【合集】Java常用代码-工具盒子

Java集合 {#java集合postjava-collection}

Guava {#guavapostguava}

【合集】EasyExcel-写出excel {#合集easyexcel-写出excelposteasy-excel-write}

【合集】EasyExcel-读取excel {#合集easyexcel-读取excelposteasy-excel-read}

【合集】EasyPOI-写出excel {#合集easypoi-写出excelposteasy-poi-write}

【合集】EasyPOI-读取excel {#合集easypoi-读取excelposteasy-poi-read}

Java并发编程 {#java并发编程postjava-concurrent}

Json使用 {#json使用postjackson}

Java枚举类示例 {#java枚举类示例}

|----------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 | java public enum SeasonEnum { SPRING, SUMMER, AUTUMN, WINTER; } // 枚举类的编译以后源代码： //public final class Season extends java.lang.Enum<Season> { // public static final Season SPRING = new Season(); // public static final Season SUMMER = new Season(); // public static final Season AUTUMN = new Season(); // public static final Season WINTER = new Season(); // // public static Season[] values(); // public static Season valueOf(java.lang.String); //} |

阿里巴巴Java开发手册错误码-枚举示例 {#阿里巴巴java开发手册错误码-枚举示例}

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| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 | java import lombok.AllArgsConstructor; import lombok.Getter; /** * 阿里巴巴Java开发手册-崇山版-2020.08.03 错误码整理 * 错误码： * 1. 五位组成 * 2. A代表用户端错误 * 3. B代表当前系统异常 * 4. C代表第三方服务异常 * 4. 若无法确定具体错误，选择宏观错误，如A0001：一级宏观错误码 A0100：二级宏观错误码 * 6. 大的错误类间的步长间距预留100 */ @Getter @AllArgsConstructor public enum ErrorCodeEnum { // 成功 SUCCESS("00000", "一切 ok"), ERROR("99999", "未归类的错误"), // 用户端错误 USER_ERROR_A0001("A0001", "用户端错误"), // A0100 USER_ERROR_A0100("A0100", "用户注册错误"), USER_ERROR_A0101("A0101", "用户未同意隐私协议"), USER_ERROR_A0102("A0102", "注册国家或地区受限"), USER_ERROR_A0110("A0110", "用户名校验失败"), USER_ERROR_A0111("A0111", "用户名已存在"), USER_ERROR_A0112("A0112", "用户名包含敏感词"), USER_ERROR_A0113("A0113", "用户名包含特殊字符"), USER_ERROR_A0120("A0120", "密码校验失败"), USER_ERROR_A0121("A0121", "密码长度不够"), USER_ERROR_A0122("A0122", "密码强度不够"), USER_ERROR_A0130("A0130", "校验码输入错误"), USER_ERROR_A0131("A0131", "短信校验码输入错误"), USER_ERROR_A0132("A0132", "邮件校验码输入错误"), USER_ERROR_A0133("A0133", "语音校验码输入错误"), USER_ERROR_A0140("A0140", "用户证件异常"), USER_ERROR_A0141("A0141", "用户证件类型未选择"), USER_ERROR_A0142("A0142", "大陆身份证编号校验非法"), USER_ERROR_A0143("A0143", "护照编号校验非法"), USER_ERROR_A0144("A0144", "军官证编号校验非法"), USER_ERROR_A0150("A0150", "用户基本信息校验失败"), USER_ERROR_A0151("A0151", "手机格式校验失败"), USER_ERROR_A0152("A0152", "地址格式校验失败"), USER_ERROR_A0153("A0153", "邮箱格式校验失败"), // A0200 USER_ERROR_A0200("A0200", "用户登录异常"), USER_ERROR_A0201("A0201", "用户账户不存在"), USER_ERROR_A0202("A0202", "用户账户被冻结"), USER_ERROR_A0203("A0203", "用户账户已作废"), USER_ERROR_A0210("A0210", "用户密码错误"), USER_ERROR_A0211("A0211", "用户输入密码错误次数超限"), USER_ERROR_A0220("A0220", "用户身份校验失败"), USER_ERROR_A0221("A0221", "用户指纹识别失败"), USER_ERROR_A0222("A0222", "用户面容识别失败"), USER_ERROR_A0223("A0223", "用户未获得第三方登录授权"), USER_ERROR_A0230("A0230", "用户登录已过期"), USER_ERROR_A0240("A0240", "用户验证码错误"), USER_ERROR_A0241("A0241", "用户验证码尝试次数超限"), // A0300 USER_ERROR_A0300("A0300", "访问权限异常"), USER_ERROR_A0301("A0301", "访问未授权"), USER_ERROR_A0302("A0302", "正在授权中"), USER_ERROR_A0303("A0303", "用户授权申请被拒绝"), USER_ERROR_A0310("A0310", "因访问对象隐私设置被拦截"), USER_ERROR_A0311("A0311", "授权已过期"), USER_ERROR_A0312("A0312", "无权限使用 API"), USER_ERROR_A0320("A0320", "用户访问被拦截"), USER_ERROR_A0321("A0321", "黑名单用户"), USER_ERROR_A0322("A0322", "账号被冻结"), USER_ERROR_A0323("A0323", "非法 IP 地址"), USER_ERROR_A0324("A0324", "网关访问受限"), USER_ERROR_A0325("A0325", "地域黑名单"), USER_ERROR_A0330("A0330", "服务已欠费"), USER_ERROR_A0340("A0340", "用户签名异常"), USER_ERROR_A0341("A0341", "RSA 签名错误"), // A0400 USER_ERROR_A0400("A0400", "用户请求参数错误"), USER_ERROR_A0401("A0401", "包含非法恶意跳转链接"), USER_ERROR_A0402("A0402", "无效的用户输入"), USER_ERROR_A0410("A0410", "请求必填参数为空"), USER_ERROR_A0411("A0411", "用户订单号为空"), USER_ERROR_A0412("A0412", "订购数量为空"), USER_ERROR_A0413("A0413", "缺少时间戳参数"), USER_ERROR_A0414("A0414", "非法的时间戳参数"), USER_ERROR_A0420("A0420", "请求参数值超出允许的范围"), USER_ERROR_A0421("A0421", "参数格式不匹配"), USER_ERROR_A0422("A0422", "地址不在服务范围"), USER_ERROR_A0423("A0423", "时间不在服务范围"), USER_ERROR_A0424("A0424", "金额超出限制"), USER_ERROR_A0425("A0425", "数量超出限制"), USER_ERROR_A0426("A0426", "请求批量处理总个数超出限制"), USER_ERROR_A0427("A0427", "请求 JSON 