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erichiroshierichiroshi
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refactor(loan): decouple domains using Spring Events and ACL interfaces
Direct repository injection across domain boundaries prevents service extraction. This change introduces domain events and anticorruption layer interfaces as a safe intermediate step before full separation. - Add LoanCreatedEvent, LoanReturnedEvent, LoanCanceledEvent records with only primitive/serializable fields (ready for Kafka migration) - Add BookSummary and UserSummary ACL records to define the minimum contract each domain exposes to others - Add BookEventListener to handle copy restoration on loan return/cancel, removing this responsibility from LoanService - LoanService now publishes events instead of directly manipulating Book - BookRepository remains in LoanService only for atomic decrement on creation — this last coupling will be resolved in the Saga step
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10 files changed

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‎.env‎

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@@ -11,4 +11,5 @@ AWS_SECRET=criar-secret-key-na-aws
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BUCKET_NAME=library-api-s3
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BUCKET_REGION=sa-east-1
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14-
ZIPKIN_ENDPOINT=http://zipkin:9411/api/v2/spans
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ZIPKIN_ENDPOINT=http://zipkin:9411/api/v2/spans
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TRACING_SAMPLING_PROBABILITY=0.1 # 10% em prod — ajustável via env

‎.env.example‎

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@@ -11,4 +11,5 @@ AWS_SECRET=
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BUCKET_NAME=
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BUCKET_REGION=
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ZIPKIN_ENDPOINT=http://zipkin:9411/api/v2/spans
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ZIPKIN_ENDPOINT=http://zipkin:9411/api/v2/spans
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TRACING_SAMPLING_PROBABILITY=0.1 # 10% em prod — ajustável via env

‎src/main/java/com/example/library/book/BookEventListener.java‎

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@@ -0,0 +1,77 @@
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package com.example.library.book;
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import java.util.List;
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import org.slf4j.Logger;
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import org.slf4j.LoggerFactory;
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import org.springframework.context.event.EventListener;
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import org.springframework.stereotype.Component;
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import org.springframework.transaction.annotation.Transactional;
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import com.example.library.loan.event.LoanCanceledEvent;
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import com.example.library.loan.event.LoanReturnedEvent;
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import lombok.RequiredArgsConstructor;
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/**
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* Listener responsável por manter o estoque de cópias dos livros
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* em resposta a eventos do domínio Loan.
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*
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* Separação de responsabilidade:
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* - LoanService publica o evento e não sabe nada sobre Book
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* - BookEventListener reage ao evento e atualiza as cópias
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*
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* @EventListener é síncrono e transacional por padrão neste contexto:
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* o listener roda na mesma transação do publicador quando anotado
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* com @Transactional — garantindo atomicidade entre criar o empréstimo
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* e decrementar as cópias enquanto ainda somos monolito.
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*
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* Quando migrarmos para microservices, este listener será substituído
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* por um consumer Kafka/RabbitMQ sem mudança nos eventos.
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*/
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@Component
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@RequiredArgsConstructor
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public class BookEventListener {
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private static final Logger log = LoggerFactory.getLogger(BookEventListener.class);
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private final BookRepository bookRepository;
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/**
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* Restaura as cópias disponíveis quando um empréstimo é devolvido.
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*/
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@EventListener
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@Transactional
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public void onLoanReturned(LoanReturnedEvent event) {
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log.info("Restoring copies on loan return: loanId={}", event.loanId());
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List<Book> books = bookRepository.findAllById(event.bookQuantities().keySet());
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books.forEach(book -> {
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Integer qty = event.bookQuantities().get(book.getId());
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if (qty != null) {
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book.setAvailableCopies(book.getAvailableCopies() + qty);
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log.debug("Copies restored: bookId={} title={} qty={}", book.getId(), book.getTitle(), qty);
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}
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});
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}
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/**
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* Restaura as cópias disponíveis quando um empréstimo é cancelado.
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*/
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@EventListener
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@Transactional
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public void onLoanCanceled(LoanCanceledEvent event) {
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log.info("Restoring copies on loan cancel: loanId={}", event.loanId());
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List<Book> books = bookRepository.findAllById(event.bookQuantities().keySet());
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books.forEach(book -> {
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Integer qty = event.bookQuantities().get(book.getId());
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if (qty != null) {
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book.setAvailableCopies(book.getAvailableCopies() + qty);
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log.debug("Copies restored: bookId={} title={} qty={}", book.getId(), book.getTitle(), qty);
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}
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});
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}
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}

