在运行时为selectOneMenu创建一个转换器

Question

So I need to create a screen that is dynamic and provides information about objects wich have an unknown number of parameters, of various types (could be texte, could be date, and, thing that causes problem, could be an item to select from a SelectOneMenu, whose binding (like "#{myBean.list}" and converter (like "#{somethingConverter}) are fields of the parameter.

So, to create the SelectOneMenu, I've got something like this:

    SelectOneMenu menu = new SelectOneMenu();
    UISelectItems items = new UISelectItems();

    ValueExpression expr = getValueExpression(param.binding); //param.binding is a String containing the expression
    items.setValueExpression("value", expr);

    menu.getChildren().add(items);
    panel.getChildren().add(menu);
}


private ValueExpression getValueExpression(String expression) {
    ExpressionFactory expressionFactory = FacesContext.getCurrentInstance().getApplication().getExpressionFactory();
    ELContext expressionContext = FacesContext.getCurrentInstance().getELContext();
    return expressionFactory.createValueExpression(expressionContext, expression, Object.class);
}

But I have to set a Converter to the menu to, and I can't use the same method because it's impossible to instantiate a Converter, so I can't juste set it an expression.

I tried using reflection, and it almost works, but in my Converters , some managers are created using

    @Inject
    private SomeManager mManager;

And if I create a converter using reflection, those managers aren't created, and I end up getting a NullPointerException when I use them.

So is there a way I can dynamically create a converter using the expression I would put after "converter=" in my XHtml page ? Or, using reflection, to force my converter classes to do the "inject" instantiation ?

Thank for your help !

Answer 1

I tried using reflection, and it almost works, but in my Converters , some managers are created using

 @Inject private SomeManager mManager; 

And if I create a converter using reflection, those managers aren't created, and I end up getting a NullPointerException when I use them.

In other words, your converters are managed beans (eg @Named or @ManagedBean ), not faces converters (eg @FacesConverter or <converter> )? In that case, you'd need to create them by programmatically evaluating the EL expression referencing it like so

Converter converter = context.getApplication().evaluateExpressionGet(context, "#{someConverter}", Converter.class);