解析失败"), USER_ERROR_A0430("A0430", "用户输入内容非法"), USER_ERROR_A0431("A0431", "包含违禁敏感词"), USER_ERROR_A0432("A0432", "图片包含违禁信息"), USER_ERROR_A0433("A0433", "文件侵犯版权"), USER_ERROR_A0440("A0440", "用户操作异常"), USER_ERROR_A0441("A0441", "用户支付超时"), USER_ERROR_A0442("A0442", "确认订单超时"), USER_ERROR_A0443("A0443", "订单已关闭"), USER_ERROR_A0444("A0444", "名称不能为空"), // A0500 USER_ERROR_A0500("A0500", "用户请求服务异常"), USER_ERROR_A0501("A0501", "请求次数超出限制"), USER_ERROR_A0502("A0502", "请求并发数超出限制"), USER_ERROR_A0503("A0503", "用户操作请等待"), USER_ERROR_A0504("A0504", "WebSocket 连接异常"), USER_ERROR_A0505("A0505", "WebSocket 连接断开"), USER_ERROR_A0506("A0506", "用户重复请求"), // A0600 USER_ERROR_A0600("A0600", "用户资源异常"), USER_ERROR_A0601("A0601", "账户余额不足"), USER_ERROR_A0602("A0602", "用户磁盘空间不足"), USER_ERROR_A0603("A0603", "用户内存空间不足"), USER_ERROR_A0604("A0604", "用户 OSS 容量不足"), USER_ERROR_A0605("A0605", "用户配额已用光"), // A0700 USER_ERROR_A0700("A0700", "用户上传文件异常"), USER_ERROR_A0701("A0701", "用户上传文件类型不匹配"), USER_ERROR_A0702("A0702", "用户上传文件太大"), USER_ERROR_A0703("A0703", "用户上传图片太大"), USER_ERROR_A0704("A0704", "用户上传视频太大"), USER_ERROR_A0705("A0705", "用户上传压缩文件太大"), // A0800 USER_ERROR_A0800("A0800", "用户当前版本异常"), USER_ERROR_A0801("A0801", "用户安装版本与系统不匹配"), USER_ERROR_A0802("A0802", "用户安装版本过低"), USER_ERROR_A0803("A0803", "用户安装版本过高"), USER_ERROR_A0804("A0804", "用户安装版本已过期"), USER_ERROR_A0805("A0805", "用户 API 请求版本不匹配"), USER_ERROR_A0806("A0806", "用户 API 请求版本过高"), USER_ERROR_A0807("A0807", "用户 API 请求版本过低"), // A0900 USER_ERROR_A0900("A0900", "用户隐私未授权"), USER_ERROR_A0901("A0901", "用户隐私未签署"), USER_ERROR_A0902("A0902", "用户摄像头未授权"), USER_ERROR_A0903("A0903", "用户相机未授权"), USER_ERROR_A0904("A0904", "用户图片库未授权"), USER_ERROR_A0905("A0905", "用户文件未授权"), USER_ERROR_A0906("A0906", "用户位置信息未授权"), USER_ERROR_A0907("A0907", "用户通讯录未授权"), // A1000 USER_ERROR_A1000("A1000", "用户设备异常"), USER_ERROR_A1001("A1001", "用户相机异常"), USER_ERROR_A1002("A1002", "用户麦克风异常"), USER_ERROR_A1003("A1003", "用户听筒异常"), USER_ERROR_A1004("A1004", "用户扬声器异常"), USER_ERROR_A1005("A1005", "用户 GPS 定位异常"), // 系统执行出错 SYSTEM_ERROR_B0001("B0001", "系统执行出错"), // B0100 SYSTEM_ERROR_B0100("B0100", "系统执行超时"), SYSTEM_ERROR_B0101("B0101", "系统订单处理超时"), // B0200 SYSTEM_ERROR_B0200("B0200", "系统容灾功能被触发"), SYSTEM_ERROR_B0210("B0210", "系统限流"), SYSTEM_ERROR_B0220("B0220", "系统功能降级"), // B0300 SYSTEM_ERROR_B0300("B0300", "系统资源异常"), SYSTEM_ERROR_B0310("B0310", "系统资源耗尽"), SYSTEM_ERROR_B0311("B0311", "系统磁盘空间耗尽"), SYSTEM_ERROR_B0312("B0312", "系统内存耗尽"), SYSTEM_ERROR_B0313("B0313", "文件句柄耗尽"), SYSTEM_ERROR_B0314("B0314", "系统连接池耗尽"), SYSTEM_ERROR_B0315("B0315", "系统线程池耗尽"), SYSTEM_ERROR_B0320("B0320", "系统资源访问异常"), SYSTEM_ERROR_B0321("B0321", "系统读取磁盘文件失败"), // 调用第三方服务出错 SERVICE_ERROR_C0001("C0001", "调用第三方服务出错"), // C0100 SERVICE_ERROR_C0100("C0100", "中间件服务出错"), SERVICE_ERROR_C0110("C0110", "RPC 服务出错"), SERVICE_ERROR_C0111("C0111", "RPC 服务未找到"), SERVICE_ERROR_C0112("C0112", "RPC 服务未注册"), SERVICE_ERROR_C0113("C0113", "接口不存在"), SERVICE_ERROR_C0120("C0120", "消息服务出错"), SERVICE_ERROR_C0121("C0121", "消息投递出错"), SERVICE_ERROR_C0122("C0122", "消息消费出错"), SERVICE_ERROR_C0123("C0123", "消息订阅出错"), SERVICE_ERROR_C0124("C0124", "消息分组未查到"), SERVICE_ERROR_C0130("C0130", "缓存服务出错"), SERVICE_ERROR_C0131("C0131", "key 长度超过限制"), SERVICE_ERROR_C0132("C0132", "value 长度超过限制"), SERVICE_ERROR_C0133("C0133", "存储容量已满"), SERVICE_ERROR_C0134("C0134", "不支持的数据格式"), SERVICE_ERROR_C0140("C0140", "配置服务出错"), SERVICE_ERROR_C0150("C0150", "网络资源服务出错"), SERVICE_ERROR_C0151("C0151", "VPN 服务出错"), SERVICE_ERROR_C0152("C0152", "CDN 服务出错"), SERVICE_ERROR_C0153("C0153", "域名解析服务出错"), SERVICE_ERROR_C0154("C0154", "网关服务出错"), // C0200 SERVICE_ERROR_C0200("C0200", "第三方系统执行超时"), SERVICE_ERROR_C0210("C0210", "RPC 执行超时"), SERVICE_ERROR_C0220("C0220", "消息投递超时"), SERVICE_ERROR_C0230("C0230", "缓存服务超时"), SERVICE_ERROR_C0240("C0240", "配置服务超时"), SERVICE_ERROR_C0250("C0250", "数据库服务超时"), // C0300 SERVICE_ERROR_C0300("C0300", "数据库服务出错"), SERVICE_ERROR_C0311("C0311", "表不存在"), SERVICE_ERROR_C0312("C0312", "列不存在"), SERVICE_ERROR_C0321("C0321", "多表关联中存在多个相同名称的列"), SERVICE_ERROR_C0331("C0331", "数据库死锁"), SERVICE_ERROR_C0341("C0341", "主键冲突"), // C0400 SERVICE_ERROR_C0400("C0400", "第三方容灾系统被触发"), SERVICE_ERROR_C0401("C0401", "第三方系统限流"), SERVICE_ERROR_C0402("C0402", "第三方功能降级"), // C0500 SERVICE_ERROR_C0500("C0500", "通知服务出错"), SERVICE_ERROR_C0501("C0501", "短信提醒服务失败"), SERVICE_ERROR_C0502("C0502", "语音提醒服务失败"), SERVICE_ERROR_C0503("C0503", "邮件提醒服务失败"); private final String errorCode; private final String errorMessage; } |