‎src/main/java/com/example/library/book/dto/BookSummary.java‎

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package com.example.library.book.dto;
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/**
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* Contrato mínimo que o domínio Book expõe para outros domínios.
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*
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* Anticorruption Layer (ACL) — outros domínios nunca dependem da
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* entidade Book diretamente, apenas deste contrato.
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*
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* Quando Book virar um microservice, este record será preenchido
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* via HTTP (BookClient) em vez de consulta direta ao repositório,
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* sem nenhuma mudança nos consumidores.
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*/
13+
public record BookSummary(
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Long id,
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String title,
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Integer availableCopies
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) {}

‎src/main/java/com/example/library/loan/LoanService.java‎

Lines changed: 47 additions & 14 deletions
Original file line numberDiff line numberDiff line change
@@ -2,9 +2,12 @@
22

33
import java.time.LocalDate;
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import java.util.List;
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import java.util.Map;
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import java.util.stream.Collectors;
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import org.slf4j.Logger;
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import org.slf4j.LoggerFactory;
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import org.springframework.context.ApplicationEventPublisher;
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import org.springframework.security.core.Authentication;
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import org.springframework.security.core.context.SecurityContextHolder;
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import org.springframework.stereotype.Service;
@@ -15,6 +18,9 @@
1518
import com.example.library.book.exception.BookNotFoundException;
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import com.example.library.loan.dto.LoanCreateDTO;
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import com.example.library.loan.dto.LoanResponseDTO;
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import com.example.library.loan.event.LoanCanceledEvent;
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import com.example.library.loan.event.LoanCreatedEvent;
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import com.example.library.loan.event.LoanReturnedEvent;
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import com.example.library.loan.exception.BookNotAvailableException;
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import com.example.library.loan.exception.LoanAlreadyReturnedException;
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import com.example.library.loan.exception.LoanNotFoundException;
@@ -33,9 +39,10 @@ public class LoanService {
3339
private static final Logger log = LoggerFactory.getLogger(LoanService.class);
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private final LoanRepository loanRepository;
36-
private final BookRepository bookRepository;
42+
private final BookRepository bookRepository; // usado apenas para verificação e decrement atômico na criação
3743
private final UserRepository userRepository;
3844
private final LoanMapper mapper;
45+
private final ApplicationEventPublisher eventPublisher;
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// ─────────────────────────────────────────────
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// CRIAR EMPRÉSTIMO
@@ -46,8 +53,10 @@ public LoanResponseDTO create(LoanCreateDTO dto) {
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4754
User user = getAuthenticatedUser();
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56+
// Valida existência de todos os livros antes de iniciar
4957
for (Long bookId : dto.booksId()) {
50-
bookRepository.findById(bookId).orElseThrow(() -> new BookNotFoundException(bookId));
58+
bookRepository.findById(bookId)
59+
.orElseThrow(() -> new BookNotFoundException(bookId));
5160
}
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5362
log.info("Creating loan for user={} books={}", user.getEmail(), dto.booksId());
@@ -75,11 +84,17 @@ public LoanResponseDTO create(LoanCreateDTO dto) {
7584
item.setQuantity(1);
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loan.getItems().add(item);
78-
7987
log.debug("Book added to loan: bookId={} title={}", bookId, book.getTitle());
8088
}
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8290
Loan saved = loanRepository.save(loan);
91+
92+
// Publica evento — outros domínios podem reagir sem acoplamento direto
93+
eventPublisher.publishEvent(new LoanCreatedEvent(
94+
saved.getId(),
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user.getId(),
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dto.booksId()
97+
));
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8499
log.info("Loan created: loanId={} user={} books={}",
85100
saved.getId(), user.getEmail(), dto.booksId().size());
@@ -111,12 +126,15 @@ public LoanResponseDTO returnLoan(Long loanId) {
111126
loan.setReturnDate(LocalDate.now());
112127
loan.setStatus(LoanStatus.RETURNED);
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114-
// Devolve as cópias — dirty checking cuida do save dentro do @Transactional
115-
loan.getItems().forEach(item -> {
116-
Book book = item.getBook();
117-
book.setAvailableCopies(book.getAvailableCopies() + item.getQuantity());
118-
log.debug("Copies restored: bookId={} title={}", book.getId(), book.getTitle());
119-
});
129+
// Monta o mapa bookId → quantidade antes de publicar o evento
130+
Map<Long, Integer> bookQuantities = buildBookQuantities(loan);
131+
132+
// Publica evento — BookEventListener restaura as cópias
133+
eventPublisher.publishEvent(new LoanReturnedEvent(
134+
loan.getId(),
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user.getId(),
136+
bookQuantities
137+
));
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121139
log.info("Loan returned: loanId={} user={}", loanId, user.getEmail());
122140

@@ -141,11 +159,14 @@ public LoanResponseDTO cancelLoan(Long loanId) {
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142160
loan.setStatus(LoanStatus.CANCELED);
143161

