Building a REST API with Spring Boot: Controllers, Services, DTOs, Validation and Errors

HTTP request    |    v+-------------------------+   knows about: HTTP, JSON, status codes, DTOs| JobApplicationController|+-------------------------+    |  calls    v+-------------------------+   knows about: the rules, the domain objects| JobApplicationService   |+-------------------------+    |  calls    v+-------------------------+   knows about: storage| JobApplicationRepository|  (an interface; in memory now, a database next)+-------------------------+

--- a/pom.xml+++ b/pom.xml@@ -13,7 +13,8 @@    <groupId>com.example</groupId>-  <artifactId>foundations</artifactId>+  <artifactId>jobtracker</artifactId>   <version>0.0.1-SNAPSHOT</version>-  <name>foundations</name>+  <name>jobtracker</name>+  <description>Job Application Tracker API</description>    <properties>

// File: src/main/java/com/example/jobtracker/JobTrackerApplication.javapackage com.example.jobtracker;import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;import org.springframework.boot.context.properties.ConfigurationPropertiesScan;@SpringBootApplication@ConfigurationPropertiesScanpublic class JobTrackerApplication {    public static void main(String[] args) {        SpringApplication.run(JobTrackerApplication.class, args);    }}

// File: src/main/java/com/example/jobtracker/TrackerSettings.javapackage com.example.jobtracker;import jakarta.validation.constraints.Max;import jakarta.validation.constraints.Min;import org.springframework.boot.context.properties.ConfigurationProperties;import org.springframework.boot.context.properties.bind.DefaultValue;import org.springframework.validation.annotation.Validated;/** Paging limits, read from properties that start with "tracker." and checked at start-up. */@ConfigurationProperties(prefix = "tracker")@Validatedpublic record TrackerSettings(        @DefaultValue("20") @Min(1) @Max(100) int defaultPageSize,        @DefaultValue("100") @Min(1) @Max(1000) int maxPageSize) {}

tracker.default-page-size=20tracker.max-page-size=50

// File: src/main/java/com/example/jobtracker/ClockConfig.javapackage com.example.jobtracker;import java.time.Clock;import org.springframework.context.annotation.Bean;import org.springframework.context.annotation.Configuration;@Configurationpublic class ClockConfig {    /** One place that decides what "now" means, so tests can replace it with a fixed clock. */    @Bean    Clock clock() {        return Clock.systemUTC();    }}

// File: src/main/java/com/example/jobtracker/ApplicationStatus.javapackage com.example.jobtracker;import java.util.EnumSet;import java.util.Set;/** Where an application is in the process, and which moves between stages are allowed. */public enum ApplicationStatus {    WISHLIST, APPLIED, INTERVIEWING, OFFER, REJECTED, WITHDRAWN;    /** The stages this one may move to. REJECTED and WITHDRAWN are final. */    public Set<ApplicationStatus> allowedNext() {        return switch (this) {            case WISHLIST -> EnumSet.of(APPLIED, WITHDRAWN);            case APPLIED -> EnumSet.of(INTERVIEWING, REJECTED, WITHDRAWN);            case INTERVIEWING -> EnumSet.of(OFFER, REJECTED, WITHDRAWN);            case OFFER -> EnumSet.of(REJECTED, WITHDRAWN);            case REJECTED, WITHDRAWN -> EnumSet.noneOf(ApplicationStatus.class);        };    }    public boolean canMoveTo(ApplicationStatus next) {        return allowedNext().contains(next);    }}

// File: src/main/java/com/example/jobtracker/JobApplication.javapackage com.example.jobtracker;import java.time.Instant;import java.time.LocalDate;/** The domain object: one job the user is pursuing. Plain Java for now. */public class JobApplication {    private Long id;    private String company;    private String position;    private ApplicationStatus status;    private LocalDate appliedOn;    private String jobUrl;    private String notes;    private Instant createdAt;    private Instant updatedAt;    public Long getId() {        return id;    }    public void setId(Long id) {        this.id = id;    }    public String getCompany() {        return company;    }    public void setCompany(String company) {        this.company = company;    }    public String getPosition() {        return position;    }    public void setPosition(String position) {        this.position = position;    }    public ApplicationStatus getStatus() {        return status;    }    public void setStatus(ApplicationStatus status) {        this.status = status;    }    public LocalDate getAppliedOn() {        return appliedOn;    }    public void setAppliedOn(LocalDate appliedOn) {        this.appliedOn = appliedOn;    }    public String getJobUrl() {        return jobUrl;    }    public void setJobUrl(String jobUrl) {        this.jobUrl = jobUrl;    }    public String getNotes() {        return notes;    }    public void setNotes(String notes) {        this.notes = notes;    }    public Instant getCreatedAt() {        return createdAt;    }    public void setCreatedAt(Instant createdAt) {        this.createdAt = createdAt;    }    public Instant getUpdatedAt() {        return updatedAt;    }    public void setUpdatedAt(Instant updatedAt) {        this.updatedAt = updatedAt;    }}

