{"id":203688,"date":"2025-05-22T13:28:09","date_gmt":"2025-05-22T05:28:09","guid":{"rendered":"https:\/\/server.hk\/cnblog\/203688\/"},"modified":"2025-05-22T13:28:09","modified_gmt":"2025-05-22T05:28:09","slug":"%e6%82%a8%e9%9c%80%e8%a6%81%e4%ba%86%e8%a7%a3%e7%9a%84%e9%ab%98%e7%ba%a7-java-stream-%e6%8a%80%e5%b7%a7","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/203688\/","title":{"rendered":"\u60a8\u9700\u8981\u4e86\u89e3\u7684\u9ad8\u7ea7 Java Stream \u6280\u5de7"},"content":{"rendered":"

<\/b> <\/p>\n

\u60a8\u9700\u8981\u4e86\u89e3\u7684\u9ad8\u7ea7 Java Stream \u6280\u5de7<\/h1>\n

<\/i>\u6536\u85cf<\/span> <\/p>\n

\u600e\u4e48\u5165\u95e8\u6587\u7ae0\u7f16\u7a0b\uff1f\u9700\u8981\u5b66\u4e60\u54ea\u4e9b\u77e5\u8bc6\u70b9\uff1f\u8fd9\u662f\u65b0\u624b\u4eec\u521a\u63a5\u89e6\u7f16\u7a0b\u65f6\u5e38\u89c1\u7684\u95ee\u9898\uff1b\u4e0b\u9762\u5c31\u6765\u7ed9\u5927\u5bb6\u6574\u7406\u5206\u4eab\u4e00\u4e9b\u77e5\u8bc6\u70b9\uff0c\u5e0c\u671b\u80fd\u591f\u7ed9\u521d\u5b66\u8005\u4e00\u4e9b\u5e2e\u52a9\u3002\u672c\u7bc7\u6587\u7ae0\u5c31\u6765\u4ecb\u7ecd\u300a\u60a8\u9700\u8981\u4e86\u89e3\u7684\u9ad8\u7ea7 Java Stream \u6280\u5de7\u300b\uff0c\u6d89\u53ca\u5230\uff0c\u6709\u9700\u8981\u7684\u53ef\u4ee5\u6536\u85cf\u4e00\u4e0b<\/p>\n

<\/p>\n

1. \u521b\u5efa\u6620\u5c04\u6765\u7f13\u5b58\u5b9e\u4f53 <\/h2>\n

\u5728 map \u4e2d\u7f13\u5b58\u5b9e\u4f53\u53ef\u4ee5\u901a\u8fc7\u51cf\u5c11\u4ece\u6570\u636e\u5e93\u6216\u5176\u4ed6\u6570\u636e\u6e90\u91cd\u590d\u83b7\u53d6\u6570\u636e\u7684\u9700\u8981\u6765\u63d0\u9ad8\u6027\u80fd\u3002\u4f7f\u7528java streams\uff0c\u60a8\u53ef\u4ee5\u8f7b\u677e\u521b\u5efa\u8fd9\u6837\u7684\u7f13\u5b58\u3002 <\/p>\n

\u793a\u4f8b\u4ee3\u7801<\/strong><\/p>\n

import java.util.list;\nimport java.util.map;\nimport java.util.stream.collectors;\n\nclass user {\n    private int id;\n    private string name;\n\n    \/\/ constructors, getters, setters\n}\n\npublic class entitycacheexample {\n    public static void main(string[] args) {\n        list<user> users = list.of(\n            new user(1, \"alice\"),\n            new user(2, \"bob\"),\n            new user(3, \"charlie\")\n        );\n\n        map<integer, user> usercache = users.stream()\n            .collect(collectors.tomap(user::getid, user -> user));\n\n        system.out.println(usercache);\n    }\n}\n<\/pre>\n
\u5728\u4e0a\u9762\u7684\u4ee3\u7801\u4e2d\uff0c\u6211\u4eec\u4f7f\u7528 collectors.tomap()<\/strong> \u5c06 user \u5bf9\u8c61\u5217\u8868\u8f6c\u6362\u4e3a map\uff0c\u5176\u4e2d\u952e\u662f\u7528\u6237\u7684 id\uff0c\u503c\u662f user \u5bf9\u8c61\u672c\u8eab\u3002\u8fd9\u6709\u6548\u5730\u521b\u5efa\u4e86\u7528\u6237\u5b9e\u4f53\u7684\u7f13\u5b58\u3002 <\/p>\n
\u6f14\u793a\u7ed3\u679c<\/strong><\/p>\n
{1=user{id=1, name='alice'}, 2=user{id=2, name='bob'}, 3=user{id=3, name='charlie'}}\n<\/pre>\n
 2. \u521b\u5efa\u5d4c\u5957\u6620\u5c04 <\/h2>\n
\u5f53\u60a8\u9700\u8981\u5c06\u6570\u636e\u5206\u7c7b\u4e3a\u591a\u4e2a\u7ea7\u522b\u65f6\uff0c\u5d4c\u5957\u6620\u5c04\u975e\u5e38\u6709\u7528\u3002\u4f8b\u5982\uff0c\u60a8\u53ef\u80fd\u5e0c\u671b\u6309\u90e8\u95e8\u7136\u540e\u6309\u89d2\u8272\u5bf9\u7528\u6237\u8fdb\u884c\u5206\u7ec4\u3002 <\/p>\n
\u793a\u4f8b\u4ee3\u7801<\/strong><\/p>\n
import java.util.list;\nimport java.util.map;\nimport java.util.stream.collectors;\n\nclass user {\n    private string department;\n    private string role;\n    private string name;\n\n    \/\/ constructors, getters, setters\n}\n\npublic class nestedmapexample {\n    public static void main(string[] args) {\n        list<user> users = list.of(\n            new user(\"hr\", \"manager\", \"alice\"),\n            new user(\"it\", \"developer\", \"bob\"),\n            new user(\"it\", \"manager\", \"charlie\")\n        );\n\n        map<string, map<string, list<user>>> nestedmap = users.stream()\n            .collect(collectors.groupingby(user::getdepartment,\n                collectors.groupingby(user::getrole)));\n\n        system.out.println(nestedmap);\n    }\n}\n<\/pre>\n
\u6b64\u4ee3\u7801\u6f14\u793a\u4e86\u5982\u4f55\u4f7f\u7528 collectors.groupingby()<\/strong> \u521b\u5efa\u5d4c\u5957 map<\/strong>\u3002\u5916\u90e8 map<\/strong> \u6309\u90e8\u95e8\u5bf9\u7528\u6237\u8fdb\u884c\u5206\u7ec4\uff0c\u800c\u5185\u90e8 map<\/strong> \u8fdb\u4e00\u6b65\u6309\u89d2\u8272\u5bf9\u7528\u6237\u8fdb\u884c\u5206\u7ec4\u3002 <\/p>\n
\u6f14\u793a\u7ed3\u679c<\/strong><\/p>\n
{hr={manager=[user{name='alice'}]}, it={developer=[user{name='bob'}], manager=[user{name='charlie'}]}}\n<\/pre>\n
 3. \u521b\u5efa\u5177\u6709\u4e24\u4e2a\u503c\u7684\u6620\u5c04 <\/h2>\n
\u6709\u65f6\uff0c\u60a8\u53ef\u80fd\u5e0c\u671b\u5728 map \u4e2d\u5b58\u50a8\u5355\u4e2a\u952e\u7684\u591a\u4e2a\u5c5e\u6027\u3002\u4f7f\u7528\u5730\u56fe
 > 
<\/strong>\u53ef\u80fd\u662f\u4e00\u4e2a\u6709\u6548\u7684\u89e3\u51b3\u65b9\u6848\u3002 <\/p>\n
\u793a\u4f8b\u4ee3\u7801<\/strong><\/p>\n
