使用Java 8 Stream API高效筛选每日期货最新时间戳数据

import java.time.LocalDateTime;
import java.time.LocalDate; // 需要导入LocalDate

class Currency {
   private Integer id;
   private String name; // 货币名称，如 "USD", "BUSD"
   private LocalDateTime lastReceived; // 最后接收时间戳

   // 构造函数
   public Currency(Integer id, String name, LocalDateTime lastReceived) {
       this.id = id;
       this.name = name;
       this.lastReceived = lastReceived;
   }

   // Getter方法
   public Integer getId() { return id; }
   public String getName() { return name; }
   public LocalDateTime getLastReceived() { return lastReceived; }

   // 为了方便打印，重写toString方法
   @Override
   public String toString() {
       return "Currency{" +
              "id=" + id +
              ", name='" + name + '\'' +
              ", lastReceived=" + lastReceived +
              '}';
   }
}

import java.time.LocalDateTime;
import java.time.LocalDate;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
import java.util.Map;
import java.util.Optional;
import java.util.stream.Collectors;

public class CurrencyProcessor {

    public static void main(String[] args) {
        List<Currency> data = Arrays.asList(
            new Currency(1, "USD", LocalDateTime.parse("2022-05-18T09:04:01.545")),
            new Currency(2, "USD", LocalDateTime.parse("2022-05-18T08:04:01.545")),
            new Currency(3, "USD", LocalDateTime.parse("2022-05-19T08:04:01.545")),
            new Currency(4, "USD", LocalDateTime.parse("2022-05-20T08:04:01.545")),
            new Currency(5, "USD", LocalDateTime.parse("2022-05-20T11:04:01.545")),
            new Currency(6, "BUSD", LocalDateTime.parse("2022-05-18T08:04:01.545"))
        );

        // 1. 分组并获取每日期货的最新记录
        List<Currency> latestByDateAndCurrency = new ArrayList<>(data
                .stream()
                .collect(Collectors.groupingBy(
                    // 复合键：货币名称 + 日期
                    curr -> Arrays.asList(curr.getName(), curr.getLastReceived().toLocalDate()),
                    // 收集器：先找到最大值，然后从Optional中取出
                    Collectors.collectingAndThen(
                        Collectors.maxBy(Comparator.comparing(Currency::getLastReceived)),
                        Optional::get // 确保Optional有值，否则抛出NoSuchElementException
                    )
                ))
                .values()); // 获取Map中的所有值，即筛选出的Currency对象

        System.out.println("所有货币在每天的最新记录 (未排序):");
        latestByDateAndCurrency.forEach(System.out::println);

        // 2. 对结果进行排序（如果需要）
        // 可以直接对上述列表进行排序
        latestByDateAndCurrency.sort(
            Comparator.comparing(Currency::getName) // 先按货币名称排序
                      .thenComparing(Currency::getLastReceived) // 再按时间戳排序
        );

        System.out.println("\n所有货币在每天的最新记录 (排序后):");
        latestByDateAndCurrency.forEach(System.out::println);
    }
}

import java.util.stream.Collectors;
import java.util.Comparator;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Optional;
import java.time.LocalDateTime;

public class SpecificCurrencyProcessor {

    public static void main(String[] args) {
        List<Currency> data = Arrays.asList(
            new Currency(1, "USD", LocalDateTime.parse("2022-05-18T09:04:01.545")),
            new Currency(2, "USD", LocalDateTime.parse("2022-05-18T08:04:01.545")),
            new Currency(3, "USD", LocalDateTime.parse("2022-05-19T08:04:01.545")),
            new Currency(4, "USD", LocalDateTime.parse("2022-05-20T08:04:01.545")),
            new Currency(5, "USD", LocalDateTime.parse("2022-05-20T11:04:01.545")),
            new Currency(6, "BUSD", LocalDateTime.parse("2022-05-18T08:04:01.545"))
        );

        String targetCurrency = "USD";
        List<Currency> lastUSDByDate = new ArrayList<>(data
            .stream()
            .filter(curr -> targetCurrency.equalsIgnoreCase(curr.getName())) // 筛选特定货币
            .collect(Collectors.groupingBy(
                curr -> curr.getLastReceived().toLocalDate(), // 此时分组键只需日期
                Collectors.collectingAndThen(
                    Collectors.maxBy(Comparator.comparing(Currency::getLastReceived)),
                    Optional::get
                )
            ))
            .values()
        );

        // 对结果进行排序
        lastUSDByDate.sort(Comparator.comparing(Currency::getLastReceived));

        System.out.println(targetCurrency + " 在每天的最新记录:");
        lastUSDByDate.forEach(System.out::println);
    }
}

SELECT id, name, last_received
FROM (
    SELECT c.*,
    ROW_NUMBER() OVER (
        PARTITION BY name, to_char(last_received, 'yyyy-MM-dd')
        ORDER BY last_received DESC
    ) AS rn -- 或者使用ROW_NUMBER(), RANK(), DENSE_RANK()
    FROM Currency c
    WHERE c.name = :currName -- 如果需要筛选特定货币
) tbl
WHERE rn = 1
ORDER BY last_received;

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;
import org.springframework.data.repository.query.Param;
import java.util.List;

public interface CurrencyRepository extends JpaRepository<Currency, Integer> {

    @Query(nativeQuery = true, value = """
        SELECT id, name, last_received
        FROM (
            SELECT c.*,
            ROW_NUMBER() OVER (
                PARTITION BY name, to_char(last_received, 'yyyy-MM-dd')
                ORDER BY last_received DESC
            ) AS rn
            FROM Currency c
            WHERE c.name = :currName
        ) tbl
        WHERE rn = 1
        ORDER BY last_received
    """)
    List<Currency> findLastByDateByCurrencyName(@Param("currName") String currName);
}