How to inject a http session attribute to a bean using CDI

Question

I have some legacy code that put objects as http session attributes using code like this:

MyObject object = new MyObject();
Map<String, Object> sessionMap = FacesContext.getCurrentInstance().getExternalContext().getSessionMap();
sessionMap.put("attrname", object);

The old facelets accessed the code using

 @ManagedProperty("#{attrname}")
 private MyObject object;

Is there any way using CDI (@Inject) to inject this session attribute to a Bean?

In new code that uses CDI what's the better way to create and inject objects that need to be created in a controlled way.

Answer 1

Get hold of it in a session scoped managed bean with a @Produces@Named on the getter.

@SessionScoped
public class MyObjectProducer implements Serializable {

    private MyObject myObject;

    @Produces
    @Named("attrname")
    public MyObject getMyObject() {
        return myObject;
    }

    public void setMyObject(MyObject myObject) {
        this.myObject = myObject;
    }

}

When you set it somehow via e.g. myObjectProducer.setMyObject(myObject) elsewhere (or perhaps a CDI @Observes event), then you can inject it anywhere using @Inject @Named.

@Inject
@Named("attrname")
private MyObject myObject;

And yes, it's still available via #{attrname} in EL the usual way. And no, it won't be auto-created when not set, it'll remain null until you actually set it as a property of the producer class.

---

Alternatively, if you really intend to keep the legacy way of setting the instance via ExternalContext#getSessionMap() (e.g. because it's third party and you can thus not change it), then you can alternatively also let the producer return it directly from the session map:

@SessionScoped
public class MyObjectProducer implements Serializable {

    @Produces
    @Named("attrname")
    public MyObject getMyObject() {
        return (MyObject) FacesContext.getCurrentInstance().getExternalContext().getSessionMap().get("attrname");
    }

}

This however isn't guaranteed to work when injected in a non-JSF artifact, such as an arbitrary @WebServlet, as the FacesContext#getCurrentInstance() would obviously return null.

Answer 2

This is the way to go, for both non-jsf and jsf artifacts.

@Qualifier
@Retention(RUNTIME)
@Target({TYPE,METHOD,FIELD,PARAMETER});
public @interface SessionAttribute {

   @NonBinding
   String value() default "";
}

@ApplicationScope
public class SessionAttributeService {

  //Dont worry, this is a proxy, and CDI will ensure that the right one called at the right time.
  @Inject
  private HttpServletRequest servletRequest;

  @Produces
  @SessionAttribute
  @RequestScope
  public String sessionAttribute(final InjectionPoint ip){
     final SessionAttribute sa = ip.getAnnotated().getAnnotation(SessionAttribute.class);
     final HttpSession session = servletRequest.getSession();
     return session.getAttribute(sa.value());
  }
}

And use case:

@RequestScope
public class MyServiceBean {

  @Inject
  @SessionAttribute("theAttribute")
  private String attribute;

}