Predicates

Overview

You can construct predicates by testing expressions for equality. For example, the predicate, simple("${header.timeOfDay} == '14:30'"), tests whether the timeOfDay header in the incoming message is equal to 14:30.

Syntax

You can also test various parts of an exchange (headers, message body, and so on) using simple predicates. Simple predicates have the following general syntax:

${LHSVariable} Op RHSValue

Where the variable on the left hand side, LHSVariable, is one of the variables shown in Table 10, “Simple language variable” and the value on the right hand side, RHSValue, is one of the following:

  • Another variable, ${RHSVariable}.

  • A string literal, enclosed in single quotes, ' '.

  • A string literal, not enclosed in quotes (no spaces allowed).

  • A numeric constant.

  • The null object, null.

The simple language always attempts to convert the RHS value to the type of the LHS value.

Operators

The complete set of operators for simple language predicates is shown in Table 11, “Simple language operators”.

Table 11. Simple language operators

OperatorDescription
==Equals.
>Greater than.
>=Greater than or equals.
<Less than.
<=Less than or equals.
!=Not equal to.
containsTest if LHS string contains RHS string.
not containsTest if LHS string does not contain RHS string.
regexTest if LHS string matches RHS regular expression.
not regexTest if LHS string does not match RHS regular expression.
inTest if LHS string appears in the RHS comma-separated list.
not inTest if LHS string does not appear in the RHS comma-separated list.
isTest if LHS is an instance of RHS Java type (using Java instanceof operator).
not isTest if LHS is not an instance of RHS Java type (using Java instanceof operator).
rangeTest if LHS number lies in the RHS range (where range has the format, min...max).
not rangeTest if LHS number does not lie in the RHS range (where range has the format, min...max).

Examples

For example, you can perform simple string comparisons and numerical comparisons as follows:

<language language="simple">${in.header.user} == 'john'</language>
<!-- Quotes are optional here -->
<language language="simple">${in.header.user} == john</language>

<language language="simple">${in.header.number} > 100</language>
<!-- String literal can be converted to integer -->
<language language="simple">${in.header.number} > '100'</language>

You can test whether the left hand side is a member of a comma-separated list, as follows:

<language language="simple">${in.header.type} not in 'gold,silver'</language>

You can test whether the left hand side matches a regular expression, as follows:

<language language="simple">${in.header.number} regex '\d{4}'</language>

You can test the type of the left hand side using the is operator, as follows:

<language language="simple">${in.header.type} is 'java.lang.String'</language>
<!-- You can abbreviate java.lang. types -->
<language language="simple">${in.header.type} is String</langauge>

You can test whether the left hand side lies in a specified numerical range, as follows:

<language language="simple">${in.header.number} range 100..199</language>

Conjunctions

You can also combine predicates using the logical conjunctions, and and or. But these conjunctions are currently subject to the restriction that a logical conjunction can appear only once in a simple expression.

For example, here is an expression using the and conjunction:

<language language="simple">
  ${in.header.title} contains 'Camel' and ${in.header.type} == 'gold'
</language>

And here is an expression using the or conjunction:

<language language="simple">
  ${in.header.title} contains 'Camel' or ${in.header.type} == 'gold'
</langauge>