1
Overview

This chapter provides an overview of the issues involved in migrating J2EE Web applications from WebLogic Server 7.0 to Oracle Application Server 10g (9.0.4), and the effort required.

The chapter contains these topics:

Overview of J2EE

The application server market is evolving rapidly. In particular, the most significant development over the last few years is the emergence of Sun Microsystems' Java 2 Platform, Enterprise Edition (J2EE) Specification that promises to create a level of cross-vendor standardization.

The J2EE platform and component specifications define, among other things, a standard platform for developing and deploying multi-tier, web-based, enterprise applications.

J2EE provides a solution to the problems encountered by companies moving to a multi-tier computing model. The problems addressed include reliability, scalability, security, application deployment, transaction processing, web interface design, and timely software development. It builds upon the Java 2 Platform, Standard Edition (J2SE) to enable Sun Microsystems' "Write Once, Run Anywhere"paradigm for multi-tier computing.

J2EE consists of the components described in Table 1-1:

Table 1-1 J2EE Standard Architecture Components

Component	Description
J2EE Application Model	An application model for developing multi-tier, thin client services
J2EE Platform	A platform for hosting J2EE applications
J2EE Compatibility Test Suite	A compatibility test suite for verifying that a J2EE platform product meets the requirements set forth in the J2EE platform and component specifications
J2EE Reference Implementation	A reference implementation of the J2EE platform

What is the J2EE Application Model?

The J2EE application model is a multi-tier application model. Application components are managed in the middle tier by containers. A container is a standard runtime environment that provides services, including life cycle management, deployment, and security services, to application components. This container-based model separates business logic from system infrastructure.

What is the J2EE Platform?

The J2EE platform consists of a runtime environment and a standard set of services that provide the necessary functionality for developing multi-tiered, web-based, enterprise applications.

The J2EE platform consists of the components described in Table 1-2.

Table 1-2 J2EE Platform Components

Component	Description
J2EE runtime environment
Application components
Application clients	A Java program, typically used for a GUI, that executes on a desktop computer
Applets	A component of a Java program that typically executes in a web browser
Servlets and JSP pages	Servlet: A Java program, used to generate dynamic content, that executes on a web server
	JSP page: A technology used to return dynamic content to a client, typically a web browser
Enterprise JavaBeans (EJB)	An applications architecture for component-based distributed computing
Containers	An entity that provides services for application components, including life cycle management, deployment, and security services
Resource manager drivers	A system-level component that enables network connectivity to external data sources
Database	A set of related files used for the storage of business data and accessible through the JDBC API
J2EE standard services
HTTP	The standard protocol used by the Internet to send and receive messages between web servers and browsers
HTTPS	A protocol used by the Internet to send and receive messages securely between web servers and browsers
Java Transaction API (JTA)	An API that allows applications and application servers to access transactions
RMI-IIOP	RMI: A protocol that enables Java objects to communicate remotely with other Java objects IIOP: A protocol that enables browsers and servers to exchange things other than text RMI-IIOP is a version of RMI that uses the CORBA IIOP protocol
JavaIDL	A standard language for interface specification primarily used for CORBA object interface definition
JDBC	An API that provides connectivity between databases and the J2EE platform
Java Message Service (JMS)	An API that enables the use of enterprise messaging systems
Java Naming and Directory Interface (JNDI)	An API that provides directory and naming services
JavaMail	An API that provides the ability to send and receive e-mail
JavaBeans Activation Framework (JAF)	An API required by the JavaMail API

What is an Application Server?

An application server is software that runs between web-based client programs and back-end databases and legacy applications. It helps separate system complexity from business logic, enabling developers to focus on solving business problems. An application server helps reduce the size and complexity of client programs by enabling these programs to share capabilities and resources in an organized and efficient way.

Application servers provide benefits in the areas of usability, flexibility, scalability, maintainability, and interoperability.

Overview of Oracle Application Server

Oracle Application Server is a comprehensive, integrated application server that provides all of the infrastructure and functionality needed to run every successful e-business. All development teams face a similar set of challenges--the need to rapidly deliver web sites and applications that run fast over any network and on every device; while providing business intelligence to support operational adjustments and strategic decisions. Oracle Application Server enables teams to address all of these e-business challenges.

Oracle Application Server has generated a great deal of interest in the application server market, and many organizations are embracing it to deploy their web-based, enterprise applications.

Oracle Application Server offers the only integrated infrastructure to develop, deploy, and secure web sites and applications. It provides a complete J2EE platform for developing enterprise Java applications. Oracle Application Server enables developers to develop web applications in any language including Java, Perl, PL/SQL, XML, and Forms. It enables the reduction of development and deployment costs through a single, unified platform for Java, XML, and SQL.