// File: src/main/java/com/example/jobtracker/ApplicationNotFoundException.javapackage com.example.jobtracker;public class ApplicationNotFoundException extends RuntimeException {    public ApplicationNotFoundException(Long id) {        super("No job application with id " + id);    }}

// File: src/main/java/com/example/jobtracker/InvalidStatusChangeException.javapackage com.example.jobtracker;public class InvalidStatusChangeException extends RuntimeException {    public InvalidStatusChangeException(ApplicationStatus from, ApplicationStatus to) {        super("An application cannot move from " + from + " to " + to                + (from.allowedNext().isEmpty() ? " because " + from + " is final"                        : ". Allowed next stages: " + from.allowedNext()));    }}

// File: src/main/java/com/example/jobtracker/JobApplicationRepository.javapackage com.example.jobtracker;import java.util.List;import java.util.Optional;/** Where applications are stored. The method names match Spring Data's, which the next articles use. */public interface JobApplicationRepository {    /** Inserts a new application (the id is null) or updates an existing one, and returns the stored object. */    JobApplication save(JobApplication application);    Optional<JobApplication> findById(Long id);    List<JobApplication> findAll();    void deleteById(Long id);}

// File: src/main/java/com/example/jobtracker/InMemoryJobApplicationRepository.javapackage com.example.jobtracker;import java.util.ArrayList;import java.util.List;import java.util.Map;import java.util.Optional;import java.util.concurrent.ConcurrentHashMap;import java.util.concurrent.atomic.AtomicLong;import org.springframework.stereotype.Repository;/** A temporary store that keeps everything in memory, so the web layer can be built and tested first. */@Repositorypublic class InMemoryJobApplicationRepository implements JobApplicationRepository {    private final Map<Long, JobApplication> byId = new ConcurrentHashMap<>();    private final AtomicLong nextId = new AtomicLong(1);    @Override    public JobApplication save(JobApplication application) {        if (application.getId() == null) {            application.setId(nextId.getAndIncrement());        }        byId.put(application.getId(), application);        return application;    }    @Override    public Optional<JobApplication> findById(Long id) {        return Optional.ofNullable(byId.get(id));    }    @Override    public List<JobApplication> findAll() {        return new ArrayList<>(byId.values());    }    @Override    public void deleteById(Long id) {        byId.remove(id);    }}

// File: src/main/java/com/example/jobtracker/JobApplicationRequest.javapackage com.example.jobtracker;import jakarta.validation.constraints.NotBlank;import jakarta.validation.constraints.PastOrPresent;import jakarta.validation.constraints.Size;import java.time.LocalDate;/** What a client sends to create or replace an application. The status is deliberately not part of it. */public record JobApplicationRequest(        @NotBlank @Size(max = 100) String company,        @NotBlank @Size(max = 100) String position,        @PastOrPresent LocalDate appliedOn,        @Size(max = 500) String jobUrl,        @Size(max = 2000) String notes) {}

// File: src/main/java/com/example/jobtracker/StatusChangeRequest.javapackage com.example.jobtracker;import jakarta.validation.constraints.NotNull;public record StatusChangeRequest(@NotNull ApplicationStatus status) {}

// File: src/main/java/com/example/jobtracker/JobApplicationResponse.javapackage com.example.jobtracker;import java.time.Instant;import java.time.LocalDate;/** What the API returns. It is a separate type from JobApplication, so the stored shape can change freely. */public record JobApplicationResponse(        Long id,        String company,        String position,        ApplicationStatus status,        LocalDate appliedOn,        String jobUrl,        String notes,        Instant createdAt,        Instant updatedAt) {    static JobApplicationResponse from(JobApplication a) {        return new JobApplicationResponse(a.getId(), a.getCompany(), a.getPosition(), a.getStatus(),                a.getAppliedOn(), a.getJobUrl(), a.getNotes(), a.getCreatedAt(), a.getUpdatedAt());    }}

