Expression language

The default expression language in Operaton BPMN models is JUEL, Java Unified Expression Language. JUEL is a simple expression language that can be used to reference objects in a Java environment.

Syntax

The syntax for JUEL expressions is ${} for immediate evaluation and #{} for deferred evaluation. Yet, in Operaton, all expressions are evaluated during runtime, when the element containing the expression is executed, so it is best to just use ${} for all expressions.

Here are some examples of JUEL expressions:

Expression	Expected Type	Result
Hello, World!	String	“Hello, World!”
Hello, ${“World!”}	String	“Hello, World!”
${3.14}	double	3.14
${null}	null	null
${true && false}	Boolean	false
${5 + 10}	int	15
${4 > 3}	Boolean	true
${5 > 3 ? “Yes” : “No”}	String	“Yes”
${3 > 5 ? “Yes” : “No”}	String	“No”
${empty “”}	Boolean	true
${empty null}	Boolean	true
${empty “text”}	Boolean	false

Operators in expressions

JUEL supports the following operators:

Type	Operators
Arithmetic	+, - (binary), *, /, div, %, mod, - (unary)
Logical	and, &&, or, `
Relational	==, eq, !=, ne, <, lt, >, gt, <=, ge, >=, le
Empty	empty (checks if a value is null or empty)
Conditional	A ? B : C

Reserved words

The following words are reserved in JUEL and cannot be used as variable names:

Word	Description
and	Logical AND
or	Logical OR
not	Logical NOT
eq	Equal to
ne	Not equal to
lt	Less than
gt	Greater than
le	Less than or equal to
ge	Greater than or equal to
true	Boolean true
false	Boolean false
null	Null value
instanceof	Checks if an object is an instance of a class
empty	Checks if a value is null or empty
div	Division
mod	Modulus

Objects in expressions

To refer to variables or objects and their properties and methods, you can use the following syntax:

Syntax	Description
${variableName}	Refers to a variable
${objectName.propertyName}	Refers to an object’s property
${objectName.methodName()}	Calls an object’s method

For example, if you have an execution object (like in Operaton expressions), you can refer to its properties and methods as follows:

Expression	Description
${execution.getBusinessKey()}	Refers to the business key property
${execution.getProcessInstancesId()}	Refers to the process instance ID
${execution.getVariable("variableName")}	Calls getVariable method on execution
${filevariable.getFilename()}	Calls getFilename method on file variable
${jsonvariable.prop("key").booleanValue()}	Calls prop("key") and booleanValue methods on JSON variable