从选择一个菜单JSF转换器异常中选择自定义对象[重复]

Question

我想从“选择一个”菜单中选择自定义对象。它既不显示错误也不显示值。怎么办？请帮帮我。提前谢谢。

现在我在getAsObject的这一行看到空指针异常：

return getCurrencyService().getCurrencyBtId(currencyId);

这是我的xhtml文档

<h:panelGrid columns="2">
    <p:outputLabel value="" />
        <p:selectOneMenu id="CurrencyMenu" value="#{CurrencyMB.currency}" converter="currencyConverter" >
        <f:selectItems value="#{CurrencyMB.currencyList}" var="currency"  itemValue="#{currency}" itemLabel="#{currency.currencyName}" >    
            </f:selectItems>
        <p:ajax update="currencyOut" />
        </p:selectOneMenu>
        <p:outputLabel value="Currency Id : #{CurrencyMB.currency.currencyId}" id="currencyOut" />
</h:panelGrid>

这是我的管理豆类。

@ManagedBean(name = "CurrencyMB")
@RequestScoped
public class CurrencyManagedBean implements Serializable{

private Currency currency;
private List<Currency> currencyList;


public Currency getCurrency() {
        return currency;
    }

public void setCurrency(Currency currency) {
        this.currency = currency;
    }
public List<Currency> getCurrencyList() {
        currencyList = new ArrayList<Currency>();
        currencyList.addAll(getiCurrencyService().getCurrencies());
        return currencyList;
    }

public void setCurrencyList(List<Currency> currencyList) {
        this.currencyList = currencyList;
    }

}

这是我的currencyConverter类代码：

**@FacesConverter("currencyConverter")
public class CurrencyConverter implements Converter {
    @ManagedProperty(value = "#{currencyService}")
    private ICurrencyService currencyService;


    public ICurrencyService getCurrencyService() {
        return currencyService;
    }
    public void setCurrencyService(ICurrencyService currencyService) {
        this.currencyService = currencyService;
    }
    @Override
    public Object getAsObject(FacesContext arg0, UIComponent arg1, String value) {

        int currencyId = Integer.valueOf(value);
        return getCurrencyService().getCurrencyBtId(currencyId);
    }
    @Override
    public String getAsString(FacesContext arg0, UIComponent arg1, Object value) {
        Currency currency = (Currency) value;
        int currencyId = currency.getCurrencyId();
        return String.valueOf(currencyId);
    }
}**

Answer 1

从许多问题及其答案中可以看出，@FacesConverter不符合注射条件。在你的例子中，你试图通过@ManagedProperty注入你的服务，这会产生NPE，就像Luiggi在对你最初问题的评论中告诉你的那样。

使用当前的JSF版本，在转换器中注入服务所能做的就是放弃使用@FacesConverter并切换到使用标准@ManagedBean注释，因此不通过id而是通过bean名称来引用您的转换器，就像在转换器="#{电流转换器}"中一样。