Spring Webflux：处理单声道中一个单声道为空时的错误。拉链

Question

我的代码如下

public Mono<Ship> getShip() { 
    //... 
}

public Mono<Car> getCar() { 
    //... 
}

public Mono<ShipAndCar> getCombinedMono() {
    Mono<Ship> shipMono = getShip();
    Mono<Car> carMono = getCar();

    return Mono.zip(shipMono, carMono
                    (ship, car) -> return new ShipAndCar(ship, car);

}

因为getShip和getCar都可能返回错误或空单声道。我想返回类似于Mono的内容。错误（新异常（“自定义消息”）消息取决于哪个Mono是空的。我该怎么做？

如果我在单声道之后添加一个开关ifempty。zip，我不知道哪个组件是空的。。。

Answer 1

您可以使用映射到可选的帮助器方法，将当值丢失时要做什么的决定推迟给以后的使用者。

例如，如果您只想默认丢失的发货，但在丢失的汽车上出现错误：

package com.example.demo;

import org.junit.jupiter.api.Test;
import reactor.core.publisher.Mono;
import reactor.test.StepVerifier;

import java.util.Optional;

public class JavaTest {

    @Test
    public void nullCarProducesSpecificException() {
        Mono<Ship> shipMono = Mono.empty();
        Mono<Car> carMono = Mono.empty();

        Mono<ShipAndCar> map = Mono.zip(
            shipMono.transform(JavaTest::toOptional),
            carMono.transform(JavaTest::toOptional))
            .map(tuple -> new ShipAndCar(
                tuple.getT1().orElse(new Ship("US Default")),
                tuple.getT2().orElseThrow(() -> new RuntimeException("Car was missing!!")))
            );

        StepVerifier.create(map)
            .verifyErrorMatches(error ->
                error instanceof RuntimeException &&
                    "Car was missing!!".equals(error.getMessage())
            );

    }

    private static <T> Mono<Optional<T>> toOptional(Mono<T> mono) {
        return mono.map(Optional::of)
            .defaultIfEmpty(Optional.empty());
    }
}

Answer 2

如果你在代码中压缩它们，你可以用像这样的开关空运算符扩展每个输入单声道

java prettyprint-override">        var carAndShip = Mono.zip(
                Optional.ofNullable(shipMono)
                        .orElseThrow(() -> new RuntimeException("ship is null"))
                        .switchIfEmpty(Mono.error(new RuntimeException("ship is empty"))),
                Optional.ofNullable(carMono)
                        .orElseThrow(() -> new RuntimeException("car is null"))
                        .switchIfEmpty(Mono.error(new RuntimeException("car is empty"))),
                ShipAndCar::new
        );