add the code

library/model/Book.java

@@ -0,0 +1,62 @@
+package com.library.model;
+
+/**
+ * Book实体类
+ */
+public class Book {
+    private String isbn;
+    private String title;
+    private String author;
+    private boolean available;
+
+    public Book(String isbn, String title, String author) {
+        this.isbn = isbn;
+        this.title = title;
+        this.author = author;
+        this.available = true;
+    }
+
+    // Getters and Setters
+    public String getIsbn() {
+        return isbn;
+    }
+
+    public void setIsbn(String isbn) {
+        this.isbn = isbn;
+    }
+
+    public String getTitle() {
+        return title;
+    }
+
+    public void setTitle(String title) {
+        this.title = title;
+    }
+
+    public String getAuthor() {
+        return author;
+    }
+
+    public void setAuthor(String author) {
+        this.author = author;
+    }
+
+    public boolean isAvailable() {
+        return available;
+    }
+
+    public void setAvailable(boolean available) {
+        this.available = available;
+    }
+
+    @Override
+    public String toString() {
+        return "Book{" +
+                "isbn='" + isbn + '\'' +
+                ", title='" + title + '\'' +
+                ", author='" + author + '\'' +
+                ", available=" + available +
+                '}';
+    }
+}
+

library/model/Member.java

@@ -0,0 +1,68 @@
+package com.library.model;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Member实体类
+ */
+public class Member {
+    private String memberId;
+    private String name;
+    private String email;
+    private List<Book> borrowedBooks;
+
+    public Member(String memberId, String name, String email) {
+        this.memberId = memberId;
+        this.name = name;
+        this.email = email;
+        this.borrowedBooks = new ArrayList<>();
+    }
+
+    // Getters and Setters
+    public String getMemberId() {
+        return memberId;
+    }
+
+    public void setMemberId(String memberId) {
+        this.memberId = memberId;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public String getEmail() {
+        return email;
+    }
+
+    public void setEmail(String email) {
+        this.email = email;
+    }
+
+    public List<Book> getBorrowedBooks() {
+        return new ArrayList<>(borrowedBooks);
+    }
+
+    public void addBorrowedBook(Book book) {
+        this.borrowedBooks.add(book);
+    }
+
+    public void removeBorrowedBook(Book book) {
+        this.borrowedBooks.remove(book);
+    }
+
+    @Override
+    public String toString() {
+        return "Member{" +
+                "memberId='" + memberId + '\'' +
+                ", name='" + name + '\'' +
+                ", email='" + email + '\'' +
+                '}';
+    }
+}
+

library/repository/BookRepository.java

@@ -0,0 +1,18 @@
+package com.library.repository;
+
+import com.library.model.Book;
+
+import java.util.List;
+import java.util.Optional;
+
+/**
+ * 书籍仓储接口 - 遵循Dependency Inversion Principle
+ */
+public interface BookRepository {
+    void save(Book book);
+    Optional<Book> findByIsbn(String isbn);
+    List<Book> findAll();
+    List<Book> findByAuthor(String author);
+    void delete(Book book);
+}
+

library/repository/InMemoryBookRepository.java

@@ -0,0 +1,45 @@
+package com.library.repository;
+
+import com.library.model.Book;
+
+import java.util.*;
+import java.util.stream.Collectors;
+
+/**
+ * 内存中的书籍仓储实现
+ */
+public class InMemoryBookRepository implements BookRepository {
+    private Map<String, Book> books;
+
+    public InMemoryBookRepository() {
+        this.books = new HashMap<>();
+    }
+
+    @Override
+    public void save(Book book) {
+        books.put(book.getIsbn(), book);
+    }
+
+    @Override
+    public Optional<Book> findByIsbn(String isbn) {
+        return Optional.ofNullable(books.get(isbn));
+    }
+
+    @Override
+    public List<Book> findAll() {
+        return new ArrayList<>(books.values());
+    }
+
+    @Override
+    public List<Book> findByAuthor(String author) {
+        return books.values().stream()
+                .filter(book -> book.getAuthor().equals(author))
+                .collect(Collectors.toList());
+    }
+
+    @Override
+    public void delete(Book book) {
+        books.remove(book.getIsbn());
+    }
+}
+

library/repository/InMemoryMemberRepository.java

@@ -0,0 +1,37 @@
+package com.library.repository;
+
+import com.library.model.Member;
+
+import java.util.*;
+
+/**
+ * 内存中的会员仓储实现
+ */
+public class InMemoryMemberRepository implements MemberRepository {
+    private Map<String, Member> members;
+
+    public InMemoryMemberRepository() {
+        this.members = new HashMap<>();
+    }
+
+    @Override
+    public void save(Member member) {
+        members.put(member.getMemberId(), member);
+    }
+
+    @Override
+    public Optional<Member> findByMemberId(String memberId) {
+        return Optional.ofNullable(members.get(memberId));
+    }
+
+    @Override
+    public List<Member> findAll() {
+        return new ArrayList<>(members.values());
+    }
+
+    @Override
+    public void delete(Member member) {
+        members.remove(member.getMemberId());
+    }
+}
+

