綜合實戰——圖書管理系統

package library.model;

import java.util.Objects;

/** 書籍：ISBN 為唯一識別；基本資料不可變，只有借閱狀態會變動 */ public class Book

private final String isbn; // 唯一識別，永不改變 private final String title; // 書名 private final String author; // 作者 private boolean available = true; // 新書進館預設可借

public Book(String isbn, String title, String author) this.isbn = isbn; this.title = title; this.author = author;

public String getIsbn() return isbn;

public String getTitle() return title;

public String getAuthor() return author;

public boolean isAvailable() return available;

/** 出借與歸還都經由這裡改變狀態（唯一的寫入口） */ public void setAvailable(boolean available) this.available = available;

/** 邏輯相等：ISBN 相同即同一本書（第 1 章範本） */ @Override public boolean equals(Object obj) if (this == obj) return true; if (!(obj instanceof Book)) return false; return isbn.equals(((Book) obj).isbn);

@Override public int hashCode() return Objects.hash(isbn);

@Override public String toString() return "《" + title + "》（" + author + "）";

package library.model;

/** 會員：個人資料與借閱額度 */ public class Member

/** 借閱上限：每人同時最多 2 本（規則改這裡就好） */ public static final int MAX_LOANS = 2;

private final String id; // 會員編號 private final String name; // 姓名 private int activeLoans; // 目前借閱中的本數

public Member(String id, String name) this.id = id; this.name = name;

public String getId() return id;

public String getName() return name;

/** 是否還有借閱額度 */ public boolean canBorrow() return activeLoans < MAX_LOANS;

/** 借出一本：額度佔用加一 */ public void incrementLoans() activeLoans++;

/** 歸還一本：額度釋放，防呆不讓它變負數 */ public void decrementLoans() if (activeLoans > 0) activeLoans–;

package library.model;

import java.time.LocalDate; import java.time.temporal.ChronoUnit;

/** 借閱記錄：一次借書行為的完整生命週期 */ public class Loan

/** 借期規則：14 天 */ public static final int LOAN_DAYS = 14;

private final String isbn; // 借了哪本書 private final String memberId; // 誰借的 private final LocalDate borrowedOn; // 借出日 private final LocalDate dueOn; // 應還日 private LocalDate returnedOn; // 實際還書日（未還為 null）

public Loan(String isbn, String memberId, LocalDate borrowedOn) this.isbn = isbn; this.memberId = memberId; this.borrowedOn = borrowedOn; // 應還日由借出日推算：plusDays 回傳新物件 this.dueOn = borrowedOn.plusDays(LOAN_DAYS);

/** 尚未歸還的記錄才是「進行中」 */ public boolean isActive() return returnedOn == null;

/** 結案：記下還書日並回傳逾期天數（準時或提早為 0） */ public long close(LocalDate returnDate) this.returnedOn = returnDate; long overdue = ChronoUnit.DAYS.between(dueOn, returnDate); return Math.max(0, overdue); // 提早還書不是負逾期

public String getIsbn() return isbn;

public String getMemberId() return memberId;

public LocalDate getDueOn() return dueOn;

package library.exception;

/** 領域例外基底：checked，強迫呼叫端面對可預期的營運狀況 */ public class LibraryException extends Exception

public LibraryException(String message) super(message);

/** 例外鏈版本：包裝底層例外（如 IOException）時使用 */ public LibraryException(String message, Throwable cause) super(message, cause);

package library.exception;

/** 規則：已被借走的書不能再借 */ public class BookNotAvailableException extends LibraryException

public BookNotAvailableException(String title) super("《" + title + "》目前出借中，請改借其他書");

package library.exception;

/** 規則：借書者必須是已註冊的會員 */ public class MemberNotFoundException extends LibraryException

public MemberNotFoundException(String memberId) super("查無會員，編號：" + memberId);

package library.exception;

/** 規則：會員同時借閱的數量有上限 */ public class LoanLimitExceededException extends LibraryException

public LoanLimitExceededException(String name, int max) super("會員 " + name + " 已達借閱上限（" + max + " 本），請先還書");

package library.repository;

import java.util.Collection;

import library.model.Book; import library.model.Member;

/** 儲存層合約：底層用記憶體、檔案還是資料庫，實作自己決定 */ public interface LibraryRepository

void addBook(Book book);

/** 依 ISBN 查書；找不到回傳 null（由服務層轉成例外） */ Book findBook(String isbn);

