Question

使用以下Bean，我填写一个表格与国家：

@ManagedBean  
@RequestScoped  
public class CreateUser {  

    @EJB  
    private ParticipantDAO participantDAO;  
    @EJB  
    private CountryDAO countryDAO;  
    private List<Country> countries = new ArrayList<Country>();  
   . . .  
   . . .  
   . . .  

    @PostConstruct  
    public void init() {  
        countries = countryDAO.getAllCountries();  
    }

在我要使用转换器的形式中：

 <h:selectOneMenu id="country" value="#{createUser.user.country}" required="true" requiredMessage="Please select a country." converter="#{countryConverter}" >
        <f:selectItem itemValue="#{null}" itemLabel="-- select one --" />
        <f:selectItems value="#{createUser.countries}" var="country" itemValue="#{country}" itemLabel="#{country.country}" />
 </h:selectOneMenu>

转换器给出NullPointerException似乎是因为它无法注入CountryDAO：

@ManagedBean
@RequestScoped
@FacesConverter(forClass = Country.class)
public class CountryConverter implements Converter {

@EJB
private CountryDAO countryDAO;

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

    return String.valueOf(((Country) value).getId());
}

@Override
public Object getAsObject(FacesContext context, UIComponent component, String value) {
    if (value == null || value.isEmpty()) {
        return null;
    }
    try {
        System.out.println("Converter Value: " + value);
        Country c = countryDAO.find(Long.valueOf(value));
        System.out.println("Converter: " + c.getCountry());
        return c;
    } catch (Exception e) {
        throw new ConverterException(new FacesMessage(String.format("Cannot convert %s to Country %s %d", value, e.toString(), Long.valueOf((value)))), e);
    }
} 
}

在控制台中，我看到“转换后的值”消息，但没有看到应由createDAO.find方法打印的“CountryDAO find”。

@Stateless
@LocalBean
public class CountryDAO {

public CountryDAO() {
}
@PersistenceContext
private EntityManager em;
@Resource
SessionContext context;

public List<Country> getAllCountries() {
    TypedQuery<Country> query = em.createNamedQuery(Country.FIND_ALL, Country.class);
    return query.getResultList();
}

public Country find(Long id) {
    System.out.println("CountryDAO find");
    Country c = em.find(Country.class, id);
    System.out.println(c.getCountry());
    return c;
}

我尝试了向Inject a EJB into a JSF converter with JEE6报告的解决方案（我不知道是否将代码放在正确的位置）。我把它放在转换器中（我获得了NullPointerException）：

@ManagedBean
@FacesConverter(forClass = Country.class)
public class CountryConverter implements Converter {

 //    @EJB
//    private CountryDAO countryDAO;
private InitialContext ic;
private CountryDAO countryDAO;

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

    return String.valueOf(((Country) value).getId());
}

@Override
public Object getAsObject(FacesContext context, UIComponent component, String value) {
    if (value == null || value.isEmpty()) {
        return null;
    }
    System.out.println("Converter Value: " + value);
    try {
        try {
            ic = new InitialContext();
            countryDAO = (CountryDAO) ic.lookup("java:global/DAO/CountryDAO");
        } catch (NamingException e) {
        }

        Country c = countryDAO.find(Long.valueOf(value));
        System.out.println("Converter: " + c.getCountry());
        return c;
    } catch (Exception e) {
        throw new ConverterException(new FacesMessage(String.format("Cannot convert %s to Country %s %d", value, e.toString(), Long.valueOf((value)))), e);
    }
}

Answer 1

我在其他一些项目中遇到了同样的问题，我正在使用转换器来处理某些primefaces组件。我解决了CDI方式的问题。

您所要做的就是使用@Named注释您的转换器类（并通过@Inject（JEE6）注入DAO类，而不是使用JEE5 - @EJB注入）。

您使用绑定属性引用转换器，例如： <f:converter binding="#{countryConverter}" />

注入DAO会产生NullPointerException

1 个答案: