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.

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 13 and the value on the right hand side, RHSValue, is one of the following:

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

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

simple("${in.header.user} == 'john'")

simple("${in.header.number} > '100'")  // String literal can be converted to integer

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

simple("${in.header.type} in 'gold,silver'")

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

simple("${in.header.number} regex '\d{4}'")

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

simple("${in.header.type} is 'java.lang.String'")
simple("${in.header.type} is 'String'") // You can abbreviate java.lang. types

You can test whether the left hand side lies in a specified numerical range (where the range is inclusive), as follows:

simple("${in.header.number} range '100..199'")

You can also combine predicates using the logical conjunctions, && and ||.

For example, here is an expression using the && conjunction (logical and):

simple("${in.header.title} contains 'Camel' && ${in.header.type} == 'gold'")

And here is an expression using the || conjunction (logical inclusive or):

simple("${in.header.title} contains 'Camel' || ${in.header.type} == 'gold'")