The J2EE server implementation in Oracle Application Server is called Oracle Application Server Containers for J2EE (OC4J). OC4J runs on the standard JDK and is extremely lightweight, provides high performance and scalability, and is simple to deploy and manage. With Oracle Application Server 10g (9.0.4), OC4J supports J2EE 1.3 APIs.

This migration guide seeks to help you understand the migration challenges you may face when migrating your J2EE applications from WebLogic Server 7.0 to Oracle Application Server 10g (9.0.4).

Note:

In this document, where WebLogic Server is mentioned without a version number, WebLogic Server 7.0 is implied. Otherwise, for other versions of WebLogic Server, a version number is specifically mentioned.

J2EE Application Migration Challenges

The varying degrees of compliance to J2EE standards can make migrating applications from one application server to another a daunting task. Some of the challenges in migrating J2EE applications from one application server to another are:

Though in theory, any J2EE application can be deployed on any J2EE-compliant application server, in practice, this is not strictly true.
Lack of knowledge of the implementation details of the given J2EE application.
Ambiguity in the meaning of 'J2EE-compliant' (usually, this means the application server has J2EE compliant features, not code-level compatibility with the J2EE specification).
The number of vendor-supplied extensions to the J2EE standards in use, which differ in deployment methods and reduce portability of Java code from one application server to another.
Differences in clustering, load balancing, and failover implementations among application servers; these differences are sparsely documented, and are thus an even bigger challenge to the migration process.

These challenges make the migration path daunting, uncertain, and difficult to reliably plan and schedule. This chapter addresses the challenges in migrating your applications from WebLogic Server to Oracle Application Server, providing an approach to migration with solutions based on the J2EE version 1.3 specification.

J2EE Application Architecture

The J2EE platform provides a multi-tiered, distributed application model. Central to the J2EE component-based development model is the notion of containers. Containers are standardized runtime environments that provide specific services to components. Thus, Enterprise JavaBeans (EJB) developed for a specific purpose in any organization can expect generic services such as transaction and EJB life cycle management to be available on any J2EE platform from any vendor.

Containers also provide standardized access to enterprise information systems; for example, providing RDBMS access through the JDBC API. Containers also provide a mechanism for selecting application behavior at assembly or deployment time.

As shown in Figure 1-1, the J2EE application architecture is a multi-tiered application model. In the middle tier, components are managed by containers; for example, J2EE web containers invoke servlet behavior, and EJB containers manage life cycle and transactions for EJBs. The container-based model separates business logic from system infrastructure.

Figure 1-1 J2EE Architecture

Text description of asmwl001.gif follows

Text description of the illustration asmwl001.gif

Migration Issues

In quantifying the migration effort, it is helpful to examine the application components to be migrated with the following issues in mind:

Portability

Code may not be portable because it contains embedded references to vendor-specific extensions to the J2EE specification. Evaluating and planning for code modifications may be a significant part of the migration effort.
Proprietary extensions

If vendor-specific extensions are in use, migration of those components becomes difficult or unfeasible. Complete redesign toward J2EE specifications is not addressed in this document. If vendor-specific extensions are in use, they may need to be redesigned and reimplemented, rather than being identified as migration candidates.
Deviations from J2EE specification.

If a component is largely non-compliant with the J2EE specification, this guide will not be helpful in determining the migration path to Oracle Application Server. If the J2EE specification version of the component is not of version 1.3 (the version on which this guide is based), then the specification implementation differences will need to be addressed.

Migration Approach

The approach in developing this migration guide was to document our experience migrating web application components from WebLogic Server to Oracle Application Server. Examples shipped with WebLogic Server were selected, tested on WebLogic Server, and migrated to Oracle Application Server. Issues encountered in the migration of these examples are the basis for this document.

Migration Effort

Moving from WebLogic Server to Oracle Application Server is a relatively simple process. Standard J2EE applications, using no proprietary APIs, can be deployed with no required code changes. The only actions required are configuration and deployment. Those applications using proprietary utilities or APIs can be ported easily.

Using This Guide

This guide details the migration of components from WebLogic Server to Oracle Application Server. While it does not claim to be an exhaustive source of solutions for every possible configuration, it provides solutions for some of the migration issues listed above, which will surface, along with others, in your migration effort. The information in this guide helps you to assess the WebLogic Server applications and plan and execute their migration to Oracle Application Server. The material in this guide supports these high-level tasks:

Survey the components according to the issues listed above
Identify migration candidates
Prepare the migration environment and tools
Migrate and test the candidate components

1 Overview