144-
// Devolve as cópias ao cancelar
145-
loan.getItems().forEach(item -> {
146-
Book book = item.getBook();
147-
book.setAvailableCopies(book.getAvailableCopies() + item.getQuantity());
148-
});
162+
Map<Long, Integer> bookQuantities = buildBookQuantities(loan);
163+
164+
// Publica evento — BookEventListener restaura as cópias
165+
eventPublisher.publishEvent(new LoanCanceledEvent(
166+
loan.getId(),
167+
user.getId(),
168+
bookQuantities
169+
));
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150171
log.info("Loan canceled: loanId={} user={}", loanId, user.getEmail());
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@@ -218,6 +239,18 @@ public List<LoanResponseDTO> findAll() {
218239
// HELPERS PRIVADOS
219240
// ─────────────────────────────────────────────
220241

242+
/**
243+
* Monta mapa bookId → quantidade a partir dos itens do empréstimo.
244+
* Usado para popular os eventos de devolução e cancelamento.
245+
*/
246+
private Map<Long, Integer> buildBookQuantities(Loan loan) {
247+
return loan.getItems().stream()
248+
.collect(Collectors.toMap(
249+
item -> item.getBook().getId(),
250+
LoanItem::getQuantity
251+
));
252+
}
253+
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/**
222255
* Busca um empréstimo pelo ID com itens e usuário já carregados via JOIN FETCH.
223256
* Garante que o mapper acessa as coleções LAZY dentro da transação ativa.

‎src/main/java/com/example/library/loan/event/LoanCanceledEvent.java‎

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package com.example.library.loan.event;
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import java.util.Map;
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/**
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* Evento publicado quando um empréstimo é cancelado.
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*
8+
* Idêntico ao LoanReturnedEvent em estrutura — separado semanticamente
9+
* pois o comportamento futuro pode divergir (ex: notificações diferentes,
10+
* métricas separadas, regras de negócio distintas).
11+
*/
12+
public record LoanCanceledEvent(
13+
Long loanId,
14+
Long userId,
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Map<Long, Integer> bookQuantities // bookId → quantidade a restaurar
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) {}

‎src/main/java/com/example/library/loan/event/LoanCreatedEvent.java‎

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package com.example.library.loan.event;
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import java.util.Set;
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/**
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* Evento publicado quando um novo empréstimo é criado com sucesso.
7+
*
8+
* Carrega apenas os IDs necessários — sem referências a entidades JPA.
9+
* Isso garante que o evento seja serializável quando migrarmos para
10+
* mensageria (Kafka/RabbitMQ) sem nenhuma mudança no contrato.
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*/
12+
public record LoanCreatedEvent(
13+
Long loanId,
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Long userId,
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Set<Long> bookIds
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) {}

‎src/main/java/com/example/library/loan/event/LoanReturnedEvent.java‎

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package com.example.library.loan.event;
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import java.util.Map;
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/**
6+
* Evento publicado quando um empréstimo é devolvido.
7+
*
8+
* Carrega um mapa de bookId → quantidade devolvida, permitindo que
9+
* o Book domain restaure as cópias disponíveis de forma precisa.
10+
*/
11+
public record LoanReturnedEvent(
12+
Long loanId,
13+
Long userId,
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Map<Long, Integer> bookQuantities // bookId → quantidade a restaurar
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) {}

‎src/main/java/com/example/library/user/dto/UserSummary.java‎

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package com.example.library.user.dto;
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/**
4+
* Contrato mínimo que o domínio User expõe para outros domínios.
5+
*
6+
* Anticorruption Layer (ACL) — outros domínios nunca dependem da
7+
* entidade User diretamente, apenas deste contrato.
8+
*
9+
* Quando User/Auth virar um microservice, este record será preenchido
10+
* via claims do JWT ou via HTTP (UserClient), sem mudança nos consumidores.
11+
*/
12+
public record UserSummary(
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Long id,
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String name,
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String email
16+
) {}

‎src/test/java/com/example/library/services/LoanServiceTest.java‎

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1414
import org.mockito.InjectMocks;
1515
import org.mockito.Mock;
1616
import org.mockito.junit.jupiter.MockitoExtension;
17+
import org.springframework.context.ApplicationEventPublisher;
1718
import org.springframework.security.authentication.UsernamePasswordAuthenticationToken;
1819
import org.springframework.security.core.Authentication;
1920
import org.springframework.security.core.context.SecurityContext;
@@ -65,6 +66,9 @@ class LoanServiceTest {
6566

6667
@Mock
6768
private SecurityContext securityContext;
69+
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@Mock
71+
private ApplicationEventPublisher eventPublisher;
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6973
@InjectMocks
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private LoanService loanService;

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