Collection<Book> allBooks();

void addMember(Member member);

/** 依編號查會員；找不到回傳 null */ Member findMember(String memberId);

package library.repository;

import java.util.Collection; import java.util.LinkedHashMap; import java.util.Map;

import library.model.Book; import library.model.Member;

/** 記憶體版儲存庫：LinkedHashMap 讓遍歷順序等於加入順序 */ public class InMemoryLibraryRepository implements LibraryRepository

private final Map<String, Book> books = new LinkedHashMap<>(); private final Map<String, Member> members = new LinkedHashMap<>();

@Override public void addBook(Book book) // 同 ISBN 再加入視為覆蓋（Map 的天然行為） books.put(book.getIsbn(), book);

@Override public Book findBook(String isbn) return books.get(isbn); // 查無此鍵回傳 null

@Override public Collection<Book> allBooks() return books.values();

@Override public void addMember(Member member) members.put(member.getId(), member);

@Override public Member findMember(String memberId) return members.get(memberId);

package library.repository;

import java.io.IOException; import java.nio.charset.StandardCharsets; import java.nio.file.Files; import java.nio.file.Path; import java.util.ArrayList; import java.util.List;

import library.exception.LibraryException; import library.model.Book;

/** 檔案版儲存庫：沿用記憶體版行為，追加文字檔存讀能力 */ public class FileLibraryRepository extends InMemoryLibraryRepository

private final Path file; // 存檔位置

public FileLibraryRepository(Path file) this.file = file;

/** 存檔：一本書一行，欄位以 | 分隔，回傳筆數 */ public int save() throws LibraryException List<String> lines = new ArrayList<>(); for (Book b : allBooks()) lines.add(b.getIsbn() + "|" + b.getTitle() + "|" + b.getAuthor() + "|" + b.isAvailable()); try Files.write(file, lines, StandardCharsets.UTF_8); catch (IOException e) // 例外鏈（第 3 章）：把底層 IO 例外包成領域例外 throw new LibraryException("存檔失敗：" + file, e); return lines.size();

/** 載入：檔案不存在視為第一次啟動，不算錯誤 */ public int load() throws LibraryException if (!Files.exists(file)) return 0; try List<String> lines = Files.readAllLines(file, StandardCharsets.UTF_8); for (String line : lines) // split 的參數是正規表示式，| 須跳脫成
| String[] cols = line.split("
|"); Book book = new Book(cols[0], cols[1], cols[2]); book.setAvailable(Boolean.parseBoolean(cols[3])); addBook(book); // 沿用父類別的加入邏輯 return lines.size(); catch (IOException e) throw new LibraryException("載入失敗：" + file, e);

package library.service;

import java.time.LocalDate; import java.util.ArrayList; import java.util.List;

import library.exception.BookNotAvailableException; import library.exception.LibraryException; import library.exception.LoanLimitExceededException; import library.exception.MemberNotFoundException; import library.model.Book; import library.model.Loan; import library.model.Member; import library.repository.LibraryRepository;

/** 服務層：借還書規則集中地；規則違反一律拋自訂例外 */ public class LibraryService

private final LibraryRepository repo; // 只認識介面 private final List<Loan> loans = new ArrayList<>();

/** 建構子注入：測試時可以塞進記憶體版儲存庫 */ public LibraryService(LibraryRepository repo) this.repo = repo;

/** 借書：四道檢查全過，才建立借閱記錄 */ public Loan borrowBook(String isbn, String memberId, LocalDate date) throws LibraryException

Book book = repo.findBook(isbn); if (book == null) throw new LibraryException("查無此書，ISBN：" + isbn); Member member = repo.findMember(memberId); if (member == null) throw new MemberNotFoundException(memberId); if (!book.isAvailable()) throw new BookNotAvailableException(book.getTitle()); if (!member.canBorrow()) throw new LoanLimitExceededException( member.getName(), Member.MAX_LOANS);

// 檢查全數通過，才真正改動狀態 book.setAvailable(false); member.incrementLoans(); Loan loan = new Loan(isbn, memberId, date); loans.add(loan); return loan;

/** 還書：結案借閱記錄，回傳逾期天數（0 表示準時） */ public long returnBook(String isbn, String memberId, LocalDate date) throws LibraryException

