Session-management design-issue with my JSF/Spring application

[balteo]

Hello,

I have a session-scoped spring bean that uses a singleton-scoped spring service bean in my application.

The problem is when a user close his/her browser and reopens it: the session-scoped bean is correctly deserialized but the dependency (the spring service bean) is null, resulting in a NullPointerException when the dependency is used...

Can anyone please provide design advice on how to prevent this?

Regards,

J.

[Marten Deinum]

In general you shouldn't be doing something like this you can end up with multiple instances of the singleton (try deserializing and serializing a singleton and you will have 2 instances).

In general you want to use a lazy proxy of some kind to retrieve/use the singleton from the context.

[balteo]

Thanks Marten,
I think I found some relevant documentation here:
LazyInitTargetSource
for those interested in this topic.

[balteo]

In general you shouldn't be doing something like this you can end up with multiple instances of the singleton (try deserializing and serializing a singleton and you will have 2 instances).

In general you want to use a lazy proxy of some kind to retrieve/use the singleton from the context.

Hi Marten,

I changed my config to this:

	<bean id="mainService" class="com.jeanbaptistemartin.service.MainServiceImpl" lazy-init="true"/>
	
	<bean id="service" class="org.springframework.aop.framework.ProxyFactoryBean">
		<property name="targetSource">
			<bean class="org.springframework.aop.target.LazyInitTargetSource">
				<property name="targetBeanName">
					<idref local="mainService" />
				</property>
			</bean>
		</property>
	</bean>

private transient MainService mainService;

    public SuggestionOeuvreView() {
        log.debug("SuggestionOeuvreView()");
    }

    @Autowired
    public SuggestionOeuvreView(MainService mainService) {
        log.debug("SuggestionOeuvreView(MainService mainService)");
        this.mainService = mainService;
        this.sculpturesNonVisitees = recupererSculpturesNonVisitees();
    }

I still get the same NPE...

Any other idea?

J.

[Marten Deinum]

Don't use a transient field that is never serialized/deserialized.

[balteo]

Marten,
The trouble is that despite the lazy-init, it still attempts to serialize my MainService bean...
I am not sure what I got wrong.
Julien.

[balteo]

Here is also the code for my session-scoped bean:

package com.jeanbaptistemartin.view;

import java.io.Serializable;
import java.util.LinkedList;
import java.util.List;

import javax.faces.event.ActionEvent;

import org.apache.log4j.Logger;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Scope;
import org.springframework.stereotype.Component;

import com.jeanbaptistemartin.domain.Sculpture;
import com.jeanbaptistemartin.service.MainService;

@Component("suggestionOeuvreView")
@Scope("session")
public class SuggestionOeuvreView implements Serializable {

	private static final long serialVersionUID = 1L;
	private static transient Logger log = Logger.getLogger("com.jeanbaptistemartin.view");
    private final static int NB_SCULPTURES_SUGGEREES = 4;
    private LinkedList<Integer> sculpturesNonVisitees;
    private List<Sculpture> sculpturesSuggerees;
    private MainService mainService;
    private boolean enabled = true;

    public SuggestionOeuvreView() {
        log.debug("SuggestionOeuvreView()");
    }

    @Autowired
    public SuggestionOeuvreView(MainService mainService) {
        log.debug("SuggestionOeuvreView(MainService mainService)");
        this.mainService = mainService;
        this.sculpturesNonVisitees = recupererSculpturesNonVisitees();
    }

