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MuleSoft DataWeave Error "Cannot coerce String (0,000000) to Number" Formatting a Decimal Number To String
Date de publication: Jan 9, 2026
Description
In MuleSoft DataWeave, when converting a decimal number to a string using the format "(0.00)" as String {format: "0.0000000"}. Instead of getting a decimal separated with a decimal point "0.0000000", you get a decimal separated with a comma "0,0000000". This would subsequently impact follow-on flows when this String value is converted back to a number and with the comma separator, as shown in the below example.
ERROR 2023-04-05 09:13:56,739 [[MuleRuntime].uber.01: [testdwissue].testdwissueFlow.CPU_INTENSIVE @da052a5] [processor: ; event: 4f080140-d381-11ed-ab5f-fe5c682c08df] org.mule.runtime.core.internal.exception.OnErrorPropagateHandler:
********************************************************************************
Message : "org.mule.weave.v2.exception.InvalidNumberException: Cannot coerce String (0,372970) to Number
3| (nsv * rate) as String {format: "0.000000"} as Number
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Trace:
at anonymous::calcNSV (line: 3, column: 3)
at anonymous::main (line: 5, column: 1)
" evaluating expression: "output application/json
fun calcNSV(nsv, rate) =
(nsv * rate) as String {format: "0.000000"} as Number
---
calcNSV(12.206284506290 default 0, 0.03055556 default 0)".
Element : testdwissueFlow/processors/0 @ testdwissue:testdwissue.xml:13 (Transform Message)
Element DSL : <ee:transform doc:name="Transform Message" doc:id="f8fcc7f6-2699-462a-8136-d3d5b7fe0912">
<ee:message>
<ee:set-payload><![CDATA[
output application/json
fun calcNSV(nsv, rate) =
(nsv * rate) as String {format: "0.000000"} as Number
---
calcNSV(12.206284506290 default 0, 0.03055556 default 0)
]]></ee:set-payload>
</ee:message>
</ee:transform>
Error type : MULE:EXPRESSION
FlowStack : at testdwissueFlow(testdwissueFlow/processors/0 @ testdwissue:testdwissue.xml:13 (Transform Message))
Payload : null
Payload Type : null
--------------------------------------------------------------------------------
Root Exception stack trace:
org.mule.runtime.api.el.ExpressionExecutionException: org.mule.weave.v2.exception.InvalidNumberException: Cannot coerce String (0,372970) to Number
3| (nsv * rate) as String {format: "0.000000"} as Number
Résolution
When receiving the error in MuleSoft's DataWeave "Cannot coerce String to Number", a locale is not specified if the application is being run on a machine that uses a regional setup and the "," is used as a decimal separator.
SOLUTION
In DataWeave, to format the decimal numbers with a "." separator as in the U.S., you will need to specify the locale as detailed in this document.
For example, this script will output "0,3400":
- 0.34 as String {format: "0.0000", locale: "ES"}
While this script will output "0.3400":
- 0.34 as String {format: "0.0000", locale: "US"}
Numéro d’article de la base de connaissances
001123351
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