Variables

Variables and variable references are needed for two reasons:

• Parts of the Enterprise Server share much configuration information but differ in specific details. For example, server instances in a cluster typically share the same configuration except for their port numbers.

• Parts of the configuration come from the system environment but must still be captured in the configuration.

Variable references appear in the domain.xml file as strings that begin with the characters ${ and end with the character }. For example, the string ${com.sun.enterprise.myVar} is a reference to the variable com.sun.enterprise.myVar .

Variables are defined both outside of and within domain.xml. Predefined variables that exist outside of domain.xml are defined as Java System Properties. Within domain.xml, a variable is defined using the system-property element or the jvm-options element.

The system-property element’s name attribute is the name of a variable; its value attribute is the definition of the variable. For example, the following system-property element defines a port-number variable with the value 6500:

<system-property name="port-number" value="6500"/>

Multiple system-property subelements are permitted within server, cluster, config, and domain elements.

A variable defined in the jvm-options element is a Java System Property with the -D flag. For example, the following jvm-options element defines a port-number variable with the value 5500:

<jvm-option>-Dport-number=5500</jvm-option>

Multiple definitions for the same variable are permitted. The Enterprise Server determines the actual value of a variable by searching for its first definition in a strict hierarchy of the elements within domain.xml. The hierarchy is as follows:

server -> cluster -> config -> jvm-options -> domain -> System

Implicit in this hierarchy is the notion of reference and containment. A variable referenced in a server element is only looked up:

• In the cluster element referenced by that specific server

• In the config element that references that specific server

• In the jvm-options subelements of the config element referenced by that server

Some topics in the documentation pertain to features that are available only in domains that are configured to support clusters. Examples of domains that support clusters are domains that are created with the cluster profile or the enterprise profile. For information about profiles, see Usage Profiles in Sun GlassFish Enterprise Server 2.1 Administration Guide.