{"id":1138,"date":"2024-12-20T12:34:54","date_gmt":"2024-12-20T03:34:54","guid":{"rendered":"https:\/\/route-zero.com\/recruit\/route\/1138\/"},"modified":"2025-04-08T09:31:48","modified_gmt":"2025-04-08T00:31:48","slug":"1138","status":"publish","type":"route","link":"https:\/\/route-zero.com\/recruit\/route\/1138\/","title":{"rendered":"Java\u306efor\u6587\u3092Stream\u306b\u66f8\u304d\u63db\u3048\u308b\u306b\u306f\uff1fSpring Boot\u3067\u306e\u5b9f\u8df5\u4f8b\u4ed8\u304d\u3067\u308f\u304b\u308b\uff01"},"content":{"rendered":"<div>\n<h2>\u300c\u3053\u306e\u51e6\u7406\u3001\u3082\u3063\u3068\u30b9\u30de\u30fc\u30c8\u306b\u66f8\u3051\u306a\u3044\u306e\uff1f\u300d\u3068\u611f\u3058\u305f\u3053\u3068\u306f\u3042\u308a\u307e\u305b\u3093\u304b\uff1f<\/h2>\n<p>Java\u3067for\u6587\u3092\u3050\u308b\u3050\u308b\u66f8\u3044\u3066\u3001\u300c\u3082\u3063\u3068\u7c21\u6f54\u306b\u3067\u304d\u306a\u3044\u304b\u306a\u300d\u3068\u601d\u3063\u305f\u7d4c\u9a13\u306f\u3042\u308a\u307e\u305b\u3093\u304b\uff1f<br \/>\u4f8b\u3048\u3070\u3001\u30ea\u30b9\u30c8\u304b\u3089\u7279\u5b9a\u6761\u4ef6\u306e\u30c7\u30fc\u30bf\u3060\u3051\u3092\u62bd\u51fa\u3057\u305f\u308a\u3001\u30c7\u30fc\u30bf\u3092\u5909\u63db\u3057\u3066\u5225\u306e\u5f62\u5f0f\u306b\u3057\u305f\u308a\u3068\u3044\u3063\u305f\u51e6\u7406\u3002<\/p>\n<p>\u305d\u3093\u306a\u3068\u304d\u306b\u5f79\u7acb\u3064\u306e\u304c <strong>Stream API<\/strong> \u3067\u3059\u3002<\/p>\n<p>\u7279\u306bSpring Boot\u306e\u958b\u767a\u73fe\u5834\u3067\u306f\u3001\u30c7\u30fc\u30bf\u30d9\u30fc\u30b9\u306e\u691c\u7d22\u7d50\u679c\u3084DTO\u306e\u6574\u5f62\u51e6\u7406\u306a\u3069\u3001Stream API\u304c\u975e\u5e38\u306b\u5f79\u7acb\u3061\u307e\u3059\u3002<br \/>\u3053\u306e\u8a18\u4e8b\u3067\u306f\u3001\u521d\u5fc3\u8005\u301c\u4e2d\u7d1a\u8005\u5411\u3051\u306b\u3001Stream API\u306e\u57fa\u672c\u304b\u3089\u3001\u3088\u304f\u4f7f\u3046\u51e6\u7406\u3001\u696d\u52d9\u3067\u3042\u308a\u304c\u3061\u306a\u843d\u3068\u3057\u7a74\u307e\u3067\u4e01\u5be7\u306b\u89e3\u8aac\u3057\u3066\u3044\u304d\u307e\u3059\u3002<\/p>\n<hr>\n<h2>Stream API\u306e\u57fa\u672c\u3068\u5b9f\u8df5\u7684\u306a\u4f7f\u3044\u65b9<\/h2>\n<h3>Stream API\u3068\u306f\uff1f<\/h3>\n<p>Java 8\u3067\u5c0e\u5165\u3055\u308c\u305fStream API\u306f\u3001<strong>\u30b3\u30ec\u30af\u30b7\u30e7\u30f3\u64cd\u4f5c\u3092\u5ba3\u8a00\u7684\u306b\u66f8\u3051\u308b\u4ed5\u7d44\u307f<\/strong>\u3067\u3059\u3002<br \/>\u5f93\u6765\u306e\u547d\u4ee4\u578b\u30b9\u30bf\u30a4\u30eb\u3068\u306f\u7570\u306a\u308a\u3001\u4f55\u3092\u3057\u305f\u3044\u304b\u3092\u7c21\u6f54\u306b\u8868\u73fe\u3067\u304d\u307e\u3059\u3002<\/p>\n<pre><code><span>List<\/span>&lt;<span>String<\/span>&gt; names = <span>Arrays<\/span>.asList(<span>\"Taro\"<\/span>, <span>\"Jiro\"<\/span>, <span>\"Hanako\"<\/span>);\r\n\r\n<span>List<\/span>&lt;<span>String<\/span>&gt; filtered = names.stream()\r\n    .<span>filter<\/span>(name -&gt; name.<span>startsWith<\/span>(<span>\"T\"<\/span>))\r\n    .collect(<span>Collectors<\/span>.toList());\r\n\r\n<span>System<\/span>.out.<span>println<\/span>(filtered); <span>\/\/ \u2192 [Taro]<\/span><\/code><\/pre>\n<h3>\u3088\u304f\u4f7f\u3046Stream\u64cd\u4f5c\u307e\u3068\u3081\uff08\u30ea\u30b9\u30c8\u5f62\u5f0f\uff09<\/h3>\n<ul>\n<li>\n<p>.filter()\uff1a\u6761\u4ef6\u3067\u7d5e\u308a\u8fbc\u307f\uff08\u4f8b\uff1aname -&gt; name.length() &gt; 3\uff09<\/p>\n<\/li>\n<li>\n<p>.map()\uff1a\u8981\u7d20\u306e\u5909\u63db\uff08\u4f8b\uff1aname -&gt; name.toUpperCase()\uff09<\/p>\n<\/li>\n<li>\n<p>.collect()\uff1a\u7d50\u679c\u3092\u30ea\u30b9\u30c8\u306a\u3069\u306b\u53ce\u96c6\uff08\u4f8b\uff1aCollectors.toList()\uff09<\/p>\n<\/li>\n<li>\n<p>.sorted()\uff1a\u4e26\u3073\u66ff\u3048\uff08\u4f8b\uff1aComparator.naturalOrder()\uff09<\/p>\n<\/li>\n<li>\n<p>.distinct()\uff1a\u91cd\u8907\u6392\u9664<\/p>\n<\/li>\n<li>\n<p>.count()\uff1a\u4ef6\u6570\u3092\u30ab\u30a6\u30f3\u30c8<\/p>\n<\/li>\n<\/ul>\n<h3>Spring Boot\u3067\u306eStream API\u6d3b\u7528\u4f8b\uff08DTO\u6574\u5f62\uff09<\/h3>\n<p>Spring Boot\u3067\u306f\u3001Entity \u2192 DTO\u5909\u63db\u306b\u3088\u304f\u4f7f\u308f\u308c\u307e\u3059\u3002<\/p>\n<pre><code><span>List<\/span>&lt;User&gt; users = userRepository.findAll();\r\n\r\n<span>List<\/span>&lt;UserDto&gt; dtos = users.stream()\r\n    .map(user -&gt; <span>new<\/span> UserDto(user.getId(), user.getName()))\r\n    .collect(Collectors.toList());<\/code><\/pre>\n<p>UserDto\u306e\u4f8b\uff1a<\/p>\n<pre><code><span>public<\/span> <span><span>class<\/span> <span>UserDto<\/span> <\/span>{\r\n    <span>private<\/span> Long id;\r\n    <span>private<\/span> String name;\r\n\r\n    <span><span>public<\/span> <span>UserDto<\/span><span>(Long id, String name)<\/span> <\/span>{\r\n        <span>this<\/span>.id = id;\r\n        <span>this<\/span>.name = name;\r\n    }\r\n}<\/code><\/pre>\n<hr>\n<h2>\u3064\u307e\u305a\u304d\u3084\u3059\u3044\u30dd\u30a4\u30f3\u30c8\u3068\u6539\u5584\u306e\u30b3\u30c4<\/h2>\n<h3>\u3042\u308a\u304c\u3061\u306a\u3064\u307e\u305a\u304d1\uff1anull\u3092\u542b\u3080\u30ea\u30b9\u30c8\u306b\u6ce8\u610f\uff01<\/h3>\n<pre><code><span>List<\/span>&lt;String&gt; <span>list<\/span> = Arrays.asList(<span>\"a\"<\/span>, <span>null<\/span>, <span>\"b\"<\/span>);\r\n\r\n<span>List<\/span>&lt;String&gt; result = <span>list<\/span>.stream()\r\n    .filter(s -&gt; s.length() &gt; <span>0<\/span>) <span>\/\/ \u2190 NullPointerException<\/span>\r\n    .collect(Collectors.toList());<\/code><\/pre>\n<p>\u89e3\u6c7a\u6cd5\uff1a<\/p>\n<pre><code><span>.filter<\/span>(<span>Objects<\/span><span>::nonNull)<\/span><\/code><\/pre>\n<p>\u307e\u305f\u306f<\/p>\n<pre><code>.filter(s -&gt; s != <span>null<\/span> &amp;&amp; s.length() &gt; <span>0<\/span>)<\/code><\/pre>\n<hr>\n<h3>\u3042\u308a\u304c\u3061\u306a\u3064\u307e\u305a\u304d2\uff1a\u526f\u4f5c\u7528\uff08print, \u30ed\u30b0\uff09\u3092map\u3067\u3084\u3089\u306a\u3044<\/h3>\n<pre><code>.<span>map<\/span>(user -&gt; {\r\n    System.out.<span>println<\/span>(user.getName()); <span>\/\/ \u2190 map\u3067\u526f\u4f5c\u7528NG<\/span>\r\n    <span>return<\/span> user.getName();\r\n})<\/code><\/pre>\n<p>\u6b63\u3057\u3044\u3084\u308a\u65b9\uff1a<\/p>\n<pre><code>.peek(user -&gt; System.out.<span>println<\/span>(user.getName())) <span>\/\/ peek\u306f\u526f\u4f5c\u7528OK<\/span>\r\n.<span>map<\/span>(User::getName)<\/code><\/pre>\n<hr>\n<h3>\u66f8\u304d\u63db\u3048\u4f8b\uff1abefore \/ after<\/h3>\n<p>Before\uff08for\u6587\uff09\uff1a<\/p>\n<pre><code>List&lt;<span>String<\/span>&gt; result = <span>new<\/span> ArrayList&lt;&gt;();\r\n<span>for<\/span> (<span>String<\/span> s : names) {\r\n    <span>if<\/span> (s.startsWith(<span>\"T\"<\/span>)) {\r\n        result.add(s.toUpperCase());\r\n    }\r\n}<\/code><\/pre>\n<p>After\uff08Stream API\uff09\uff1a<\/p>\n<pre><code>List&lt;<span>String<\/span>&gt; result = names.stream()\r\n    .filter(s -&gt; s.startsWith(<span>\"T\"<\/span>))\r\n    .map(<span>String<\/span>::toUpperCase)\r\n    .collect(Collectors.toList());<\/code><\/pre>\n<p>\u30b3\u30fc\u30c9\u91cf\u304c\u6e1b\u308a\u3001\u8aad\u307f\u3084\u3059\u304f\u306a\u308a\u307e\u3059\u3002<\/p>\n<hr>\n<h2>\u307e\u3068\u3081\u3068\u6b21\u306e\u30b9\u30c6\u30c3\u30d7<\/h2>\n<h3>\u307e\u3068\u3081<\/h3>\n<ul>\n<li>\n<p>Stream