Question

I’m the following error when calling purchaseService.updatePurchase(purchase) inside my TagController:

SEVERE: Servlet.service() for servlet [PurchaseAPIServer] in context with path [/PurchaseAPIServer] threw exception [Request processing failed; nested exception is org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.app.model.Purchase.tags, no session or session was closed] with root cause
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.app.model.Purchase.tags, no session or session was closed
    at org.hibernate.collection.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:383)
    at org.hibernate.collection.AbstractPersistentCollection.throwLazyInitializationExceptionIfNotConnected(AbstractPersistentCollection.java:375)
    at org.hibernate.collection.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:368)
    at org.hibernate.collection.PersistentSet.add(PersistentSet.java:212)
    at com.app.model.Purchase.addTags(Purchase.java:207)
    at com.app.controller.TagController.createAll(TagController.java:79)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:212)
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:126)
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:96)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:617)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:578)
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:80)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:900)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:827)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:882)
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:789)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:641)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:225)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:169)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:927)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:999)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:565)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:309)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
    at java.lang.Thread.run(Thread.java:662)

TagController:

@RequestMapping(value = "purchases/{purchaseId}/tags", method = RequestMethod.POST, params = "manyTags")
@ResponseStatus(HttpStatus.CREATED)
public void createAll(@PathVariable("purchaseId") final Long purchaseId, @RequestBody final Tag[] entities)
{
    Purchase purchase = purchaseService.getById(purchaseId);

    Set<Tag> tags = new HashSet<Tag>(Arrays.asList(entities));

    purchase.addTags(tags);
    purchaseService.updatePurchase(purchase);
}

Purchase:

@Entity
@XmlRootElement
public class Purchase implements Serializable
{

    /**
     * 
     */
    private static final long serialVersionUID = 6603477834338392140L;

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @OneToMany(mappedBy = "purchase", fetch = FetchType.LAZY, cascade={CascadeType.ALL})
    private Set<Tag> tags;

    @JsonIgnore
    public Set<Tag> getTags()
    {
        if (tags == null)
        {
            tags = new LinkedHashSet<Tag>();
        }
        return tags;
    }

    public void setTags(Set<Tag> tags)
    {
        this.tags = tags;
    }

    public void addTag(Tag tag)
    {
        tag.setPurchase(this);
        this.tags.add(tag);
    }

    public void addTags(Set<Tag> tags)
    {
        Iterator<Tag> it = tags.iterator();

        while (it.hasNext())
        {
            Tag tag = it.next();
            tag.setPurchase(this);
            this.tags.add(tag);
        }
    }

    ...
}

Tag:

@Entity
@XmlRootElement
public class Tag implements Serializable
{
    /**
     * 
     */
    private static final long serialVersionUID = 5165922776051697002L;

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumns({@JoinColumn(name = "PURCHASEID", referencedColumnName = "ID")})
    private Purchase purchase;

    @JsonIgnore
    public Purchase getPurchase()
    {
        return purchase;
    }

    public void setPurchase(Purchase purchase)
    {
        this.purchase = purchase;
    }
}

PurchaseService:

@Service
public class PurchaseService implements IPurchaseService
{
    @Autowired
    private IPurchaseDAO purchaseDAO;

    public PurchaseService()
    {

    }

    @Transactional
    public List<Purchase> getAll()
    {
        return purchaseDAO.findAll();
    }

    @Transactional
    public Purchase getById(Long id)
    {
        return purchaseDAO.findOne(id);
    }

    @Transactional
    public void addPurchase(Purchase purchase)
    {
        purchaseDAO.save(purchase);
    }

    @Transactional
    public void updatePurchase(Purchase purchase)
    {
        purchaseDAO.update(purchase);
    }
}

TagService:

@Service
public class TagService implements ITagService
{
    @Autowired
    private ITagDAO tagDAO;

    public TagService()
    {

    }

    @Transactional
    public List<Tag> getAll()
    {
        return tagDAO.findAll();
    }

    @Transactional
    public Tag getById(Long id)
    {
        return tagDAO.findOne(id);
    }

    @Transactional
    public void addTag(Tag tag)
    {
        tagDAO.save(tag);
    }

    @Transactional
    public void updateTag(Tag tag)
    {
        tagDAO.update(tag);
    }
}

Any ideas on how I can fix this? (I want to avoid using EAGER loading).

Do I need to setup some form of session management for transactions?

Thanks

Updates based on JB suggestions

TagController

@RequestMapping(value = "purchases/{purchaseId}/tags", method = RequestMethod.POST, params = "manyTags")
@ResponseStatus(HttpStatus.CREATED)
public void createAll(@PathVariable("purchaseId") final Long purchaseId, @RequestBody final Tag[] entities)
{
    Purchase purchase = purchaseService.getById(purchaseId);

    // Validation
    RestPreconditions.checkRequestElementNotNull(purchase);
    RestPreconditions.checkRequestElementIsNumeric(purchaseId);

    Set<Tag> tags = new HashSet<Tag>(Arrays.asList(entities));

    purchaseService.addTagsToPurchase(purchaseId, tags);
}

PurchaseService

@Transactional
public void addTagsToPurchase(Long purchaseId, Set<Tag> tags)
{
    Purchase p = purchaseDAO.findOne(purchaseId);

    p.addTags(tags);
}

Answer 1

You load the Purchase without initializing its tags collection and then, in your controller, once the transaction is committed and the session closed, you’re adding a tag to this non-initialized collection. So obviously, this exception is thrown.

You have two possibilities:

1. Load the tags with the Purchase, either by calling Hibernate.initialize(purchase.getTags()), or by executing a JPQL query that loads the tag along with its tags, in a single query (select distinct p from Purchase p left join fetch p.tags).
2. Instead of having a service class that offers noting more than the DAO, add a real service method addTagsToPurchase(Long purchaseId, Set<Tag> tags) which reloads the purchase and adds the tags to this purchase. This is in fact the service method needed by your controller.

I of course prefer the second solution by far:

• it shows why a service layer is useful,
• it removes business code from the presentation layer to put it in the service layer,
• it’s more efficient
• it’s safer because it uses attached entities, and thus avoids the kind of exception you’re having.

In general, if your controller, to execute a single atomic action, needs several calls to the service layer, it means that the service layer doesn’t offer the needed functionality, and that the service is implemented in the presentation layer instead.