// File: src/main/java/com/example/jobtracker/PageResponse.javapackage com.example.jobtracker;import java.util.List;/** One page of results, with enough information for a client to ask for the next one. */public record PageResponse<T>(List<T> items, int page, int size, long totalItems, int totalPages) {}

// File: src/main/java/com/example/jobtracker/JobApplicationService.javapackage com.example.jobtracker;import java.time.Clock;import java.time.Instant;import java.util.Comparator;import java.util.List;import java.util.Locale;import org.springframework.stereotype.Service;/** The rules of the application. It knows nothing about HTTP and nothing about how data is stored. */@Servicepublic class JobApplicationService {    private final JobApplicationRepository repository;    private final Clock clock;    private final TrackerSettings settings;    public JobApplicationService(JobApplicationRepository repository, Clock clock, TrackerSettings settings) {        this.repository = repository;        this.clock = clock;        this.settings = settings;    }    /** A new application starts as APPLIED if the user says when they applied, otherwise as WISHLIST. */    public JobApplicationResponse create(JobApplicationRequest request) {        JobApplication application = new JobApplication();        copyFields(request, application);        application.setStatus(request.appliedOn() == null ? ApplicationStatus.WISHLIST : ApplicationStatus.APPLIED);        Instant now = Instant.now(clock);        application.setCreatedAt(now);        application.setUpdatedAt(now);        return JobApplicationResponse.from(repository.save(application));    }    public JobApplicationResponse get(Long id) {        return JobApplicationResponse.from(find(id));    }    /** Filters by status and by part of the company name, then returns one page, oldest first. */    public PageResponse<JobApplicationResponse> list(ApplicationStatus status, String company, Integer page, Integer size) {        int pageSize = size == null ? settings.defaultPageSize() : Math.min(size, settings.maxPageSize());        int pageNumber = page == null ? 0 : page;        String needle = company == null ? null : company.toLowerCase(Locale.ROOT);        List<JobApplication> matching = repository.findAll().stream()                .filter(a -> status == null || a.getStatus() == status)                .filter(a -> needle == null || a.getCompany().toLowerCase(Locale.ROOT).contains(needle))                .sorted(Comparator.comparing(JobApplication::getId))                .toList();        List<JobApplicationResponse> items = matching.stream()                .skip((long) pageNumber * pageSize)                .limit(pageSize)                .map(JobApplicationResponse::from)                .toList();        int totalPages = (int) Math.ceil(matching.size() / (double) pageSize);        return new PageResponse<>(items, pageNumber, pageSize, matching.size(), totalPages);    }    /** Replaces the editable fields. The status is not editable here, see changeStatus. */    public JobApplicationResponse replace(Long id, JobApplicationRequest request) {        JobApplication application = find(id);        copyFields(request, application);        application.setUpdatedAt(Instant.now(clock));        return JobApplicationResponse.from(repository.save(application));    }    public JobApplicationResponse changeStatus(Long id, ApplicationStatus next) {        JobApplication application = find(id);        if (!application.getStatus().canMoveTo(next)) {            throw new InvalidStatusChangeException(application.getStatus(), next);        }        application.setStatus(next);        application.setUpdatedAt(Instant.now(clock));        return JobApplicationResponse.from(repository.save(application));    }    public void delete(Long id) {        find(id);                                   // throws if it does not exist        repository.deleteById(id);    }    private JobApplication find(Long id) {        return repository.findById(id).orElseThrow(() -> new ApplicationNotFoundException(id));    }    private static void copyFields(JobApplicationRequest request, JobApplication application) {        application.setCompany(request.company().strip());        application.setPosition(request.position().strip());        application.setAppliedOn(request.appliedOn());        application.setJobUrl(request.jobUrl());        application.setNotes(request.notes());    }}

