Enterprise software development is inherently complex, and multi-user systems open the door to concerns such as transactional integrity, security, persistence integration, and interaction between components. Very simply put, the mission of the Java Enterprise Edition is to enable an out-of-the-box set of configurable services that allows the programmer to write less and focus on delivering clean business logic.

To this end, Java EE 6 is an aggregate of many interoperable technologies designed to deliver a unified experience. Application Servers that are certified to the standards defined by the Java Community Process are intended to service applications written to the specifications within the platform.

For the sake of brevity, this reference card will focus on the key APIs of Java EE 6 that are most relevant to modern development.

JSR-316

This umbrella specification ties together the various subsystems that comprise the platform and provides additional integration support.

Profiles

New to Java EE 6 is the notion of the “Web Profile”, a subset of the full specification that is targeted to cater to more specialized and minimal webbased application requirements. It is guaranteed to support the platform common annotations for injection and lifecycle (JSR-250), JNDI Naming standards, and the Java Transaction API. Additionally, the Web Profile focuses on Servlet and closely related technologies such as persistence, view presentation (JavaServer Faces and JavaServer Pages), and the business logic elements of EJB Lite.

Code Example

The simple class below is all it takes in Java EE 6 to define a POJO-based managed component capable of lifecycle callbacks, interceptors, and resource injection.

/**
* Interceptor logging that an invocation has been received
*/

public class LoggingInterceptor {
@AroundInvoke
public Object intercept(InvocationContext context) throws Exception {
System.out.println(“Been intercepted: “ + context);
return context.proceed(); }
}

/**
* Defines a simple managed bean able to receive an injection
*/
@ManagedBean
@Interceptors({LoggingInterceptor.class}) // Invocations will be
// intercepted
public class ComponentResourceInjection {

  @Resource
private UserTransaction userTransaction;
// ... business methods will be intercepted
  // by LoggingInterceptor

Reference

The full JavaDoc for the Java EE 6 API is located at: http://download.oracle.com/javaee/6/api/

JSR-250

The common annotations for Java EE are a shared package used throughout the platform specifications that generally focus on shared services like lifecycle, injection, and security.

JSR-315

Servlet technology models the request/response programming model and is commonly used to extend HTTP servers to tie into server-side business logic. In Servlet 3.0, the specification has been expanded to include support for annotations, asynchronous processing, pluggability, and general ease-of-configuration.

Code Example

Because Servlet 3.0 includes annotations to define servlets, the descriptor web.xml is no longer required in most of the common cases; below is an example of all that’s needed to create a simple servlet.

/**
        * Simple Servlet which welcomes the user by name specified
        * by the request parameter “name”.
        */
@WebServlet(urlPatterns =
{“/welcome”}) // Will service requests to the path “/welcome”
public class WelcomeServlet extends HttpServlet
{
        /**
         * Inject a reference to an EJB
         */
        @EJB
        private WelcomeBean bean;
/**
* Service HTTP GET Requests
*/
  @Override
  protected void doGet(final HttpServletRequest request, final HttpServletResponse
response) throws ServletException,
IOException
{
        // Get the name from the request
        final String name = request.getParameter(“name”);
        // Precondition checks
        if (name == null)
        {
        response.sendError(HttpServletResponse.SC_BAD_REQUEST, “Request
parameter \”name\” is required”);
        }
        // Set content type
        response.setContentType(“text/plain”);
        // Get the welcome message
        final String welcomeMessage = bean.welcome(name);
        // Write out
        response.getWriter().write(welcomeMessage);
}
}

Public API from javax.servlet.annotation:

JSR-311

New to Java EE, the JAX-RS specification allows for standard development adhering to the Representational State Transfer (REST) paradigm. These applications are packaged as a Servlet inside a web application archive.

/**
* JAXB Model of a Name
*/
@XmlRootElement
public class Name {
        private String name;

        public Name(String name) {
        this.name = name;
        }
        public Name() {}
        public String getName() {return this.name;}

        public void setName(String name) {
        this.name = name;
        }
}

/**
  * Services requests for the path “/name”
  * returning the JAXB-formed Name XML
  */
@Path(“/name”)
@Produces({“application/xml”})
public class NamedResource extends javax.ws.rs.core.Application {
        @GET
        public Name get(@QueryParam(“name”) String name) {
                return new Name(name);
}
}

...and HTTP GET requests to “{baseUrl}/myapp/name?name=andrew” will return the XML form for the Name.

Public API Annotation Selection from javax.ws.rs:

JSR-299

The Java Contexts and Dependency Injection (CDI) specification introduces a standard set of application component management services to the Java EE platform. CDI manages the lifecycle and interactions of stateful components bound to well defined contexts. CDI provides typesafe dependency injection between components. CDI also provides interceptors and decorators to extend the behavior of components, an event model for loosely coupled components and an SPI allowing portable extensions to integrate cleanly with the Java EE environment. Additionally, CDI provides for easy integration with view layers such as JavaServer Faces 2.0 (JSR-314).

Code Example

Below is a simple example of a CDI Bean that is placed in scope alongside the HTTP session, given a String-based name binding (such that it may be used in JSF view components, for example) and injects the FacesContext such that it may be used in business methods.

