If Tomcat is unable to identify the appropriate resource factory and/or additional configuration information is required, additional Tomcat specific configuration must be specified before Tomcat can create the resource. Tomcat specific resource configuration is entered in the <Context> elements that can be specified in either$CATALINA_BASE/conf/server.xml or, preferably, the per-web-application context XML file (META-INF/context.xml).
Tomcat specific resource configuration is performed using the following elements in the <Context> element:
- <Environment> – Configure names and values for scalar environment entries that will be exposed to the web application through the JNDI InitialContext (equivalent to the inclusion of an <env-entry> element in the web application deployment descriptor).
- <Resource> – Configure the name and data type of a resource made available to the application (equivalent to the inclusion of a <resource-ref> element in the web application deployment descriptor).
- <ResourceLink> – Add a link to a resource defined in the global JNDI context. Use resource links to give a web application access to a resource defined in the <GlobalNamingResources> child element of the <Server>element.
- <Transaction> – Add a resource factory for instantiating the UserTransaction object instance that is available at java:comp/UserTransaction.
Any number of these elements may be nested inside a <Context> element and will be associated only with that particular web application.
If a resource has been defined in a <Context> element it is not necessary for that resource to be defined in /WEB-INF/web.xml. However, it is recommended to keep the entry in /WEB-INF/web.xml to document the resource requirements for the web application.
Where the same resource name has been defined for a <env-entry> element included in the web application deployment descriptor (/WEB-INF/web.xml) and in an <Environment> element as part of the <Context> element for the web application, the values in the deployment descriptor will take precedence only if allowed by the corresponding <Environment> element (by setting the override attribute to “true”).
