Java日常使用

---

字符串

（1）使用 TypeReference序列化复合结构

Map<String, List<String>> reqVO = JsonUtil.string2Obj(paramString, 
    new TypeReference<Map<String, List<String>>>() {});

（2）正则处理

// 手机号中间4位隐藏为 *
phone.replaceAll("(\\d{3})\\d*(\\d{4})", "$1****$2")

（3）正则匹配

Pattern p = Pattern.compile("^[a-zA-Z0-9_\\u4e00-\\u9fa5]+$");
Matcher m = p.matcher("hello_");
System.out.println(m.matches());

日期

（1）LocalDataTime与其他类型互转

// String to LocalDataTime
DateTimeFormatter DATE_TIME_FORMATTER = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
LocalDateTime startTime = LocalDateTime.parse("2024-02-06 12:00:00", DATE_TIME_FORMATTER);

// LocalDataTime to String
String startTimeString = DATE_TIME_FORMATTER.format(startTime);

// LocalDataTime to Long（时间戳，8位）
long timestamp = LocalDateTime.now().toEpochSecond(ZoneOffset.of("+8"));

（2）获取当天零点

LocalDateTime.of(LocalDateTime.now().toLocalDate(), LocalTime.MIN);

数组

（1）list to list

// list 转 list
List<Integer> l = Arrays.asList(2, 2, 3);
List<Integer> l2 = l.stream().map(i -> i + 1).collect(Collectors.toList());
System.out.println(l2); // [3, 3, 4]

// list 去重
List<Integer> l3 = l.stream().distinct().collect(Collectors.toList());
System.out.println(l3); // [2, 3]

（2）list to map

List<Integer> l = Arrays.asList(1, 2, 3);
Map<Integer, Integer> m = l.stream().collect(Collectors.toMap(Function.identity(), Function.identity()));
System.out.println(m); // {1=1, 2=2, 3=3}

（3）数组 to list

String[] s = "a,b,c".split(",");
List<String> l = Arrays.asList(s); // 注意此时 l 不可变更，如需变更可在外层包一下 new ArrayList<>()

集合

（1）交集

@Test
public void test5() {
    String cacheRoomData = "1,2,4";
    List<Long> finishedRoomIdList = Arrays.stream(cacheRoomData.split(","))
            .map(s -> Long.parseLong(s.trim())).collect(Collectors.toList()); // [1,2,4]
    List<Long> roomIdList = new ArrayList<>(Arrays.asList(1L,2L,3L,5L)); // [1,2,3,5]
    boolean updateCache = finishedRoomIdList.retainAll(roomIdList); // finishedRoomIdList 取交集
    System.out.println(updateCache); // true
    System.out.println(finishedRoomIdList); // [1, 2]
    System.out.println(roomIdList); // [1, 2, 3, 5]

    roomIdList.removeAll(finishedRoomIdList); // roomIdList 取差集
    System.out.println(finishedRoomIdList); // [1, 2]
    System.out.println(roomIdList); // [3, 5]
}

（2）初始化

// HashMap 初始化
public static final Map<String, String> OCEAN_ENGINE_COOKIE_MAP = new HashMap<String, String>() {{
    put("a", 1);
    put("b", 2);
}};

（3）常规操作

// HashMap computeIfAbsent: 如果没有对应元素，则进行初始化操作
Map<Integer, List<String>> m = new HashMap<>();
m.computeIfAbsent(1, k -> new ArrayList<>()).add("a");
m.computeIfAbsent(1, k -> new ArrayList<>()).add("b");
m.computeIfAbsent(2, k -> new ArrayList<>()).add("c");
m.computeIfAbsent(2, k -> new ArrayList<>());
m.computeIfAbsent(3, k -> new ArrayList<>());
System.out.println(m); // {1=[a, b], 2=[c], 3=[]}

参数校验

（1）@Valid注解

常用注解如下:

• 注意在Controller参数前面加上 @Valid

  import javax.validation.Valid;
  
  @PostMapping("/add")
  public void add(@Valid @RequestBody AddReqVO reqVO) {
      return;
  }

• 如果是多层嵌套，注意在每一层嵌套参数上加上 @Valid

  import javax.validation.Valid;
  import javax.validation.constraints.NotEmpty;
  
  public class AddReqVO {
      @NotEmpty(message = "id不能为空")
      private String id;
  
      @Valid
      private Address address;
  }
  
  public static class Address {
      @NotEmpty(message = "name不能为空")
      private String name;
  }

• 如果是在Service层进行校验，则需要如下处理：

  // interface
  public interface MyService {
      void add(@Valid Entity e);
  }
  
  // impl
  @Validated // 注意加上这个注解
  public class MyServiceImpl implementsMyService {
      @Override
      public void add(Entity e) {
      }
  }

• 如果想在Service层复用VO上配置的校验规则（例如 @NotEmpty,@NotNull等），可以直接使用使用进行校验：

  import javax.validation.ConstraintViolation;
  import javax.validation.Validator;
  
  @Resource
  private Validator validator;
  
