{"id":1880,"date":"2017-08-29T11:04:38","date_gmt":"2017-08-29T03:04:38","guid":{"rendered":"http:\/\/www.xttblog.com\/?p=1880"},"modified":"2017-08-29T11:04:38","modified_gmt":"2017-08-29T03:04:38","slug":"java-8%e4%b8%ad%e7%9a%84-java-util-optional-%e4%bd%bf%e7%94%a8%e6%95%99%e7%a8%8b","status":"publish","type":"post","link":"https:\/\/www.xttblog.com\/?p=1880","title":{"rendered":"Java 8\u4e2d\u7684 java.util.Optional \u4f7f\u7528\u6559\u7a0b"},"content":{"rendered":"

\n\tJava.util.Optional\u662fJava 8\u65b0\u589e\u7684\u7c7b\uff0c\u4f5c\u4e3a\u4e00\u4e2a\u6301\u6709\u5b9e\u4f8b\u7684\u5bb9\u5668\u7c7b\uff0c\u53ef\u4ee5\u5e2e\u6211\u4eec\u628a\u5224\u7a7a\u7684\u4ee3\u7801\u5199\u5f97\u66f4\u4f18\u96c5\uff0c\u5e76\u4e14\u8be5\u7c7b\u8fd8\u63d0\u4f9b\u4e86\u4e00\u4e9b\u5b9e\u7528\u7684api\uff0c\u5b98\u65b9\u6587\u6863\u5728\u8fd9\u91cc<\/a>\u3002\u672c\u6587\u5c06\u7ed3\u5408java 8\u7684\u7279\u6027\u6765\u8bb2\u89e3Java.util.Optional\u7684\u5404\u79cd\u7528\u6cd5\u3002\n<\/p>\n

\n\tOptional \u4e3b\u8981\u7528\u6765\u5224\u65ad\u662f\u5426\u4e3a\u7a7a\uff0c\u5728Optional\u4e4b\u524d\uff0c\u6211\u4eec\u53ea\u8981\u4f7f\u7528StringUtils\u7684\u5de5\u5177\u7c7b\u6765\u5224\u65ad\u4f20\u5165\u7684\u53c2\u6570\u662f\u5426\u4e3a\u7a7a\u3002\u73b0\u5728\u6211\u4eec\u53ef\u4ee5\u4f7f\u7528 Optional \u6765\u66ff\u4ee3\u5b83\u4e86\u3002\n<\/p>\n

\n\t\"java.util.Optional\"\n<\/p>\n

\n\tOptional.of(Object object)
\n<\/h2>\n

\n\tOptional.of(Object object)\uff1a\u5165\u53c2object\u4e0d\u80fd\u4e3a\u7a7a\uff0c\u5426\u5219\u4f1a\u629b\u51fa\u7a7a\u6307\u9488\u5f02\u5e38\u3002\u5b83\u6700\u7ec8\u8c03\u7528\u7684\u662fObjects.requireNonNull\u65b9\u6cd5\u3002\n<\/p>\n