// File: src/main/java/com/example/jobtracker/JobApplicationController.javapackage com.example.jobtracker;import jakarta.validation.Valid;import jakarta.validation.constraints.Min;import java.net.URI;import org.springframework.http.HttpStatus;import org.springframework.http.ResponseEntity;import org.springframework.web.bind.annotation.DeleteMapping;import org.springframework.web.bind.annotation.GetMapping;import org.springframework.web.bind.annotation.PathVariable;import org.springframework.web.bind.annotation.PostMapping;import org.springframework.web.bind.annotation.PutMapping;import org.springframework.web.bind.annotation.RequestBody;import org.springframework.web.bind.annotation.RequestMapping;import org.springframework.web.bind.annotation.RequestParam;import org.springframework.web.bind.annotation.ResponseStatus;import org.springframework.web.bind.annotation.RestController;import org.springframework.web.util.UriComponentsBuilder;/** The HTTP layer: translate requests into service calls and results into responses. No rules live here. */@RestController@RequestMapping("/api/applications")public class JobApplicationController {    private final JobApplicationService service;    public JobApplicationController(JobApplicationService service) {        this.service = service;    }    @PostMapping    public ResponseEntity<JobApplicationResponse> create(@Valid @RequestBody JobApplicationRequest request,                                                         UriComponentsBuilder uriBuilder) {        JobApplicationResponse created = service.create(request);        URI location = uriBuilder.path("/api/applications/{id}").buildAndExpand(created.id()).toUri();        return ResponseEntity.created(location).body(created);    }    @GetMapping("/{id}")    public JobApplicationResponse get(@PathVariable Long id) {        return service.get(id);    }    @GetMapping    public PageResponse<JobApplicationResponse> list(            @RequestParam(required = false) ApplicationStatus status,            @RequestParam(required = false) String company,            @RequestParam(required = false) @Min(0) Integer page,            @RequestParam(required = false) @Min(1) Integer size) {        return service.list(status, company, page, size);    }    @PutMapping("/{id}")    public JobApplicationResponse replace(@PathVariable Long id, @Valid @RequestBody JobApplicationRequest request) {        return service.replace(id, request);    }    @PostMapping("/{id}/status")    public JobApplicationResponse changeStatus(@PathVariable Long id, @Valid @RequestBody StatusChangeRequest request) {        return service.changeStatus(id, request.status());    }    @DeleteMapping("/{id}")    @ResponseStatus(HttpStatus.NO_CONTENT)    public void delete(@PathVariable Long id) {        service.delete(id);    }}

// File: src/main/java/com/example/jobtracker/ApiExceptionHandler.javapackage com.example.jobtracker;import java.util.Map;import java.util.TreeMap;import org.slf4j.Logger;import org.slf4j.LoggerFactory;import org.springframework.http.HttpHeaders;import org.springframework.http.HttpStatus;import org.springframework.http.HttpStatusCode;import org.springframework.http.ProblemDetail;import org.springframework.http.ResponseEntity;import org.springframework.web.bind.MethodArgumentNotValidException;import org.springframework.web.bind.annotation.ExceptionHandler;import org.springframework.web.bind.annotation.RestControllerAdvice;import org.springframework.web.context.request.WebRequest;import org.springframework.web.servlet.mvc.method.annotation.ResponseEntityExceptionHandler;/** * Turns every failure into the same JSON shape (RFC 9457 problem details). * The base class already handles the standard web exceptions: unreadable JSON, wrong method, wrong media type. */@RestControllerAdvicepublic class ApiExceptionHandler extends ResponseEntityExceptionHandler {    private static final Logger log = LoggerFactory.getLogger(ApiExceptionHandler.class);    @ExceptionHandler(ApplicationNotFoundException.class)    ProblemDetail notFound(ApplicationNotFoundException e) {        ProblemDetail problem = ProblemDetail.forStatusAndDetail(HttpStatus.NOT_FOUND, e.getMessage());        problem.setTitle("Application not found");        return problem;    }    @ExceptionHandler(InvalidStatusChangeException.class)    ProblemDetail invalidStatusChange(InvalidStatusChangeException e) {        ProblemDetail problem = ProblemDetail.forStatusAndDetail(HttpStatus.CONFLICT, e.getMessage());        problem.setTitle("Invalid status change");        return problem;    }    /** Adds the list of invalid fields to the standard 400 response. */    @Override    protected ResponseEntity<Object> handleMethodArgumentNotValid(MethodArgumentNotValidException ex,            HttpHeaders headers, HttpStatusCode status, WebRequest request) {        Map<String, String> errors = new TreeMap<>();        ex.getBindingResult().getFieldErrors()                .forEach(error -> errors.merge(error.getField(), String.valueOf(error.getDefaultMessage()),                        (first, second) -> first + "; " + second));        ProblemDetail problem = ProblemDetail.forStatusAndDetail(HttpStatus.BAD_REQUEST, "The request has invalid fields");        problem.setTitle("Validation failed");        problem.setProperty("errors", errors);        return handleExceptionInternal(ex, problem, headers, status, request);    }    /** The last resort: log the details for us, tell the client nothing about the internals. */    @ExceptionHandler(Exception.class)    ProblemDetail unexpected(Exception e) {        log.error("Unexpected error", e);        ProblemDetail problem = ProblemDetail.forStatusAndDetail(HttpStatus.INTERNAL_SERVER_ERROR,                "An unexpected error occurred");        problem.setTitle("Internal error");        return problem;    }}

