Mule Message Data and Expression Language

Accessing information about Mule messages using Datasense :

• DataSense is Anypoint Studio’s ability to proactively discover metadata from internal and external resources.

• Keeps you from having to manually discover information about the data.

• Facilitates transformations by providing DataWeave expected input or output.

• We saw this with Transform Message component.

Other ways to view message information :

• Add a Logger component to a flow and view its output in the Anypoint Studio console.

• Use the Anypoint Studio Visual Debugger which is the most comprehensive way. We also have a Mule Expression Evaluator.

• Use autocomplete when writing expressions in the Anypoint Studio Visual Editor.

Reviewing the structure of Mule messages:

• Mule message is a core part of mule applications.

• Message processors may or may not modify Mule messages.

• We can enrich Mule messages through Message Enricher which is a part of Mule's advanced training.

Message Properties :

• Inbound properties

  • Set from the message source

  • Read-only access

  • Persist throughout the flow

• Outbound properties

  • Added by

  • Read/write access

  • Can set, remove, copy 

Inbound message properties :

• These message properties are read only.

• Query parameters, URI parameters, Method name, and Content-type are examples of inbound properties.

Outbound message properties:

• We can use the Set Property transformer to set outbound properties.

Payload representation:

• This is a core part of Mule Message.

• We can use Set Payload or the Ddataweave Transformer to modify payloads accordingly.

Setting message properties:

Debugging applications with the Mule Debugger:

• Locate the port used by the Mule Debugger.

• Add a breakpoint, debug an application, and step through the code.

• Use the Mule Debugger to view message properties.

• Pass query parameters to a request and locate them in the Debugger.

• You can add breakpoints to processors and step through the application.

• By default, Debugger listens for incoming TCP connections on localhost port 6666.

Mule Expression Language (MEL):

• Use MEL to access and evaluate the data in the payload, properties, and variables of a Mule message.

• MEL is a lightweight, Mule-specific expression language.

• Accessible and usable from within virtually every message processor in Mule.

• Is used to modify the way the processors act upon the message such as routing or filtering.

• Makes use of Mule-specific context objects.

• Case-sensitive.

• Easy to use with autocomplete everywhere.

Basic MEL Syntax:

Context Objects:

Accessing message data:

Accessing message payload data:

Accessing relational map data :

Accessing relational map data :

• Evaluation: ==, !=, >, <, >=, <=, contains, is #[message.inboundProperties.'http.query.params'.lastname != null]

• The literal empty tests the emptiness of a value.

• XPath: #[xpath('expression')]

• RegEx: #[regex('expression')]