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Set Variable Transformer

The Set Variable (set-variable) component is for creating or updating a Mule variable to store values for use within the flow of a Mule app. A Mule variable is part of the Mule event. You can store simple literal values such as strings or messages, message payloads, or attribute objects. For example, you might store the original payload of a message (before it is processed) so you can use it later in the flow or within an error handler.

The set-variable component is not recommended for complex expressions or transformations. You should instead use it for simple ones, such as selections, and use the Transform Component for complex scenarios.


Set Variable provides a way to set the name and value of Mule variable, along with configurable properties.

Field Usage Description

Variable Name (variableName)


Name of the variable, which must be a string. Variable names can include only numbers, characters, and underscores. For example, hyphens are not allowed in the name.

Value (value)


Value for the variable, which can be a string or a DataWeave expression. For an example that uses an expression, see Use Dynamic Writer Properties.

Mime Type (mimeType)


Sets the variable MIME type, such as text/plain or application/json.

Encoding (encoding)


Sets the variable encoding, such as ISO 10646/Unicode(UTF-8).

The mimeType and encoding attributes do not affect a DataWeave expression used as value. They only affect the output value stored. If a transformation is required, the DataWeave expression must contain an explicit output directive.


This example sets the variable to a string:

  • Name = myVar

  • Value = my first variable

This example sets the variable by using a DataWeave operation that results in a value of 5:

  • Name = myVar

  • Value = #[max([1,2,3] ++ [3,4,5])] in Anypoint Studio.

This example sets the variable to the message payload:

  • Name = myVar

  • Value = payload in Design Center, #[payload] in Anypoint Studio.

This example sets the variable to the message attributes:

  • Name = myVar

  • Value = attributes in Design Center, #[attributes] in Anypoint Studio.

This example sets the variable to the entire message:

  • Name = myVar

  • Value = message in Design Center, #[message] in Anypoint Studio.

This XML example sets a variable that takes a map as a value: <set-variable variableName="employee" value="{ 'name' : 'Ana', 'office' : 'BA' }" mimeType="application/json" encoding="UTF-8"/>

This example sets the same variable using selectors in a DataWeave script. It assumes the name attribute is available as input to Set Variable: <set-variable variableName="employee" value="#[output application/java ---]"/>

These examples set the variable to a Boolean value, true:

  • Name = myVar

  • Value =

    • true in Design Center, #[true] in Anypoint Studio

    • true as Boolean in Design Center, #[true as Boolean] in Anypoint Studio

    • (1 + 1 == 2) evaluates to true in Design Center, #[(1 + 1 == 2)] evaluates to true in Anypoint Studio.

This example sets a variable to a Java object by using a DataWeave script. The script outputs the object in Java format: <set-variable value='#[%dw 2.0 output application/java --- { name: "Tomo", lastName: "Chibana", expirationDate: now(), salesRepr: { name: "Mariano", lastName: "de Achaval", } } as Object {class: "Customer"}]' doc:name="Set Variable" variableName="Variable to Java Object"/>.

For more information about the Java data format, refer to the Java Format examples documentation.

To display the value of a variable through the Logger component in Design Center, you might need to use the Anypoint Studio syntax, for example, #[vars.myVar] instead of vars.myVar.

Accessing Variables in Other Event Processors

Set Variable sets a variable in the current Mule event, and the variables then travel with the Mule event to downstream event processors. You can access any variable with DataWeave using vars. So if you set a variable named lastMessage, you can access it as vars.lastMessage. You can set variables in a Transform Message component, and also many connectors and event processors have a Target that can be set in the Advanced tab. These all set flow variables and they are accessed the same way, through the keyword vars..