import java.util.list;\nimport java.util.map;\nimport java.util.abstractmap.simpleentry;\nimport java.util.stream.collectors;\n\nclass user {\n    private int id;\n    private string name;\n    private int age;\n\n    \/\/ constructors, getters, setters\n}\n\npublic class mapwithtwovaluesexample {\n    public static void main(string[] args) {\n        list<user> users = list.of(\n            new user(1, \"alice\", 30),\n            new user(2, \"bob\", 25),\n            new user(3, \"charlie\", 35)\n        );\n\n        map<integer, map.entry<string, integer>> usermap = users.stream()\n            .collect(collectors.tomap(user::getid, user -> \n                new simpleentry<>(user.getname(), user.getage())));\n\n        system.out.println(usermap);\n    }\n}\n<\/pre>\n
\u5728\u8fd9\u91cc\uff0c\u6211\u4eec\u4f7f\u7528 simpleentry<\/strong> \u521b\u5efa\u4e00\u4e2a map\uff0c\u5176\u4e2d\u5305\u542b\u4e0e\u6bcf\u4e2a\u7528\u6237 id \u5173\u8054\u7684\u4e24\u4e2a\u503c\uff08\u59d3\u540d\u548c\u5e74\u9f84\uff09\u3002 <\/p>\n
\u6f14\u793a\u7ed3\u679c<\/strong><\/p>\n
{1=alice=30, 2=bob=25, 3=charlie=35}\n<\/pre>\n
 4. \u5206\u7ec4\u4f9d\u636e\u548c\u6620\u5c04 <\/h2>\n
\u5206\u7ec4\u548c\u6620\u5c04\u5728\u4e00\u8d77\u53ef\u4ee5\u7b80\u5316\u590d\u6742\u7684\u6570\u636e\u8f6c\u6362\uff0c\u4f8b\u5982\u5c06\u5bf9\u8c61\u5217\u8868\u8f6c\u6362\u4e3a\u5206\u7ec4\u7684map<\/strong>\uff0c\u5176\u4e2d\u6bcf\u4e2a\u7ec4\u5305\u542b\u7279\u5b9a\u5c5e\u6027\u3002 <\/p>\n
\u793a\u4f8b\u4ee3\u7801<\/strong><\/p>\n
import java.util.list;\nimport java.util.map;\nimport java.util.stream.collectors;\n\nclass user {\n    private string department;\n    private string name;\n\n    \/\/ constructors, getters, setters\n}\n\npublic class groupingbymappingexample {\n    public static void main(string[] args) {\n        list<user> users = list.of(\n            new user(\"hr\", \"alice\"),\n            new user(\"it\", \"bob\"),\n            new user(\"hr\", \"charlie\")\n        );\n\n        map<string, list<string>> groupedmap = users.stream()\n            .collect(collectors.groupingby(user::getdepartment,\n                collectors.mapping(user::getname, collectors.tolist())));\n\n        system.out.println(groupedmap);\n    }\n}\n<\/pre>\n
\u5728\u6b64\u793a\u4f8b\u4e2d\uff0c\u6211\u4eec\u6309\u90e8\u95e8\u5bf9\u7528\u6237\u8fdb\u884c\u5206\u7ec4\uff0c\u7136\u540e\u5c06 user<\/strong> \u5bf9\u8c61\u6620\u5c04\u5230\u4ed6\u4eec\u7684\u540d\u79f0\uff0c\u521b\u5efa\u4e00\u4e2a map<\/strong>\uff0c\u5176\u4e2d\u6bcf\u4e2a\u90e8\u95e8\u4e0e\u540d\u79f0\u5217\u8868\u76f8\u5173\u8054\u3002 <\/p>\n
\u6f14\u793a\u7ed3\u679c<\/strong><\/p>\n
{hr=[alice, charlie], it=[bob]}\n<\/pre>\n
 5. \u5206\u7ec4\u4f9d\u636e\u3001\u6620\u5c04\u548c\u5f52\u7ea6 <\/h2>\n
\u7ed3\u5408\u5206\u7ec4\u3001\u6620\u5c04\u548c\u5f52\u7ea6\u53ef\u4ee5\u8ba9\u60a8\u6709\u6548\u5730\u805a\u5408\u6570\u636e\uff0c\u4f8b\u5982\u5bf9\u503c\u6c42\u548c\u6216\u67e5\u627e\u6bcf\u4e2a\u7ec4\u4e2d\u7684\u6700\u5927\u503c\u3002 <\/p>\n
\u793a\u4f8b\u4ee3\u7801<\/strong><\/p>\n
