In the geronimo-web.xml file, application deployer maps the security roles, ejb names, database resources, JMS resources, etc. declared in web.xml to corresponding entities deployed in the server. In addition to that, if there are any web container specific configurations, such as Tomcat or Jetty specific, depending on the application needs, all these settings are configured as well here. If the web application depends on any third party libraries or other services running in the server, all these dependencies are declared in the plan. Some web applications require class loading requirements different from the default class loading behavior. The geronimo-web.xml allows application deployer to configure this as well. There are many more configurations that could be done through geronimo-web.xml depending on the needs of web application. The following sections briefly explain how geronimo-web.xml can be used to configure the web container and web applications.
The geronimo-web.xml uses XML elements from http://geronimo.apache.org/xml/ns/j2ee/web-2.0.1 namespace and one or more namespaces mentioned in Common elements and Configuration section earlier in the document.
For example, the following web.xml and geronimo-web.xml are the deployment descriptor and Geronimo deployment plan respectively, of a web application that connects to a datasource deployed on DB2 and retrieves data from a table.
The web module connects to back end datasource using its JNDI name jdbc/DataSource as declared in the web.xml.
In geronimo-web.xml, a <dependency> element is added to make the the resource archive (RAR) visible to your application, and then a mapping is provided in <resource-ref>.
Observe the various XML tags and corresponding namespaces used in the deployment plan for various purposes.
<sys:environment> .. </sys:environment> : These elements provide the moduleid configuration and the dependencies. The moduleId elements provide the configuration name for the web module. So, when the web module is deployed, it is given the configuration name samples/samples/2.5/jar. The dependencies elements provide the configurations and third party libraries on which the web module is dependent on. These configurations and libraries will be available to the web module via a classloader hierarchy. In this case, the web module is dependent on samples/EmployeeDatasource/2.5/rar which is the configuration of the deployed Datasource that connects to a back end DB2 database. The Datasource deploys a database connection pool (javax.sql.Datasource) with name jdbc/EmployeeDatasource.
<sys:context-root> .. </sys:context-root> : The XML elements used to provide the web context root of the web applications.
<naming:resource-ref> .. </naming:resource-ref> : These elements help us to configure the resource references. In this case, the datasource reference jdbc/DataSource is mapped to jdbc/EmployeeDatasource.
In the EMPdemo.jsp, the following java code snippet is used to obtain a connection from the datasource. It reference the resource from the java:comp/env context entries.
The above descriptor and the plan files are the simple illustrations that explain how web modules are developed and assembled for Apache Geronimo. Similarly, many other configurations can be performed in the geronimo-web.xml.
All the XML schema files are located at <geronimo_home>/schema directory. Please go through the .xsd files to have a feel of XML tags that can be used in geronimo-web.xml for configuring web applications.