RESTful Data Access Services with Java EE

Getting a Good REST (Service) on the Run(time) Shaun Smith Principal Product Manager, Oracle TopLink EclipseLink and Gemini Committer

Java Persistence: The Problem Space JAXB : Java Architecture for XML Binding <customer id=“…”> <name>…</name> … </contact-info> </customer> XML JPA : Java Persistence API CUST ID NAME C_RATING Relational Customer id: int name: String creditRating: int Java JPA JAXB DBWS

Use Case – Data Access Service
In Java EE:
Framework - Java API for RESTful Services (JAX-RS)
Message Binding - Java Architecture for XML Binding (JAXB)
Persistence - Java Persistence API (JPA)
Data Access Service Data Source XML JSON Objects JPA JAXB JAXB

What is REST?
REST – RE presentational S tate T ransfer
Priniciples:
Addressable resources (URI per resource)
Small set of well-defined methods (i.e. GET, PUT, POST, DELETE)
Representation-oriented
Communicate statelessly

What is JAX-RS?
JAX-RS - Java API for RESTful Services
Principles
Java EE framework for implementing RESTful services
Provides annotations to bind combination of URI and HTTP operation to Java methods.
Specifications
JAX-RS 1.0 (JSR 311) – Released October 2008
JAX-RS 2.0 (JSR 339) – In Progress

REST Service – Read (GET)
REST GET operations correspond to JPA queries.
@GET
@Path("{id}")
@Produces({"application/xml", "application/json"})
public Customer read(@PathParam("id") int id) {
return entityManager.find(Customer.class, id);
}
Relational Database JAX-RS EclipseLink JPA EclipseLink JAXB XML Document

REST Service – Create (POST)
REST POST operations correspond to JPA persist
operations.
@POST
@Consumes({"application/xml", "application/json"})
public void create(Customer customer) {
entityManager.persist(customer);
}

REST Service – Update (PUT)
REST PUT operations correspond to JPA merge
operations.
@PUT
@Consumes({"application/xml", "application/json"})
public void update(Customer customer) {
entityManager.merge(customer);
}

REST Service – Delete (DELETE)
REST DELETE operations correspond to JPA remove
operations.
@DELETE
@Path("{id}")
public void delete(int id) {
Customer customer
= entityManager.find(Customer.class, id);
if(null != customer) {
entityManager.remove(entity);
}
}

Java Persistence API (JPA) & JAXB @XmlRootElement @Entity public class Customer { @XmlAttribute @Id public int getId() {…} public void setId(int id) {…} @XmlElement(name=“billing-address”) @OneToOne @JoinColumn(name="ADDR_ID") public Address getBillingAddress() {…} public void setBillingAddress(Address address) {…} } Combining JAXB and JPA Annotations

Pain Points – Mapping JPA Entities to XML
Bidirectional/Cyclical Relationships
Composite Keys/Embedded Key Classes

Pain Points – Bidirectional Relationships
JAXB
Standard JAXB does not support bidirectional relationships. One side must be marked @XmlTransient .
JAXB implementations may provide extensions for handling bidirectional relationships such as @XmlInverseReference(mappedBy=“foo”) in MOXy.

Pain Points – Shared References
Privately owned references can be represented through key/foreign key relationships in XML.
Use @XmlID/@XmlIDREF.

Pain Points – Embedded Key Classes
Standard JAXB does not support embedded key classes.
JAXB implementations such as EclipseLink MOXy offer extensions to handle this use case (mapping is the same as for composite keys).

Pain Points – Composite Keys
Standard JAXB does not support composite keys.
Sample extension, EclipseLink JAXB (MOXy):
@XmlJoinNodes({ @XmlJoinNode(xmlPath="address/@id", referencedXmlPath="@id"), @XmlJoinNode(xmlPath=“address/@city", referencedXmlPath="city/text()") }) public Address address;

For More Information
EclipseLink
http://www.eclipse.org/eclipselink/
http://wiki.eclipse.org/EclipseLink
bdoughan.blogspot.com

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RESTful Data Access Services with Java EE

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