Guidelines: Assembling J2EE Applications
Topics
Introduction
J2EE application assemblers assemble J2EE Modules into a J2EE Application. Application Assemblers can pick off-the-shelf modules and use them in their applications simply by modifying the deployment descriptors or by providing alternative descriptors.
Some application servers require an EAR "wrapper" around the EJB-JAR, WAR, and other JAR archives for deployment, which means that the J2EE application component provider may also need to assemble an EAR for testing.
Detailed steps assembling a J2EE Application are provided by the J2EE specification, section J2EE.8.3 Application Assembly. The following is a summarized extract of this guidance.
Assembling a J2EE Application
Assembling a J2EE Application involves the following steps:
- Select the J2EE Modules that will be used by the application.
- Create an application directory structure.
- Reconcile J2EE Module deployment descriptors.
- Edit J2EE Module deployment descriptors to link internally satisfied dependencies and eliminate redundant security role names.
- Define transactions, security roles, method permissions, etc.
- Optionally use the alt-dd element to specify an alternative deployment descriptor while preserving the original deployment descriptor.
- Assign a context root for each web module included in the J2EE application.
- Ensure component dependencies are correctly described.
- Ensure there is only one version of each class in the application.
- Create an XML deployment descriptor for the application named "application.xml".
- Package the application.
a. Place the J2EE modules in the appropriate directories. Place the deployment descriptor in META-INF/application.xml.
b. Package into a ".EAR" file.
Adding/Removing Modules
J2EE modules may be added to an application before
deployment, using the following steps:
- Decide on a location in the application package for the new module. Optionally
create new directories in the application package hierarchy. - Copy the new J2EE Modules to the desired location in the application package.
- Edit the deployment descriptors for the J2EE Modules to link the dependencies
which are internally satisfied by the J2EE Modules included in the application. - Edit the J2EE Application deployment descriptor as required.
Similarly a module can be removed by removing the module from the application package hierarchy and editing the deployment descriptors to remove inconsistencies.
Validating the Application
It is a good idea to valid the contents of the archive before attempting deployment, as obscure errors, especially on the application server side, may result in obscure or non-existent error messages. For example, confirm there is at least one module defined in the EAR
The EAR can also be validated using a J2EE verifier tool that is provided with the J2EE SDK. It makes sure that the EAR is internally consistent and well-formed. For example, it makes sure that the module and application archives are consistent with the standard specifications (J2EE, Servlet, and EJB).
