Spring Boot Engineer

by jeffallan1be15d8064f8MIT11K starsListed Oct 8, 2026Updated Oct 8, 2026Repository updated 5 days ago

Generates Spring Boot 3.x configurations, creates REST controllers, implements Spring Security 6 authentication flows, sets up Spring Data JPA repositories, and configures reactive WebFlux endpoints. Use when building Spring Boot 3.x applications, microservices, or reactive Java applications; invoke for Spring Data JPA, Spring Security 6, WebFlux, Spring Cloud integration, Java REST API design, or Microservices Java architecture.

Instructions onlySoftware Development

AI-generated overview

Guides Spring Boot 3.x backend implementation: REST controllers, JPA data access, Security 6, WebFlux and testing.

What it does: Provides a workflow and reference guidance for building Spring Boot 3.x applications, including layered service, repository and REST controller code samples, DTOs, exception handling and test slices. It covers Spring Data JPA, Spring Security 6 authentication, reactive WebFlux endpoints and Spring Cloud integration through five reference documents. It also lists mandatory and forbidden patterns such as constructor injection, input validation and externalized secrets.
When to use it: Use when implementing or reviewing Spring Boot 3.x services, microservices or reactive Java applications. It fits work involving Spring Data JPA, Spring Security 6, WebFlux, Spring Cloud or Java REST API design.
Requirements: Instructions and reference documents only; no scripts are shipped. The described work assumes a Java project with Spring Boot 3.x and a Maven or Gradle wrapper for running tests.

Spring Boot Engineer

Core Workflow

Analyze requirements — Identify service boundaries, APIs, data models, security needs
Design architecture — Plan microservices, data access, cloud integration, security; confirm design before coding
Implement — Create services with constructor injection and layered architecture (see Quick Start below)
Secure — Add Spring Security, OAuth2, method security, CORS configuration; verify security rules compile and pass tests. If compilation or tests fail: review error output, fix the failing rule or configuration, and re-run before proceeding
Test — Write unit, integration, and slice tests; run ./mvnw test (or ./gradlew test) and confirm all pass before proceeding. If tests fail: review the stack trace, isolate the failing assertion or component, fix the issue, and re-run the full suite
Deploy — Configure health checks and observability via Actuator; validate /actuator/health returns UP. If health is DOWN: check the components detail in the response, resolve the failing component (e.g., datasource, broker), and re-validate

Reference Guide

Load detailed guidance based on context:

Topic	Reference	Load When
Web Layer	`references/web.md`	Controllers, REST APIs, validation, exception handling
Data Access	`references/data.md`	Spring Data JPA, repositories, transactions, projections
Security	`references/security.md`	Spring Security 6, OAuth2, JWT, method security
Cloud Native	`references/cloud.md`	Spring Cloud, Config, Discovery, Gateway, resilience
Testing	`references/testing.md`	@SpringBootTest, MockMvc, Testcontainers, test slices

Quick Start — Minimal Working Structure

A standard Spring Boot feature consists of these layers. Use these as copy-paste starting points.

Entity

java

@Entity@Table(name = "products")public class Product {    @Id    @GeneratedValue(strategy = GenerationType.IDENTITY)    private Long id;
    @NotBlank    private String name;
    @DecimalMin("0.0")    private BigDecimal price;
    // getters / setters or use @Data (Lombok)}

Repository

Service (constructor injection)

java

@Servicepublic class ProductService {    private final ProductRepository repo;
    public ProductService(ProductRepository repo) { // constructor injection — no @Autowired        this.repo = repo;    }
    @Transactional(readOnly = true)    public List<Product> search(String name) {        return repo.findByNameContainingIgnoreCase(name);    }
    @Transactional    public Product create(ProductRequest request) {        var product = new Product();        product.setName(request.name());        product.setPrice(request.price());        return repo.save(product);    }}

REST Controller

java

@RestController@RequestMapping("/api/v1/products")@Validatedpublic class ProductController {    private final ProductService service;
    public ProductController(ProductService service) {        this.service = service;    }
    @GetMapping    public List<Product> search(@RequestParam(defaultValue = "") String name) {        return service.search(name);    }
    @PostMapping    @ResponseStatus(HttpStatus.CREATED)    public Product create(@Valid @RequestBody ProductRequest request) {        return service.create(request);    }}

DTO (record)

Global Exception Handler

java

@RestControllerAdvicepublic class GlobalExceptionHandler {    @ExceptionHandler(MethodArgumentNotValidException.class)    @ResponseStatus(HttpStatus.BAD_REQUEST)    public Map<String, String> handleValidation(MethodArgumentNotValidException ex) {        return ex.getBindingResult().getFieldErrors().stream()            .collect(Collectors.toMap(FieldError::getField, FieldError::getDefaultMessage));    }
    @ExceptionHandler(EntityNotFoundException.class)    @ResponseStatus(HttpStatus.NOT_FOUND)    public Map<String, String> handleNotFound(EntityNotFoundException ex) {        return Map.of("error", ex.getMessage());    }}