        @SessionScoped // Bind to the web session
        @Named // To be used in view components by name
        public class GreeterBean implements Serializable {

                @Inject // Used to integrate w/ JSF
                private FacesContext context;

                public GreeterBean() {}

                // ... business methods

        }

Relevent Public Annotation API from JSR-330, Dependency Injection for Java in package javax.inject:

For a deeper dive into CDI, check out DZone’s CDI Refcard: http://refcardz.dzone.com/refcardz/contexts-and-depencency

Bean Validation 1.0

New to Java EE 6, the Bean Validation Specification provides for unified declaration of validation constraints upon bean data. It may be used to maintain the integrity of an object at all levels of an application: from user form input in the presentation tier all the way to the persistence layer.

Code Example

Here is an example of how to apply Bean Validation constraints in a declarative fashion to ensure the integrity of a User object.

public class User {
                @NotNull
                @Size(min=1, max=15)
                private String firstname;

                @NotNull
                @Size(min=1, max=30)
                private String lastname;

                @Pattern(regexp=”\b[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,4}\b”)
                public String email;
        }

Public Annotation API for javax.validation

JSR-314

JavaServer Faces is a user interface (UI) framework for the development of Java web applications. Its primary function is to provide a componentbased toolset for easily displaying dynamic data to the user. It also integrates a rich set of tools to help manage state and promote code reuse.

Additionally, JSF is an extensible specification that encourages the authoring of custom user views. It’s designed with tooling in mind such that integrated development environments (IDEs) can intelligently assist with design.

Code Example

Here we’ll show a simple example of a JSF managed bean whose state is scope to the HTTP request, and is registered to a bean name that may be accessed by the view layer.

        /**
  * This class defines a bean to live bound to the HTTP
  * request scope, and may be accessed by the view layer
  * under the name “hitchhikersGuide”.
  */
import javax.annotation.PostConstruct;
import javax.enterprise.context.RequestScoped;
import javax.faces.application.ProjectStage;
import javax.faces.bean.ManagedBean;
import javax.faces.bean.ManagedProperty;

@RequestScoped
@ManagedBean(name = “hitchhikersGuide”)
public class HitchhikersGuide {
private String ultimateAnswer;

        @ManagedProperty(value = “#{facesContext.application.projectStage}”)
        private ProjectStage journeyStage;
        public String getUltimateAnswer() {
          return ultimateAnswer;
        }
        public void setUltimateAnswer(String ultimateAnswer) {
          this.ultimateAnswer = ultimateAnswer;
        }
        public ProjectStage getJourneyStage() {
          return journeyStage;
        }
        public void setJourneyStage(ProjectStage journeyStage) {
          this.journeyStage = journeyStage;
        }
        @PostConstruct
        public void findUltimateAnswerToUltimateQuestion() {
          ultimateAnswer = “42”;
        }

}

index.xhtml View:

<!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.0 Transitional//EN”
         “http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd”>
<html xmlns=”http://www.w3.org/1999/xhtml”
        xmlns:h=”http://java.sun.com/jsf/html”
        xmlns:f=”http://java.sun.com/jsf/core”>
        <head>
                <title>Sample JSF Page</title>
        </head>
        <body>
        <f:view>
                <h2><h:outputText value=”Test Managed Bean Annotations”/></h2>
                <p><h:outputText value=”hitchhikersGuide.ultimateAnswer =
#{hitchhikersGuide.ultimateAnswer}”/></p>
                <h2><h:outputText value=”Test Project Stage”/></h2>
                <p><h:outputText value=”project stage = #{hitchhikersGuide.
journeyStage}”/></p>
        </f:view>
        </body>
</html>

Public API from javax.faces.bean:

JSR-318

Enterprise JavaBeans provide a component model to encapsulate business logic. As such, they provide a few bean types:

• Session Beans
• Stateless
• No conversational state between requests
• Stateful
• Same bean instance used to service each client/session
• Singleton
• One shared bean instance for all users
• Message-Driven
• Event Listener
• JCA endpoint
• Asynchronous
• Entity
• Integration point w/ Java Persistence

Code Example

It’s simple to define an EJB capable of greeting a user.

/**
 * Stateless Session EJB
 */
@Stateless // Defines a Stateless Session Bean
@LocalBean // No-interface view
public class GreeterBean {
        @Override
        public String greet(String name) {
                return “Hi, “ + name + “!”;
        }
}

Other components, such as Servlets, may now inject a proxy to the above EJB:

@EJB private GreeterBean greeterEjb;

Public API Annotation Selection from javax.ejb:

JSR-317

Most enterprise applications will need to deal with persistent data, and interaction with relational databases can be a tedious and difficult endeavor. The Java Persistence specification aims to provide an object view of backend storage in a transactionally aware manner. By dealing with POJOs, JPA enables developers to perform database operations without the need for manually tuning SQL.

Code Example

A JPA entity is simply a POJO with some annotations to provide additional mapping metadata. For instance:

@Entity
        public class SimpleEmployee {
                @Id @Auto
                private Long id;
                private String name;
                public Long getId(){ return id; }
                public void setId(final Long id) { this.id = id; }
                public String getName() { return name; }
                public void setName(final String name) { this.name = name; }
}

Now a managed component such as an EJB or CDI bean can interact with the database through our entity by associating it with an EntityManager

@PersistenceContext
private EntityManager em;
public void createUser(){
        final SimpleEmployee andrew = new SimpleEmployee();
        andrew.setId(100L);
        andrew.setName(“Andrew Lee Rubinger”);
        em.persist(andrew); // Store in the DB
        // Now any state changes done to this managed object will be
        // reflected in the database when the Tx completes
}

Public API Annotation Selection from javax.persistence: