Welcome!

Java IoT Authors: Liz McMillan, Elizabeth White, Pat Romanski, Yeshim Deniz, Zakia Bouachraoui

Related Topics: Java IoT

Java IoT: Article

Are the JPA Callback Methods Useful?

The restrictions JPA imposes on callback methods made them practically useless in real-life applications

Definitely no. The section 3.5 of JPA specification states:

"In general, the lifecycle method of a portable application should not invoke EntityManager or Query operations, access other entity instances, or modify relationships within the same persistence context. A lifecycle callback method may modify the non-relationship state of the entity on which it is invoked."

Surely these restrictions have a good technical reason behind them, but from a business application developer perspective they mean that JPA callback methods are practically useless.

For example, these scenarios are typical:

  • In order to remove some entity we need to verify if some data exists, and we want do it using a JPA query.
  • When an entity is saved, some other entities must be automatically created and saved, and we want to use the JPA EntityManager to do so.

Unfortunately, it's difficult to solve such cases using the standard annotations: @PrePersist, @PostPersist, @PreRemove, @PostRemove, @PreUpdate, @PostUpdate or @PostLoad.

What can we do?
We have several options such as:

  • Using JDBC from the callback methods: Horror!
  • Create a new EntityManager in the callback method: This works sometimes, but you can have problems with isolation levels. Moreover, you lose the transactional behavior.
  • Put the on-save or on-remove logic in the controller layer, that is in the actions. Of course, this works just fine, but if you access the entities from other actions, from a batch process, or from a web service, the on-logic or on-remove will not be executed.

Obviously, these options are messy and unnatural, and even worse, they mean more work for us.

Create your own callback annotations
In OpenXava, we have opted for the simplest solution for the poor application developer, just creating some new callback annotations that allow them to use JPA inside them. OpenXava 4.0.1 includes the next new annotations: @PreCreate, @PostCreate and @PreDelete.

For example, if we need to create a customer and assign it to an invoice when the customer is not specified, you can write:

@PreCreate
public void onPreCreate() {
// Automatically create a new customer
if (getCustomer() == null) {
Customer cust = new Customer();
cust.setName(getName());
cust.setAddress(getAddress());
cust = XPersistence.getManager().merge(cust); // Here we use the EntityManager
setCustomer(cust); // and here we change a relationship
}
}

If you want to enjoy these annotations just use OpenXava to develop your application. Although if you are not still ready for rapid development, you can create these annotations easily, just use the decorator pattern over the EntityManager or use AOP to refine the behavior of persist() and remove() methods.

Learn more about these annotations

More Stories By Javier Paniza

Javier Paniza is the project lead for OpenXava project. He works as software developer at Gestión 400, a software company for public administration in Spain. He has been developing with Java Enterprise since 1998. Also he has been J2EE mentor for development teams in banking projects.

IoT & Smart Cities Stories
SYS-CON Events announced today that DatacenterDynamics has been named “Media Sponsor” of SYS-CON's 18th International Cloud Expo, which will take place on June 7–9, 2016, at the Javits Center in New York City, NY. DatacenterDynamics is a brand of DCD Group, a global B2B media and publishing company that develops products to help senior professionals in the world's most ICT dependent organizations make risk-based infrastructure and capacity decisions.
CloudEXPO New York 2018, colocated with DXWorldEXPO New York 2018 will be held November 11-13, 2018, in New York City and will bring together Cloud Computing, FinTech and Blockchain, Digital Transformation, Big Data, Internet of Things, DevOps, AI, Machine Learning and WebRTC to one location.
DXWordEXPO New York 2018, colocated with CloudEXPO New York 2018 will be held November 11-13, 2018, in New York City and will bring together Cloud Computing, FinTech and Blockchain, Digital Transformation, Big Data, Internet of Things, DevOps, AI, Machine Learning and WebRTC to one location.
@DevOpsSummit at Cloud Expo, taking place November 12-13 in New York City, NY, is co-located with 22nd international CloudEXPO | first international DXWorldEXPO and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. The widespread success of cloud computing is driving the DevOps revolution in enterprise IT. Now as never before, development teams must communicate and collaborate in a dynamic, 24/7/365 environment. There is no time t...
Cloud-enabled transformation has evolved from cost saving measure to business innovation strategy -- one that combines the cloud with cognitive capabilities to drive market disruption. Learn how you can achieve the insight and agility you need to gain a competitive advantage. Industry-acclaimed CTO and cloud expert, Shankar Kalyana presents. Only the most exceptional IBMers are appointed with the rare distinction of IBM Fellow, the highest technical honor in the company. Shankar has also receive...
A valuable conference experience generates new contacts, sales leads, potential strategic partners and potential investors; helps gather competitive intelligence and even provides inspiration for new products and services. Conference Guru works with conference organizers to pass great deals to great conferences, helping you discover new conferences and increase your return on investment.
Headquartered in Plainsboro, NJ, Synametrics Technologies has provided IT professionals and computer systems developers since 1997. Based on the success of their initial product offerings (WinSQL and DeltaCopy), the company continues to create and hone innovative products that help its customers get more from their computer applications, databases and infrastructure. To date, over one million users around the world have chosen Synametrics solutions to help power their accelerated business or per...
DXWorldEXPO LLC announced today that ICOHOLDER named "Media Sponsor" of Miami Blockchain Event by FinTechEXPO. ICOHOLDER gives detailed information and help the community to invest in the trusty projects. Miami Blockchain Event by FinTechEXPO has opened its Call for Papers. The two-day event will present 20 top Blockchain experts. All speaking inquiries which covers the following information can be submitted by email to [email protected] Miami Blockchain Event by FinTechEXPOalso offers sp...
SYS-CON Events announced today that IoT Global Network has been named “Media Sponsor” of SYS-CON's @ThingsExpo, which will take place on June 6–8, 2017, at the Javits Center in New York City, NY. The IoT Global Network is a platform where you can connect with industry experts and network across the IoT community to build the successful IoT business of the future.
IoT is rapidly becoming mainstream as more and more investments are made into the platforms and technology. As this movement continues to expand and gain momentum it creates a massive wall of noise that can be difficult to sift through. Unfortunately, this inevitably makes IoT less approachable for people to get started with and can hamper efforts to integrate this key technology into your own portfolio. There are so many connected products already in place today with many hundreds more on the h...