// 找「這位會員、這本書、進行中」的那筆記錄 Loan target = null; for (Loan loan : loans) if (loan.isActive() && loan.getIsbn().equals(isbn) && loan.getMemberId().equals(memberId)) target = loan; break; if (target == null) throw new LibraryException( "查無進行中的借閱記錄：" + memberId + " / " + isbn);

long overdueDays = target.close(date); repo.findBook(isbn).setAvailable(true); // 書變回可借 repo.findMember(memberId).decrementLoans(); // 額度釋放 return overdueDays;

package library.app;

import java.nio.file.Path; import java.time.LocalDate; import java.util.Scanner;

import library.exception.LibraryException; import library.model.Book; import library.model.Loan; import library.model.Member; import library.repository.FileLibraryRepository; import library.service.LibraryService;

/** 主控台進入點：只做三件事——讀輸入、呼叫 service、顯示結果 */ public class LibraryApp

// 教學用固定營業日，讓輸出可重現；實務改用 LocalDate.now() private static final LocalDate TODAY = LocalDate.of(2026, 8, 14);

private final Scanner scanner = new Scanner(System.in); private final FileLibraryRepository repo = new FileLibraryRepository(Path.of("books.txt")); private final LibraryService service = new LibraryService(repo);

public static void main(String[] args) LibraryApp app = new LibraryApp(); app.seedData(); app.run();

/** 種子資料：讓系統一啟動就有東西可操作 */ private void seedData() repo.addBook(new Book("978-1", "Java 核心技術", "王小凡")); repo.addBook(new Book("978-2", "演算法圖解", "林大同")); repo.addBook(new Book("978-3", "資料庫實戰", "陳美心")); repo.addMember(new Member("M001", "小明"));

/** 主迴圈：直到使用者選擇離開 */ private void run() System.out.println("=== 圖書管理系統（營業日 " + TODAY + "）==="); boolean running = true; while (running) printMenu(); String choice = scanner.nextLine().trim(); try switch (choice) case "1" -> addBook(); case "2" -> listBooks(); case "3" -> registerMember(); case "4" -> borrowBook(); case "5" -> returnBook(); case "6" -> saveData(); case "0" -> running = false; default -> System.out.println("無效選項，請重新輸入"); catch (LibraryException e) // 統一的錯誤出口：訊息友善，程式不中斷 System.out.println("[操作失敗] " + e.getMessage()); System.out.println("感謝使用，再見！");

private void printMenu() System.out.println(); System.out.println("[1]新增書籍 [2]書籍列表 [3]註冊會員 " + "[4]借書 [5]還書 [6]存檔 [0]離開"); System.out.print("請選擇：");

private void addBook() System.out.print("ISBN："); String isbn = scanner.nextLine().trim(); System.out.print("書名："); String title = scanner.nextLine().trim(); System.out.print("作者："); String author = scanner.nextLine().trim(); repo.addBook(new Book(isbn, title, author)); System.out.println("已新增《" + title + "》");

private void listBooks() System.out.println("— 書籍列表（共 " + repo.allBooks().size() + " 本）—"); for (Book b : repo.allBooks()) String state = b.isAvailable() ? "可借" : "出借中"; System.out.println("[" + state + "] " + b.getIsbn() + " " + b.getTitle() + "／" + b.getAuthor());

private void registerMember() System.out.print("會員編號："); String id = scanner.nextLine().trim(); System.out.print("姓名："); String name = scanner.nextLine().trim(); repo.addMember(new Member(id, name)); System.out.println("已註冊會員 " + name + "（" + id + "）");

private void borrowBook() throws LibraryException System.out.print("會員編號："); String memberId = scanner.nextLine().trim(); System.out.print("書籍 ISBN："); String isbn = scanner.nextLine().trim(); Loan loan = service.borrowBook(isbn, memberId, TODAY); System.out.println("借閱成功，應還日期：" + loan.getDueOn());

private void returnBook() throws LibraryException System.out.print("會員編號："); String memberId = scanner.nextLine().trim(); System.out.print("書籍 ISBN："); String isbn = scanner.nextLine().trim(); long overdue = service.returnBook(isbn, memberId, TODAY); if (overdue > 0) System.out.println("還書成功，逾期 " + overdue + " 天，請補繳逾期費"); else System.out.println("還書成功，未逾期");

private void saveData() throws LibraryException int count = repo.save(); System.out.println("書目已寫入 books.txt（共 " + count + " 筆）");