import java.util.list;\nimport java.util.map;\nimport java.util.stream.collectors;\n\nclass transaction {\n    private string type;\n    private int amount;\n\n    \/\/ constructors, getters, setters\n}\n\npublic class groupingbymappingreducingexample {\n    public static void main(string[] args) {\n        list<transaction> transactions = list.of(\n            new transaction(\"deposit\", 100),\n            new transaction(\"deposit\", 200),\n            new transaction(\"withdrawal\", 50),\n            new transaction(\"withdrawal\", 30)\n        );\n\n        map<string, integer> transactionsums = transactions.stream()\n            .collect(collectors.groupingby(transaction::gettype,\n                collectors.reducing(0, transaction::getamount, integer::sum)));\n\n        system.out.println(transactionsums);\n    }\n}\n<\/pre>\n
\u5728\u6b64\u4ee3\u7801\u4e2d\uff0c\u6211\u4eec\u6309\u7c7b\u578b\u5bf9\u4ea4\u6613\u8fdb\u884c\u5206\u7ec4\uff0c\u5c06\u5b83\u4eec\u6620\u5c04\u5230\u5176\u91d1\u989d\uff0c\u7136\u540e\u901a\u8fc7\u6c42\u548c\u6765\u51cf\u5c11\u91d1\u989d\u3002\u7ed3\u679c\u662f\u4e00\u4e2a\u663e\u793a\u6bcf\u79cd\u4ea4\u6613\u7c7b\u578b\u603b\u91d1\u989d\u7684\u5730\u56fe\u3002 <\/p>\n
\u6f14\u793a\u7ed3\u679c<\/strong><\/p>\n
{Deposit=300, Withdrawal=80}\n<\/pre>\n
 \u516d\u3001\u7ed3\u8bba <\/h2>\n
\u8fd9\u4e9b\u9ad8\u7ea7 java stream \u6280\u5de7\u53ef\u4ee5\u663e\u7740\u63d0\u9ad8\u60a8\u7684\u7f16\u7801\u6548\u7387\u548c\u53ef\u8bfb\u6027\u3002\u901a\u8fc7\u638c\u63e1\u8fd9\u4e9b\u6280\u672f\uff0c\u60a8\u53ef\u4ee5\u8f7b\u677e\u5904\u7406\u590d\u6742\u7684\u6570\u636e\u5904\u7406\u4efb\u52a1\u3002\u5982\u679c\u60a8\u6709\u4efb\u4f55\u7591\u95ee\u6216\u9700\u8981\u8fdb\u4e00\u6b65\u8bf4\u660e\uff0c\u8bf7\u968f\u65f6\u5728\u4e0b\u9762\u53d1\u8868\u8bc4\u8bba\uff01 <\/p>\n
\u9605\u8bfb\u66f4\u591a\u5e16\u5b50<\/strong>\uff1a\u60a8\u9700\u8981\u4e86\u89e3\u7684 5 \u4e2a\u9ad8\u7ea7 java stream \u6280\u5de7<\/p>\n
\u5230\u8fd9\u91cc\uff0c\u6211\u4eec\u4e5f\u5c31\u8bb2\u5b8c\u4e86\u300a\u60a8\u9700\u8981\u4e86\u89e3\u7684\u9ad8\u7ea7 Java Stream \u6280\u5de7\u300b\u7684\u5185\u5bb9\u4e86\u3002\u4e2a\u4eba\u8ba4\u4e3a\uff0c\u57fa\u7840\u77e5\u8bc6\u7684\u5b66\u4e60\u548c\u5de9\u56fa\uff0c\u662f\u4e3a\u4e86\u66f4\u597d\u7684\u5c06\u5176\u8fd0\u7528\u5230\u9879\u76ee\u4e2d\uff0c\u6b22\u8fce\u5173\u6ce8\u516c\u4f17\u53f7\uff0c\u5e26\u4f60\u4e86\u89e3\u66f4\u591a\u5173\u4e8e\u7684\u77e5\u8bc6\u70b9\uff01<\/p>\n
      \u7248\u672c\u58f0\u660e \u672c\u6587\u8f6c\u8f7d\u4e8e\uff1adev.to \u5982\u6709\u4fb5\u72af\uff0c\u8bf7\u8054\u7cfb\u5220\u9664<\/p>\n","protected":false},"excerpt":{"rendered":"
\u60a8\u9700\u8981\u4e86\u89e3\u7684\u9ad8\u7ea7 Java St...<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4925],"tags":[],"class_list":["post-203688","post","type-post","status-publish","format-standard","hentry","category-4925"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/203688","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/comments?post=203688"}],"version-history":[{"count":0,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/203688\/revisions"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=203688"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=203688"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=203688"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}