Robust RESTful Services with Spring Boot Hands-On Exercises

Exercise 1: Implement Validation in RESTful Services

Objective: Use Hibernate Validator to enforce constraints on your data model and handle validation errors.

1. Add Validation Dependency:

   • Ensure your pom.xml includes the validation starter.

xml

    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-validation</artifactId>
    </dependency>

2. Update the Product Entity with Validation:

   • Use validation annotations to enforce constraints.

java

    package com.example.demo;

    import javax.persistence.Entity;
    import javax.persistence.GeneratedValue;
    import javax.persistence.GenerationType;
    import javax.persistence.Id;
    import javax.validation.constraints.Min;
    import javax.validation.constraints.NotBlank;

    @Entity
    public class Product {
        @Id
        @GeneratedValue(strategy = GenerationType.AUTO)
        private Long id;

        @NotBlank(message = "Name is mandatory")
        private String name;

        @Min(value = 0, message = "Price must be non-negative")
        private double price;

        // Getters and setters
    }

3. Modify the ProductController to Handle Validation:

   • Use @Valid to trigger validation on request bodies.

java

    package com.example.demo;

    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.http.ResponseEntity;
    import org.springframework.validation.annotation.Validated;
    import org.springframework.web.bind.annotation.*;

    import javax.validation.Valid;

    @RestController
    @RequestMapping("/products")
    public class ProductController {

        @Autowired
        private ProductRepository productRepository;

        @PostMapping
        public ResponseEntity<Product> createProduct(@Valid @RequestBody Product product) {
            Product savedProduct = productRepository.save(product);
            return ResponseEntity.ok(savedProduct);
        }

        // Other CRUD methods...
    }

4. Handle Validation Errors:

   • Create a global exception handler for MethodArgumentNotValidException.

java

    package com.example.demo;

    import org.springframework.http.HttpStatus;
    import org.springframework.http.ResponseEntity;
    import org.springframework.validation.FieldError;
    import org.springframework.web.bind.MethodArgumentNotValidException;
    import org.springframework.web.bind.annotation.ControllerAdvice;
    import org.springframework.web.bind.annotation.ExceptionHandler;
    import org.springframework.web.bind.annotation.ResponseStatus;

    import java.util.HashMap;
    import java.util.Map;

    @ControllerAdvice
    public class GlobalExceptionHandler {

        @ExceptionHandler(MethodArgumentNotValidException.class)
        @ResponseStatus(HttpStatus.BAD_REQUEST)
        public ResponseEntity<Map<String, String>> handleValidationExceptions(MethodArgumentNotValidException ex) {
            Map<String, String> errors = new HashMap<>();
            ex.getBindingResult().getAllErrors().forEach((error) -> {
                String fieldName = ((FieldError) error).getField();
                String errorMessage = error.getDefaultMessage();
                errors.put(fieldName, errorMessage);
            });
            return new ResponseEntity<>(errors, HttpStatus.BAD_REQUEST);
        }

        // Other exception handlers...
    }

5. Test Validation:

   • Use Postman to send requests with invalid data and observe validation error messages.

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Exercise 2: Implement Pagination and Sorting

Objective: Enhance the REST API to support pagination and sorting of resources.

1. Add Pagination and Sorting to Repository:

   • Extend PagingAndSortingRepository for pagination and sorting capabilities.

java

    package com.example.demo;

    import org.springframework.data.repository.PagingAndSortingRepository;

    public interface ProductRepository extends PagingAndSortingRepository<Product, Long> {
    }

2. Update ProductController for Pagination and Sorting:

   • Use Pageable to handle pagination and sorting.

java

    package com.example.demo;

    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.data.domain.Page;
    import org.springframework.data.domain.Pageable;
    import org.springframework.web.bind.annotation.GetMapping;
    import org.springframework.web.bind.annotation.RequestMapping;
    import org.springframework.web.bind.annotation.RestController;

    @RestController
    @RequestMapping("/products")
    public class ProductController {

        @Autowired
        private ProductRepository productRepository;

        @GetMapping
        public Page<Product> getProducts(Pageable pageable) {
            return productRepository.findAll(pageable);
        }

        // Other CRUD methods...
    }

3. Test Pagination and Sorting:

   • Use Postman to fetch products with pagination parameters: http://localhost:8081/products?page=0&size=5&sort=name,asc.

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Exercise 3: Implement a Simple Search Functionality

Objective: Add a search feature to filter products by name.

1. Add a Custom Query Method to ProductRepository:

   • Define a query method using Spring Data JPA conventions.

java

    package com.example.demo;

    import org.springframework.data.repository.CrudRepository;

    import java.util.List;

    public interface ProductRepository extends CrudRepository<Product, Long> {
        List<Product> findByNameContaining(String name);
    }

2. Add a Search Endpoint in ProductController:

   • Implement a new endpoint to search products by name.

java

    package com.example.demo;

    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.web.bind.annotation.*;

    import java.util.List;

    @RestController
    @RequestMapping("/products")
    public class ProductController {

        @Autowired
        private ProductRepository productRepository;

        @GetMapping("/search")
        public List<Product> searchProducts(@RequestParam String name) {
            return productRepository.findByNameContaining(name);
        }

        // Other CRUD methods...
    }

3. Test the Search Functionality:

   • Use Postman to search for products by name: http://localhost:8081/products/search?name=phone.

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These exercises should provide a deeper understanding of building robust RESTful services with Spring Boot.