Mule Expression Language - Part 1

Karthik Selvaraj

IntroductionMule Expression Language (MEL) was

introduced in Mule 3.3.0Prior to version 3.3.0, expressions in Mule

varied in syntax according to their specific evaluator.

The variation in syntax rules was time-consuming to learn and hence MEL was created to address this complexity.

Mule Expression Language (MEL), implements a single set of syntax rules.

Expression VS Scripting languageAn expression language, such as MEL, is similar,

but not the same as, a scripting language. It allows you to write short scripts that resolve dynamically to get values, set values, or perform an operation on data.

Scripting languages are generally more useful if you are writing something complex enough to require more than just a few lines of code, or if you need to include conditional logic.

If you need to get or set values, invoke methods, or perform functions, you can do so quickly and easily using an expression language. 

MEL – Assigning ValuesPoint the cursor to value field and press

CTRL + Space key to get the list of values to assign

MEL Context ObjectsContext Objects

server: this object provides access to the fields for the hardware, operating system, user, and network interface.

mule: this object provides access to the fields for your Mule instance.

app: this object provides access to the fields of your Mule application.

message: this object provides access to the fields of the Mule message.

MEL VariablesVariables

flowVarssessionVars

UsageflowVars

#[flowVars.firstname = Karthik]sessionVars

#[sessionVars.lastname = Selvaraj]

MEL VariableYou can use the variable name directly in a

MEL expression#[firstname] is equivalent to #[flowVars.firstname]#[lastname] is equivalent to #[sessionVars.lastname]

Mule assumes that it is a flowVars and, when MEL evaluates the expression, looks for a variable by that name. If Mule cannot find a flowVars by that name, it looks for a sessionVars by that name before failing.

MEL VariableIf you wish to disable this auto-resolution of

variables by name, please include the below flow configuration xml <configuration> <expression-language

autoResolveVariables="false"/> </configuration>

MEL Variable

Referencehttps://

docs.mulesoft.com/mule-user-guide/v/3.7/mule-expression-language-mel

https://docs.mulesoft.com/mule-user-guide/v/3.6/mule-expression-language-basic-syntax

https://docs.mulesoft.com/mule-user-guide/v/3.6/mule-expression-language-reference

https://docs.mulesoft.com/mule-user-guide/v/3.6/mule-expression-language-examples

https://docs.mulesoft.com/mule-user-guide/v/3.7/mule-expression-language-tips

Referencehttp://

blogs.mulesoft.com/wp-content/uploads/2012/12/refcard-mel.pdf

https://dzone.com/articles/mule-expression-language-cheat

Mule Expression Language

THANK YOU