《Java 消息中间件·事件驱动架构》13.1 libraryd 领域模型

final class LoanId {
    private final String value;
    LoanId(String value) {
        if (value == null || value.isEmpty()) throw new IllegalArgumentException("loanId required");
        this.value = value;
    }
    public String value() { return value; }
    @Override public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof LoanId)) return false;
        return value.equals(((LoanId) o).value);
    }
    @Override public int hashCode() { return value.hashCode(); }
    @Override public String toString() { return "LoanId[" + value + "]"; }
}

final class LoanPeriod {
    private final int days;
    LoanPeriod(int days) {
        if (days < 1 || days > 365) throw new IllegalArgumentException("days must be 1-365");
        this.days = days;
    }
    public Instant dueFrom(Instant start) { return start.plus(days, ChronoUnit.DAYS); }
}

class Book {
    private final ISBN isbn;
    private String title;
    private BookStatus status;
    enum BookStatus { AVAILABLE, BORROWED, RESERVED, LOST }

    Book(ISBN isbn, String title) {
        this.isbn = isbn; this.title = title; this.status = BookStatus.AVAILABLE;
    }

    void markBorrowed() {
        if (status != BookStatus.AVAILABLE) {
            throw new IllegalStateException("Book not available: " + status);
        }
        this.status = BookStatus.BORROWED;
    }

    void markReturned() {
        if (status != BookStatus.BORROWED) {
            throw new IllegalStateException("Book not borrowed: " + status);
        }
        this.status = BookStatus.AVAILABLE;
    }
}

public List<LoanId> activeLoans() {
    return Collections.unmodifiableList(activeLoans);
}

public boolean canBorrow() {
    return activeLoans.size() < maxLoans;
}

class Loan {
    private final LoanId loanId;
    private final ISBN bookIsbn;
    private final MemberId memberId;
    private final Instant borrowedAt;
    private Instant dueAt;
    private Instant returnedAt;
    private LoanStatus status;
    private int version;
    private int renewalCount;

    enum LoanStatus { ACTIVE, RETURNED, OVERDUE, LOST }

    Loan(LoanId loanId, ISBN bookIsbn, MemberId memberId,
         Instant borrowedAt, LoanPeriod period) {
        this.loanId = loanId;
        this.bookIsbn = bookIsbn;
        this.memberId = memberId;
        this.borrowedAt = borrowedAt;
        this.dueAt = period.dueFrom(borrowedAt);
        this.status = LoanStatus.ACTIVE;
        this.version = 1;
        this.renewalCount = 0;
    }

    void renew(LoanPeriod extension) {
        if (status != LoanStatus.ACTIVE) {
            throw new IllegalStateException("Cannot renew " + status + " loan");
        }
        if (renewalCount >= 3) {
            throw new IllegalStateException("Max renewals (3) reached");
        }
        this.dueAt = extension.dueFrom(dueAt);
        this.renewalCount++;
        this.version++;
    }

    void returnBook(Instant returnedAt) {
        if (status != LoanStatus.ACTIVE && status != LoanStatus.OVERDUE) {
            throw new IllegalStateException("Cannot return " + status + " loan");
        }
        this.returnedAt = returnedAt;
        this.status = LoanStatus.RETURNED;
        this.version++;
    }

    void assertVersion(int expected) {
        if (version != expected) {
            throw new IllegalStateException(
                "Version mismatch: expected " + expected + ", actual " + version);
        }
    }
}

interface LoanRepository {
    void save(Loan loan);
    Loan findById(LoanId id);
    List<Loan> findByMember(MemberId memberId);
    List<Loan> findOverdue(Instant before);
}

javac LibrarydDomainModel.java
java LibrarydDomainModel

=== libraryd 领域模型验证 ===

1. 值对象不可变性验证
   ISBN[9780134685991]
   MemberId[M-1001]
   LoanPeriod: 14 days

2. 实体创建
   Book[isbn=ISBN[9780134685991], title=Effective Java, 3rd Edition, status=AVAILABLE]
   Member[id=MemberId[M-1001], name=张三, active=0/5]
   Can borrow: true

3. 聚合根：借阅生命周期
   创建: Loan[LoanId[L-2026-0001], book=ISBN[9780134685991], member=MemberId[M-1001], status=ACTIVE, due=2026-11-12T08:39:00Z, v=1, renewals=0]
   续借: Loan[LoanId[L-2026-0001], ... status=ACTIVE, due=2026-11-26T08:39:00Z, v=2, renewals=1]
   超限拒绝: Max renewals (3) reached

4. 归还流程
   归还后: Loan[LoanId[L-2026-0001], ... status=RETURNED, v=5, renewals=3]

5. 乐观并发控制
   版本冲突: Version mismatch: expected 2, actual 1

6. 逾期检测
   到期前逾期? true
   标记后状态: OVERDUE

7. ISBN 校验
   非法ISBN拒绝: Invalid ISBN: invalid

8. 仓储查询
   按ID查询: Loan[...]
   按会员查询: 2 笔
   逾期笔数: 0 笔

9. 值对象相等性
   isbn.equals(isbn2): true
   same hash: true

=== 全部验证通过 ===