This document discusses the basic syntax rules of Mule Expression Language (MEL). It covers expressions that access context objects like the message payload and variables, multi-line expressions, operators, boolean expressions, bean property access, method invocations, assignments, literals, wildcards, and inline lists, maps, and arrays. MEL provides a way to dynamically extract and manipulate data within Mule applications and workflows.

1. Mule Concepts
Mule Expression Language (MEL)
Basics -III

2. • Basic Syntax Rules:
– #[ ] :
• Always bounds an expression.
• Example :
#[message.id]
– Simple expressions :
• The simplest type of expression.
• consist of just a context object and a field
• or simply a variable.
• Provides access to information from the message
including payload, properties, and variables.
• Example :
[message.field]
[sessionVars.age
Mule Expression Language (MEL)

3. • Basic Syntax Rules:
– Multi line expressions:
• You can include several lines in a single expression
• Each line must end with a ;
• Example :
#[calendar = Calendar.getInstance();
message.payload =
``neworg.mule.el.datetime.DateTime(calendar);]
– Operators :
• Performs operations in expressions
• Can be unary, comparison, logical, bitwise, arithmetic, and
more.
• Example :
#['Cookie' + flowVars.cookie]
Mule Expression Language (MEL)

4. • Basic Syntax Rules:
– Boolean expressions:
• Produces Boolean values.
• Example :
#['foo'=='bar']
#[2 + 2 == 4]
– Bean Property Access:
• Access information from bean.
• Example :
#[payload.property1.property2]
Mule Expression Language (MEL)

5. • Basic Syntax Rules:
– Method invocations:
• Calls a method.
• Then performs it on an object according to the parameter (if
any) specified within the parentheses.
• Method calls always follow the syntax:object.method()
• Example :
#[message.header.get()]
– Assignments:
• Evaluates to assign a value.
• The example below resolves dynamically to set the payload
to sample.
• Example :
#[payload = 'sample']
Mule Expression Language (MEL)

6. • Basic Syntax Rules:
– Literals:
• Strings, numbers, Boolean values, types, and nulls.
• Example :
'expression'
255
null
– xpath and regex:
• xpath3 and regex provide ways of extracting context
information that doesn’t already exist as a single value.
• Example :
xpath3('/orders/order[0]')
Mule Expression Language (MEL)

7. • Basic Syntax Rules:
– Wildcards:
• Matches a value (the message payload, by default) against
a wildcard pattern.
• these use the meta-characters '?' to represent any single
character and '*' for a repetition of any character.
• It’s case sensitive by default.
• Example :
wildcard("Hello*")
Mule Expression Language (MEL)

8. • Basic Syntax Rules:
– Inline list:
• Evaluates to produce a list.
• Example :
[item1, item2, . . .]
– Inline map:
• Evaluates to produce a map.
• Example :
[key1 : value1, key2: value2, …​]
– Inline array:
• Evaluates to produce an array.
• Example :
{item1, item2, . . .}
Mule Expression Language (MEL)