BooksDB.java

package com.springapp.mvc;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

public enum BooksDB {
    INSTANCE;

    private final ConcurrentMap<String, ArrayList<BookData>> books = new ConcurrentHashMap<String, ArrayList<BookData>>();
    private final Map<String, BookData> isbnToBook = new HashMap<String, BookData>();

    private volatile boolean initialized = false;

    public void initialize() {
        if (!initialized) {
            synchronized (INSTANCE) {
                if (!initialized) {
                    books.put("Thriller", getThrillerBooks());
                    books.put("Romance", getRomanceBooks());
                    books.put("Science Fiction", getScienceFictionBooks());
                    books.put("Drama", getDramaBooks());
                    books.put("Comedy", getComedyBooks());

                    initialized = true;
                }
            }
        }
    }

    public ArrayList<BookData> getBooks(String id) {
        return books.get(id);
    }

    public void loanBook(String isbn) throws Exception {
        BookData bookData = isbnToBook.get(isbn);
        if (bookData.isLoaned()) {
            throw new Exception("Error, book already loaned");
        }

        bookData.setLoaned(true);
    }

    private ArrayList<BookData> getThrillerBooks() {
        ArrayList<BookData> b = new ArrayList<BookData>();
        b.add(new BookData(new Book("The Da Vinci Code", "Dan Brown", "0307474275")));
        b.add(new BookData(new Book("Gone Girl", "Gillian Flynn", "030758836x")));
        b.add(new BookData(new Book("The Lost Symbol", "Dan Brown", "0307950689")));
        b.add(new BookData(new Book("Digital Fortress", "Dan Brown", "0312944926")));

        for (BookData bookData : b) {
            isbnToBook.put(bookData.getBook().getIsbn10(), bookData);
        }
        return b;
    }

    private ArrayList<BookData> getRomanceBooks() {
        ArrayList<BookData> b = new ArrayList<BookData>();
        b.add(new BookData(new Book("Twilight", "Stephenie Meyer", "0316015849")));
        b.add(new BookData(new Book("Pride and Prejudice", "Jane Austen", "0486284735")));
        b.add(new BookData(new Book("Fifty Shades of Grey", "E.L. James", "0345803485")));
        b.add(new BookData(new Book("The Fault in Our Stars", "John Green", "014242417X")));

        addByIsbn(b);
        return b;
    }

    private ArrayList<BookData> getScienceFictionBooks() {
        ArrayList<BookData> b = new ArrayList<BookData>();
        b.add(new BookData(new Book("Mockingjay", "Suzanne Collins", "0545663261")));
        b.add(new BookData(new Book("Breaking Dawn", "Stephenie Meyer", "9780316067935")));
        b.add(new BookData(new Book("The Sea of Monsters", "Dan Brown", "1423103343")));
        b.add(new BookData(new Book("Stranger in a Strange Land", "Robert A. Heinlein", "0441788386")));

        addByIsbn(b);
        return b;
    }

    private ArrayList<BookData> getDramaBooks() {
        ArrayList<BookData> b = new ArrayList<BookData>();
        b.add(new BookData(new Book("Romeo and Juliet", "William Shakespeare", "0743477111")));
        b.add(new BookData(new Book("The Crucible", "Arthur Miller", "0142437336")));
        b.add(new BookData(new Book("The Tempest", "William Shakespeare", "0743482832")));
        b.add(new BookData(new Book("The Importance of Being Earnest", "Oscar Wilde", "0486264785")));

        addByIsbn(b);
        return b;
    }

    private ArrayList<BookData> getComedyBooks() {
        ArrayList<BookData> b = new ArrayList<BookData>();
        b.add(new BookData(new Book("Bossypants", "Tina Fey", "0316056898")));
        b.add(new BookData(new Book("Is Everyone Hanging Out Without Me?", "Mindy Kaling", "9780307886279")));
        b.add(new BookData(new Book("The Color of Magic", "Terry Pratchett", "0062225677")));
        b.add(new BookData(new Book("Me Talk Pretty One Day", "David Sedaris", "0316776963")));

        addByIsbn(b);
        return b;
    }

    private void addByIsbn(ArrayList<BookData> b) {
        for (BookData bookData : b) {
            isbnToBook.put(bookData.getBook().getIsbn10(), bookData);
        }
    }
}