uff0c\u6211\u4eec\u7ecf\u5e38\u9700\u8981\u83b7\u53d6\u7b2c\u4e00\u4e2a\u5143\u7d20\u6216\u67e5\u627e\u6ee1\u8db3\u6761\u4ef6\u7684\u5143\u7d20\u3002Stream API \u63d0\u4f9b\u4e86 findFirst() \u548c findAny() \u65b9\u6cd5\uff0c\u5b83\u4eec\u8fd4\u56de Optional \u7c7b\u578b\u3002<\/p>\n\n\n\n
List<String> list = Arrays.asList(\"A\", \"B\", \"C\");\nOptional<String> first = list.stream().findFirst();<\/pre>\n\n\n\n
\u3000<\/p>\n\n\n\n
\u4e09\u3001Optional \u7684\u5e38\u7528\u64cd\u4f5c<\/strong><\/p>\n\n\n\n
\n\n\n\n
Optional \u63d0\u4f9b\u4e86\u4e30\u5bcc\u7684\u64cd\u4f5c\u65b9\u6cd5\uff0c\u8fd9\u4e9b\u65b9\u6cd5\u53ef\u4ee5\u5206\u4e3a\u51e0\u4e2a\u4e3b\u8981\u7c7b\u522b\uff1a\u503c\u83b7\u53d6\u3001\u503c\u68c0\u67e5\u3001\u503c\u8f6c\u6362\u548c\u94fe\u5f0f\u64cd\u4f5c\u3002\u638c\u63e1\u8fd9\u4e9b\u64cd\u4f5c\u53ef\u4ee5\u8ba9\u6211\u4eec\u7684\u4ee3\u7801\u66f4\u52a0\u4f18\u96c5\u548c\u9ad8\u6548\u3002<\/p>\n\n\n\n
1. \u503c\u83b7\u53d6\u64cd\u4f5c<\/strong><\/p>\n\n\n\n
\u503c\u83b7\u53d6\u64cd\u4f5c\u7528\u4e8e\u4ece Optional \u4e2d\u63d0\u53d6\u503c\u3002\u8fd9\u4e9b\u64cd\u4f5c\u63d0\u4f9b\u4e86\u4e0d\u540c\u7684\u65b9\u5f0f\u6765\u5904\u7406\u503c\u4e0d\u5b58\u5728\u7684\u60c5\u51b5\uff0c\u4ece\u7b80\u5355\u7684\u9ed8\u8ba4\u503c\u5230\u590d\u6742\u7684\u5f02\u5e38\u5904\u7406\u3002<\/p>\n\n\n\n
1.1 get()\uff1a\u83b7\u53d6\u503c<\/p>\n\n\n\n
get() \u65b9\u6cd5\u7528\u4e8e\u83b7\u53d6 Optional \u4e2d\u7684\u503c\u3002\u5982\u679c\u503c\u4e0d\u5b58\u5728\uff0c\u4f1a\u629b\u51fa NoSuchElementException\u3002\u8fd9\u4e2a\u65b9\u6cd5\u5e94\u8be5\u8c28\u614e\u4f7f\u7528\uff0c\u901a\u5e38\u53ea\u5728\u786e\u5b9a\u503c\u5b58\u5728\u7684\u60c5\u51b5\u4e0b\u4f7f\u7528\u3002<\/p>\n\n\n\n
Optional<String> optional = Optional.of(\"Hello\");\nString value = optional.get(); \/\/ \u5982\u679c\u503c\u4e3a\u7a7a\uff0c\u4f1a\u629b\u51fa NoSuchElementException<\/pre>\n\n\n\n
\u3000<\/p>\n\n\n\n
1.2 orElse()\uff1a\u83b7\u53d6\u503c\u6216\u9ed8\u8ba4\u503c<\/p>\n\n\n\n
orElse() \u65b9\u6cd5\u63d0\u4f9b\u4e86\u83b7\u53d6\u503c\u6216\u9ed8\u8ba4\u503c\u7684\u529f\u80fd\u3002\u5f53\u503c\u4e0d\u5b58\u5728\u65f6\uff0c\u8fd4\u56de\u6307\u5b9a\u7684\u9ed8\u8ba4\u503c\u3002\u8fd9\u79cd\u65b9\u5f0f\u6bd4 get() \u66f4\u5b89\u5168\uff0c\u56e0\u4e3a\u5b83\u5904\u7406\u4e86\u503c\u4e0d\u5b58\u5728\u7684\u60c5\u51b5\u3002<\/p>\n\n\n\n
