KalpaD

{
    "errors": [
        {
            "code": "firstName",
            "message": "First name must be between 2 and 25 characters"
        },
        {
            "code": "title",
            "message": "Title cannot be null"
        },

KalpaD

public class FormattedNameResponseMapper {

    private FormattedNameResponseMapper() {
    }

    public static FormattedNameResponse fromWebExchangeBindException(WebExchangeBindException ex) {
        FormattedNameResponse res = new FormattedNameResponse();
        List<Error> errors = ex.getFieldErrors().stream()
                .map(fieldError -> new Error(fieldError.getField(), fieldError.getDefaultMessage()))
                .collect(Collectors.toList());

KalpaD

@RestController
public class ValidationDemoController {

    @PostMapping("/format")
    public Mono<ResponseEntity<FormattedNameResponse>> format(@Valid @RequestBody Mono<FormatNameRequest> request) {
        return request
                .map(res -> ResponseEntity.status(HttpStatus.OK).body(FormattedNameResponseMapper.fromFormatNameRequest(res)))
                .onErrorResume(WebExchangeBindException.class,
                        ex -> Mono.just(ResponseEntity.status(HttpStatus.BAD_REQUEST)
                                        .body(FormattedNameResponseMapper.fromWebExchangeBindException(ex))));

KalpaD

package org.kds.reactive.model;

import javax.validation.constraints.NotBlank;
import javax.validation.constraints.NotNull;
import javax.validation.constraints.Size;

public class FormatNameRequest {

    @NotNull(message = "Title cannot be null")
    private String title;

KalpaD

plugins {
	id 'org.springframework.boot' version '2.3.0.RELEASE'
	id 'java'
	id 'idea'
}

apply plugin: 'io.spring.dependency-management'

group = 'org.kds.reactive'
version = '0.0.1-SNAPSHOT'

KalpaD

Request
POST http://host:port/format
Content-Type: application/json
{
    "title":"Mr",
    "firstName":"Jhon",
    "middleName": "Martin",
    "lastName": "Smith"
}

KalpaD

private static void debuggingUsingHook() {
        Hooks.onOperatorDebug();

        List<String> nameList = Arrays.asList("Rochel", "April", "Hong");

        Flux<String> stringFlux = Flux.fromIterable(nameList)
                .distinct()
                .map(name -> name.substring(0, 3))
                .map(String::toUpperCase)
                .map(name -> {

KalpaD

private static void debuggingUsingCheckpoints() {
        List<String> nameList = Arrays.asList("Rochel", "April", "Hong");

        Flux<String> stringFlux = Flux.fromIterable(nameList)
                .distinct()
                .checkpoint("after distinct()")
                .map(name -> name.substring(0, 3))
                .checkpoint("after substring")
                .map(String::toUpperCase)
                .checkpoint("after toUpperCase")

KalpaD

private static void debuggingWithOutCheckpoints() {
        List<String> nameList = Arrays.asList("Rochel", "April", "Hong");

        Flux<String> stringFlux = Flux.fromIterable(nameList)
                .distinct()
                .map(name -> name.substring(0, 3))
                .map(String::toUpperCase)
                .map(name -> {
                    if (name.equals("HON")) {
                        throw new RuntimeException("Boom!");

KalpaD

private static void debuggingUsingLogOperator() {
        List<String> nameList = Arrays.asList("Rochel", "April", "Hong");

        Flux<String> stringFlux = Flux.fromIterable(nameList)
                .distinct()
                .map(name -> name.substring(0, 3))
                .map(String::toUpperCase)
                .log();

        stringFlux.subscribe(log::info);