\r\npublic static <T> T requireNonNull(T obj) {\r\n\tif (obj == null)\r\n\t\tthrow new NullPointerException();\r\n\treturn obj;\r\n}<\/pre>\n
\n\tOptional.ofNullable(Object object)
\n<\/h2>\n
\n\tOptional.ofNullable(Object object)\uff1a\u5165\u53c2object\u53ef\u4ee5\u4e3a\u7a7a\uff0c\u5982\u679cobject\u4e0d\u4e3a\u7a7a\uff0c\u5c31\u521b\u5efa\u4e00\u4e2aOptional\u5b9e\u4f8b\uff1b\u5982\u679cobject\u4e3a\u7a7a\u5c31\u8fd4\u56de\u4e00\u4e2astatic fainal\u7684Option\u5bf9\u8c61\uff0c\u6ce8\u610f\u8fd9\u91cc\u4e0d\u4f1a\u65b0\u5efaOption\u5b9e\u4f8b\uff0c\u800c\u662f\u4f7f\u7528\u4e00\u4e2astatic final\u7684\u5b9e\u4f8bEMPTY\uff0c\u8fd9\u91cc\u6bd4\u8f83\u6709\u610f\u601d\u7684\u662f\u6cdb\u578b\u7684\u95ee\u9898\uff0c\u4f8b\u5982\u6211\u9700\u8981\u4e24\u4e2aOptional\u5bf9\u8c61\uff0c\u7c7b\u578b\u5206\u522b\u662fString\u548cInteger\u3002\n<\/p>\n
\r\nOptional<String> optionalStr = Optional.ofNullable(null);\r\nOptional<Integer> optionalInt = Optional.ofNullable(null);<\/pre>\n
\n\t\u7c7b\u578b\u4e0d\u540c\u53c8\u5982\u4f55\u4fdd\u8bc1\u8fd4\u56de\u540c\u4e00\u4e2a\u5bf9\u8c61\u5462\uff1f\u76f4\u63a5\u770bofNullable\u7684\u6e90\u7801\uff0c\u53d1\u73b0\u4f1a\u8c03\u7528empty\u65b9\u6cd5\uff1a\n<\/p>\n
\r\npublic static<T> Optional<T> empty() {\r\n\t@SuppressWarnings("unchecked")\r\n\tOptional<T> t = (Optional<T>) EMPTY;\r\n\treturn t;\r\n}<\/pre>\n
\n\t\u539f\u6765\u662f\u901a\u8fc7\u5f3a\u5236\u8f6c\u6362\u5b9e\u73b0\u7684\uff0c\u518d\u770bEMPTY\u5bf9\u8c61\uff1a\n<\/p>\n
\r\nprivate static final Optional<?> EMPTY = new Optional<>();<\/pre>\n
\n\tOptional.empty()
\n<\/h2>\n
\n\tOptional.empty()\uff1a\u5c31\u662f\u4e0a\u9762\u5206\u6790Optional.ofNullable\u7684\u65f6\u5019\u7528\u5230\u7684empty\u65b9\u6cd5\uff0c\u76f4\u63a5\u8fd4\u56de\u4e00\u4e2astatic final\u7684\u5b9e\u4f8bEMPTY\uff1b\n<\/p>\n
\n\tOptional.of()\u65b9\u6cd5\u7684\u7528\u6cd5\u6709\u70b9\u50cf\u65ad\u8a00\uff0c\u5bf9\u8c61\u4e3a\u7a7a\u7684\u65f6\u5019\u4ee3\u8868\u7740\u67d0\u79cd\u4e1a\u52a1\u4e0a\u4e0d\u53ef\u63a5\u53d7\u7684\u5f02\u5e38\uff0c\u9700\u8981\u5c3d\u65e9\u5904\u7406\uff0c\u5e76\u4e14\u4e1a\u52a1\u62d2\u7edd\u6267\u884c\uff0c\u8fd9\u79cd\u573a\u666f\u4e0b\u53ef\u4ee5\u4f7f\u7528Optional.of\uff1b\n<\/p>\n
\n\t\u4e0b\u9762\u6765\u4e00\u8d77\u770b\u4e00\u4e2a\u4f8b\u5b50\u3002\n<\/p>\n
\n\tUser \u5b9e\u4f53\u7c7b\u4ee3\u7801\u5982\u4e0b\uff1a\n<\/p>\n
\r\npublic class User {\r\n    private int id;\r\n    private String name;\r\n    private int age;\r\n    \/\/\u7701\u7565get\u3001set\u3002www.xttblog.com\r\n    public User(int id, String name, int age) {\r\n        this.id = id;\r\n        this.name = name;\r\n        this.age = age;\r\n    }\r\n}<\/pre>\n
\n\t\u7528Optional\u6765\u907f\u514d\u7a7a\u5f02\u5e38\u95ee\u9898\u3002\n<\/p>\n
\r\npublic User getStudent(int id){\r\n\tUser user = null;\r\n\tOptional<User> optional = Optional.ofNullable(user);\r\n\t\/\/\u5982\u679c\u4e3a\u7a7a\u5c31\u8fd4\u56deDEFAULT\u5bf9\u8c61\r\n\treturn optional.orElse(DEFAULT);\r\n}<\/pre>\n
\n\torElse\u65b9\u6cd5\u53ef\u4ee5\u6307\u5b9a\u4e00\u4e2avalue\u4e3a\u7a7a\u65f6\u7684\u8fd4\u56de\u5bf9\u8c61\uff0c\u5982\u679c\u8fd9\u4e2a\u5bf9\u8c61\u9700\u8981\u8c03\u7528\u65b9\u6cd5\u624d\u80fd\u83b7\u53d6(\u4f8b\u5982\u6211\u4eec\u62ff\u4e0d\u5230DEFAULT\u5bf9\u8c61\uff0c\u8981\u901a\u8fc7getDefault()\u65b9\u6cd5\u624d\u80fd\u62ff\u5230)\uff0c\u8fd9\u662f\u5c31\u9700\u8981orElseGet\u65b9\u6cd5\u6765\u8fbe\u5230\u76ee\u7684\uff0c\u5982\u4e0b\uff1a\n<\/p>\n
