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D-Dᴙum
Asked: 2023-10-24 21:52:06 +0800 CST

反应式变换函数的行为不符合预期

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当我提取各个步骤并单独执行它们时，我创建的反应器变换函数不会给出相同的结果。

我有包含价格类型列表的 DTO 记录。

public record CarrierDto(MetaData metaData, List<Daily> dailySeries) {

    public record MetaData(String name, String information) {};
    public record Daily(String date, Integer price) {};
}

Mono<CarrierDto>我想从a中提取Flux<Daily>然后将其转换为Flux<Price>.

@Table("price")
public record Price (
        @Column("p_date") String date,
        @Column("p_price") Integer price) {
}

为了进行这种转换，我有这个功能：

static Function<Mono<CarrierDto>, Flux<Price>> transform = carrierDtoMono ->
            carrierDtoMono.map(CarrierDto::dailySeries)
                    .flatMapMany(Flux::fromIterable)
                    .map(daily -> new Price(daily.date(), daily.price()));

然而，当我尝试使用此功能时，订阅时仅给出一个价格。如果我提取每个单独的步骤并执行提供的所有价格。例如这个测试类：

import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;

import java.util.Arrays;
import java.util.List;
import java.util.function.Function;

public class TestMain {

    static Function<Mono<CarrierDto>, Flux<Price>> transform = carrierDtoMono ->
            carrierDtoMono.map(CarrierDto::dailySeries)
                    .flatMapMany(Flux::fromIterable)
                    .map(daily -> new Price(daily.date(), daily.price()));

    public static void main(String[] args) {
        final CarrierDto dto = new CarrierDto(new CarrierDto.MetaData("Test", "Test information"),
                Arrays.asList(new CarrierDto.Daily("2023-01-01", 100),
                        new CarrierDto.Daily("2023-01-02", 101),
                        new CarrierDto.Daily("2023-01-03", 102),
                        new CarrierDto.Daily("2023-01-04", 103)));

        System.out.println("Using Transform function.");
        Mono.just(dto)
                .transform(transform)
                .subscribe(price -> System.out.println(String.format("Date: %s Price: %d", price.date(), price.price())));

        System.out.println("Without transform function.");

        final Mono<List<CarrierDto.Daily>> monoDailySeries = Mono.just(dto).map(CarrierDto::dailySeries);
        final Flux<CarrierDto.Daily> dailyFlux = monoDailySeries.flatMapMany(Flux::fromIterable);
        final Flux<Price> priceFlux = dailyFlux.map(daily -> new Price(daily.date(), daily.price()));

        priceFlux.subscribe(price -> System.out.println(String.format("Date: %s Price: %d", price.date(), price.price())));
    }
}

给出结果：

Using Transform function.
Date: 2023-01-01 Price: 100
Without transform function.
Date: 2023-01-01 Price: 100
Date: 2023-01-02 Price: 101
Date: 2023-01-03 Price: 102
Date: 2023-01-04 Price: 103

为什么结果不同？

java

1 个回答

  1. Best Answer

    这是因为transformerinMono生成一个新的Mono，即仅向发布者请求第一项。

    其内部有：

    Mono<V> transform(...) {
   ...
   from(transformer.apply(this))
}

    我建议从 Flux 开始（或将 Mono 转换为 Flux）。就像你的例子一样：

    static Function<Flux<CarrierDto>, Flux<Price>> transform = carrierDtoFlux ->
        carrierDtoFlux.map(CarrierDto::dailySeries)
                .flatMap(Flux::fromIterable)
                .map(daily -> new Price(daily.date(), daily.price()));

Flux.just(dto)
        .transform(transform)
        .subscribe(price -> System.out.println(String.format("Date: %s Price: %d", price.date(), price.price())));
    • 1

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