Optional<String> optional = Optional.empty();\nString value = optional.orElse(\"Default\"); \/\/ \u5982\u679c\u503c\u4e3a\u7a7a\uff0c\u8fd4\u56de\u9ed8\u8ba4\u503c<\/pre>\n\n\n\n
\u3000<\/p>\n\n\n\n
1.3 orElseGet()\uff1a\u83b7\u53d6\u503c\u6216\u901a\u8fc7 Supplier \u83b7\u53d6\u9ed8\u8ba4\u503c<\/p>\n\n\n\n
orElseGet() \u65b9\u6cd5\u4e0e orElse() \u7c7b\u4f3c\uff0c\u4f46\u5b83\u63a5\u53d7\u4e00\u4e2a Supplier \u51fd\u6570\u5f0f\u63a5\u53e3\u4f5c\u4e3a\u53c2\u6570\u3002\u8fd9\u79cd\u65b9\u5f0f\u7684\u597d\u5904\u662f\uff0c\u53ea\u6709\u5728\u503c\u4e0d\u5b58\u5728\u65f6\u624d\u4f1a\u6267\u884c Supplier \u6765\u83b7\u53d6\u9ed8\u8ba4\u503c\uff0c\u53ef\u4ee5\u907f\u514d\u4e0d\u5fc5\u8981\u7684\u8ba1\u7b97\u3002<\/p>\n\n\n\n
Optional<String> optional = Optional.empty();\nString value = optional.orElseGet(() -> \"Default from Supplier\");<\/pre>\n\n\n\n
\u3000<\/p>\n\n\n\n
1.4 orElseThrow()\uff1a\u83b7\u53d6\u503c\u6216\u629b\u51fa\u5f02\u5e38<\/p>\n\n\n\n
orElseThrow() \u65b9\u6cd5\u5728\u503c\u4e0d\u5b58\u5728\u65f6\u629b\u51fa\u6307\u5b9a\u7684\u5f02\u5e38\u3002\u8fd9\u79cd\u65b9\u5f0f\u9002\u5408\u5728\u503c\u5fc5\u987b\u5b58\u5728\u7684\u60c5\u51b5\u4e0b\u4f7f\u7528\uff0c\u53ef\u4ee5\u81ea\u5b9a\u4e49\u5f02\u5e38\u4fe1\u606f\u3002<\/p>\n\n\n\n
Optional<String> optional = Optional.empty();\nString value = optional.orElseThrow(() -> new RuntimeException(\"Value not present\"));<\/pre>\n\n\n\n
\u3000<\/p>\n\n\n\n
2. \u503c\u68c0\u67e5\u64cd\u4f5c<\/strong><\/p>\n\n\n\n
\u503c\u68c0\u67e5\u64cd\u4f5c\u7528\u4e8e\u68c0\u67e5 Optional \u4e2d\u662f\u5426\u5b58\u5728\u503c\uff0c\u5e76\u6839\u636e\u68c0\u67e5\u7ed3\u679c\u6267\u884c\u76f8\u5e94\u7684\u64cd\u4f5c\u3002\u8fd9\u4e9b\u64cd\u4f5c\u63d0\u4f9b\u4e86\u51fd\u6570\u5f0f\u7684\u7f16\u7a0b\u65b9\u5f0f\uff0c\u4f7f\u4ee3\u7801\u66f4\u52a0\u7b80\u6d01\u3002<\/p>\n\n\n\n
\u3000<\/p>\n\n\n\n
2.1 isPresent()\uff1a\u68c0\u67e5\u503c\u662f\u5426\u5b58\u5728<\/p>\n\n\n\n
isPresent() \u65b9\u6cd5\u7528\u4e8e\u68c0\u67e5 Optional \u4e2d\u662f\u5426\u5b58\u5728\u503c\u3002\u5b83\u8fd4\u56de\u4e00\u4e2a\u5e03\u5c14\u503c\uff0c\u8868\u793a\u503c\u662f\u5426\u5b58\u5728\u3002\u8fd9\u4e2a\u65b9\u6cd5\u901a\u5e38\u4e0e if \u8bed\u53e5\u4e00\u8d77\u4f7f\u7528\u3002<\/p>\n\n\n\n
Optional<String> optional = Optional.of(\"Hello\");\nif (optional.isPresent()) {\n    System.out.println(optional.get());\n}<\/pre>\n\n\n\n
\u3000<\/p>\n\n\n\n
