Jpa

Let’s start with a short quiz. TxMergeBean is a SLSB that uses CMT and EntityManager. Assume the following local and remote business interfaces: public interface TxMergeCommon { void methodA(); void methodB(MeineEntity entity); } @Local public interface TxMergeLocal {} @Remote public interface TxMergeRemote {} and the following SLSB: @Stateless public class TxMergeBean implements TxMergeRemote, TxMergeLocal { @PersistenceContext private EntityManager em; @EJB private TxMergeLocal self; @Resource private SessionContext sctx; public void methodA() { MeineEntity entity = new MeineEntity("methodA"); em....

Being in EJB and JPA world using CMT (Container Managed Transactions) is very comfortable. Just define few annotations to demarcate transaction boundary (or use the defaults) and that’s it – no fiddling with manual begin, commit or rollback operations. One way to rollback your transaction is to throw non-application exception (or application exception with rollback = true) from your EJB’s business method. It seems simple: if during some operation there is a possibility that an exception will be thrown and you don’t want to rollback your tx than you should just catch this exception and you’re fine....

JPA specification defines few types of EntityManagers / Persistence Contexts. We can have: extended and transactional-scoped EntityManagers, container-managed or application-managed EntityManagers. JTA or resource-local EntityManager, Besides the above distinction, we also have two main contexts in which EntityManager / Persistence Context can exist – Java EE and Java SE. Not every option is available for Java EE and not every is possible in Java SE. In the rest of the post I refer to the Java EE environment....

In this post you can find often used Java EE 6 configuration files (along with their schema declarations to aid your IDE’s code assistant): CDI Name: beans.xml Version: 1.0 Content: <?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/beans_1_0.xsd"> </beans> JPA Name: persistence.xml Version: 2.0 Content: <?xml version="1.0" encoding="UTF-8"?> <persistence xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd" version="2.0"> </persistence> Servlets, JSP, EL Name: web.xml Version: 3.0 Content: <?xml version="1.0" encoding="UTF-8"?> <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java....

Few days ago I’ve created a simple interceptors spike-solution at Github. Its purpose was to show my colleagues that in the EJB’s interceptors you can implement a code that exists in the same transaction and the same security context as the called EJB business method. Moreover, you can benefit from all the dependency injection you need. This project uses the following resources injected by the Application Server: TransactionSynchronizationRegistry – used for getting current transaction key and checking if we’re in the same transaction (I’ve written about it e....

More than 18 months ago I’ve posted my mock exam for Oracle Certified Expert Web Component Developer certification. Until now it’s quite popular and useful (deducting from the comments) for many of you. What I dislike about this exam is that it’s published as a plain WordPress post and it’s rather awful to edit it and it’s not so easy to read as well. So, that’s the aim of my small side project: to create a basic platform for presenting exam questions and their answers....

JPA’s FETCH JOIN is useful in cases when you want to eagerly load some lazy loaded collection of your entity. By default all @OneToMany and @ManyToMany relationships are lazy loaded. There are some valid cases when (despite the settings in your mapped entity), you want to eagerly load the related entity. One of the way of doing it is to use JOIN FETCH JPQL clause. It’s worth remembering that JOIN FETCH is used mainly because of its side-effect of populating the pointed relationship – it’s still a JOIN and must be treated like it when it comes to the duplicated result set problem....

Yesterday I took the SpringSource Certified Spring 3.0 Professional exam and passed it successfully with 94%. Below you can find some information about my preparation process, the exam form and the type of questions. So, here we go. Preparation I attended the Spring 3 Core training and described it here. This was the entry point for my learning process. I’ve done a lot of notes during the training, so even after three months, the slides + notes were pretty decent source of knowledge....

Recently, I’ve bumped into few posts on StackOverflow where people tend to compare container managed EntityManager instances (so the one injected by the container) by invoking EntityManager#toString() method. I’ve felt that it’s fundamentally wrong to compare EntityManager instances without knowing how they’re managed by the JPA provider or the Server Application. And what if this behaviour differs between Application Server vendors? The JPA provider provides an implementation of EntityManager – that’s obvious....