Spring UnsatisfiedDependencyException而不是托管类型：class java.lang.Object

Question

我想为两个域对象创建一个通用的存储库类：Product和Category，并能够列出index.html中的所有元素。

这是我的代码：

@Controller
public class IndexController {

private final ProdCatService<Category> categoryProdCatService;

public IndexController(ProdCatService<Category> categoryProdCatService) {
    this.categoryProdCatService = categoryProdCatService;
}

@RequestMapping({"","/","index"})
public String getIndexPage(Model model)
{       
    model.addAttribute("cat", categoryProdCatService.getAll());
    return "index";
}
}

库：

public interface ProdCatRepository<T> extends CrudRepository<T, Long> { }

服务：

public interface ProdCatService<T> {

Set<T> getAll();
T findById(Long id);
}


@Service
public class ProdCatServiceImpl<T> implements ProdCatService {

private final ProdCatRepository<T> prodCatRepository;

public ProdCatServiceImpl(ProdCatRepository<T> prodCatRepository) {
    this.prodCatRepository = prodCatRepository;
}

@Override
public Set<T> getAll() {
    Set<T> productsSet = new HashSet<>();
    prodCatRepository.findAll().iterator().forEachRemaining(productsSet::add);
    return productsSet;
}

@Override
public T findById(Long id) {
    return prodCatRepository.findById(id).get();
}
}

所以问题是我得到像以下错误：

org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'indexController' defined in file [C:\Users\Michał\Documents\webstore-v-1\target\classes\info\mike\webstorev1\controllers\IndexController.class]: Unsatisfied dependency expressed through constructor parameter 0; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'prodCatServiceImpl' defined in file [C:\Users\Michał\Documents\webstore-v-1\target\classes\info\mike\webstorev1\service\ProdCatServiceImpl.class]: Unsatisfied dependency expressed through constructor parameter 0; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'prodCatRepository': Invocation of init method failed; nested exception is java.lang.IllegalArgumentException: Not a managed type: class java.lang.Object

和

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'prodCatRepository': Invocation of init method failed; nested exception is java.lang.IllegalArgumentException: Not a managed type: class java.lang.Object

我在寻求帮助。我查看了S / O，但找不到答案。

编辑类别域类。

@Entity
public class Category {

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String categoryName;

@ManyToMany(mappedBy = "categories")
private Set<Product> products;

@Override
public int hashCode() {
    final int prime = 31;
    int result = 1;
    result = prime * result + ((id == null) ? 0 : id.hashCode());
    return result;
}

@Override
public boolean equals(Object obj) {
    if (this == obj)
        return true;
    if (obj == null)
        return false;
    if (getClass() != obj.getClass())
        return false;
    Category other = (Category) obj;
    if (id == null) {
        if (other.id != null)
            return false;
    } else if (!id.equals(other.id))
        return false;
    return true;
}

Answer 1

我想为两个域对象创建一个通用的存储库类：Product和Category，并能够列出index.html中的所有元素。

你的要求毫无意义。 要实现它，您应该在Product和Category之间定义一个基类，并在通用存储库中指定此基类。 类别是与产品不同的概念。 因此，通过扭曲层次结构，您将无法定义此基类。 即使您定义了它，也不会反映类别和产品中所需的字段。 那么在这些条件下，您想如何在客户端正确列出它们？

那么，你为什么要重新发明轮子？ 实际上，您使用Spring Data来减少锅炉板代码：

public interface ProdCatRepository<T> extends CrudRepository<T, Long> { }

这显然足够容易申报。 不要试图通过关联不应该的事情而过于聪明，并为每个事物定义一个独特的存储库：

public interface ProductRepository extends CrudRepository<Product, Long> { }
public interface CategoryRepository extends CrudRepository<Category, Long> { }