CODEWITHSUNDEEP
javajakarta-ee
LuckyLuke
LuckyLuke

Reputation: 49077

What is correct about packaging a Java EE application

I am reading Beginning Java EE 6 with GlassFish 3 and I am confused about what is correct about packaging a Java EE application.

EJBs Lite can be pacakaged directly in a war or in a jar file. If you need to use the full EJB specification (e.g., remote interface, JMS, asynchrounous calls...) you have to packaged it inot a jar, not a war.

What does this mean? If I deploy an application packaged as a WAR in Glassfish, doesn't it give me all the Java EE services? If so what am I missing.

I understand that 3.1 introduced a new profile EJB Lite which is intended to be a subset of the full specification was targeted to implementors which doesn't want to implement everything, and that you from 3.1 can package EJBs in the WAR and use the services specified by the EJB Lite spec. But if you deploy a WAR in a full spec container it should give you everything as it would if you had created a JAR? Isn't a WAR just another name for a JAR? The distinction can't be on how it is packaged but what it actually supports?

Could somebody clarify.

Upvotes: 0

Views: 297

Answers (1)

Łukasz Rżanek
Łukasz Rżanek

Reputation: 5836

The motivation of putting EJB logic beans in JAR files comes from a separation between business logic and view logic. At this time, as far as I am aware, there is no need to package all the EJBs into JAR and then combine this JAR with a WAR into EAR.

But... since EJBs are supposed to concentrate only on business logic, it makes sense to package them in a separate archive. WAR on the other hand is an archive of all things related to showing the GUI to the user, so JSPs, Facelets, images, CSS files and JavaScript libraries. WAR files can have a set of Classes in a WEB-INF\classes folder, as well as their own libraries in WEB-INF\lib. WAR file does not have to be a file, anyway. WAR file can become an exploded WAR, basically a directory with the same structure as it was in the archive.

A key aspect of that comes to class loader isolation in the class loader hierarchy. The WAR module has access to resources in EJB archive (JAR) and EJB module can reference and access resources (libraries) in the EAR file itself. The other direction, specifically an access to WAR resources from EJB module, is prohibited. And it is that way by design, as it prevents the developers - working under pressure - to mix those concerns and create a spaghetti code. Business Logic should be separated from View Logic, as it can and should be reused by Java SE clients, different Web Module clients, JAX-RS or within SOA based solution. If the business logic had any dependencies among JSFs or Servlets, using them in Java SE desktop solution would be impossible.

So, having a structure of EJB archive, which consists of many JAR and WAR files may not be necessary, but it is a best practice and one should be careful and concious about violating that rule.

Upvotes: 2

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