Test Slice

java

@WebMvcTest(ProductController.class)class ProductControllerTest {    @Autowired MockMvc mockMvc;    @MockBean ProductService service;
    @Test    void createProduct_validRequest_returns201() throws Exception {        var product = new Product(); product.setName("Widget"); product.setPrice(BigDecimal.TEN);        when(service.create(any())).thenReturn(product);
        mockMvc.perform(post("/api/v1/products")                .contentType(MediaType.APPLICATION_JSON)                .content("""{"name":"Widget","price":10.0}"""))            .andExpect(status().isCreated())            .andExpect(jsonPath("$.name").value("Widget"));    }}

Constraints

MUST DO

Rule	Correct Pattern
Constructor injection	`public MyService(Dep dep) { this.dep = dep; }`
Validate API input	`@Valid @RequestBody MyRequest req` on every mutating endpoint
Type-safe config	`@ConfigurationProperties(prefix = "app")` bound to a record/class
Appropriate stereotype	`@Service` for business logic, `@Repository` for data, `@RestController` for HTTP
Transaction scope	`@Transactional` on multi-step writes; `@Transactional(readOnly = true)` on reads
Hide internals	Catch domain exceptions in `@RestControllerAdvice`; return problem details, not stack traces
Externalize secrets	Use environment variables or Spring Cloud Config — never `application.properties`

MUST NOT DO

Use field injection (@Autowired on fields)
Skip input validation on API endpoints
Use @Component when @Service/@Repository/@Controller applies
Mix blocking and reactive code (e.g., calling .block() inside a WebFlux chain)
Store secrets or credentials in application.properties/application.yml
Hardcode URLs, credentials, or environment-specific values
Use deprecated Spring Boot 2.x patterns (e.g., WebSecurityConfigurerAdapter)

Maintained by @jeffallan, Principal Consultant at Synergetic Solutions

Source and attribution

Source:jeffallan/claude-skillsinskills/spring-boot-engineerat commit1be15d8

License: MIT

Content belongs to its original authors. SourceWeft indexes it from a public repository.

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@Entity@Table(name = "products")public class Product {    @Id    @GeneratedValue(strategy = GenerationType.IDENTITY)    private Long id;
    @NotBlank    private String name;
    @DecimalMin("0.0")    private BigDecimal price;
    // getters / setters or use @Data (Lombok)}

@Servicepublic class ProductService {    private final ProductRepository repo;
    public ProductService(ProductRepository repo) { // constructor injection — no @Autowired        this.repo = repo;    }
    @Transactional(readOnly = true)    public List<Product> search(String name) {        return repo.findByNameContainingIgnoreCase(name);    }
    @Transactional    public Product create(ProductRequest request) {        var product = new Product();        product.setName(request.name());        product.setPrice(request.price());        return repo.save(product);    }}

@RestController@RequestMapping("/api/v1/products")@Validatedpublic class ProductController {    private final ProductService service;
    public ProductController(ProductService service) {        this.service = service;    }
    @GetMapping    public List<Product> search(@RequestParam(defaultValue = "") String name) {        return service.search(name);    }
    @PostMapping    @ResponseStatus(HttpStatus.CREATED)    public Product create(@Valid @RequestBody ProductRequest request) {        return service.create(request);    }}

@RestControllerAdvicepublic class GlobalExceptionHandler {    @ExceptionHandler(MethodArgumentNotValidException.class)    @ResponseStatus(HttpStatus.BAD_REQUEST)    public Map<String, String> handleValidation(MethodArgumentNotValidException ex) {        return ex.getBindingResult().getFieldErrors().stream()            .collect(Collectors.toMap(FieldError::getField, FieldError::getDefaultMessage));    }
    @ExceptionHandler(EntityNotFoundException.class)    @ResponseStatus(HttpStatus.NOT_FOUND)    public Map<String, String> handleNotFound(EntityNotFoundException ex) {        return Map.of("error", ex.getMessage());    }}

@WebMvcTest(ProductController.class)class ProductControllerTest {    @Autowired MockMvc mockMvc;    @MockBean ProductService service;
    @Test    void createProduct_validRequest_returns201() throws Exception {        var product = new Product(); product.setName("Widget"); product.setPrice(BigDecimal.TEN);        when(service.create(any())).thenReturn(product);
        mockMvc.perform(post("/api/v1/products")                .contentType(MediaType.APPLICATION_JSON)                .content("""{"name":"Widget","price":10.0}"""))            .andExpect(status().isCreated())            .andExpect(jsonPath("$.name").value("Widget"));    }}