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Mule Expression Language (MEL)

Cheat

Sheet

Server, Mule, Application and Message variables

Overview of the global contexts and the variables they give access to.

Server

Mule

App

Message

osArch

dataType

fileSeparator

clusterId

encoding

osVersion

payload

host

home

name

rootId

systemProperties

inboundProperties

nodeId

standalone

correlationId

timeZone

inboundAttachments

locale

version

workdir

correlationSequence

tmpDir

outboundProperties

javaVersion

registry

correlationGroupSize

userName

outboundAttachments

javaVendor

replyTo

userHome

exception

osName

userDir

Create a directory named target in the system’s temporary directory and

<expression-component>

set it as the current payload:

targetDir = new java.io.File(server.tmpDir, ‘target’);

targetDir.mkdir();

payload = targetDir

</expression-component>

Set the username and password for an

<https:outbound-endpoint address=”https://#[message.inboundProperties.username]:

HTTP endpoint at runtime based on inbound

message properties:

Flow and session variables

Flow variables are available in the flowVars context or directly as top level variables (unless autoResolveVariables is false or their name violates the

MVEL naming conventions). Session variables are available in the sessionVars context.

To create a session variable named sessionId whose value is the concatenation of the current message ID, “@” and the Mule instance node ID, use

either set-session-variable or MEL code, both shown hereafter:

<set-session-variable variableName=”sessionId” value=”#[message.id+’@’+mule.nodeId]” />

<expression-component>sessionVars.sessionId = message.id+’@’+mule.nodeId;</expression-component>

Payload and attachments

Copy the current payload in a flow variable named

<set-variable variableName=”originalPayload” value=”#[message.payload]” />

originalPayload then restore it:

<set-payload value=”#[originalPayload]” />

To retrieve the message payload in a particular format, using Mule’s auto-

transformation capability, use payloadAs:

To extract all *.txt and *.xml attachments, use

<expression-transformer expression=”#[($.value in

a filtered projection:

message.inboundAttachments.entrySet() if $.key ~= ‘(.*\\.txt|.*\\.xml)’)]” />

The following shows how a bean can be dynamically retrieved from the registry, based on a name created by taking a value from a bean payload with a

getTargetService() accessor:

<set-variable variableName=”beanName” value=”#[message.payload.targetService+’Processor’]” />

<set-variable variableName=”bean” value=”#[app.registry[beanName]]” />

Cheat-Sheet-Mel-4

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