// File: src/test/java/com/example/jobtracker/JobApplicationServiceTest.javapackage com.example.jobtracker;import static org.junit.jupiter.api.Assertions.assertEquals;import static org.junit.jupiter.api.Assertions.assertThrows;import java.time.Clock;import java.time.Instant;import java.time.LocalDate;import java.time.ZoneOffset;import java.util.List;import org.junit.jupiter.api.BeforeEach;import org.junit.jupiter.api.Test;/** A plain unit test: no Spring, an in-memory repository and a fixed clock. */class JobApplicationServiceTest {    private static final Clock CLOCK = Clock.fixed(Instant.parse("2026-03-15T10:00:00Z"), ZoneOffset.UTC);    private JobApplicationService service;    @BeforeEach    void setUp() {        service = new JobApplicationService(new InMemoryJobApplicationRepository(), CLOCK, new TrackerSettings(2, 3));    }    private static JobApplicationRequest request(String company, LocalDate appliedOn) {        return new JobApplicationRequest(company, "Java Developer", appliedOn, null, null);    }    @Test    void anApplicationWithoutAnAppliedDateStartsAsWishlist() {        JobApplicationResponse created = service.create(request("Acme", null));        assertEquals(ApplicationStatus.WISHLIST, created.status());        assertEquals(Instant.parse("2026-03-15T10:00:00Z"), created.createdAt());        assertEquals(1L, created.id());    }    @Test    void anApplicationWithAnAppliedDateStartsAsApplied() {        JobApplicationResponse created = service.create(request("Acme", LocalDate.of(2026, 3, 1)));        assertEquals(ApplicationStatus.APPLIED, created.status());    }    @Test    void gettingAnUnknownIdThrows() {        assertThrows(ApplicationNotFoundException.class, () -> service.get(99L));    }    @Test    void listFiltersByStatusAndByCompanyIgnoringCase() {        service.create(request("Acme Corp", null));        service.create(request("Globex", LocalDate.of(2026, 3, 1)));        service.create(request("ACME Labs", LocalDate.of(2026, 3, 2)));        List<String> applied = service.list(ApplicationStatus.APPLIED, null, null, null).items().stream()                .map(JobApplicationResponse::company).toList();        List<String> acme = service.list(null, "acme", null, null).items().stream()                .map(JobApplicationResponse::company).toList();        assertEquals(List.of("Globex", "ACME Labs"), applied);        assertEquals(List.of("Acme Corp", "ACME Labs"), acme);    }    @Test    void listReturnsPagesAndLimitsThePageSize() {        for (int i = 1; i <= 7; i++) {            service.create(request("Company " + i, null));        }        PageResponse<JobApplicationResponse> defaultPage = service.list(null, null, null, null);        PageResponse<JobApplicationResponse> lastPage = service.list(null, null, 3, 2);        PageResponse<JobApplicationResponse> hugeSize = service.list(null, null, 0, 100);        assertEquals(2, defaultPage.items().size());          // the default page size is 2        assertEquals(7, defaultPage.totalItems());        assertEquals(4, defaultPage.totalPages());        assertEquals(1, lastPage.items().size());             // page 3 of size 2 holds only item 7        assertEquals(3, hugeSize.size());                     // 100 was reduced to the maximum of 3    }    @Test    void replaceChangesTheFieldsButNotTheStatus() {        long id = service.create(request("Acme", LocalDate.of(2026, 3, 1))).id();        JobApplicationResponse replaced = service.replace(id, request("  Acme Ltd ", null));        assertEquals("Acme Ltd", replaced.company());        assertEquals(ApplicationStatus.APPLIED, replaced.status());    }    @Test    void statusFollowsTheAllowedMoves() {        long id = service.create(request("Acme", null)).id();        service.changeStatus(id, ApplicationStatus.APPLIED);        service.changeStatus(id, ApplicationStatus.INTERVIEWING);        JobApplicationResponse offer = service.changeStatus(id, ApplicationStatus.OFFER);        assertEquals(ApplicationStatus.OFFER, offer.status());    }    @Test    void aFinalStatusCannotChange() {        long id = service.create(request("Acme", LocalDate.of(2026, 3, 1))).id();        service.changeStatus(id, ApplicationStatus.REJECTED);        InvalidStatusChangeException e = assertThrows(InvalidStatusChangeException.class,                () -> service.changeStatus(id, ApplicationStatus.APPLIED));        assertEquals("An application cannot move from REJECTED to APPLIED because REJECTED is final", e.getMessage());    }    @Test    void skippingAStageIsRejected() {        long id = service.create(request("Acme", null)).id();        assertThrows(InvalidStatusChangeException.class, () -> service.changeStatus(id, ApplicationStatus.OFFER));    }    @Test    void deleteRemovesTheApplicationAndADeleteOfAMissingOneThrows() {        long id = service.create(request("Acme", null)).id();        service.delete(id);        assertThrows(ApplicationNotFoundException.class, () -> service.get(id));        assertThrows(ApplicationNotFoundException.class, () -> service.delete(id));    }}

