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Mule expression language - Part 1

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Karthik Selvaraj
Karthik Selvaraj

This presentation provides you an introduction to Mule Expression Language. You can watch the demo through the following link : https://youtu.be/fAj98tFqv_M

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Karthik Selvaraj
Introduction Mule Expression Language (MEL) was introduced in Mule 3.3.0 Prior 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 language An 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 Values Point the cursor to value field and press CTRL + Space key to get the list of values to assign
MEL Context Objects Context 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 Variables Variables flowVars sessionVars Usage flowVars #[flowVars.firstname = Karthik] sessionVars #[sessionVars.lastname = Selvaraj]
MEL Variable You 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 Variable If 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
Reference https://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
Reference http://blogs.mulesoft.com/wp- content/uploads/2012/12/refcard-mel.pdf https://dzone.com/articles/mule-expression- language-cheat
Mule Expression Language THANK YOU

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Mule expression language - Part 1

  • 2. Introduction Mule Expression Language (MEL) was introduced in Mule 3.3.0 Prior 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.
  • 3. Expression VS Scripting language An 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.
  • 4. MEL Assigning Values Point the cursor to value field and press CTRL + Space key to get the list of values to assign
  • 5. MEL Context Objects Context 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.
  • 6. MEL Variables Variables flowVars sessionVars Usage flowVars #[flowVars.firstname = Karthik] sessionVars #[sessionVars.lastname = Selvaraj]
  • 7. MEL Variable You 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.
  • 8. MEL Variable If you wish to disable this auto-resolution of variables by name, please include the below flow configuration xml <configuration> <expression-language autoResolveVariables="false"/> </configuration>
  • 10. Reference https://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