Every non-trivial GWT application requires integration with the server side. While GWT itself ships with the integration capabilities (i.e GWT RPC) it doesn't go beyond that. Developers have to decide how to build the backend to their GWT applications. While freedom of choice is a good thing, it doesn’t always lead to a good decision. In this session we’ll look at two options, JSR-299 [1] and JSR-311 [2], both part of the EE6 specification and see how they interplay with GWT. We'll discuss the use cases and justifications for each technology see how they are applied in practice by looking at some code examples. [1] JSR-299: Java Contexts and Dependency Injection for the Java EE platform (CDI) is the new Java standard for dependency injection and contextual lifecycle management. [2] JSR-311: A that specification defines a set of Java APIs for the development of Web services built according to the Representational State Transfer[1] (REST) architectural style.

1. GWT, CDI & JAX-RS
“A match made in heaven”
Heiko Braun <hbraun@redhat.com>

2. About me
• Heiko Braun
• Senior Software Engineer JBoss / Red Hat
• 4 years JBoss, 12 years industry
• Focus on SOA, BPM, GWT
• Contributor:
JBossWS, jBPM, Riftsaw, Errai, SAM, Savarra
> http://jboss.org

3. Topics
• GWT ecosystem
• Integrating with CDI
• When to use JAX-RPC

4. GWT ecosystem

5. GWT: Strong client side
• GWT SDK: Tools & API to build Ajax clients &
frameworks
• Integration capabilities:
- GWT RPC
- XHR (Request Builder)
• Data formats: JSON, XML
• Rich set of widget libraries:
- Mosaic, Smart GWT, etc

6. GWT: Weak server side
• Service implementation choice:
- rely on GWT RPC
- or handle the low level protocol manually
• Existing domain & component model?
- Adapters, DTO’s, parallel hierarchy, etc
- TX, Security, etc
• A lot of boilerplate needs to be written

7. Backend implementation
options

8. Java EE choices
• CDI: Context and dependency injection for
the EE platform
(http://jcp.org/en/jsr/summary?id=299)
• Java API for RESTful web services
(http://jcp.org/en/jsr/detail?id=311)
• Both part of EE 6

9. Relation to Errai
• CDI integration build on Errai
(http://jboss.org/errai)
• Integration is actually an extension to Errai
and vice versa
• Knowledge about Errai Message Bus helpful,
but not mandatory

10. GWT & CDI

11. GWT & CDI goals
• Similar to GWT-RPC:
• re-use domain model
• transparent wire protocol (serialization)
• In addition to GWT-RPC:
• Bypass the servlet tier (merely transport)
• Deep integration with EE component model
• Richer programming model & reduction of boiler
plate

12. CDI Concepts
• Portable Extensions
• Integration point when container bootstraps
• Create beans, annotation processing, meta data
modifications
• Scope & Lifecycle
• ApplicationScoped, RequestScoped, ConversationScoped
• Bean context & reference
• Lookup and instance (reference) creation
12

13. GWT & CDI Samples

14. Using Pub/Sub
GWT Client
• Most low level use cases
(Errai Bus, Pub/Sub)
• Similar to MessageDriven
Bean
(actual maps to it) CDI Component
• Service implementation
fully managed by CDI
container
• Message Bus instance
injected
14

15. Exposing RPC endpoints
GWT Client
• Exposes a typed
interface
• Similar to EJB Session
beans
(maps to it) CDI Component
• RPC style, type safe
Remote interface
client API
15

16. Working with CDI events
GWT Client
• Bi-directional event
exchange
• Discriminate on:
- Event Type
- Qualifier Annotations
CDI Component
• Exposes high level CDI
client API
• Integrate with default and
custom CDI events
16

17. When to integrate with
CDI
• Benefits of Java EE 6 and GWT as an
alternative view layer technology
• Concise Java component model
• Tool chain: GWT, EJB, CDI, JPA, JCA, JMS
17

18. GWT & JAX-RPC

19. GWT & JAX-RPC goals
• RESTful web services:
- RESTful API: open to non-java clients
- Intermediaries: proxies, gateways, firewalls
- [...] (See other Jazoon talks on this topic)
• Expose low level protocol with a decent API
• Directly expose XML, HTML from other resources
- BIRT reporting (mashup, iframe)
- Use of XML documents
• Integrate with XHR (RequestBuilder)
• Reuse domain model (serialization)

20. JAX-RPC Concepts
@Path("/customerservice/")
@Produces("application/xml")
public class CustomerService {
@GET
@Path("/customers/{id}")
@Produces("application/json")
public Customer getCustomer(@PathParam("id") String id) {
......
}
@PUT
@Path("/customers/{id}")
@Consumes("application/xml")
public Response updateCustomer(@PathParam("id") Long id, Customer customer) {
......
}
@POST
@Path("/customers")
public Response addCustomer(Customer customer) {
......
}
@DELETE
@Path("/customers/{id}/")
public Response deleteCustomer(@PathParam("id") String id) {
......
}
}

21. GWT & JAX-RPC
samples

22. Request a JAX-RPC
resource
GWT Client
Server Resource

23. Conclusion
• CDI integration probably most reasonable choice for
within EE 6 environments
• Integration & boilerplate missing: Errai [1] to the rescue
• JAX-RPC is more open, but very low level.
Still better then writing your own servlet code
• Remember: You can mix and match JAX-RPC and CDI
within the same components (at least on JBoss 6)
[1] http://anonsvn.jboss.org/repos/errai/projects/weld-integration/trunk/

24. Q&A
> http://jboss.org/errai
> http://errai-blog.blogspot.com/

25. Appendix A:
Errai Message Bus

26. Errai Basics
• Backbone to application
design
• Federated architecture
• Asynchronous & bi-
directional
• Supports POJO
serialization
• Common shared API
• Supports OpenHUB spec
• HTTP + NIO

27. Errai API
Publisher
Subscriber