Java手机号正则校验 {#java手机号正则校验}

示例1

|----------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 | java /** * 手机号校验 * @param mobileNumber */ public static boolean mobileValidate(String mobileNumber) { String regex = "^1[3456789]\\d{9}$"; Pattern pattern = Pattern.compile(regex); Matcher matcher = pattern.matcher(mobileNumber); return matcher.matches(); } |

示例2

|-------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 | java public class MobileNumberValidator { // 定义正则表达式 private static final String MOBILE_REGEX = "^1(3|4|5|6|7|8|9)\\d{9}$"; /** * 校验手机号 * * @param mobile 手机号 * @return 是否为合法的手机号 */ public static boolean isValidMobile(String mobile) { if (mobile == null || mobile.trim().isEmpty()) { return false; } return mobile.matches(MOBILE_REGEX); } public static void main(String[] args) { String[] mobiles = {"13800138000", "12345678901", "14512345678", "17612345678", "not a mobile", null, ""}; for (String mobile : mobiles) { System.out.println(mobile + " is valid mobile number? " + isValidMobile(mobile)); } } } |

Java校验车牌号格式 {#java校验车牌号格式}

|----------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 | java public class LicensePlateValidator { // 正则表达式解释： // ^[京津沪渝冀豫云辽黑湘皖鲁新苏浙赣鄂桂甘晋蒙陕吉闽贵粤青藏川宁琼使领A-Z]{1}[A-Z·]{0,1}[A-Z0-9]{4}[A-Z0-9挂学警港澳]{1}$ // ^ 表示字符串开始 // [京津沪渝冀豫云辽黑湘皖鲁新苏浙赣鄂桂甘晋蒙陕吉闽贵粤青藏川宁琼使领] 表示省份简称 // [A-Z]{1} 表示第一个字母（新能源车牌可能不含此部分） // [A-Z·]{0,1} 表示新能源车牌中的点（可选），普通车牌则不包含 // [A-Z0-9]{4} 表示接下来的4位字母或数字 // [A-Z0-9挂学警港澳]{1} 表示最后一位字母、数字或特殊字符（挂、学、警、港、澳） // $ 表示字符串结束 private static final String LICENSE_PLATE_REGEX = "^[京津沪渝冀豫云辽黑湘皖鲁新苏浙赣鄂桂甘晋蒙陕吉闽贵粤青藏川宁琼使领A-Z]{1}[A-Z·]{0,1}[A-Z0-9]{4}[A-Z0-9挂学警港澳]{1}$"; /** * 校验车牌号 * * @param licensePlate 车牌号 * @return 是否为合法的车牌号 */ public static boolean isValidLicensePlate(String licensePlate) { if (licensePlate == null || licensePlate.trim().isEmpty()) { return false; } return licensePlate.matches(LICENSE_PLATE_REGEX); } public static void main(String[] args) { String[] licensePlates = {"京A12345", "沪A·1234D", "川A1234挂", "京A1234学", "粤B12345港", "不存在的车牌", "京A123", "京A123456"}; for (String licensePlate : licensePlates) { System.out.println(licensePlate + " is valid? " + isValidLicensePlate(licensePlate)); } } } |

注意：

上述正则表达式假设省份简称和特殊字符（如"挂"、"学"、"警"、"港"、"澳"）都是大写。如果实际情况中可能包含小写，请将对应的部分修改为不区分大小写的正则表达式（Java中可以通过Pattern.CASE_INSENSITIVE标志来实现，但这里为了简单起见没有包含）。
新能源车牌中的点（·）在正则表达式中可能需要根据实际编码进行转义（在某些环境下可能需要写作\u00B7或其他形式的转义序列）。上面的示例中直接使用了·字符，这可能在某些环境下无法正常工作。
该正则表达式可能无法覆盖所有特殊情况，如临时车牌、军用车牌、警用车牌等，这些车牌的格式与普通车牌和新能源车牌有所不同。如果需要校验这些特殊车牌，请根据实际情况调整正则表达式。