  Set<ConstraintViolation<BatchAddBaseTag>> violations = validator.validate(entity1);
  if (!CollectionUtils.isEmpty(violations)) {
      violations.forEach(violation -> errorMessageList.add(violation.getMessage()));
  }

文件

（1）MultipartFile

MultipartFile file;
// 文件大小比较
file.getSize() > 1 * 1024 * 1024 // 1M大小

// 文件名（包含文件后缀）
String imageName = file.getOriginalFilename();

Mybatis

（1）Mybatis Plus 添加 分页插件

// 添加 config
@Configuration
public class MybatisPlusConfig {
    @Bean
    public MybatisPlusInterceptor mybatisPlusInterceptor(){
        MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
        interceptor.addInnerInterceptor(new PaginationInnerInterceptor());
        return interceptor;
    }
}

// LambdaQueryWrapper 使用
// 注意，queryWrapper 存在缓存，如果需要重复使用 queryWrapper，使用前要调用 queryWrapper.clear();
LambdaQueryWrapper<Hello> queryWrapper = new QueryWrapper<Hello>().lambda();
queryWrapper.eq(Hello::getType, reqVO.getType())
            .eq(Hello::getName, reqVO.getName())
            .orderByDesc(Hello::getId());

// Page 使用
com.baomidou.mybatisplus.extension.plugins.pagination.Page<Hello> recordPage =
    new com.baomidou.mybatisplus.extension.plugins.pagination.Page<>(page, pageSize);
com.baomidou.mybatisplus.extension.plugins.pagination.Page<Hello> recordList =
    this.getBaseMapper().selectPage(recordPage, queryWrapper);

（2）MybatisPlusGenerator使用示例

import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.generator.FastAutoGenerator;
import com.baomidou.mybatisplus.generator.config.OutputFile;
import com.baomidou.mybatisplus.generator.config.TemplateType;
import com.baomidou.mybatisplus.generator.config.po.LikeTable;
import com.baomidou.mybatisplus.generator.config.rules.NamingStrategy;
import com.baomidou.mybatisplus.generator.engine.FreemarkerTemplateEngine;

import java.util.HashMap;

public class MybatisPlusGenerator {
    // 注意修改表名和作者名
    public static final String TABLE_NAME = "comment_record";
    public static final String AUTHOR = "";

    // 暂时使用 tracking 数据库
    public static final String MYSQL_HOST = "jdbc:mysql://127.0.0.1:8080/tracking" +
            "?serverTimezone=Asia/Shanghai&allowPublicKeyRetrieval=true&verifyServerCertificate=false&useSSL=false";
    public static final String MYSQL_USER_NAME = "";
    public static final String MYSQL_USER_PASSWORD = "";
    public static final String DATA_FORMAT = "yyyy-MM-dd";

    public static final String PROJECT_NAME = "commentservice";
    public static final String PARENT_PACKAGE = String.format("cn.com.hello.health.%s", PROJECT_NAME);
    public static final String SERVICE_PACKAGE = "service.i";
    public static final String SERVICE_IMPL_PACKAGE = "service.impl";
    public static final String ENTITY_PACKAGE = "model.po";
    public static final String MAPPER_PACKAGE = "mapper";

    public static final String SERVICE_PATH = String.format("src/main/java/cn/com/hello/%s/service/i", PROJECT_NAME);
    public static final String SERVICE_IMPL_PATH = String.format("src/main/java/cn/com/hello/%s/service/impl", PROJECT_NAME);
    public static final String ENTITY_PATH = String.format("src/main/java/cn/com/hello/%s/model/po", PROJECT_NAME);
    public static final String MAPPER_PATH = String.format("src/main/java/cn/com/hello/%s/mapper", PROJECT_NAME);
    public static final String XML_PATH = "src/main/resources/mapper";


    public static void main(String[] args) {
        FastAutoGenerator
                .create(MYSQL_HOST, MYSQL_USER_NAME, MYSQL_USER_PASSWORD)
                .globalConfig(b -> {
                    //用户名，日期，swagger可选
                    b.author(AUTHOR).commentDate(DATA_FORMAT)
//                .enableSwagger()
                            .disableOpenDir()
                            .build();
                }).packageConfig(b -> {
                    //只需要实体、mapper和xml
                    b.parent(PARENT_PACKAGE)
                            .service(SERVICE_PACKAGE)
                            .serviceImpl(SERVICE_IMPL_PACKAGE)
                            .entity(ENTITY_PACKAGE)
                            .mapper(MAPPER_PACKAGE)
//                            .xml("")
                            .pathInfo(new HashMap<OutputFile, String>() {{
                                put(OutputFile.service, SERVICE_PATH);
                                put(OutputFile.serviceImpl, SERVICE_IMPL_PATH);
                                put(OutputFile.entity, ENTITY_PATH);
                                // mapper接口的保存路径
                                put(OutputFile.mapper, MAPPER_PATH);
                                // mapper.xml文件的保存路径
                                put(OutputFile.xml, XML_PATH);
                            }});
                }).templateConfig(b -> b.disable(TemplateType.CONTROLLER
//                        ,TemplateType.SERVICE
//                        ,TemplateType.SERVICEIMPL
                        // 阻止生成 mapper
//                        ,TemplateType.MAPPER
                        // 阻止生成 xml
//                        ,TemplateType.XML
                ))
                .strategyConfig(b -> {
                    //表，驼峰命名，相关注解等更详细配置 TableField可选
                    b.addTablePrefix("_").likeTable(new LikeTable(TABLE_NAME))
                            .entityBuilder().naming(NamingStrategy.underline_to_camel).enableLombok().enableRemoveIsPrefix()
                            // 开启链式模型。会在实体类前添加 [@Accessors(chain = true)] 注解。
                            // 用法如 [User user=new User().setAge(31).setName("snzl");]（这是Lombok的注解，需要添加Lombok依赖）
                            .enableChainModel()
                            .idType(IdType.AUTO)
//                    .enableTableFieldAnnotation()
                            .fileOverride()
                            .mapperBuilder()
                            // 开启 @Mapper 注解。
                            // 会在mapper接口上添加注解[@Mapper]
//                    .enableMapperAnnotation()
                            .enableBaseResultMap().enableBaseColumnList().fileOverride()
                            .build();
                })//engine可选，org.freemarker/org.apache.velocity
                .templateEngine(new FreemarkerTemplateEngine())
                .execute();
    }
}

