Get a property value with an optional default

Summary

The def macro looks up a property by key and returns its value, or returns a default value if the property is not set. The default is an empty string if not specified.

Syntax 

${def;<key>[;<default>]}

Parameters

  • key - The property name to look up
  • default (optional) - Value to return if property not set (default: empty string)

Behavior

  • Looks up property by key
  • Returns property value if set
  • Returns default if property not set
  • Default is empty string if not specified
  • Handles undefined properties gracefully

Examples

Get property with default:

${def;version;1.0.0}
# Returns property value or "1.0.0" if not set

Empty default:

${def;optional.setting}
# Returns property value or "" if not set

Use in paths:

output.dir=${def;custom.dir;target}

Conditional with default:

${if;${def;debug.mode;false};debug-on;debug-off}

Use Cases

  • Providing default values
  • Optional properties
  • Configuration fallbacks
  • Safe property access
  • Avoiding undefined property errors

Notes

  • Safer than direct property reference
  • Default prevents empty/undefined issues
  • Unlike ${key}, returns default instead of literal
  • Empty string is valid default
  • See also: ${get} for list element access
  • See also: ${if} for conditional defaults

See test cases in MacroTestsForDocsExamples.java