OkHttp3请求示例 {#okhttp3请求示例}

|-------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 | xml  <dependency> <groupId>com.squareup.okhttp3</groupId> <artifactId>okhttp</artifactId> <version>5.0.0-alpha.14</version> </dependency> |

|----------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 | java private final OkHttpClient client = new OkHttpClient(); HttpUrl url = HttpUrl.get("https://api.weixin.qq.com/wxa/getwxacodeunlimit").newBuilder() .addQueryParameter("access_token", "accessToken") .build(); Map<String, String> map = new HashMap<>(); map.put("k1", "v1"); map.put("k2", "v2"); String jsonString = new ObjectMapper().writeValueAsString(map); RequestBody requestBody = RequestBody.create(jsonString, MediaType.parse("application/json")); Headers headers = new Headers.Builder() .add("Authorization", "eyJhbGciOiJIUzUxMiJ9.eyJsb2dpbl91c2VyX2tleSI6ImUwMzAyNDI5LTZmMzEtNDM2Ny1iNDk1LWIxZGY3MTM2ZTQ0NSJ9.QtRJtXAI-yUc39QsfWgpL3WoHi7RGDG1IOBkfyLLSE_wDWICp6PDtf9bzoSV7vi2SkQUHi3ndE75nNWwUbKeMA") .add("User-Agent", "Apifox/1.0.0 (https://www.apifox.cn)") .add("Accept", "*/*") .add("Host", "localhost:8600") .add("Connection", "keep-alive") .add("Content-Type", "application/json") .build(); Response response = client.newCall(new Request.Builder().url(url).build()).execute(); Response response2 = client.newCall(new Request.Builder().url(url).post(requestBody).headers(headers).build()).execute(); |

Java测试NullPointerException空指针异常 {#java测试nullpointerexception空指针异常}

|----------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 | java class NPE { public static void main(String[] args) { List<User> nulls = null; Object[] arr = null; // NPE Arrays.stream(arr); nulls.stream(); nulls.forEach(u -> reverseOrder()); for (User user : nulls) { } // null流在map等操作NPE Lists.newArrayList(null, new User()).stream() .map(User::getAge); // 如果value为null，Collectors.toMap会调用Map.merge方法，而在这个方法中，null值会导致抛出NullPointerException异常。 Lists.newArrayList(User.builder().age(1).name(null).build(), User.builder().age(1).name(null).build()).stream() .collect(toMap(User::getAge, User::getName, (s1, s2) -> s1)); // 可以加上.filter(s -> s.getName() != null) // 不会NPE Collections.emptyList().stream(); Collections.emptyList().forEach(u -> reverseOrder()); for (Object o : Collections.emptyList()) { } Optional.ofNullable(nulls).orElse(Collections.emptyList()).forEach(s -> { }); } } |

IntelliJ IDEA - HTTP Client 插件http请求示例GET POST PUT DELETE {#intellij-idea---http-client-插件http请求示例get-post-put-delete}

环境

GET

|---------|-------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 | java ### GET请求 GET {{host}}/mobile/getUserList?pageNum=1&pageSize=10 authorization: {{authorization}} deviceNo: {{deviceNo}} |

POST

|-----------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 | java ### POST请求 POST {{host}}/mobile/switchStatus authorization: {{authorization}} token: 15b5f8e4212d4a108a5b31a224ff269b deviceNo: {{deviceNo}} Content-Type: application/json {"userId":"123","status":false} |

java.math使用 {#javamath使用}

|-------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 | java // 格式化成货币 1 -> "¥1.00" String format1 = NumberFormat.getCurrencyInstance().format(bigDecimal); // 格式化成百分比 1 -> "100%" String format2 = NumberFormat.getPercentInstance().format(bigDecimal); // 绝对值 int abs = Math.abs(-3); // 3 // 向上取整 double ceil = Math.ceil(4.00000001); // 5.0 // 向下取整 double floor = Math.floor(4.99999999); // 4.0 // 四舍五入取整 long round = Math.round(4.49999); // 4 long round1 = Math.round(4.500000); // 5 // 获取a的b次幂 Math.pow(2, 3); // 2^3 = 8.0 // 字符串支持16进制字符串，并且会自动去除字符串中的空格： NumberUtils.parseNumber("1", Integer.class); // 自动处理数字溢出（抛出异常） NumberUtils.convertNumberToTargetClass(1, Integer.class); |

类的五大成分：成员变量，方法，构造器，代码块，内部类。 {#类的五大成分成员变量方法构造器代码块内部类}

静态内部类 {#静态内部类}

有static修饰，类有的成分它都有，属于外部类本身，只会加载一次。所以它的特点与外部类是完全一样的，只是位置在别人里面而已。

|----------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 | java class Outter { public static class Inner { } } // 使用 Outter.Inner in = new Outter.Inner(); in.setName("张三"); System.out.println(in.getName()); in.show(); |

实例内部类。（成员内部类） {#实例内部类成员内部类}

无static修饰的内部类，属于外部类的每个对象的，跟着对象一起加载的。实例内部类中不能定义静态成员，其他都可以定义。可以定义常量。

|-------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 | java class Outter { public static int age = 1; private double salary; // 实例内部类：无static修饰，属于外部类的对象 public class Inner { private String name; public static final String schoolName = "黑马"; // 不能在实例内部类中定义静态成员！！！ // public static String schoolName = "黑马"; // public static void test(){ // // } // 实例方法 public void show() { System.out.println(name + "名称！"); System.out.println(age); System.out.println(salary); } } } // 使用 Outter.Inner in = new Outter().new Inner(); in.show(); |

局部内部类（几乎不用，局部内部类没啥用） {#局部内部类几乎不用局部内部类没啥用}

定义在方法中，在构造器中，代码块中，for循环中定义的内部类。只能定义实例成员，不能定义静态成员，可以定义常量的。

匿名内部类（重点） {#匿名内部类重点}

简化代码，也是开发中常用的形式。
匿名内部类是一个没有名字的内部类。
匿名内部类一旦写出来，就会立即创建一个匿名内部类的对象返回。
匿名内部类的对象的类型相当于是当前new的那个的类型的子类类型。

|-------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 11 12 13 | java new 类名|抽象类|接口(形参){ 方法重写。 } // 匿名内部类写法 new Thread(new Runnable(){ @Override public void run(){ for(int i=0;i< 10;i++){ System.out.println(Thread.currentThread().getName()+"==>"+i); } } }).start(); |