// File: src/test/java/com/example/jobtracker/JobApplicationControllerTest.javapackage com.example.jobtracker;import static org.mockito.ArgumentMatchers.any;import static org.mockito.BDDMockito.given;import static org.mockito.Mockito.verifyNoInteractions;import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.patch;import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.post;import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.content;import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.header;import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.jsonPath;import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;import java.time.Instant;import org.junit.jupiter.api.Test;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.boot.webmvc.test.autoconfigure.WebMvcTest;import org.springframework.http.MediaType;import org.springframework.test.context.bean.override.mockito.MockitoBean;import org.springframework.test.web.servlet.MockMvc;/** Tests only the HTTP layer: the service is a mock, so these tests check requests, responses and errors. */@WebMvcTest(JobApplicationController.class)class JobApplicationControllerTest {    @Autowired    MockMvc mvc;    @MockitoBean    JobApplicationService service;    private static JobApplicationResponse sample(long id) {        return new JobApplicationResponse(id, "Acme", "Java Developer", ApplicationStatus.WISHLIST, null, null, null,                Instant.parse("2026-03-15T10:00:00Z"), Instant.parse("2026-03-15T10:00:00Z"));    }    @Test    void createReturns201WithALocationHeaderAndTheNewResource() throws Exception {        given(service.create(any())).willReturn(sample(7));        mvc.perform(post("/api/applications").contentType(MediaType.APPLICATION_JSON)                        .content("""                                {"company": "Acme", "position": "Java Developer"}                                """))                .andExpect(status().isCreated())                .andExpect(header().string("Location", "http://localhost/api/applications/7"))                .andExpect(jsonPath("$.id").value(7))                .andExpect(jsonPath("$.status").value("WISHLIST"));    }    @Test    void invalidFieldsReturn400WithAProblemThatListsThem() throws Exception {        mvc.perform(post("/api/applications").contentType(MediaType.APPLICATION_JSON)                        .content("""                                {"company": " ", "position": "Java Developer", "appliedOn": "2999-01-01"}                                """))                .andExpect(status().isBadRequest())                .andExpect(content().contentTypeCompatibleWith(MediaType.APPLICATION_PROBLEM_JSON))                .andExpect(jsonPath("$.title").value("Validation failed"))                .andExpect(jsonPath("$.errors.company").exists())                .andExpect(jsonPath("$.errors.appliedOn").exists());        verifyNoInteractions(service);    }    @Test    void anUnknownIdReturns404() throws Exception {        given(service.get(99L)).willThrow(new ApplicationNotFoundException(99L));        mvc.perform(get("/api/applications/99"))                .andExpect(status().isNotFound())                .andExpect(jsonPath("$.detail").value("No job application with id 99"));    }    @Test    void anIllegalStatusChangeReturns409() throws Exception {        given(service.changeStatus(1L, ApplicationStatus.OFFER))                .willThrow(new InvalidStatusChangeException(ApplicationStatus.WISHLIST, ApplicationStatus.OFFER));        mvc.perform(post("/api/applications/1/status").contentType(MediaType.APPLICATION_JSON)                        .content("{\"status\": \"OFFER\"}"))                .andExpect(status().isConflict())                .andExpect(jsonPath("$.title").value("Invalid status change"));    }    @Test    void malformedJsonReturns400() throws Exception {        mvc.perform(post("/api/applications").contentType(MediaType.APPLICATION_JSON).content("{\"company\":"))                .andExpect(status().isBadRequest());    }    @Test    void anUnknownStatusValueInTheBodyReturns400() throws Exception {        mvc.perform(post("/api/applications/1/status").contentType(MediaType.APPLICATION_JSON)                        .content("{\"status\": \"HIRED\"}"))                .andExpect(status().isBadRequest());    }    @Test    void aNegativePageReturns400() throws Exception {        mvc.perform(get("/api/applications").param("page", "-1"))                .andExpect(status().isBadRequest());    }    @Test    void anUnsupportedMethodReturns405AndAWrongContentTypeReturns415() throws Exception {        mvc.perform(patch("/api/applications")).andExpect(status().isMethodNotAllowed());        mvc.perform(post("/api/applications").contentType(MediaType.TEXT_PLAIN).content("hello"))                .andExpect(status().isUnsupportedMediaType());    }}

