java 39 lines · 8 steps

Validating query params in a Spring controller

A Spring REST endpoint that validates paginated search parameters and reports violations as clean JSON.

Explained by highlit

Spring Intermediate validation pagination rest-api exception-handling dependency-injection

1@RestController
2@RequestMapping("/api/products")
3@Validated
4public class ProductSearchController {
5 
  private final ProductService productService;
7 
  public ProductSearchController(ProductService productService) {
      this.productService = productService;
  }
11 
  @GetMapping
  public Page<ProductSummary> search(
          @RequestParam @NotBlank @Size(max = 100) String query,
          @RequestParam(defaultValue = "0") @Min(0) int page,
          @RequestParam(defaultValue = "20") @Min(1) @Max(100) int size,
          @RequestParam(required = false) @DecimalMin("0.0") BigDecimal minPrice,
          @RequestParam(required = false) @Pattern(regexp = "ASC|DESC") String direction) {
19 
      Sort.Direction sortDir = direction == null
              ? Sort.Direction.ASC
              : Sort.Direction.valueOf(direction);
      Pageable pageable = PageRequest.of(page, size, Sort.by(sortDir, "price"));
      return productService.search(query, minPrice, pageable);
  }
26 
  @ExceptionHandler(ConstraintViolationException.class)
  @ResponseStatus(HttpStatus.BAD_REQUEST)
  public Map<String, String> handleConstraintViolations(ConstraintViolationException ex) {
      return ex.getConstraintViolations().stream()
              .collect(Collectors.toMap(
                      v -> {
                          String path = v.getPropertyPath().toString();
                          return path.substring(path.lastIndexOf('.') + 1);
                      },
                      ConstraintViolation::getMessage,
                      (first, second) -> first));
  }
39}

01 / 01

STEP 01

Walkthrough

Space play ←→ step click any line

Three takeaways

1@Validated on the class activates method-level bean validation for individual @RequestParam values.
2PageRequest lets you turn raw page, size, and sort inputs into a reusable Pageable for the service layer.
3A local @ExceptionHandler converts validation failures into a tidy field-to-message map instead of a stack trace.

Related explainers

typescript

import { registerLocaleData } from '@angular/common';
import localeFr from '@angular/common/locales/fr';
import localeFrExtra from '@angular/common/locales/extra/fr';
import localeDe from '@angular/common/locales/de';

Locale-aware bootstrapping in Angular

i18n localization dependency-injection

Intermediate 8 steps

typescript

import { Module } from '@nestjs/common';
import { ConfigModule } from '@nestjs/config';
import * as Joi from 'joi';

Validating env config at boot in NestJS

configuration schema-validation environment-variables

Intermediate 8 steps

php

<?php
 
namespace App\Services\Checkout;

Validating coupons with Laravel's Pipeline

pipeline chain of responsibility transactions

Intermediate 7 steps

java

@Component
@Converter
public class EncryptedStringConverter implements AttributeConverter<String, String> {

Transparent column encryption in Spring & JPA

encryption aes-gcm jpa-converter

Advanced 10 steps

typescript

import { Inject, Injectable, Logger } from '@nestjs/common';
import { CACHE_MANAGER } from '@nestjs/cache-manager';
import { Cache } from 'cache-manager';
import { InjectRepository } from '@nestjs/typeorm';