方法继承 {#方法继承}

子类不能继承父类的构造器：子类有自己的构造器。
子类是否可以继承父类的私有成员（私有成员变量，私有成员方法）? 需要暴力访问。
子类是否可以继承父类的静态成员？共享并非继承。
继承后-成员变量/成员方法的访问特点：就近原则
继承后-构造器的特点：子类的全部构造器默认一定会先访问父类的无参数构造器，再执行子类自己的构造器。

方法重写 {#方法重写}

方法签名相同（申明不变，重新实现）
两小一大
- 返回值类型：子类≤父类
- 抛出的异常：子类≤父类
- 权限修饰符：子类≥父类

@Override优势：可读性好，安全，优雅！！
super可以用在子类的实例方法中调用父类被重写的方法。
静态方法和私有方法不可以被重写（拓展语法）

多态 {#多态}

|----------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 | java class Animal { public void run() { System.out.println("动物跑！"); } } class Dog extends Animal { @Override public void run() { System.out.println("🐕跑的贼快~~~~！"); } // 独有功能 public void lookDoor() { System.out.println("🐶看门"); } } class Cat extends Animal { @Override public void run() { System.out.println("🐱跑的飞快~~~~！"); } // 独有功能 public void catchMouse() { System.out.println("🐱抓🐀"); } } class Wolf extends Animal { @Override public void run() { System.out.println("狼跑的飞快~~~"); } public void catchSheep() { System.out.println("🐺抓🐏"); } } |

父类类型对象名称 = new 子类构造器;
接口对象名称 = new 实现类构造器;
父类类型的范围 > 子类类型范围的。
多态的识别技巧：对于方法的调用：编译看左边，运行看右边。对于变量的调用：编译看左边，运行看左边。

|---------------|----------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 | java class class1 { viod method() { Animal dlam = new Dog(); dlam.run(); // 对于方法的调用：编译看左边，运行看右边。 dlam.lookDoor(); // 报错了，多态形式下，编译看左边，左边没有独有功能 } } |

多态的使用前提

必须存在继承或者实现关系。
必须存在父类类型的变量引用子类类型的对象。
需要存在方法重写。

在多态形式下，右边对象可以实现组件化切换，业务功能也随之改变，便于扩展和维护。可以实现类与类之间的解耦。
实际开发的过程中，父类类型作为方法形式参数，传递子类对象给方法，可以传入一切子类对象进行方法的调用，更能体现出多态的扩展性与便利。

Java关键字-final {#java关键字-final}

Java关键字-finally {#java关键字-finally}

|----------------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 | java /** * 以前用来释放资源，现在用try-with-resources语句代替 */ class finally_test { /* - finally的作用: 可以在代码执行完毕以后进行资源的释放操作。什么是资源？资源都是实现了Closeable接口的，都自带close()关闭方法！！ - try: 1次。 catch：0-N次 (如果有finally那么catch可以没有!!) finally: 0-1次 */ public static void chu() { InputStream is = null; try { is = new FileInputStream("D:/cang.png"); } catch (Exception e) { e.printStackTrace(); } finally { // 回收资源。用于在代码执行完毕以后进行资源的回收操作！ try { if (is != null) is.close(); } catch (Exception e) { e.printStackTrace(); } } } /* 从 java 7 build 105 版本开始，java 7 的编译器和运行环境支持新的 try-with-resources 语句，称为 ARM 块(Automatic Resource Management) ，自动资源管理。 */ private static void customBufferStreamCopy(File source, File SDCard) { try (InputStream fis = new FileInputStream(source); OutputStream fos = new FileOutputStream(SDCard)) { byte[] buf = new byte[8192]; int i; while ((i = fis.read(buf)) != -1) { fos.write(buf, 0, i); } } catch (Exception e) { e.printStackTrace(); } } } |

Java关键字-synchronized {#java关键字-synchronized}

Java队列示例 {#java队列示例}

|----------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 11 12 | java // 做一个队列：先进先出 LinkedList<String> queue = new LinkedList<>(); // 入队 queue.addLast("1号"); queue.addLast("2号"); queue.addLast("3号"); queue.addLast("4号"); System.out.println(queue); // [1号, 2号, 3号, 4号] // 出队 System.out.println(queue.removeFirst()); System.out.println(queue.removeFirst()); System.out.println(queue); |

Java栈示例 {#java栈示例}

|----------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 11 12 | java // 做一个栈：先进后出 LinkedList<String> stack = new LinkedList<>(); // 压栈 stack.push("第1颗子弹"); stack.push("第2颗子弹"); stack.push("第3颗子弹"); stack.push("第4颗子弹"); System.out.println(stack); // [第4颗子弹, 第3颗子弹, 第2颗子弹, 第1颗子弹] // 弹栈 System.out.println(stack.pop()); System.out.println(stack.pop()); System.out.println(stack); |

Java反射 {#java反射}

|-------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 | java class 反射机制 { public static void main(String[] args) throws Exception { // 方式1 User user = new User(); Class<? extends User> clazz = user.getClass(); // 方式2 Class<?> clazz2 = Class.forName("com.zx.alice.allcode.Java_反射机制.Fruit"); // 无参构造 Fruit fruit = (Fruit) clazz2.getConstructor().newInstance(); // 有参构造 Fruit fruit2 = (Fruit) clazz2.getConstructor(String.class).newInstance("Apple"); // 方式3 Class<User> clazz3 = User.class; } static class Fruit { public Fruit() { System.out.println("无参构造器 Run..........."); } public Fruit(String type) { System.out.println("有参构造器 Run..........." + type); } } static class User { } } |

Java-可变参数 {#java-可变参数}

|----------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 | java /** * - 可变参数的格式：数据类型... 参数名称 * - 可变参数在方法内部本质上就是一个数组。 * - 可变参数的注意事项 * - 一个形参列表中可变参数只能有一个！ * - 可变参数必须放在形参列表的最后面！！ */ class 可变参数 { public static void main(String[] args) { sum(); // 可以不传输参数。 sum(10); // 可以传输一个参数。 sum(10, 20, 30); // 可以传输多个参数。 sum(new int[]{10, 30, 50, 70, 90}); // 可以传输一个数组。 } public static void sum(int... nums) { // 可变参数在方法内部本质上就是一个数组。 System.out.println("元素个数：" + nums.length); System.out.println("元素内容：" + Arrays.toString(nums)); System.out.println("--------------------------"); } } |