$ curl -i -X POST http://localhost:18081/api/applications -H 'Content-Type: application/json' -d '{"company":"Acme","position":"Java Developer"}'HTTP/1.1 201 Location: http://localhost:18081/api/applications/1Content-Type: application/json{"id":1,"company":"Acme","position":"Java Developer","status":"WISHLIST","appliedOn":null,"jobUrl":null,"notes":null,"createdAt":"<now>","updatedAt":"<now>"}$ curl -i -X POST http://localhost:18081/api/applications -H 'Content-Type: application/json' -d '{"company":"Globex","position":"Backend Engineer","appliedOn":"2026-09-20","jobUrl":"https://example.com/jobs/42"}'HTTP/1.1 201 Location: http://localhost:18081/api/applications/2Content-Type: application/json{"id":2,"company":"Globex","position":"Backend Engineer","status":"APPLIED","appliedOn":"2026-09-20","jobUrl":"https://example.com/jobs/42","notes":null,"createdAt":"<now>","updatedAt":"<now>"}$ curl -i -X POST http://localhost:18081/api/applications -H 'Content-Type: application/json' -d '{"company":"Initech","position":"Platform Engineer","appliedOn":"2026-09-25"}'HTTP/1.1 201 Location: http://localhost:18081/api/applications/3Content-Type: application/json{"id":3,"company":"Initech","position":"Platform Engineer","status":"APPLIED","appliedOn":"2026-09-25","jobUrl":null,"notes":null,"createdAt":"<now>","updatedAt":"<now>"}$ curl -i http://localhost:18081/api/applications/1HTTP/1.1 200 Content-Type: application/json{"id":1,"company":"Acme","position":"Java Developer","status":"WISHLIST","appliedOn":null,"jobUrl":null,"notes":null,"createdAt":"<now>","updatedAt":"<now>"}$ curl -i 'http://localhost:18081/api/applications?status=APPLIED'HTTP/1.1 200 Content-Type: application/json{"items":[{"id":2,"company":"Globex","position":"Backend Engineer","status":"APPLIED","appliedOn":"2026-09-20","jobUrl":"https://example.com/jobs/42","notes":null,"createdAt":"<now>","updatedAt":"<now>"},{"id":3,"company":"Initech","position":"Platform Engineer","status":"APPLIED","appliedOn":"2026-09-25","jobUrl":null,"notes":null,"createdAt":"<now>","updatedAt":"<now>"}],"page":0,"size":20,"totalItems":2,"totalPages":1}$ curl -i 'http://localhost:18081/api/applications?company=ac&size=1'HTTP/1.1 200 Content-Type: application/json{"items":[{"id":1,"company":"Acme","position":"Java Developer","status":"WISHLIST","appliedOn":null,"jobUrl":null,"notes":null,"createdAt":"<now>","updatedAt":"<now>"}],"page":0,"size":1,"totalItems":1,"totalPages":1}$ curl -i -X PUT http://localhost:18081/api/applications/1 -H 'Content-Type: application/json' -d '{"company":"Acme Corp","position":"Java Developer","notes":"Referred by Sam"}'HTTP/1.1 200 Content-Type: application/json{"id":1,"company":"Acme Corp","position":"Java Developer","status":"WISHLIST","appliedOn":null,"jobUrl":null,"notes":"Referred by Sam","createdAt":"<now>","updatedAt":"<now>"}$ curl -i -X POST http://localhost:18081/api/applications/1/status -H 'Content-Type: application/json' -d '{"status":"APPLIED"}'HTTP/1.1 200 Content-Type: application/json{"id":1,"company":"Acme Corp","position":"Java