library/repository/MemberRepository.java

@@ -0,0 +1,17 @@
+package com.library.repository;
+
+import com.library.model.Member;
+
+import java.util.List;
+import java.util.Optional;
+
+/**
+ * 会员仓储接口
+ */
+public interface MemberRepository {
+    void save(Member member);
+    Optional<Member> findByMemberId(String memberId);
+    List<Member> findAll();
+    void delete(Member member);
+}
+

library/service/EmailNotificationService.java

@@ -0,0 +1,14 @@
+package com.library.service;
+
+/**
+ * 邮件通知服务实现
+ */
+public class EmailNotificationService implements NotificationService {
+    @Override
+    public void sendEmail(String to, String subject, String message) {
+        System.out.println("Sending email to: " + to);
+        System.out.println("Subject: " + subject);
+        System.out.println("Message: " + message);
+    }
+}
+

library/service/EmailReminderService.java

@@ -0,0 +1,30 @@
+package com.library.service;
+
+import com.library.model.Member;
+import com.library.repository.MemberRepository;
+
+/**
+ * 到期提醒服务 - 遵循Single Responsibility Principle
+ */
+public class EmailReminderService {
+    private MemberRepository memberRepository;
+    private NotificationService notificationService;
+
+    public EmailReminderService(MemberRepository memberRepository, NotificationService notificationService) {
+        this.memberRepository = memberRepository;
+        this.notificationService = notificationService;
+    }
+
+    public void sendDueReminder(String memberId) {
+        var memberOpt = memberRepository.findByMemberId(memberId);
+        if (memberOpt.isPresent()) {
+            Member member = memberOpt.get();
+            notificationService.sendEmail(
+                    member.getEmail(),
+                    "Book Due Reminder",
+                    "Dear " + member.getName() + ", please return your borrowed books."
+            );
+        }
+    }
+}
+

library/service/LibraryService.java

@@ -0,0 +1,79 @@
+package com.library.service;
+
+import com.library.model.Book;
+import com.library.model.Member;
+import com.library.repository.BookRepository;
+import com.library.repository.MemberRepository;
+
+import java.util.List;
+import java.util.Optional;
+
+/**
+ * 图书馆服务类 - 遵循Single Responsibility Principle
+ * 只负责图书借还业务逻辑
+ */
+public class LibraryService {
+    private BookRepository bookRepository;
+    private MemberRepository memberRepository;
+
+    public LibraryService(BookRepository bookRepository, MemberRepository memberRepository) {
+        this.bookRepository = bookRepository;
+        this.memberRepository = memberRepository;
+    }
+
+    public boolean borrowBook(String memberId, String isbn) {
+        Optional<Member> memberOpt = memberRepository.findByMemberId(memberId);
+        Optional<Book> bookOpt = bookRepository.findByIsbn(isbn);
+
+        if (memberOpt.isEmpty() || bookOpt.isEmpty()) {
+            return false;
+        }
+
+        Book book = bookOpt.get();
+        if (!book.isAvailable()) {
+            return false;
+        }
+
+        Member member = memberOpt.get();
+        book.setAvailable(false);
+        member.addBorrowedBook(book);
+        bookRepository.save(book);
+        memberRepository.save(member);
+
+        return true;
+    }
+
+    public boolean returnBook(String memberId, String isbn) {
+        Optional<Member> memberOpt = memberRepository.findByMemberId(memberId);
+        Optional<Book> bookOpt = bookRepository.findByIsbn(isbn);
+
+        if (memberOpt.isEmpty() || bookOpt.isEmpty()) {
+            return false;
+        }
+
+        Member member = memberOpt.get();
+        Book book = bookOpt.get();
+
+        if (!member.getBorrowedBooks().contains(book)) {
+            return false;
+        }
+
+        book.setAvailable(true);
+        member.removeBorrowedBook(book);
+        bookRepository.save(book);
+        memberRepository.save(member);
+
+        return true;
+    }
+
+    public List<Book> getAvailableBooks() {
+        return bookRepository.findAll().stream()
+                .filter(Book::isAvailable)
+                .toList();
+    }
+
+    public List<Book> searchBooksByAuthor(String author) {
+        return bookRepository.findByAuthor(author);
+    }
+}
+

library/service/NotificationService.java

@@ -0,0 +1,9 @@
+package com.library.service;
+
+/**
+ * 通知服务接口 - 遵循Interface Segregation Principle
+ */
+public interface NotificationService {
+    void sendEmail(String to, String subject, String message);
+}
+