Java реализация интерфейса в клиенте

Question

Привет, я пытаюсь сделать книжный магазин простым приложением из книги Vishal Layka Learn Java для веб-разработки. У меня проблема в клиенте уровня доступа к данным BookAPP. java, который должен использовать интерфейс BookDAO. Я включил коды BookAPP, BookDAO, BookDAOImpl.

Ошибки: метод «невозможно создать» c метод «ссылка на не-статус» c из типа bookDAO Список книг = BookDAO.findAllBooks (); Список книг = BookDAO.searchBooksByKeyWord (keyWord);

package com.apress.books.client;
import java.util.List;


import com.apress.books.dao.BookDAO;
import com.apress.books.dao.BookDAOImpl;
import com.apress.books.model.Book;



public class BookApp {
    private static BookDAO bookDao = new BookDAOImpl();

    public static void main(String[] args) {

        // Show list of all books 
        System.err.println("List of all books: ");
        findAllBooks();
        System.out.println();

        //Seach books by keyword
        System.out.println("Search books with keyword 'Groovy' in title: ");

        searchBooks("Groovy");
        System.out.println();

        System.err.println("Searching books with keyword 'Josh' for author name: ");
        searchBooks("Josh");

    }

    private static void findAllBooks() {
        List<Book> books = BookDAO.findAllBooks();
        for (Book book : books) {
            System.out.println(book);
        }
    }

    private static void searchBooks(String keyWord) {
        List<Book> books = BookDAO.searchBooksByKeyWord(keyWord);
        for (Book book : books) {
            System.out.println(book);
        }
    }   
}

BookDAO. java интерфейс

package com.apress.books.dao;

import java.util.List;

import com.apress.books.model.Book;
import com.apress.books.model.Category;

public interface BookDAO {

    public List<Book>findAllBooks();

    public List<Book>searchBooksByKeyWord(String keyWord);

    public List<Category>findAllCategories();

    public void insert(Book book);

    public void update(Book book);

    public void delete(Book bookId);
}

BookDAOImpl

package com.apress.books.dao;


import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;

import com.apress.books.model.Author;
import com.apress.books.model.Book;
import com.apress.books.model.Category;

// Uwaga w książce Brak Insert Update Delete

public class BookDAOImpl implements BookDAO {

    static {

        try {
            Class.forName("com.mysql.jdbc.Driver");
        }
        catch (ClassNotFoundException ex){}
    }

    private Connection getConnection() throws SQLException {
        return DriverManager.getConnection("jdbc:mysql://localhost:3306/książki", "root", "admin");

    }

    private void closeConnection(Connection connection) {

        if (connection == null)
            return;
        try {
            connection.close();
        }catch (SQLException ex) {      
        }       
    }


    public List<Book>findAllBooks() {
        List<Book> result = new ArrayList<>();
        List<Author> authorList = new ArrayList<>();

        String sql = "select * from książki inner join autor on książka.id = autor.id_książki";

        Connection connection = null;   

    try {
        connection = getConnection();
        PreparedStatement statement = connection.prepareStatement(sql);
        ResultSet resultSet = statement.executeQuery();
        while (resultSet.next()) {
            Book book = new Book();
            Author author = new Author();
            book.setId(resultSet.getLong("id"));
            book.setBookTitle(resultSet.getString("tytuł_książki"));
            book.setCategoryId(resultSet.getLong("ID_KATEGORII"));
            author.setBookId(resultSet.getLong("ID_KSIĄŻKI"));
            author.setFirstName(resultSet.getString("imię"));
            author.setLastName(resultSet.getString("nazwisko"));
            authorList.add(author);
            book.setAuthors(authorList);
            book.setPublisherName(resultSet.getString("wydawca"));
            result.add(book);       
        }   
    } catch (SQLException ex) {
        ex.printStackTrace();
    } finally {
        closeConnection(connection);
    }
    return result;

    }



    public List<Book>searchBooksByKeyWord(String keyWord)  {
        List<Book> result = new ArrayList<>();
        List<Author> authorList = new ArrayList<>();

        String sql = "select * from książka inner join author on książka.id = autor.id_książki"
                + " where tutył_książki like '%"
                + keyWord.trim()
                + "%'"
                + " or imię like '%"
                + keyWord.trim()
                + "%'"
                + " or nazwisko like '%" + keyWord.trim() + "%'";

        Connection connection = null;

        try {
            connection = getConnection();
            PreparedStatement statement = connection.prepareStatement(sql);
            ResultSet resultSet = statement.executeQuery();
            while (resultSet.next()) {
                Book book = new Book();
                Author author = new Author();

                book.setId(resultSet.getLong("id"));
                book.setBookTitle(resultSet.getString("tytuł_książki"));
                book.setPublisherName(resultSet.getString("wydawca"));

                author.setFirstName(resultSet.getString("imię"));
                author.setLastName(resultSet.getString("nazwisko"));
                author.setBookId(resultSet.getLong("ID_KSIĄŻKI"));
                authorList.add(author);
                book.setAuthors(authorList);
                result.add(book);       
            }   
        } catch (SQLException ex) {
            ex.printStackTrace();
        } finally {
            closeConnection(connection);
        }
        return result;

        }


    public List<Category> findAllCategories() {
        List<Category> result = new ArrayList<>();
        String sql = "select * from category";

        Connection connection = null;

        try {
            connection = getConnection();
            PreparedStatement statement = connection.prepareStatement(sql);
            ResultSet resultSet = statement.executeQuery();
            while (resultSet.next()) {
                Category category = new Category();

                category.setId(resultSet.getLong("id"));
                category.setCategoryDescription(resultSet.getString("opis_kategorii"));
                result.add(category);
            }   
        } catch (SQLException ex) {
            ex.printStackTrace();
        } finally {
            closeConnection(connection);
        }
        return result;

        }


    public void insert(Book book) {
    }

    public void update(Book book) {
    }

    public void delete(Book book) {
    }


    }

Answer 1

Методы

findAllBooks() и searchBooksByKeyWord() не являются статичными c, поэтому вам необходимо создать экземпляр для их использования.

BookDAO - это интерфейс с абстрактными методами, не имеющими реализации. BookDAOImpl имеет свои реализации. Он уже присутствует в вашем коде: BookDAO bookDao = new BookDAOImpl();

Так что это должно быть bookDAO вместо BookDAO:

List<Book> books = bookDAO.findAllBooks();
List<Book> books = bookDAO.searchBooksByKeyWord(keyWord);

Answer 2

Поскольку вы используете Spring, вам придется автоматически подключать класс DAO

public class BookApp {
@Autowire
private BookDAO bookDAO;

//now you can call methods
List<Book> books = bookDAO.findAllBooks();