Java接口与抽象类 {#java接口与抽象类}

接口中，没有构造器，不能创建对象。(重点)

接口只能定义静态常量，抽象类可以定义非静态的。

|----------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 | java public abstract class One { public static final String n = null; private String n2 = null; abstract void method1(); } // public static final 在IDEA里面，不写也默认有 public interface Two { public static final String n = null; } |

java中，子类继承父类，子类实例化，首先要执行父类的构造器，所以抽象类里面有构造器，有构造器就有实例化，只是这种实例化是比较特殊的实例化，也不能通过new创建实例，但是可以通过该特殊的实例化调用该抽象类里面的非静态字段，通过下面的代码可以发现

Java泛型 {#java泛型}

泛型接口 {#泛型接口}

泛型通配符 {#泛型通配符}

通配符：？

? 可以用在使用泛型的时候代表一切类型。

E , T , K , V是在定义泛型的时候使用代表一切类型。

泛型的上下限：

? extends Car : 那么?必须是Car或者其子类。(泛型的上限)

? super Car :那么?必须是Car或者其父类。（泛型的下限。不是很常见）

|-------------------------------------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 | java public class GenericDemo { public static void main(String[] args) { ArrayList<BMW> bmws = new ArrayList<>(); bmws.add(new BMW()); bmws.add(new BMW()); bmws.add(new BMW()); run(bmws); ArrayList<BENZ> benzs = new ArrayList<>(); benzs.add(new BENZ()); benzs.add(new BENZ()); benzs.add(new BENZ()); run(benzs); ArrayList<Dog> dogs = new ArrayList<>(); dogs.add(new Dog()); dogs.add(new Dog()); dogs.add(new Dog()); // run(dogs); // 就进不来了！ } // 定义一个方法，可以让很多汽车一起进入参加比赛 public static void run(ArrayList<? extends Car> cars) { } } class Car { } class BMW extends Car { } class BENZ extends Car { } class Dog { } |

自定义泛型方法 {#自定义泛型方法}

|-------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 | java 修饰符 <泛型变量> 返回值类型方法名称(形参列表){ } class class1 { public static <T> String arrToString(T[] nums) { StringBuilder sb = new StringBuilder(); sb.append("["); if (nums != null && nums.length > 0) { for (int i = 0; i < nums.length; i++) { T ele = nums[i]; sb.append(i == nums.length - 1 ? ele : ele + ", "); } } sb.append("]"); return sb.toString(); } } |

自定义泛型类 {#自定义泛型类}

Java数组在内存中的分配 {#java数组在内存中的分配}

对于 java 数组的初始化，有以下两种方式，这也是面试中经常考到的经典题目。

静态初始化:初始化时由程序员显式指定每个数组元素的初始值，由系统决定数组长度，如:

|-----------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 | java //只是指定初始值，并没有指定数组的长度，但是系统为自动决定该数组的长度为4 String[]computers={"Dell","Lenovo","Apple","Acer"}; //1 //只是指定初始值，并没有指定数组的长度，但是系统为自动决定该数组的长度为3 String[]names=new String[]{"多啦A梦","大雄","静香"}; //2 |

动态初始化:初始化时由程序员显示的指定数组的长度，由系统为数据每个元素分配初始值，如:

|-----|--------------------------------------------------------------------------------------------------| | 1 2 | java //只是指定了数组的长度，并没有显示的为数组指定初始值，但是系统会默认给数组数组元素分配初始值为null String[]cars=new String[4]; //3 |

因为 java 数组变量是引用类型的变量，所以上述几行初始化语句执行后，三个数组在内存中的分配情况如下图所示

由上图可知，静态初始化方式，程序员虽然没有指定数组长度，但是系统已经自动帮我们给分配了，而动态初始化方式，程序员虽然没有显示的指定初始化值，但是因为 java 数组是引用类型的变量，所以系统也为每个元素分配了初始化值 null ，当然不同类型的初始化值也是不一样的，假设是基本类型int类型，那么为系统分配的初始化值也是对应的默认值0。

Pagehelper逻辑分页 {#pagehelper逻辑分页}

|-----------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 | xml <dependency> <groupId>com.github.pagehelper</groupId> <artifactId>pagehelper-spring-boot-starter</artifactId> <version>2.1.0</version> </dependency> |

|---|-------------------------------------------------------------------------------------| | 1 | java PageInfo<Demo> demoPageInfo = logicPagination(pageNum, pageSize, list); |

|-------------------------------------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 | java /** * 逻辑分页 * * @param pageNum 当前页 * @param pageSize 每页的数量 * @param list 所有数据的集合 */ private static PageInfo<Demo> logicPagination(int pageNum, int pageSize, List<Demo> list) { PageInfo<Demo> pageInfo = new PageInfo<>(); //当前页 pageInfo.setPageNum(pageNum); //每页的数量 pageInfo.setPageSize(pageSize); //当前页的数量 pageInfo.setSize(0); //总页数 pageInfo.setPages(1); //总行数 pageInfo.setTotal(0); if (ObjectUtils.isEmpty(list)) { return pageInfo; } // 总大小 int count = list.size(); // 总页数 int pageTotals = (count / pageSize) + ((count % pageSize > 0) ? 1 : 0); pageInfo.setPages(pageTotals); pageInfo.setTotal(count); // 要返回的列表 List<Demo> contentList = new ArrayList<>(); if (pageNum <= pageTotals) { // 开始下标 int fromIndex = (pageNum - 1) * pageSize; // 结束下标 int toIndex = ((pageNum == pageTotals) ? count : (pageNum * pageSize)); contentList = list.subList(fromIndex, toIndex); } pageInfo.setSize(contentList.size()); pageInfo.setList(contentList); return pageInfo; } |