2.2 ifPresent()\uff1a\u5982\u679c\u503c\u5b58\u5728\u5219\u6267\u884c\u64cd\u4f5c<\/p>\n\n\n\n
ifPresent() \u65b9\u6cd5\u63a5\u53d7\u4e00\u4e2a Consumer \u51fd\u6570\u5f0f\u63a5\u53e3\u4f5c\u4e3a\u53c2\u6570\uff0c\u5f53\u503c\u5b58\u5728\u65f6\u6267\u884c\u6307\u5b9a\u7684\u64cd\u4f5c\u3002\u8fd9\u79cd\u65b9\u5f0f\u6bd4 isPresent() \u548c get() \u7684\u7ec4\u5408\u66f4\u52a0\u7b80\u6d01\u3002<\/p>\n\n\n\n
Optional<String> optional = Optional.of(\"Hello\");\noptional.ifPresent(System.out::println);<\/pre>\n\n\n\n
\u3000<\/p>\n\n\n\n
2.3 ifPresentOrElse()\uff1a\u5982\u679c\u503c\u5b58\u5728\u5219\u6267\u884c\u64cd\u4f5c\uff0c\u5426\u5219\u6267\u884c\u53e6\u4e00\u4e2a\u64cd\u4f5c<\/p>\n\n\n\n
ifPresentOrElse() \u65b9\u6cd5\u63d0\u4f9b\u4e86\u66f4\u5b8c\u6574\u7684\u6761\u4ef6\u5904\u7406\uff0c\u5b83\u63a5\u53d7\u4e24\u4e2a\u53c2\u6570\uff1a\u4e00\u4e2a Consumer \u7528\u4e8e\u503c\u5b58\u5728\u65f6\u7684\u64cd\u4f5c\uff0c\u4e00\u4e2a Runnable \u7528\u4e8e\u503c\u4e0d\u5b58\u5728\u65f6\u7684\u64cd\u4f5c\u3002<\/p>\n\n\n\n
Optional<String> optional = Optional.empty();\noptional.ifPresentOrElse(\n    System.out::println,\n    () -> System.out.println(\"Value not present\")\n);<\/pre>\n\n\n\n
\u3000<\/p>\n\n\n\n
3. \u503c\u8f6c\u6362\u64cd\u4f5c<\/strong><\/p>\n\n\n\n
\u503c\u8f6c\u6362\u64cd\u4f5c\u7528\u4e8e\u5bf9 Optional \u4e2d\u7684\u503c\u8fdb\u884c\u8f6c\u6362\u3002\u8fd9\u4e9b\u64cd\u4f5c\u8fd4\u56de\u65b0\u7684 Optional \u5bf9\u8c61\uff0c\u652f\u6301\u94fe\u5f0f\u8c03\u7528\uff0c\u4f7f\u4ee3\u7801\u66f4\u52a0\u6d41\u7545\u3002<\/p>\n\n\n\n
\u3000<\/p>\n\n\n\n
3.1 map()\uff1a\u8f6c\u6362\u503c<\/p>\n\n\n\n
map() \u65b9\u6cd5\u7528\u4e8e\u5bf9 Optional \u4e2d\u7684\u503c\u8fdb\u884c\u8f6c\u6362\u3002\u5b83\u63a5\u53d7\u4e00\u4e2a Function \u51fd\u6570\u5f0f\u63a5\u53e3\u4f5c\u4e3a\u53c2\u6570\uff0c\u8fd4\u56de\u8f6c\u6362\u540e\u7684\u503c\u7684 Optional\u3002<\/p>\n\n\n\n
Optional<String> optional = Optional.of(\"Hello\");\nOptional<Integer> length = optional.map(String::length);<\/pre>\n\n\n\n
\u3000<\/p>\n\n\n\n
3.2 flatMap()\uff1a\u8f6c\u6362\u503c\u5e76\u5c55\u5e73<\/p>\n\n\n\n
flatMap() \u65b9\u6cd5\u7528\u4e8e\u5904\u7406\u5d4c\u5957\u7684 Optional\u3002\u5b83\u63a5\u53d7\u4e00\u4e2a\u8fd4\u56de Optional \u7684 Function \u4f5c\u4e3a\u53c2\u6570\uff0c\u81ea\u52a8\u5c55\u5e73\u5d4c\u5957\u7684 Optional \u7ed3\u6784\u3002<\/p>\n\n\n\n
