Question

I have a Spring controller bean set to a session scope, it looks somewhat like this:

@Controller
@Scope(WebApplicationContext.SCOPE_SESSION)
@RequestMapping("/test")
public class SessionTestController implements Serializable {

    private static final long serialVersionUID = -7735095657091576437L;

    private transient Log log;

    @PostConstruct
    public void initialise() {
        log = LogFactory.getLog(getClass());
    }

    @RequestMapping(method=RequestMethod.GET)
    @ResponseBody
    public String doGet() throws InterruptedException {
        log.warn("This line will fail after deserialisation..."); // Causes NPE
    }

}

It seems Spring does not call @PostConstruct after de-serialisation, this causes my “log” field to become null and throw a NullPointerException in my doGet() method.

How do you usually deal with non-serialisable fields like the logger in session-scoped beans? Do I need to implement some session aware interface to make this work?

Answer 1

I think a typical way is to use readObject() to initialize transient fields, no matter whether it’s a Spring bean or not:

private void readObject(ObjectInputStream stream)
     throws IOException, ClassNotFoundException {
    stream.defaultReadObject();
    initializeTransientFields();
}