\r\nprivate User getDefault(){\r\n    return DEFAULT;\r\n}\r\npublic User getStudent(int id){\r\n\tUser user = null;\r\n    Optional<User> optional = Optional.ofNullable(user);\r\n    \/\/\u5982\u679c\u4e3a\u7a7a\u5c31\u8fd4\u56deDEFAULT\u5bf9\u8c61\r\n    return optional.orElseGet(() -> getDefault());\r\n}<\/pre>\n
\n\t\u672c\u6587\u76f8\u5173\u6e90\u4ee3\u7801\u5df2\u4e0a\u4f20\u5230github\uff1ahttps:\/\/github.com\/zq2599\/blog_demos\/tree\/master\/optionaldemo<\/a>\u3002\n<\/p>\n
\n\t\u4ee5\u4e0a\u5c31\u662fOptional\u7684\u57fa\u672c\u7528\u6cd5\uff0c\u5bf9Optional\u7684\u4f7f\u7528\u662f\u5728\u4e60\u60ef\u4e0a\u5bf9\u4e4b\u524d\u5224\u7a7a\u5199\u6cd5\u7684\u6311\u6218\u3002<\/p>\n
\"\u4e1a\u4f59\u8349\u516c\u4f17\u53f7\"\/<\/p>
\u6700\u540e\uff0c\u6b22\u8fce\u5173\u6ce8\u6211\u7684\u4e2a\u4eba\u5fae\u4fe1\u516c\u4f17\u53f7\uff1a\u4e1a\u4f59\u8349\uff08yyucao\uff09\uff01\u53ef\u52a0\u4f5c\u8005\u5fae\u4fe1\u53f7\uff1axttblog2<\/font>\u3002\u5907\u6ce8\uff1a\u201c1\u201d\uff0c\u6dfb\u52a0\u535a\u4e3b\u5fae\u4fe1\u62c9\u4f60\u8fdb\u5fae\u4fe1\u7fa4\u3002\u5907\u6ce8\u9519\u8bef\u4e0d\u4f1a\u540c\u610f\u597d\u53cb\u7533\u8bf7\u3002<\/b>\u518d\u6b21\u611f\u8c22\u60a8\u7684\u5173\u6ce8\uff01\u540e\u7eed\u6709\u7cbe\u5f69\u5185\u5bb9\u4f1a\u7b2c\u4e00\u65f6\u95f4\u53d1\u7ed9\u60a8\uff01\u539f\u521b\u6587\u7ae0\u6295\u7a3f\u8bf7\u53d1\u9001\u81f3532009913@qq.com\u90ae\u7bb1\u3002\u5546\u52a1\u5408\u4f5c\u4e5f\u53ef\u6dfb\u52a0\u4f5c\u8005\u5fae\u4fe1\u8fdb\u884c\u8054\u7cfb\uff01<\/p>
\u672c\u6587\u539f\u6587\u51fa\u5904\uff1a\u4e1a\u4f59\u8349<\/a>\uff1a » Java 8\u4e2d\u7684 java.util.Optional \u4f7f\u7528\u6559\u7a0b<\/a><\/p>","protected":false},"excerpt":{"rendered":"
Java.util.Optional\u662fJava 8\u65b0\u589e\u7684\u7c7b\uff0c\u4f5c\u4e3a\u4e00\u4e2a\u6301\u6709\u5b9e\u4f8b\u7684\u5bb9\u5668\u7c7b\uff0c\u53ef\u4ee5\u5e2e\u6211\u4eec\u628a\u5224\u7a7a\u7684\u4ee3\u7801\u5199 […]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[5],"tags":[618,1471],"class_list":["post-1880","post","type-post","status-publish","format-standard","hentry","category-java","tag-java8","tag-optional"],"_links":{"self":[{"href":"https:\/\/www.xttblog.com\/index.php?rest_route=\/wp\/v2\/posts\/1880","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.xttblog.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.xttblog.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.xttblog.com\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.xttblog.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1880"}],"version-history":[{"count":1,"href":"https:\/\/www.xttblog.com\/index.php?rest_route=\/wp\/v2\/posts\/1880\/revisions"}],"predecessor-version":[{"id":1881,"href":"https:\/\/www.xttblog.com\/index.php?rest_route=\/wp\/v2\/posts\/1880\/revisions\/1881"}],"wp:attachment":[{"href":"https:\/\/www.xttblog.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1880"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.xttblog.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1880"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.xttblog.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1880"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}