WeakReference弱引用回收测试 {#weakreference弱引用回收测试}

|----------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 | java public class 弱引用回收测试 { public static WeakReference<String> weakReference; public static void main(String[] args) throws InterruptedException { test1(); // 可以输出hello值，此时两个弱引用扔持有对象，而且未进行gc System.out.println("未进行gc时，只有弱引用指向value内存区域：" + weakReference.get()); // value // 方法执行完毕，hello强引用的地址出栈，String对象仅有一个弱引用，GC会回收对象。 System.gc(); // 对象已被GC，此时输出都为null Thread.sleep(100); System.out.println("进行gc时，只有弱引用指向value内存区域：" + weakReference.get()); // null } public static void test1() { String hello = "value"; weakReference = new WeakReference<>(hello); System.gc(); // 此时gc不会回收弱引用，因为字符串"value"仍然被hello强引用 System.out.println("进行gc时，强引用与弱引用同时指向value内存区域：" + weakReference.get()); // value } } |

TimerTask定时任务 {#timertask定时任务}

|-------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 | java public class 定时任务_TimerTask { public static void main(String[] args) throws InterruptedException { timerTask(); } // TimerTask 单线程 private static void timerTask() throws InterruptedException { Timer timer = new Timer(); TimerTask timerTask = new TimerTask() { @Override public void run() { System.out.println("hi, 欢迎关注：java技术栈"); } }; // 第一次任务延迟时间 long delay = 2000; // 任务执行频率 long period = 3 * 1000; // 开始调度 timer.schedule(timerTask, delay, period); // 指定首次运行时间 // timer.schedule(timerTask, DateUtils.addSeconds(new Date(), 5), period); Thread.sleep(20000); // 终止并移除任务 timer.cancel(); timer.purge(); } } |

测试数据生成 {#测试数据生成}

https://gitee.com/binary/java-generator

|-------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 | xml  <dependency> <groupId>com.github.binarywang</groupId> <artifactId>java-testdata-generator</artifactId> <version>1.1.2</version> </dependency> |

|----------------------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 | java public class 数据生成 { public static void main(String[] args) throws IOException { String address = ChineseAddressGenerator.getInstance().generate(); // 河南省漯河市休缄接路7556号窄箍小区3单元2148室 String idCard = ChineseIDCardNumberGenerator.getInstance().generate(); // 41841319980703055X if (idCard.charAt(idCard.length() - 2) % 2 == 0) { System.err.println("女"); } else { System.err.println("男"); } String issueOrg = ChineseIDCardNumberGenerator.generateIssueOrg(); // 巴音郭楞蒙古自治州公安局某某分局 String result = ChineseIDCardNumberGenerator.generateValidPeriod(); // 19730519-19930519 String mobileNum = ChineseMobileNumberGenerator.getInstance().generate(); // 18844719147 String mobileNumFake = ChineseMobileNumberGenerator.getInstance().generateFake(); // 19825602718 String chineseName = ChineseNameGenerator.getInstance().generate(); // 牛恩苞 String chineseNameOdd = ChineseNameGenerator.getInstance().generateOdd(); // 金煣 String email = EmailAddressGenerator.getInstance().generate(); // e4jpwflcf3@cuojs.ajv String englishName = EnglishNameGenerator.getInstance().generate(); // Paula CSVFileGeneratorTest(); } static void CSVFileGeneratorTest() throws IOException { String fileName = 数据生成.class.getResource("/").getPath() + "test" + File.separator + "tmp.csv"; List<HashMap<String, Object>> data = Lists.newArrayList( new HashMap<>(ImmutableMap.<String, Object>of("1", "1a", "2", "2a", "3", "3a")), new HashMap<>(ImmutableMap.<String, Object>of("1", "1b", "2", "2b", "3", "3b")), new HashMap<>(ImmutableMap.<String, Object>of("1", "1c", "2", "2c", "3", "3c"))); CSVFileGenerator.generate(data, new String[]{"1", "2", "3"}, fileName); List<String> strings = Files.readLines(new File(fileName), StandardCharsets.UTF_8); // [1a,2a,3a, 1b,2b,3b, 1c,2c,3c] } } |

Java-接口防刷、防止重复访问 {#java-接口防刷防止重复访问}

|-----------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 | java private static final String LOCK_BATTERY_SWAP_KEY = "brpLock:batterySwap:"; public static String getLockBatterySwapKeyKey(String userId) { return LOCK_BATTERY_SWAP_KEY + userId; } |

|----------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 11 12 | java /** * 接口防刷 */ private void antiBush() { String lockKey = RedisKeyConstant.getLockBatterySwapKeyKey(UserHolderUtils.getUserId()); Object isLock = stringRedisTemplate.opsForValue().get(lockKey); if (Objects.isNull(isLock)) { stringRedisTemplate.opsForValue().set(lockKey, "1", 60, TimeUnit.SECONDS); } else { throw new RespStatusException(HttpStatus.TOO_MANY_REQUESTS, "正在换电中，请勿重复点击"); } } |

|----------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 11 12 | java /** * 50秒之内不能重复提交相同数据 */ public void duplicateGetNumber(String submitContent, Duration duration) { String redisKey = "duplicateGetNumber:" + submitContent; if(stringRedisTemplate.opsForValue().get(redisKey) != null){ log.info("50秒之内重复取号"); throw new RespStatusException(HttpStatus.FORBIDDEN, "请勿重复提交，可以稍候重试，或者尝试联系管理员"); } else { stringRedisTemplate.opsForValue().set(redisKey, "1", duration); } } |

Java操作-传id更新，不传id新增，少的删除 {#java操作-传id更新不传id新增少的删除}

|-------------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 | java // 传id更新，不传id新增，少的删除操作 // 1. 传入id的更新 // 传入有id值的对象列表 List<BrpContactInfoDto> haveIds = contactList.stream().filter(s -> s.getId() != null).collect(Collectors.toList()); // 根据id更新 haveIds.forEach(dto -> { BrpContactInfo contactInfo = new BrpContactInfo(); contactInfo.setId(dto.getId()); contactInfo.setInOutType(dto.getInOutType()); brpContactInfoMapper.updateByPrimaryKeySelective(contactInfo); }); // 2. 减少的部分删除 // 数据库现有对象列表 List<BrpContactInfo> select = brpContactInfoMapper.select(BrpContactInfo.builder().fleetId(fleet.getId()).status("1").build()); Set<Long> idSelects = select.stream().map(s -> s.getId()).collect(Collectors.toSet()); Set<Long> idIns = haveIds.stream().map(s -> s.getId()).collect(Collectors.toSet()); Sets.difference(idSelects, idIns) .forEach(id -> brpContactInfoMapper.updateByPrimaryKey(BrpContactInfo.builder().id(id).status("-1").build())); // 3. 添加的部分插入 // 传入无id值的对象列表 List<BrpContactInfoDto> noIds = contactList.stream().filter(s -> s.getId() == null).collect(Collectors.toList()); List<BrpContactInfo> toInsert = noIds.stream() .map(dto -> { BrpContactInfo contactInfo = new BrpContactInfo(); contactInfo.setId(null); contactInfo.setFleetId(fleet.getId()); contactInfo.setInOutType(dto.getInOutType()); return contactInfo; }) .collect(Collectors.toList()); if (!CollectionUtils.isEmpty(toInsert)) { brpContactInfoMapper.insertList(toInsert); } |