Optional<User> user = Optional.of(new User());\nOptional<String> name = user.flatMap(User::getName);<\/pre>\n\n\n\n
\u3000<\/p>\n\n\n\n
3.3 filter()\uff1a\u8fc7\u6ee4\u503c<\/p>\n\n\n\n
filter() \u65b9\u6cd5\u7528\u4e8e\u6839\u636e\u6761\u4ef6\u8fc7\u6ee4 Optional \u4e2d\u7684\u503c\u3002\u5b83\u63a5\u53d7\u4e00\u4e2a Predicate \u51fd\u6570\u5f0f\u63a5\u53e3\u4f5c\u4e3a\u53c2\u6570\uff0c\u53ea\u6709\u5f53\u503c\u6ee1\u8db3\u6761\u4ef6\u65f6\u624d\u4fdd\u7559\u3002<\/p>\n\n\n\n
Optional<String> optional = Optional.of(\"Hello\");\nOptional<String> filtered = optional.filter(s -> s.length() > 3);<\/pre>\n\n\n\n
\u3000<\/p>\n\n\n\n
4. \u94fe\u5f0f\u64cd\u4f5c<\/strong><\/p>\n\n\n\n
Optional \u652f\u6301\u94fe\u5f0f\u64cd\u4f5c\uff0c\u53ef\u4ee5\u5c06\u591a\u4e2a\u64cd\u4f5c\u7ec4\u5408\u5728\u4e00\u8d77\uff0c\u4f7f\u4ee3\u7801\u66f4\u52a0\u7b80\u6d01\u548c\u53ef\u8bfb\u3002\u8fd9\u79cd\u65b9\u5f0f\u7279\u522b\u9002\u5408\u5904\u7406\u53ef\u80fd\u4e3a\u7a7a\u7684\u5bf9\u8c61\u94fe\u3002<\/p>\n\n\n\n
Optional<User> user = Optional.of(new User());\nString name = user\n    .map(User::getProfile)\n    .map(Profile::getAddress)\n    .map(Address::getCity)\n    .orElse(\"Unknown\");<\/pre>\n\n\n\n
\u3000<\/p>\n\n\n\n
\u56db\u3001Optional \u7684\u6700\u4f73\u5b9e\u8df5<\/strong><\/p>\n\n\n\n
\n\n\n\n
\u5728\u4f7f\u7528 Optional \u65f6\uff0c\u6709\u4e00\u4e9b\u6700\u4f73\u5b9e\u8df5\u53ef\u4ee5\u5e2e\u52a9\u6211\u4eec\u5199\u51fa\u66f4\u597d\u7684\u4ee3\u7801\u3002\u8fd9\u4e9b\u5b9e\u8df5\u57fa\u4e8e\u5b9e\u9645\u5f00\u53d1\u7ecf\u9a8c\uff0c\u53ef\u4ee5\u5e2e\u52a9\u6211\u4eec\u907f\u514d\u5e38\u89c1\u7684\u95ee\u9898\u3002<\/p>\n\n\n\n
1. \u5728\u65b9\u6cd5\u8fd4\u56de\u503c\u4e2d\u4f7f\u7528<\/p>\n\n\n\n
\u5728\u65b9\u6cd5\u8fd4\u56de\u503c\u4e2d\u4f7f\u7528 Optional \u53ef\u4ee5\u660e\u786e\u8868\u793a\u8fd4\u56de\u503c\u53ef\u80fd\u4e3a\u7a7a\uff0c\u4f7f\u8c03\u7528\u8005\u5fc5\u987b\u5904\u7406\u8fd9\u79cd\u60c5\u51b5\u3002\u8fd9\u79cd\u65b9\u5f0f\u6bd4\u8fd4\u56de null \u66f4\u52a0\u7c7b\u578b\u5b89\u5168\u548c\u660e\u786e\u3002<\/p>\n\n\n\n
public Optional<User> findUserById(Long id) {\n    return Optional.ofNullable(userRepository.findById(id));\n}<\/pre>\n\n\n\n
\u3000<\/p>\n\n\n\n
2. \u5728 Stream \u4e2d\u4f7f\u7528<\/p>\n\n\n\n
