2、 模仿SystemUserDAO类，实现BookDAO类，并改造BookManager类，使之通过BookDAO操作数据库。 【实验结果与分析】 A、 给出BookDAO类代码。 B、 给出改造后BookManager类的各个方法的代码。

好的，针对你的问题，我可以提供以下解决方案：

A、BookDAO类代码

public class BookDAO {
    private Connection conn;

    public BookDAO(Connection conn) {
        this.conn = conn;
    }

    public List<Book> getAllBooks() throws SQLException {
        List<Book> books = new ArrayList<>();
        String sql = "SELECT * FROM book";
        try (PreparedStatement pstmt = conn.prepareStatement(sql)) {
            try (ResultSet rs = pstmt.executeQuery()) {
                while (rs.next()) {
                    Book book = new Book(rs.getString("barcode"), rs.getString("book_name"), rs.getString("author"), rs.getString("publisher"));
                    books.add(book);
                }
            }
        }
        return books;
    }

    public Book getBookByBarcode(String barcode) throws SQLException {
        String sql = "SELECT * FROM book WHERE barcode = ?";
        try (PreparedStatement pstmt = conn.prepareStatement(sql)) {
            pstmt.setString(1, barcode);
            try (ResultSet rs = pstmt.executeQuery()) {
                if (rs.next()) {
                    Book book = new Book(rs.getString("barcode"), rs.getString("book_name"), rs.getString("author"), rs.getString("publisher"));
                    return book;
                } else {
                    return null;
                }
            }
        }
    }

    public boolean addBook(Book book) throws SQLException {
        String sql = "INSERT INTO book(barcode, book_name, author, publisher) VALUES(?, ?, ?, ?)";
        try (PreparedStatement pstmt = conn.prepareStatement(sql)) {
            pstmt.setString(1, book.getBarcode());
            pstmt.setString(2, book.getBookName());
            pstmt.setString(3, book.getAuthor());
            pstmt.setString(4, book.getPublisher());
            int count = pstmt.executeUpdate();
            return count > 0;
        }
    }

    public boolean deleteBook(String barcode) throws SQLException {
        String sql = "DELETE FROM book WHERE barcode = ?";
        try (PreparedStatement pstmt = conn.prepareStatement(sql)) {
            pstmt.setString(1, barcode);
            int count = pstmt.executeUpdate();
            return count > 0;
        }
    }

    public boolean updateBook(Book book) throws SQLException {
        String sql = "UPDATE book SET book_name = ?, author = ?, publisher = ? WHERE barcode = ?";
        try (PreparedStatement pstmt = conn.prepareStatement(sql)) {
            pstmt.setString(1, book.getBookName());
            pstmt.setString(2, book.getAuthor());
            pstmt.setString(3, book.getPublisher());
            pstmt.setString(4, book.getBarcode());
            int count = pstmt.executeUpdate();
            return count > 0;
        }
    }
}

B、改造后BookManager类的各个方法的代码

public class BookManager {
    private BookDAO bookDAO;

    public BookManager(BookDAO bookDAO) {
        this.bookDAO = bookDAO;
    }

    public List<Book> getAllBooks() {
        try {
            return bookDAO.getAllBooks();
        } catch (SQLException e) {
            e.printStackTrace();
            return null;
        }
    }

    public Book getBookByBarcode(String barcode) {
        try {
            return bookDAO.getBookByBarcode(barcode);
        } catch (SQLException e) {
            e.printStackTrace();
            return null;
        }
    }

    public boolean addBook(Book book) {
        try {
            return bookDAO.addBook(book);
        } catch (SQLException e) {
            e.printStackTrace();
            return false;
        }
    }

    public boolean deleteBook(String barcode) {
        try {
            return bookDAO.deleteBook(barcode);
        } catch (SQLException e) {
            e.printStackTrace();
            return false;
        }
    }

    public boolean updateBook(Book book) {
        try {
            return bookDAO.updateBook(book);
        } catch (SQLException e) {
            e.printStackTrace();
            return false;
        }
    }
}

以上是模仿SystemUserDAO类，实现BookDAO类，并改造BookManager类，使之通过BookDAO操作数据库的解决方案。其中，BookDAO类用于对图书信息的增删改查操作，BookManager类用于调用BookDAO类中的方法以实现对图书信息的管理。需要注意的是，以上代码仅供参考，具体实现需要根据实际情况进行调整。