The following sections give a brief summary of the technologies required by the Java EE platform, and the APIs used in Java EE applications.
An Enterprise JavaBeans (EJB) component, or enterprise bean, is a body of code having fields and methods to implement modules of business logic. You can think of an enterprise bean as a building block that can be used alone or with other enterprise beans to execute business logic on the Java EE server.
A session bean represents a transient conversation with a client. When the client finishes executing, the session bean and its data are gone.
A message-driven bean combines features of a session bean and a message listener, allowing a business component to receive messages asynchronously. Commonly, these are Java Message Service (JMS) messages.
In the Java EE 6 platform, new enterprise bean features include the following:
The ability to package local enterprise beans in a WAR file
Singleton session beans, which provide easy access to shared state
A lightweight subset of Enterprise JavaBeans functionality that can be provided within Java EE Profiles such as the Java EE Web Profile.
Java servlet technology lets you define HTTP-specific servlet classes. A servlet class extends the capabilities of servers that host applications that are accessed by way of a request-response programming model. Although servlets can respond to any type of request, they are commonly used to extend the applications hosted by web servers.
In the Java EE 6 platform, new Java servlet technology features include the following:
Ease of configuration
Enhancements to existing APIs
A GUI component framework.
A flexible model for rendering components in different kinds of HTML or different markup languages and technologies. A Renderer object generates the markup to render the component and converts the data stored in a model object to types that can be represented in a view.
A standard RenderKit for generating HTML/4.01 markup.
The following features support the GUI components:
Data conversion between model objects and components
Managed model object creation
Page navigation configuration
All this functionality is available using standard Java APIs and XML-based configuration files.
In the Java EE 6 platform, new features of JavaServer Faces include the following:
The ability to use annotations instead of a configuration file to specify managed beans
Facelets, a display technology that replaces JavaServer Pages (JSP) technology using XHTML files
JavaServer Pages (JSP) technology lets you put snippets of servlet code directly into a text-based document. A JSP page is a text-based document that contains two types of text: static data (which can be expressed in any text-based format such as HTML, WML, and XML) and JSP elements, which determine how the page constructs dynamic content.
The JavaServer Pages Standard Tag Library (JSTL) encapsulates core functionality common to many JSP applications. Instead of mixing tags from numerous vendors in your JSP applications, you employ a single, standard set of tags. This standardization allows you to deploy your applications on any JSP container that supports JSTL and makes it more likely that the implementation of the tags is optimized.
JSTL has iterator and conditional tags for handling flow control, tags for manipulating XML documents, internationalization tags, tags for accessing databases using SQL, and commonly used functions.
The Java Persistence API is a Java standards-based solution for persistence. Persistence uses an object-relational mapping approach to bridge the gap between an object oriented model and a relational database. The Java Persistence API can also be used in Java SE applications, outside of the Java EE environment. Java Persistence consists of three areas:
The Java Persistence API
The query language
Object/relational mapping metadata
The Java Transaction API (JTA) provides a standard interface for demarcating transactions. The Java EE architecture provides a default auto commit to handle transaction commits and rollbacks. An auto commit means that any other applications that are viewing data will see the updated data after each database read or write operation. However, if your application performs two separate database access operations that depend on each other, you will want to use the JTA API to demarcate where the entire transaction, including both operations, begins, rolls back, and commits.
The Java API for RESTful Web Services (JAX-RS) defines APIs for the development of Web services built according to the Representational State Transfer (REST) architectural style. A JAX-RS application is a web application that consists of classes that are packaged as a servlet in a WAR file along with required libraries.
The JAX-RS API is new to the Java EE 6 platform.
The Java Message Service (JMS) API is a messaging standard that allows Java EE application components to create, send, receive, and read messages. It enables distributed communication that is loosely coupled, reliable, and asynchronous.
The Java EE Connector architecture is used by tools vendors and system integrators to create resource adapters that support access to enterprise information systems that can be plugged in to any Java EE product. A resource adapter is a software component that allows Java EE application components to access and interact with the underlying resource manager of the EIS. Because a resource adapter is specific to its resource manager, typically there is a different resource adapter for each type of database or enterprise information system.
The Java EE Connector architecture also provides a performance-oriented, secure, scalable, and message-based transactional integration of Java EE-based web services with existing EISs that can be either synchronous or asynchronous. Existing applications and EISs integrated through the Java EE Connector architecture into the Java EE platform can be exposed as XML-based web services by using JAX-WS and Java EE component models. Thus JAX-WS and the Java EE Connector architecture are complementary technologies for enterprise application integration (EAI) and end-to-end business integration.
Java EE applications use the JavaMail API to send email notifications. The JavaMail API has two parts: an application-level interface used by the application components to send mail, and a service provider interface. The Java EE platform includes the JavaMail API with a service provider that allows application components to send Internet mail.
The Java ACC specification defines a contract between a Java EE application server and an authorization policy provider. All Java EE containers support this contract.
The Java ACC specification defines java.security.Permission classes that satisfy the Java EE authorization model. The specification defines the binding of container access decisions to operations on instances of these permission classes. It defines the semantics of policy providers that employ the new permission classes to address the authorization requirements of the Java EE platform, including the definition and use of roles.
The Java Authentication Service Provider Interface for Containers (JASPIC) specification defines a service provider interface (SPI) by which authentication providers that implement message authentication mechanisms may be integrated in client or server message processing containers or runtimes. Authentication providers integrated through this interface operate on network messages provided to them by their calling container. They transform outgoing messages so that the source of the message may be authenticated by the receiving container, and the recipient of the message may be authenticated by the message sender. They authenticate incoming messages and return to their calling container the identity established as a result of the message authentication.
The Java API for XML Registries (JAXR) lets you access business and general-purpose registries over the web. JAXR supports the ebXML Registry and Repository standards and the emerging UDDI specifications. By using JAXR, developers can learn a single API and gain access to both of these important registry technologies.
Additionally, businesses can submit material to be shared and search for material that others have submitted. Standards groups have developed schemas for particular kinds of XML documents; two businesses might, for example, agree to use the schema for their industry’s standard purchase order form. Because the schema is stored in a standard business registry, both parties can use JAXR to access it.
The Java EE platform is a platform-independent, full systems integration solution that creates an open marketplace in which every vendor can sell to every customer. Such a marketplace encourages vendors to compete, not by trying to lock customers into their technologies but instead by trying to outdo each other in providing products and services that benefit customers, such as better performance, better tools, or better customer support.
The Java EE 6 APIs enable systems and applications integration through the following:
Unified application model across tiers with enterprise beans
Simplified request-and-response mechanism with web pages and servlets
Reliable security model with JAAS
XML-based data interchange integration with JAXP, SAAJ, and JAX-WS
Simplified interoperability with the Java EE Connector architecture
Easy database connectivity with the Java DataBase Connectivity (JDBCTM) API
Enterprise application integration with message-driven beans and JMS, JTA, and JNDI