\u5728 Stream \u64cd\u4f5c\u4e2d\u4f7f\u7528 Optional \u53ef\u4ee5\u4f18\u96c5\u5730\u5904\u7406\u53ef\u80fd\u4e3a\u7a7a\u7684\u503c\u3002\u8fd9\u79cd\u65b9\u5f0f\u7279\u522b\u9002\u5408\u5904\u7406\u96c6\u5408\u4e2d\u7684\u5143\u7d20\u3002<\/p>\n\n\n\n
List<String> names = users.stream()\n    .map(User::getName)\n    .filter(Optional::isPresent)\n    .map(Optional::get)\n    .collect(Collectors.toList());<\/pre>\n\n\n\n
\u3000<\/p>\n\n\n\n
3. \u5728\u6784\u9020\u51fd\u6570\u4e2d\u4f7f\u7528<\/p>\n\n\n\n
\u5728\u6784\u9020\u51fd\u6570\u4e2d\u4f7f\u7528 Optional \u53ef\u4ee5\u5904\u7406\u53ef\u9009\u53c2\u6570\u3002\u8fd9\u79cd\u65b9\u5f0f\u6bd4\u4f7f\u7528\u591a\u4e2a\u6784\u9020\u51fd\u6570\u66f4\u52a0\u7075\u6d3b\u3002<\/p>\n\n\n\n
public class User {\n    private final String name;\n    private final Optional<String> email;\n\n    public User(String name, String email) {\n        this.name = Objects.requireNonNull(name, \"Name cannot be null\");\n        this.email = Optional.ofNullable(email);\n    }\n}<\/pre>\n\n\n\n
\u3000<\/p>\n\n\n\n
4. \u5728\u914d\u7f6e\u4e2d\u4f7f\u7528<\/p>\n\n\n\n
\u5728\u914d\u7f6e\u7c7b\u4e2d\u4f7f\u7528 Optional \u53ef\u4ee5\u5904\u7406\u53ef\u9009\u7684\u914d\u7f6e\u9879\u3002\u8fd9\u79cd\u65b9\u5f0f\u4f7f\u914d\u7f6e\u66f4\u52a0\u7075\u6d3b\u548c\u7c7b\u578b\u5b89\u5168\u3002<\/p>\n\n\n\n
public class Configuration {\n    private final Optional<String> apiKey;\n    private final Optional<Integer> timeout;\n\n    public Configuration(String apiKey, Integer timeout) {\n        this.apiKey = Optional.ofNullable(apiKey);\n        this.timeout = Optional.ofNullable(timeout);\n    }\n}<\/pre>\n\n\n\n
\u3000<\/p>\n\n\n\n
\u4e94\u3001Optional \u7684\u5e38\u89c1\u9677\u9631<\/strong><\/p>\n\n\n\n
\n\n\n\n
\u867d\u7136 Optional \u662f\u4e00\u4e2a\u5f3a\u5927\u7684\u5de5\u5177\uff0c\u4f46\u5728\u4f7f\u7528\u8fc7\u7a0b\u4e2d\u4e5f\u5b58\u5728\u4e00\u4e9b\u5e38\u89c1\u7684\u9677\u9631\u3002\u4e86\u89e3\u8fd9\u4e9b\u9677\u9631\u53ef\u4ee5\u5e2e\u52a9\u6211\u4eec\u907f\u514d\u9519\u8bef\u3002<\/p>\n\n\n\n
1. \u4e0d\u8981\u8fc7\u5ea6\u4f7f\u7528 Optional<\/p>\n\n\n\n
\/\/ \u4e0d\u63a8\u8350\nOptional<List<String>> list = Optional.of(new ArrayList<>());\n\n\/\/ \u63a8\u8350\nList<String> list = new ArrayList<>();<\/pre>\n\n\n\n
\u3000<\/p>\n\n\n\n
2. \u4e0d\u8981\u4f7f\u7528 Optional \u4f5c\u4e3a\u5b57\u6bb5\u7c7b\u578b<\/p>\n\n\n\n
\u4f7f\u7528 Optional \u4f5c\u4e3a\u5b57\u6bb5\u7c7b\u578b\u4f1a\u589e\u52a0\u4e0d\u5fc5\u8981\u7684\u590d\u6742\u6027\uff0c\u800c\u4e14\u53ef\u80fd\u5bfc\u81f4\u5e8f\u5217\u5316\u95ee\u9898\u3002<\/p>\n\n\n\n
\/\/ \u4e0d\u63a8\u8350\npublic class User {\n    private Optional<String> name;\n}\n\n\/\/ \u63a8\u8350\npublic class User {\n    private String name;\n}<\/pre>\n\n\n\n
\u3000<\/p>\n\n\n\n
3. \u4e0d\u8981\u4f7f\u7528 Optional \u4f5c\u4e3a\u65b9\u6cd5\u53c2\u6570<\/p>\n\n\n\n
\u4f7f\u7528 Optional \u4f5c\u4e3a\u65b9\u6cd5\u53c2\u6570\u4f1a\u4f7f API \u53d8\u5f97\u590d\u6742\uff0c\u800c\u4e14\u53ef\u80fd\u5bfc\u81f4\u8c03\u7528\u8005\u56f0\u60d1\u3002<\/p>\n\n\n\n
\/\/ \u4e0d\u63a8\u8350\npublic void process(Optional<String> value) {\n    value.ifPresent(this::doSomething);\n}\n\n\/\/ \u63a8\u8350\npublic void process(String value) {\n    if (value != null) {\n        doSomething(value);\n    }\n}<\/pre>\n\n\n\n
\u3000<\/p>\n\n\n\n
\u516d\u3001\u5b9e\u9645\u5e94\u7528\u573a\u666f<\/strong><\/p>\n\n\n\n
\n\n\n\n
Optional \u5728\u5b9e\u9645\u5f00\u53d1\u4e2d\u6709\u5f88\u591a\u5e94\u7528\u573a\u666f\u3002\u4e86\u89e3\u8fd9\u4e9b\u573a\u666f\u53ef\u4ee5\u5e2e\u52a9\u6211\u4eec\u66f4\u597d\u5730\u4f7f\u7528 Optional\u3002<\/p>\n\n\n\n
1. \u6570\u636e\u5e93\u67e5\u8be2\u7ed3\u679c\u5904\u7406<\/p>\n\n\n\n
\u5728\u5904\u7406\u6570\u636e\u5e93\u67e5\u8be2\u7ed3\u679c\u65f6\uff0cOptional \u53ef\u4ee5\u4f18\u96c5\u5730\u5904\u7406\u53ef\u80fd\u4e0d\u5b58\u5728\u7684\u8bb0\u5f55\u3002<\/p>\n\n\n\n
public Optional<User> findUserByEmail(String email) {\n    return Optional.ofNullable(userRepository.findByEmail(email));\n}\n\n\/\/ \u4f7f\u7528\nfindUserByEmail(\"user@example.com\")\n    .ifPresent(user -> sendWelcomeEmail(user));<\/pre>\n\n\n\n
\u3000<\/p>\n\n\n\n
2. \u914d\u7f6e\u5c5e\u6027\u5904\u7406<\/p>\n\n\n\n
\u5728\u5904\u7406\u914d\u7f6e\u5c5e\u6027\u65f6\uff0cOptional \u53ef\u4ee5\u4f18\u96c5\u5730\u5904\u7406\u53ef\u80fd\u4e0d\u5b58\u5728\u7684\u914d\u7f6e\u9879\u3002<\/p>\n\n\n\n
public Optional<String> getProperty(String key) {\n    return Optional.ofNullable(System.getProperty(key));\n}\n\n\/\/ \u4f7f\u7528\nString value = getProperty(\"app.name\")\n    .orElse(\"Default App Name\");<\/pre>\n\n\n\n
\u3000<\/p>\n\n\n\n
3. \u94fe\u5f0f\u8c03\u7528\u5904\u7406<\/p>\n\n\n\n
\u5728\u5904\u7406\u5bf9\u8c61\u94fe\u65f6\uff0cOptional \u53ef\u4ee5\u4f18\u96c5\u5730\u5904\u7406\u53ef\u80fd\u4e3a\u7a7a\u7684\u4e2d\u95f4\u5bf9\u8c61\u3002<\/p>\n\n\n\n