Json

（1）主动去除 null 值

private final static ObjectMapper objectMapper =
            new ObjectMapper().setSerializationInclusion(JsonInclude.Include.NON_NULL);

private Map<String, Object> transferToMap(Object data) {
    try {
        return objectMapper.readValue(objectMapper.writeValueAsString(data),
                new TypeReference<Map<String, Object>>() {
                });
    } catch (JsonProcessingException e) {
        log.error("序列化失败", e);
    }
}

Http

（1）HttpServletResponse构造返回

private void buildSuccessResponse(HttpServletResponse response) throws IOException {
    response.setCharacterEncoding("utf-8");
    response.setContentType("application/json; charset=utf-8");
    PrintWriter writer = response.getWriter();
    writer.write("jsonString"); // 写入Json格式字符串
    response.getWriter().flush();
}

easyexcel

easyexcel读取

依赖引入

<dependency>
  <groupId>com.alibaba</groupId>
  <artifactId>easyexcel</artifactId>
  <version>3.2.1</version>
</dependency>

实体类

public class Data {

    @ExcelProperty(value = "名称")
    private String name;

    // 按 String 读，转为 Long
    @ExcelProperty(value = "编号", converter = LongStringConverter.class)
    private Long no;

    // 按 String 读，转为 LocalDate
    @ExcelProperty(value = "日期",converter = LocalDateNumberConverter.class)
    private LocalDate date;

    // 按 String 读，转为 LocalDateTime
    @ExcelProperty(value = "时间", converter = LocalDateTimeNumberConverter.class)
    private LocalDateTime time;
}

读取类
```java
import com.alibaba.excel.EasyExcel;

@PostMapping("/upload-data")
public void uploadData(@RequestParam("file") MultipartFile file) {
    if (file == null || file.isEmpty()) {
        return;
    }

    List<Data> readResult = new ArrayList<>();
    try {
        EasyExcel.read(file.getInputStream(), UploadDataVO.class, 
            new UploadDataListener(readResult)).sheet().doRead();
    } catch (IOException e) {
        //
    }
}

UploadDataListener类

import com.alibaba.excel.context.AnalysisContext;
import com.alibaba.excel.event.AnalysisEventListener;

public class UploadDataListener extends AnalysisEventListener<Data> {

    private List<Data> readResult;

    public UploadDataListener(List<Data> readResult) {
        this.readResult = readResult;
    }

    @Override
    public void invoke(Data data, AnalysisContext context) {
        // data即为每行数据
        // 获取当前行号
        Integer currentRowNum = context.readRowHolder().getRowIndex() + 1;
        // 处理 readResult
        this.readResult.add(data);
    }

    @Override
    public void doAfterAllAnalysed(AnalysisContext context) {
        // 所有数据解析完成后可在此处执行其他操作
    }
}

easyexcel写入

Controller中写入Excel文件返回

// controller代码
@PostMapping("/test")
public void test(@RequestParam("file") MultipartFile file, HttpServletResponse response) throws IOException {
    HttpServletResponse response;

    // 待写入数据
    List<Data> result;

    //表头集合
    response.setHeader("Content-Disposition", "attachment; filename=1.xlsx");

    // 如果文件名包含中文等字符，需要如下处理
    String fileName = URLEncoder.encode("文件名", "UTF-8").replaceAll("\\+", "%20");
    response.setHeader("Content-disposition", "attachment;filename*=utf-8''" + fileName);   

    // 响应类型,编码
    response.setContentType("application/vnd.openxmlformats-officedocument.spreadsheetml.sheet");
    response.setCharacterEncoding("utf-8");
    EasyExcel.write(response.getOutputStream(), Data.class)
                .registerWriteHandler(new SimpleColumnWidthStyleStrategy(null)).sheet("Sheet1").doWrite(result);
}

Data类

@Data
public class Data {
    @ExcelProperty(value = "姓名")
    private String name;

    @ExcelProperty(value = "年龄")
    private String age;
}