Maven Dependency

<dependency> <groupId>org.apache.juneau</groupId> <artifactId>juneau-svl</artifactId> <version>7.1.0</version> </dependency>

Java Library

juneau-svl-7.1.0.jar

OSGi Module

org.apache.juneau.svl_7.1.0.jar

The juneau-svl module defines an API for a language called "Simple Variable Language". In a nutshell, Simple Variable Language (or SVL) is text that contains variables of the form "$varName{varKey}".

Variables can be recursively nested within the varKey (e.g. "$FOO{$BAR{xxx},$BAZ{xxx}}"). Variables can also return values that themselves contain more variables.

// Use the default variable resolver to resolve a string that contains $S (system property) variables String myProperty = VarResolver.DEFAULT.resolve("The Java home directory is $S{java.home}");

The following shows how variables can be arbitrarily nested...

// Look up a property in the following order: // 1) MYPROPERTY environment variable. // 2) 'my.property' system property if environment variable not found. // 3) 'not found' string if system property not found. String myproperty = VarResolver.DEFAULT.resolve("$E{MYPROPERTY,$S{my.property,not found}}");

SVL is a large topic on it's own. It is used extensively in the ConfigFile, REST and Microservice APIs.

The following is the default list of supported variables:

• $ARG{keyOrIndex[,defaultValue]} - Command-line argument.
• $C{key[,defaultValue]} - Config file entry.
• $E{envVar[,defaultValue]} - Environment variable.
• $F{path[,defaultValue]} - File resource.
• $I{name[,defaultValue]} - Servlet init parameter.
• $L{key[,args...]} - Localized message.
• $MF{key[,defaultValue]} - Manifest file entry.
• $R{key[,args...]} - Request variable.
• $S{systemProperty[,defaultValue]} - System property.
• $SA{contentType,key[,defaultValue]} - Serialized request attribute.
• $U{uri} - URI resolver.
• $UE{uriPart} - URL-Encoder.
• $W{widgetName} - HTML widget variable.

Plugging in your own variables is also easy.

• See juneau-svl for more information.