在 Spring 4 中返回缓存中的嵌套对象

Question

我在这里遵循 Spring 缓存指南 - https://spring.io/guides/gs/caching/，但我的对象有点复杂。

对于我的用例，我也有一个 Author 字段。这是我的整个Book 课程。

public class Book {

    private String isbn;
    private String title;
    private Author author;

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

    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 Author getAuthor() {
        return author;
    }

    public void setAuthor(Author author) {
        this.author = author;
    }

    @Override
    public String toString() {
        return String.format("Book{isbn='%s',title='%s',author=%s}", isbn, title, author);
    }
}

现在，我添加了另一种按作者 ID 获取书籍的方法（假设只返回一本书）。这是我的SimpleBookRepository。

@Component
public class SimpleBookRepository implements BookRepository {

    private List<Book> books;

    public SimpleBookRepository() {
        books = new ArrayList<>();
        books.add(new Book("1234", "Some book", new Author(1, "Author1")));
        books.add(new Book("4567", "Some another book", new Author(2, "Author2")));
    }

    @Override
    @Cacheable("books")
    public Book getByIsbn(String isbn) {
        simulateSlowService();
        return books.stream().filter(o -> o.getIsbn().equals(isbn)).findFirst().orElse(null);
    }

    @Override
    public Book getByAuthorId(int id) {
        simulateSlowService();
        return books.stream().filter(o -> o.getAuthor().getId() == id).findFirst().orElse(null);
    }

    // Don't do this at home
    private void simulateSlowService() {
        try {
            long time = 1000L;
            Thread.sleep(time);
        } catch (InterruptedException e) {
            throw new IllegalStateException(e);
        }
    }
}

现在，我想知道是否可以通过在缓存中查找 Author.id 来从缓存中获取 Book 实例。

这是我的执行和预期行为。

logger.info(".... Fetching books");
logger.info("isbn-1234 -->" + bookRepository.getByIsbn("1234"));   // Gets the original object
logger.info("isbn-4567 -->" + bookRepository.getByIsbn("4567"));   // Gets the original object
logger.info("isbn-1234 -->" + bookRepository.getByIsbn("1234"));   // Should fetch from cache - WORKS FINE
logger.info("isbn-4567 -->" + bookRepository.getByIsbn("4567"));   // Should fetch from cache - WORKS FINE
logger.info("isbn-1234 -->" + bookRepository.getByIsbn("1234"));   // Should fetch from cache - WORKS FINE
logger.info("isbn-1234 -->" + bookRepository.getByIsbn("1234"));   // Should fetch from cache - WORKS FINE

logger.info(".... Fetching books by author");
logger.info("author-1 -->" + bookRepository.getByAuthorId(1));   // Should fetch from cache - NOT WORKING
logger.info("author-2 -->" + bookRepository.getByAuthorId(2));   // Should fetch from cache - NOT WORKING
logger.info("author-1 -->" + bookRepository.getByAuthorId(1));   // Should fetch from cache - NOT WORKING
logger.info("author-2 -->" + bookRepository.getByAuthorId(2));   // Should fetch from cache - NOT WORKING
logger.info("author-1 -->" + bookRepository.getByAuthorId(1));   // Should fetch from cache - NOT WORKING
logger.info("author-1 -->" + bookRepository.getByAuthorId(1));   // Should fetch from cache - NOT WORKING

有没有办法做到这一点，或者我需要另一个缓存来实现这个目的？

Answer 1

您不需要其他缓存。只需在您的 getByAuthorId 方法中指定您也想缓存该方法。每次调用该方法时，如果该方法尚不存在，Spring 将在缓存中创建一个具有关键作者 ID 和值 Book 的条目。只需将 @Cacheable("books") 添加到您的 getByAuthorId 方法中。

所以现在在您的 books 缓存中，您将拥有映射到 Books 的带有 isbn 键和 author.id 键的条目。

作为回应我能想到的解决方案是，如果您手动将条目添加到缓存中，例如：

@Component
public class SimpleBookRepository implements BookRepository {

    // inject this bean
    private CacheManager cacheManager;

    @Override
    @Cacheable("books")
    public Book getByIsbn(String isbn) {
        simulateSlowService();
        Book b = books.stream().filter(o -> o.getIsbn().equals(isbn)).findFirst().orElse(null);

        if (b != null && b.getAuthor() != null && b.getAuthor().getId() != null) {
            Cache cache = cacheManager.getCache("books");
            cache.put(b.getAuthor().getId(), b);
        }

        return b;
    }

    // ......
}