JSF 2.0 view parameters to pass objects

问题

I am trying to pass an object from one page to another page where each page is in a different view.

On the first page I have an input text, where myBean is a ViewScoped Bean and name is an object. <h:inputText value="#{myBean.name}"/>

The second page contains,
<f:metadata>
<f:viewParam name="userId" value="#{myBean.name}"/>
</f:metadata>

I get the error Conversion Error setting value mypackage.myBean@257100b' for 'null Converter'. Can we pass objects other than String values to view parameters?

回答1:

Yes, you can. You just have to supply a converter which converts between the string representation of the object type behind #{myBean.name} and the real object. The string representation is usually the unique technical/natural identifier of the object in question. For example, the table's PK. It has got to be a string, simply because HTTP request parameters can be strings only. You can't pass complex Java objects around in URLs. URLs are just strings.

Here's a kickoff example:

E.g. the following in the initial view:

<h:link value="Edit" outcome="edit">
    <f:param name="id" value="#{personViewer.person.id}" />
</h:link>

(which generates an <a href="edit.xhtml?id=123">Edit</a>)

and the following in the linked view:

<f:metadata>
    <f:viewParam name="id" value="#{personEditor.person}"
        converter="#{personConverter}" converterMessage="Bad request. Unknown person."
        required="true" requiredMessage="Bad request. Please use a link from within the system."
    />
</f:metadata>
<h:messages />

with this converter

@ManagedBean
@RequestScoped
public class PersonConverter implements Converter {

    @EJB
    private PersonService personService;

    @Override
    public String getAsString(FacesContext context, UIComponent component, Object value) {
        return String.valueOf(((Person) value).getId());
    }

    @Override
    public Object getAsObject(FacesContext context, UIComponent component, String value) {
        return personService.find(Long.valueOf(value));
    }

}

(oversimplified; all null/number checks omitted, but you got the idea)

See also:

• Communication in JSF 2.0 - Converting and validating GET request parameters

---

Update as per the comments, you actually want to fire a POST request. You don't need a <f:viewParam> at all. It's for setting/validating/converting GET request parameters only. Attempting to serialize the whole object makes also no utter sense. Just use @ManagedProperty.

E.g.

@ManagedBean
@ViewScoped
public class PersonEditor implements Serializable {

    @ManagedProperty("#{personViewer.person}")
    private Person person;

    // ...
}

It's only not bookmarkable anymore and not SEO-friendly (but that's the nature of POST, you're probably already for long aware of this). Note that the #{personViewer} bean must by itself also be @ViewScoped (and thus not @ReqestScoped). You also need to make sure that you don't navigate back with a redirect, but just a forward.

来源：https://stackoverflow.com/questions/8609378/jsf-2-0-view-parameters-to-pass-objects