Request parameter is null during postback

Question

I have a view that display a list of users, from this view I can go to another view of \"details\" of any selected user. In the details view I need to select some values fro

Answer 1

Bad getter!

    public Usuario getU() {
    getParam();
    return u;
    }

The getter above is a very bad idea. You've said it yourself that the variable makes it into the usuario backing bean(this I doubt). It is just plain wrong to perform business logic inside a getter because of inconsistencies (like you're experiencing) and the fact that the getter is called multiple times during a request. There are more elegant and cleaner ways to pass and initialise parameters between JSF pages.

private Usuario u=new Usuario(); is also a bad idea. Why is this necessary when you have

      this.setU(controlador.getUser(param));

All that should happen inside your @PostConstructor

    @PostConstruct
    public void init() {


    controlador=new usuarioController();
    FacesContext facesContext = FacesContext.getCurrentInstance();
    ExternalContext externalContext = facesContext.getExternalContext();

    //Obtener parametros del request
    Map<String, String> parameterMap = (Map<String, String>) externalContext.getRequestParameterMap();
    Long param = Long.valueOf(parameterMap.get("id_usuario"));
    System.out.println(param);
    this.setU(controlador.getUser(param));

    }

The getter should just be plain

public Usuario getU() {
    return u;
}

Answer 2

The cause of this error is that parameterMap.get("id_usuario") is null. You should investigate how you pass this parameter from the UI to the backing bean.