API\u306f\u3001\u30b3\u30ec\u30af\u30b7\u30e7\u30f3\u64cd\u4f5c\u3092\u7c21\u6f54\u306b\u8a18\u8ff0\u3067\u304d\u308bJava\u306e\u6a5f\u80fd\u3002<\/p>\n<\/li>\n<li>\n<p>Spring Boot\u3067\u306fDTO\u5909\u63db\u3084\u30c7\u30fc\u30bf\u6574\u5f62\u306b\u3088\u304f\u767b\u5834\u3002<\/p>\n<\/li>\n<li>\n<p>filter, map, collect \u306a\u3069\u306e\u57fa\u672c\u64cd\u4f5c\u3092\u4f7f\u3044\u3053\u306a\u305d\u3046\u3002<\/p>\n<\/li>\n<li>\n<p>null\u3084\u526f\u4f5c\u7528\u306b\u306f\u6ce8\u610f\u304c\u5fc5\u8981\u3002<\/p>\n<\/li>\n<li>\n<p>for\u6587\u304b\u3089Stream\u3078\u306e\u66f8\u304d\u63db\u3048\u3067\u3001\u30b3\u30fc\u30c9\u306e\u53ef\u8aad\u6027\u304c\u5927\u5e45\u30a2\u30c3\u30d7\uff01<\/p>\n<\/li>\n<\/ul>\n<h3>\u3010\u5916\u90e8\u30ea\u30f3\u30af\u3011<\/h3>\n<p><a href=\"https:\/\/spring.io\/projects\/spring-boot\">Spring Boot\u516c\u5f0f\u30b5\u30a4\u30c8<\/a><\/p>\n<p><a href=\"https:\/\/spring.io\/guides\/gs\/serving-web-content\/\">Spring Framework\u516c\u5f0f\u30ac\u30a4\u30c9 \u2013 Spring MVC<\/a><\/p>\n<h3>\u3010\u5185\u90e8\u30ea\u30f3\u30af\u3011<\/h3>\n<p><a href=\"https:\/\/route-zero.com\/recruit\/route\/1104\/\">Spring Boot\u306e\u3088\u304f\u4f7f\u308f\u308c\u308b\u30a2\u30ce\u30c6\u30fc\u30b7\u30e7\u30f3\u3068\u306f\uff1f\u521d\u5fc3\u8005\u5fc5\u898b\u306e\u89e3\u8aac\u3068\u6d3b\u7528\u6cd5<\/a><\/p>\n<p><a href=\"https:\/\/route-zero.com\/recruit\/route\/1115\/\">Spring Boot \u30d0\u30ea\u30c7\u30fc\u30b7\u30e7\u30f3\u5165\u9580\uff5cMVC\u7d71\u5408\u3068\u30ab\u30b9\u30bf\u30e0\u30a2\u30ce\u30c6\u30fc\u30b7\u30e7\u30f3\u5b9f\u8df5\u4f8b<\/a><\/p>\n<p><a href=\"https:\/\/route-zero.com\/recruit\/route\/1068\/\">Thymeleaf\u3068JavaScript\u3067\u30bf\u30b0\u3092\u4f7f\u3063\u305f\u30d5\u30a9\u30fc\u30e0\u4f5c\u6210\u6cd5\u3068\u30c7\u30fc\u30bf\u9001\u4fe1\u306e\u65b9\u6cd5<\/a><\/p>\n<\/div>\n","protected":false},"featured_media":1139,"template":"","_links":{"self":[{"href":"https:\/\/route-zero.com\/recruit\/wp-json\/wp\/v2\/route\/1138"}],"collection":[{"href":"https:\/\/route-zero.com\/recruit\/wp-json\/wp\/v2\/route"}],"about":[{"href":"https:\/\/route-zero.com\/recruit\/wp-json\/wp\/v2\/types\/route"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/route-zero.com\/recruit\/wp-json\/wp\/v2\/media\/1139"}],"wp:attachment":[{"href":"https:\/\/route-zero.com\/recruit\/wp-json\/wp\/v2\/media?parent=1138"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}