Basic Web Application Migration
basiC Web appliCation migRation Migrating basic web applications that were developed according to the servlet specification and Java EE specifications is the easiest and most cost-effective way to start migrations. It can be an excellent measure of the effort involved. If the applications were developed with a standards-based Integrated Development Environment (IDE) such as Eclipse, this will go quite smoothly. Many proprietary IDEs embed links to proprietary libraries and thus can add additional challenges to migration. JBOSS STANDARDS-BASED FRAMEWORKS CURRENT Add required jars to deploy directory or EAR STANDARDS-BASED JMS, EJB, JPA, etc. FRAMEWORKS Hibernate, Spring, Seam, Flex, Struts, JBPM, Rules engines, Workflow engines Remove proprietary imports from applications and migrate Standard web applications include a deployment descriptor called “web.xml.” Forgiving behavior by application servers often leads to the use of syntax and notations that are not portable. Red Hat tries to document such examples and has a ready list of changes that are often needed when migrating from specific application servers to JBoss solutions. Most application servers also include a second proprietary deployment descriptor for web applications to support value-added features that are not included in the standard specifications. This second descriptor is called weblogic.xml for WebLogic Server (WLS) and jboss-web.xml for JBoss. Red Hat often maintains XML style sheets that can be used to automatically transform other vendor descriptors to the JBoss-supported “jboss-web.xml,” where features and capabilities overlap. Red Hat Consulting Strategic Migration Planning Guide6 www.jboss.com Migrating a web application that is developed and deployed to WebLogic can be very simple or somewhat complicated depending on how proprietary the application architecture and dependencies are. Many web applications can simply be copied over and directly deployed to JBoss with no changes at all. Some of the common barriers to migrating web applications can include: 1. When deployed as an exploded directory, a .war extension for the directory may be required when deployed to JBoss. A similar naming convention in WebLogic is uncommon. 2. WebLogic web applications almost always bundle a weblogic.xml deployment descriptor. This descriptor can often include no relevant configuration information whatsoever and would therefore be ignored and not cause any harm under JBoss. When it provides a relevant configuration, it is very often comprised of simple items such as the context root of the web application or security settings for it, which are similarly provided in a jboss-web.xml file under JBoss. 3. Web applications may use libraries provided by WebLogic, including but not limited to JSP tag libraries and WebLogic helper classes. This is where the migration effort can potentially become substantial, depending on the exact nature of the library being used and what it takes to replace it with a standard open source alternative.