Creating master-detail pages for entities, how to link them and which bean scope to choose

Question

I have started learning JSF, but sadly most tutorials out there present only a log in or a register section.

Can you point me to some more in depth examples? One thi

Answer 1

What is the correct usage of session scope

Use it for session scoped data only, nothing else. For example, the logged-in user, its settings, the chosen language, etcetera.

See also:

• How to choose the right bean scope?

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And every time I visit the page, the product list will be created from the latest entries in the database. How can I handle this?

Typically you use the request or view scope for it. Loading of the list should happen in a @PostConstruct method. If the page doesn't contain any , then the request scope is fine. A view scoped bean would behave like a request scoped when there's no anyway.

All "view product" and "edit product" links/buttons which just retrieve information (i.e. idempotent) whould be just plain GET / wherein you pass the entity identifier as a request parameter by .

All "delete product" and "save product" links/buttons which will manipulate information (i.e. non-idempotent) should perform POST by / (you don't want them to be bookmarkable/searchbot-indexable!). This in turn requires a . In order to preserve the data for validations and ajax requests (so that you don't need to reload/preinitialize the entity on every request), the bean should preferably be view scoped.

Note that you should basically have a separate bean for each view and also note that those beans doesn't necessarily need to reference each other.

So, given this "product" entity:

@Entity
public class Product {

    @Id
    private Long id;
    private String name;
    private String description;

    // ...
}

And this "product service" EJB:

@Stateless
public class ProductService {

    @PersistenceContext
    private EntityManager em;

    public Product find(Long id) {
        return em.find(Product.class, id);
    }

    public List list() {
        return em.createQuery("SELECT p FROM Product p", Product.class).getResultList();
    }

    public void create(Product product) {
        em.persist(product);
    }

    public void update(Product product) {
        em.merge(product);
    }

    public void delete(Product product) {
        em.remove(em.contains(product) ? product : em.merge(product));
    }

    // ...
}

You can have this "view products" on /products.xhtml:

    #{product.id}
    #{product.name}
    #{product.description}
    
        
            
        
    

@Named
@RequestScoped
public class ViewProducts {

    private List products; // +getter

    @EJB
    private ProductService productService;

    @PostConstruct
    public void init() {
        products = productService.list();
    }

    // ...
}

And you can have this "edit product" on /products/edit.xhtml:

    





    
    ...
    

@Named
@ViewScoped
public class EditProduct {

    private Product product; // +getter +setter

    @EJB
    private ProductService productService;

    public String save() {
        productService.update(product);
        return "/products?faces-redirect=true";
    }

    // ...
}

And this converter for of "edit product":

@Named
@RequestScoped
public class ProductConverter implements Converter {

    @EJB
    private ProductService productService;

    @Override
    public Object getAsObject(FacesContext context, UIComponent component, String value) {
        if (value == null || value.isEmpty()) {
            return null;
        }

        try {
            Long id = Long.valueOf(value);
            return productService.find(id);
        } catch (NumberFormatException e) {
            throw new ConverterException("The value is not a valid Product ID: " + value, e);
        }
    }

    @Override    
    public String getAsString(FacesContext context, UIComponent component, Object value) {        
        if (value == null) {
            return "";
        }

        if (value instanceof Product) {
            Long id = ((Product) value).getId();
            return (id != null) ? String.valueOf(id) : null;
        } else {
            throw new ConverterException("The value is not a valid Product instance: " + value);
        }
    }

}

You can even use a generic converter, this is explained in Implement converters for entities with Java Generics.

See also:

• How to navigate in JSF? How to make URL reflect current page (and not previous one)
• JSF Controller, Service and DAO
• JSF Service Layer
• How to inject @EJB, @PersistenceContext, @Inject, @Autowired, etc in @FacesConverter?
• Communication in JSF 2.0 - Contains several examples/hints