public Optional<String> getCityName(User user) {\n    return Optional.ofNullable(user)\n        .map(User::getAddress)\n        .map(Address::getCity)\n        .map(City::getName);\n}<\/pre>\n\n\n\n
\u3000<\/p>\n\n\n\n
\u4e03\u3001\u603b\u7ed3<\/strong><\/p>\n\n\n\n
\n\n\n\n
Optional \u662f Java 8 \u5f15\u5165\u7684\u4e00\u4e2a\u5f3a\u5927\u5de5\u5177\uff0c\u5b83\u53ef\u4ee5\u5e2e\u52a9\u6211\u4eec\uff1a<\/p>\n\n\n\n
    \n
  1. 1. \u907f\u514d\u7a7a\u6307\u9488\u5f02\u5e38<\/li>\n\n\n\n
  2. 2. \u4f7f\u4ee3\u7801\u66f4\u52a0\u4f18\u96c5\u548c\u53ef\u8bfb<\/li>\n\n\n\n
  3. 3. \u660e\u786e\u8868\u8fbe\u53ef\u80fd\u4e3a\u7a7a\u7684\u503c<\/li>\n\n\n\n
  4. 4. \u63d0\u4f9b\u51fd\u6570\u5f0f\u7684\u7a7a\u503c\u5904\u7406\u65b9\u5f0f<\/li>\n<\/ol>\n\n\n\n
    \u901a\u8fc7\u5408\u7406\u4f7f\u7528 Optional\uff0c\u6211\u4eec\u53ef\u4ee5\u5199\u51fa\u66f4\u52a0\u5065\u58ee\u548c\u4f18\u96c5\u7684\u4ee3\u7801\u3002\u5e0c\u671b\u672c\u6587\u80fd\u5e2e\u52a9\u4f60\u5728\u65e5\u5e38\u5f00\u53d1\u4e2d\u66f4\u597d\u5730\u4f7f\u7528 Optional\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"
    \u8f6c\u8f7d\uff1aJava Optional\uff1a\u4f18\u96c5\u5904\u7406\u7a7a\u503c\u7684\u6700\u4f73\u5b9e\u8df5 \u4f60\u662f\u5426\u7ecf\u5e38\u9047\u5230 NullPointerExcepti […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[26],"tags":[],"_links":{"self":[{"href":"https:\/\/92it.top\/index.php?rest_route=\/wp\/v2\/posts\/18335"}],"collection":[{"href":"https:\/\/92it.top\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/92it.top\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/92it.top\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/92it.top\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=18335"}],"version-history":[{"count":1,"href":"https:\/\/92it.top\/index.php?rest_route=\/wp\/v2\/posts\/18335\/revisions"}],"predecessor-version":[{"id":18336,"href":"https:\/\/92it.top\/index.php?rest_route=\/wp\/v2\/posts\/18335\/revisions\/18336"}],"wp:attachment":[{"href":"https:\/\/92it.top\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=18335"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/92it.top\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=18335"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/92it.top\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=18335"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}