Conversion Error setting value '52' for &#

问题:

This question already has an answer here:

• Conversion Error setting value for 'null Converter' - Why do I need a Converter in JSF? 2 answers

I'm new to JSF and I have been trying to store data from a form that uses a h:selectOneMenu to get the category of a product. The h:selectOneMenu is being populated from the DB, however, when trying to store a product in the DB, I am getting an error: Conversion Error setting value '52' for 'null Converter'. I have reviewed similar problems in StackOverflow and tutorials online but I am still getting the error.

This is the xhtml:

<h:selectOneMenu id="category_fk" value="#{productController.product.category_fk}" 
                                 converter="#{categoryConverter}" title="Category_fk" >
                    <!-- DONE: update below reference to list of available items-->
                    <f:selectItems value="#{productController.categoryList}" var="prodCat"
                                   itemValue="#{prodCat}" itemLabel="#{prodCat.name}"/>
                </h:selectOneMenu>

This is the product controller:

@Named
@RequestScoped
public class ProductController {

    @EJB
    private ProductEJB productEjb;
    @EJB
    private CategoryEJB categoryEjb;

    private Product product = new Product();
    private List<Product> productList = new ArrayList<Product>();

    private Category category;
    private List<Category> categoryList = new ArrayList<Category>();

    public String doCreateProduct()
    {
        product = productEjb.createProduct(product);
        productList = productEjb.findAllProducts();
        return "listProduct";
    }

    @PostConstruct
    public void init()
    {
        categoryList = categoryEjb.findAllCategory();
        productList = productEjb.findAllProducts();
    }        

    // Getters/Setters and other methods omitted for simplicity

This is the EJB simplified for simplicity:

   @Stateless
    public class ProductEJB{

        @PersistenceContext(unitName = "luavipuPU")
        private EntityManager em;

        public List<Product> findAllProducts()
        {
            TypedQuery<Product> query = em.createNamedQuery("findAllProducts", Product.class);
            return query.getResultList();
        }

        public Product createProduct(Product product)
        {
            em.persist(product);
            return product;
        }    

    }

This is the product Entity simplified for simplicity:

@Entity
@NamedQueries({
    @NamedQuery(name="findAllProducts", query = "SELECT p from Product p")
})
public class Product implements Serializable
{
    private static final long serialVersionUID = 1L;

    @Id @GeneratedValue(strategy= GenerationType.AUTO)
    private int product_id;
    private String name;
    private String description;
    protected byte[] imageFile;
    private Float price;
    @Temporal(TemporalType.TIMESTAMP)
    private Date dateAdded;
    @ManyToOne    
    private Category category_fk;
    @ManyToOne
    private SaleDetails saleDetails_fk;

This is the updated converter I am using:

@ManagedBean
@FacesConverter(value="categoryConverter")
public class CategoryConverter implements Converter{

    @PersistenceContext
    private transient EntityManager em;

    @Override
    public Object getAsObject(FacesContext context, UIComponent component, String value) {
        return em.find(Category.class, new Integer(value));
    }

    @Override
    public String getAsString(FacesContext context, UIComponent component, Object value) {

        Category category;
        category = (Category) value;
        return String.valueOf(category.getCategory_id());

    }

}

The code has been updated from the Orignal problem, the code perfectly works now.

回答1:

You can't use a custom type on the <h:selectOneMenu/> component (or any of the <h:selectXXXX/>) without creating a JSF Converter. Converters exist in JSF to assist with translating essentially custom or sever-side items/constructs into web page friendly/human readable formats and also to be able to save selections from the client side back to the server side. So what the error message is essentially telling you there is that it cannot make sense enough of the value 52 submitted from the client side to save it to the server side as a Category object/type

So what you're required to do is to create an implementation of a JSF converter that essentially helps JSF make sense of your Category object.

Here's a rough estimation of what you need to do:

1. Implement a converter for your Category type:

   // You must annotate the converter as a managed bean, if you want to inject
   // anything into it, like your persistence unit for example.
   @ManagedBean(name = "categoryConverterBean") 
   @FacesConverter(value = "categoryConverter")
   public class CategoryConverter implements Converter {
   
       @PersistenceContext(unitName = "luavipuPU")
       // I include this because you will need to 
       // lookup  your entities based on submitted values
       private transient EntityManager em;  
   
       @Override
       public Object getAsObject(FacesContext ctx, UIComponent component,
               String value) {
         // This will return the actual object representation
         // of your Category using the value (in your case 52) 
         // returned from the client side
         return em.find(Category.class, new BigInteger(value)); 
       }
   
       @Override
       public String getAsString(FacesContext fc, UIComponent uic, Object o) {
           //This will return view-friendly output for the dropdown menu
           return ((Category) o).getId().toString(); 
       }
   }
   

2. Reference your new converter in your <h:selectOneMenu/>

   <h:selectOneMenu id="category_fk" 
     converter="#{categoryConverterBean}"
     value="#productController.product.category_fk}" 
     title="Category_fk" >
   <!-- DONE: update below reference to list of available items-->
       <f:selectItems value="#{productController.categoryList}" 
         var="prodCat" itemValue="#{prodCat.category_id}" 
         itemLabel="#{prodCat.name}"/>
   </h:selectOneMenu>
   

We're using the name categoryConverterBean because we want to take advantage of the entity manager trick you pulled in the converter. Any other case, you would've used the name you set on the converter annotation.

回答2:

Product.category_fk seems to be of type Category and I suspect prodCat.category_id to be an Integer or something...

in your xhtml you seem to set the value of the selectItems to: itemValue="#{prodCat.category_id}"

when selectOneMenu expects a value value="#{productController.product.category_fk}"

which are most probably not of the same type.