    @Autowired
    public void setMainService(MainService mainService) {
        this.mainService = mainService;
    }

    public Sculpture suggererSculpture() {
        log.debug("suggererSculpture");
        return _suggererSculpture();
    }

    private Sculpture _suggererSculpture() {
        log.debug("_suggererSculpture");
        log.debug("Etat de la liste: " + this.sculpturesNonVisitees);
        if (!this.sculpturesNonVisitees.isEmpty() && this.sculpturesNonVisitees.peek() != null) {
            Integer idSculptureSuggeree = this.sculpturesNonVisitees.pollFirst();
            this.sculpturesNonVisitees.addLast(idSculptureSuggeree);
            log.debug("jbmService: " + mainService);
            return mainService.findByID(idSculptureSuggeree);//NPE HERE!!
        } else {
            log.error("Probleme dans _suggererSculpture");
            return null;//todo
        }
    }

    public List<Sculpture> suggererSculptures() {
        log.debug("suggererSculptures");
        return _suggererSculptures();
    }

    private List<Sculpture> _suggererSculptures() {
        log.debug("_suggererSculptures");
        if (!this.sculpturesNonVisitees.isEmpty() && this.sculpturesNonVisitees.peek() != null) {
            if (this.sculpturesNonVisitees.size() > NB_SCULPTURES_SUGGEREES) {
                return mainService.findByIDs(this.sculpturesNonVisitees.subList(0, NB_SCULPTURES_SUGGEREES));//TODO: est null quand la session existe déjà!
            } else {
                return mainService.findByIDs(this.sculpturesNonVisitees.subList(0, this.sculpturesNonVisitees.size()));
            }
        } else {
            log.error("Probleme dans _suggererSculptures");
            return null;//todo
        }
    }

    public void enable(ActionEvent evt) {
        log.debug("enable");
        this.enabled = true;
    }

    public void disable(ActionEvent evt) {
        log.debug("disable");
        this.enabled = false;
    }

    public Sculpture sculpturePrecedente() {
        log.debug("sculpturePrecedente");
        return _sculpturePrecedente();

    }

    private Sculpture _sculpturePrecedente() {
        log.debug("_sculpturePrecedente");
        this.enabled = false;
        if (!this.sculpturesNonVisitees.isEmpty() && this.sculpturesNonVisitees.peek() != null) {
            Integer idSculpturePrecedente = this.sculpturesNonVisitees.pollLast();
            this.sculpturesNonVisitees.addFirst(idSculpturePrecedente);
            return mainService.findByID(idSculpturePrecedente);
        } else {
            return null;
        }

    }

    public Sculpture sculptureSuivante() {
        log.debug("sculptureSuivante");
        return _sculptureSuivante();
    }

    private Sculpture _sculptureSuivante() {
        log.debug("_sculpturePrecedente");
        this.enabled = false;
        if (!this.sculpturesNonVisitees.isEmpty() && this.sculpturesNonVisitees.peek() != null) {
            Integer idSculptureSuivante = this.sculpturesNonVisitees.pollFirst();
            this.sculpturesNonVisitees.addLast(idSculptureSuivante);
            return mainService.findByID(idSculptureSuivante);
        } else {
            return null;
        }

    }

    public LinkedList<Integer> recupererSculpturesNonVisitees() {
        log.debug("recupererSculpturesNonVisitees() ");
        return mainService.findAllSculptureIDs();
    }

    public synchronized void enleverSculptureDeListeNonVisitees(Integer sculptureId) {
        log.debug("enleverSculptureDeListeNonVisitees");
        this.sculpturesNonVisitees.remove(sculptureId);
    }

    public boolean isEnabled() {
        log.debug("isEnabled");
        return this.enabled;
    }

    public void setEnabled(boolean enabled) {
        log.debug("setEnabled");
        this.enabled = enabled;
    }

    public void setSculpturesNonVisitees(LinkedList<Integer> sculpturesNonVisitees) {
        log.debug("setSculpturesNonVisitees");
        this.sculpturesNonVisitees = sculpturesNonVisitees;
    }

    public LinkedList<Integer> getSculpturesNonVisitees() {
        log.debug("getSculpturesNonVisitees");
        return sculpturesNonVisitees;
    }

    public List<Sculpture> getSculpturesSuggerees() {
        log.debug("getSculpturesSuggerees");
        return sculpturesSuggerees;
    }

    public void setSculpturesSuggerees(List<Sculpture> sculpturesSuggerees) {
        log.debug("setSculpturesSuggereess");
        this.sculpturesSuggerees = sculpturesSuggerees;
    }

}