HttpServletResponse导出文件，输入流InputStream流导出文件 {#httpservletresponse导出文件输入流inputstream流导出文件}

|----------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 | java /** * 通过inputStream流导出文件 */ @SneakyThrows private void inputStreamExportExport(HttpServletResponse response) { try (BufferedInputStream in = new BufferedInputStream(this.getClass().getResourceAsStream("/换电站运营周报表模板.xlsx"))) { // 构建response response.setHeader("content-disposition", "attachment;fileName=" + URLEncoder.encode("fileName", StandardCharsets.UTF_8) .replaceAll("\\+", "%20") .replaceAll("%2F", "/") + ".xlsx"); response.setContentType("application/vnd.ms-excel"); // application/json application/pdf response.setCharacterEncoding(StandardCharsets.UTF_8.name()); BufferedOutputStream out = new BufferedOutputStream(response.getOutputStream()); byte[] buffer = new byte[1024]; int len; while ((len = in.read(buffer)) != -1) { out.write(buffer, 0, len); } out.flush(); } } |

Properties {#properties}

重试机制实现 {#重试机制实现}

|-------------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 | java @RequiredArgsConstructor @Slf4j public class 重试机制 { private final DemoRepository demoRepository; /* 1. 代码方式：尝试5次查询Demo */ private final Map<String, AtomicInteger> retryMap = new ConcurrentHashMap<>(); private Demo get(DemoDTO dto, Supplier<Demo> supplier) throws JsonProcessingException { Demo demo = supplier.get(); if (demo != null) { return demo; } // 最多尝试5次共10秒 int retryTimes = 5; AtomicInteger ai = retryMap.computeIfAbsent(dto.getName(), k -> new AtomicInteger(1)); if (ai.getAndIncrement() <= retryTimes) { try { Thread.sleep(2000); return get(dto, supplier); } catch (Exception e) { log.error("getApplyRetry={}, e=", new ObjectMapper().writeValueAsString(dto), e); retryMap.remove(dto.getName()); return null; } } retryMap.remove(dto.getName()); return demo; } /* 2. 注解方式：getDemo方法将在发生异常时重试5次，每次重试之间的间隔为2秒（2000毫秒） */ @Retryable(value = {Exception.class}, maxAttempts = 5, backoff = @Backoff(delay = 2000)) public List<Demo> getDemo(String name) { return demoRepository.findAll(Example.of(Demo.builder().name(name).build())); } } |

ThreadLocal的生命周期 {#threadlocal的生命周期}

|----------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 | java public class ThreadLocalTest { private final List<String> messages = Lists.newArrayList(); public static final ThreadLocal<ThreadLocalTest> holder = ThreadLocal.withInitial(ThreadLocalTest::new); public static void main(String[] args) { ThreadLocalTest.add("zxalive.com"); System.out.println(holder.get().messages); // 清除并返回清除的内容 ThreadLocalTest.clear(); } public static void add(String message) { holder.get().messages.add(message); } public static List<String> clear() { List<String> messages = holder.get().messages; holder.remove(); System.out.println("size: " + holder.get().messages.size()); return messages; } } |

IO流 {#io流}

正则Pattern {#正则pattern}

Pattern.matches正则使用 {#patternmatches正则使用}

|----------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 | java // 计算站外充电的服务费价格,它与当月费率的服务费价格一致。 private BigDecimal getAverageServicePrice(BillVO s) { String settlementCycle = s.getSettlementCycle(); if (settlementCycle == null || settlementCycle.isEmpty()) { return BigDecimal.ONE; } else if (Pattern.matches("^\\d{4}-\\d{2}-\\d{2} ~ \\d{4}-\\d{2}-\\d{2}$", settlementCycle)) { String[] parts = settlementCycle.split("~"); LocalDate startDate = LocalDate.parse(parts[0].trim(), dateFormatter); LocalDate endDate = LocalDate.parse(parts[1].trim(), dateFormatter); return rateTemplateMapper.selectAverageServicePrice(startDate, endDate, s.getStationNo()); } else if (Pattern.matches("^\\d{4}-\\d{2}-\\d{2}~\\d{4}-\\d{2}-\\d{2}$", settlementCycle)) { String[] parts = settlementCycle.split("~"); LocalDate startDate = LocalDate.parse(parts[0].trim(), dateFormatter); LocalDate endDate = LocalDate.parse(parts[1].trim(), dateFormatter); return rateTemplateMapper.selectAverageServicePrice(startDate, endDate, s.getStationNo()); } else if (Pattern.matches("^\\d{4}-\\d{2}-\\d{2}-\\d{4}-\\d{2}-\\d{2}$", settlementCycle)) { String[] parts = settlementCycle.split("-"); LocalDate startDate = LocalDate.parse(parts[0].trim(), dateFormatter); LocalDate endDate = LocalDate.parse(parts[1].trim(), dateFormatter); return rateTemplateMapper.selectAverageServicePrice(startDate, endDate, s.getStationNo()); } else if (Pattern.matches("^\\d{4}-\\d{2}-\\d{2} \\d{2}:\\d{2}$", settlementCycle)) { LocalDate localDate = LocalDate.parse(settlementCycle, dateTimeFormatter); return rateTemplateMapper.selectAverageServicePrice(localDate, localDate, s.getStationNo()); } return BigDecimal.ONE; } |