如何将泛型 class 类型转换为特定类型？

Question

我正在尝试使用 Java 8 中的泛型类型创建一个 Flux 泛型转换器。我的代码基于此 answer。这个想法基本上是实现这个特定的转换器 String -> Integer:

    public Flux<Integer> createFluxConverterStringToInt(String[] data) {
        Flux<Integer> stringFlux = Flux
                .just(data)
                .map(value -> Integer.parseInt(value))
                .log();
        return stringFlux;
    }

到类型转换器 String -> 到我想要的任何类型。因此，我正在使用构造函数 FluxAndMonoGeneric(Class<OUT> typeArgumentClass) 创建类型 <OUT> 的 class FluxAndMonoGeneric，并返回方法 public Flux<OUT> createFluxConverter(String[] data)。我正在考虑像这样创建多个条目：this.typeArgumentClass.isInstance(Integer.class) 在 map 调用上，但具有不同的 class 类型。但它甚至对整数不起作用。

import lombok.extern.slf4j.Slf4j;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;

@Slf4j
public class FluxAndMonoGeneric<OUT> {

    private final Class<OUT> typeArgumentClass;

    public FluxAndMonoGeneric(Class<OUT> typeArgumentClass) {
        this.typeArgumentClass = typeArgumentClass;
    }

    public Flux<OUT> createFluxConverter(String[] data) {
        Flux<OUT> stringFlux = Flux
                .just(data)
                .map(value -> {
                    // NEVER ENTERS ON THIS IF
                    if (this.typeArgumentClass.isInstance(Integer.class))
                        return this.typeArgumentClass.cast(Integer.parseInt(value));
                    // ALWAYS ENTERS ON THIS ELSE AND STRING CANNOT BE CASTED TO INTEGER
                    else return this.typeArgumentClass.cast(value);
                })
                .log();
        return stringFlux;
    }

    public Mono<OUT> createMonoConverter(String data) {
        Mono<OUT> integerMono = Mono.just(data)
                .map(value -> this.typeArgumentClass.cast(value))
                .log();
        return integerMono;
    }
}

我收到错误：java.lang.ClassCastException: Cannot cast java.lang.String to java.lang.Integer 当我使用此单元测试进行测试时。

import org.junit.jupiter.api.Test;
import reactor.core.publisher.Flux;
import reactor.test.StepVerifier;
public class FluxAndMonoGenericTest {
    // this works.
    @Test
    void testCreateGenericFluxWithString() {

        String expect = "Spring,Spring Boot,Reactive Spring";
        String delimiter = ",";
        String[] messages = expect.split(delimiter);

        FluxAndMonoGeneric<String> myFluxGenericTest = new FluxAndMonoGeneric<String>(String.class);

        Flux<String> stringFlux = myFluxGenericTest.createFluxConverter(messages);

        StepVerifier.create(stringFlux)
                .expectNext(messages[0])
                .expectNext(messages[1])
                .expectNext(messages[2])
                .verifyComplete();
    }
    // THIS DOES NOT WORK
    @Test
    void testCreateGenericFluxWithInteger() {

        String expect = "1,1234,7654,34";
        String delimiter = ",";
        String[] messages = expect.split(delimiter);
        Integer[] expectedMessages = new Integer[]{1, 1234, 7654, 34};

        FluxAndMonoGeneric<Integer> myFluxGenericTest = new FluxAndMonoGeneric<Integer>(Integer.class);

        Flux<Integer> stringFlux = myFluxGenericTest.createFluxConverter(messages);

        StepVerifier.create(stringFlux)
                .expectNext(expectedMessages[0])
                .expectNext(expectedMessages[1])
                .expectNext(expectedMessages[2])
                .expectNext(expectedMessages[3])
                .verifyComplete();
    }
}

Answer 1

    public <T> Flux<T> createFluxConverterStringToInt(String[] data, Function<String, T> mapper) {
        return Flux
                .just(data)
                .map(mapper)
                .log();
    }

然后，无需传入所需的输出类型，只需传入要将数据转换为正确输出类型的映射器即可。

例如Integer::parseInt 或 String::trim 或其他。

如何将泛型 class 类型转换为特定类型？

How to convert a generic class type to a specific type?

java

generics

project-reactor