Developer","status":"APPLIED","appliedOn":null,"jobUrl":null,"notes":"Referred by Sam","createdAt":"<now>","updatedAt":"<now>"}$ curl -i -X PUT http://localhost:18081/api/applications/1 -H 'Content-Type: application/json' -d '{"company":"Acme Corp","position":"Java Developer","status":"OFFER"}'HTTP/1.1 200 Content-Type: application/json{"id":1,"company":"Acme Corp","position":"Java Developer","status":"APPLIED","appliedOn":null,"jobUrl":null,"notes":null,"createdAt":"<now>","updatedAt":"<now>"}$ curl -i -X POST http://localhost:18081/api/applications/1/status -H 'Content-Type: application/json' -d '{"status":"OFFER"}'HTTP/1.1 409 Content-Type: application/problem+json{"detail":"An application cannot move from APPLIED to OFFER. Allowed next stages: [INTERVIEWING, REJECTED, WITHDRAWN]","instance":"/api/applications/1/status","status":409,"title":"Invalid status change"}$ curl -i -X POST http://localhost:18081/api/applications -H 'Content-Type: application/json' -d '{"company":"","position":"x","appliedOn":"2999-01-01"}'HTTP/1.1 400 Content-Type: application/problem+json{"detail":"The request has invalid fields","instance":"/api/applications","status":400,"title":"Validation failed","errors":{"appliedOn":"must be a date in the past or in the present","company":"must not be blank"}}$ curl -i -X POST http://localhost:18081/api/applications -H 'Content-Type: application/json' -d '{"company":'HTTP/1.1 400 Content-Type: application/problem+json{"detail":"Failed to read request","instance":"/api/applications","status":400,"title":"Bad Request"}$ curl -i http://localhost:18081/api/applications/99HTTP/1.1 404 Content-Type: application/problem+json{"detail":"No job application with id 99","instance":"/api/applications/99","status":404,"title":"Application not found"}$ curl -i 'http://localhost:18081/api/applications?status=HIRED'HTTP/1.1 400 Content-Type: application/problem+json{"detail":"Failed to convert 'status' with value: 'HIRED'","instance":"/api/applications","status":400,"title":"Bad Request"}$ curl -i 'http://localhost:18081/api/applications?page=-1'HTTP/1.1 400 Content-Type: application/problem+json{"detail":"Validation failure","instance":"/api/applications","status":400,"title":"Bad Request"}$ curl -i -X PATCH http://localhost:18081/api/applications/1HTTP/1.1 405 Content-Type: application/problem+json{"detail":"Method 'PATCH' is not supported.","instance":"/api/applications/1","status":405,"title":"Method Not Allowed"}$ curl -i -X POST http://localhost:18081/api/applications -H 'Content-Type: text/plain' -d 'hello'HTTP/1.1 415 Content-Type: application/problem+json{"detail":"Content-Type 'text/plain;charset=UTF-8' is not supported.","instance":"/api/applications","status":415,"title":"Unsupported Media Type"}$ curl -i -X DELETE http://localhost:18081/api/applications/1HTTP/1.1 204 $ curl -i -X DELETE http://localhost:18081/api/applications/1HTTP/1.1 404 Content-Type: application/problem+json{"detail":"No job application with id 1","instance":"/api/applications/1","status":404,"title":"Application not found"}