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J2EE In Web Services

Web services are providing the infrastructure and tools for automating business-to-business relationships over the Internet.

The Java 2 Platform, Enterprise Edition (J2EE) was developed to integrate web services.

The integration of web services into the J2EE 1.4 platform simplifies the task of building and consuming web services, by releasing Java developers from the low-level details of XML and web services standards.

Benefits Of Using J2EE In Web Services

The benefits of using the J2EE platform for web services include:

Portability
Scalability
Reliability
Vendor independent

J2EE containers provide transaction support, database connections, life cycle management, and other services that are scalable and require no code from application developers.

Developing In J2EE

Developing web services normally requires extensive knowledge of XML-based standards and protocols [WSDL and SOAP], and programming experience.

Java APIs for XML Registries [JAXR] and Java APIs are automatically generated for XML Remote Procedure Calls [JAX-RPC]

Using the J2EE 1.4 platform, developing web services is seamless. Knowledge of WSDL and SOAP are not required. Instead, the mapping between the Java language and XML-based standards is handled by the web service runtime system. This frees developers from low level programming to concentrate of the application function.

Building an XML-RPC style web service using the J2EE 1.4 platform involves five easy steps:

Design and code the web service endpoint interface
Implement the interface
Write a configuration file
Generate the necessary files
Use the deploytool to package the service in a WAR file and deploy it.

Deploying J2EE Web Services

The J2EE 1.4 platform supports web services through:

JAX-RPC 1.1 API - to develop service endpoints based on SOAP. JAX-RPC 1.1 interoperability with web services is based on the Web Services Description Language [WSDL] and Simple Object Access Protocol [SOAP].
JSR 109 - builds upon JAX-RPC focusing on the programming model for implementing web services, as well as deploying web services in the J2EE 1.4 platform.
WS-I Basic Profile - to extend portabilty beyond J2EE implementations to any web service developed using WS-I compliant platforms.

JSR 109

JSR 109 [Implementing Enterprise Web Services] is The Java Community Process [JCP] specification.

It leverages J2EE technologies to provide an industry standard for developing and deploying web services on the J2EE platform, as well as providing a service architecture familiar to J2EE developers.

Development Lifecycle

The JSR 109 specification outlines the lifecycle of web services:

Development - Standardizes the web services programming model as well as the deployment descriptors
Deployment - Describes the deployment actions expected of a J2EE 1.4 container
Service publication - Specifies how the WSDL is made available to clients
Service consumption - Standardizes the client deployment descriptors and a JNDI lookup model

J2EE 1.4 Platform

The J2EE 1.4 SDK includes:

J2EE 1.4 Application Server
Java 2 Platform, Standard Edition (J2SE) 1.4.2_01
J2EE Samples (Java Pet Store, Java Adventure Builder, Smart Ticket, and others)
Sun ONE Message Queue
PointBase Database Server

Download J2EE 1.4 Platform

How A J2EE Web Service Works

A Java User Client makes a request.
The request is handled by the client-side runtime JAX-RPC.
The JAX-RPC API maps the Java to XML to assemble an XML-based Remote Procedure Calls [RPC] to clients that use RPC and XML.
The RPC uses an XML-based protocol such as SOAP [to define the envelope structure, encoding rules, and convention for representing RPC calls and responses] to transmit a SOAP messages over HTTP.
The client - a proxy [or a local object that represents the remote service] that is automatically generated.
The client accesses the SOAP message via the web service port using a Service Endpoint Interface as defined by JAX-RPC.
The remote client receives the RPC and determines whether it is acceptable according to its programmed rules.
If the RPC is accepted, The SOAP handler actions container services.
The SOAP message is dissassembled, the XML is mapped back to Java.
The web service methods perform business logic on behalf of the client, by invoking the methods on the proxy. J2EE web services can be invoked by any web service client, and any J2EE web service client can invoke any web service.
The Java response is mapped back to XML to the SOAP message container and routes back via the SOAP message handler, Web services Port to another SOAP handler on the user-client, maps the XML back to Java so the response can be displayed to the user.

NOTE: The developer does not need to generate or parse SOAP messages; this is done by the JAX-RPC runtime system.

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