Camel supports a pluggable interface called Predicate which can be used to integrate a dynamic predicate into Enterprise Integration Patterns such as when using the Message Filter or Content Based Router.
A Predicate is being evaluated to a boolean value so the result is either
A simple example is to route an Exchange based on a header value:
In the route above the Predicate is the
Sometimes the fluent builders can get long and a bit complex to read, then you can just define your predicate outside the route and then just refer to the predicate in the route:
And then you can refer to it in the route as:
Negating a Predicate
You can use the not method on the
First we import the not static, so it makes our route nice and easy to read:
And then we can use it to enclose an existing predicate and negate it as the example shows:
You can also create compound predicates using boolean operators such as
Currently this feature is only available in the Java-based DSLs, but not in the Spring nor Blueprint DSLs.
Combining different Expression Languages is also possible, e.g.:
The sample below demonstrates further use cases:
Camel supports extensible Predicates using multiple Languages; the following languages are supported out of the box
Most of these languages is also supported used as Annotation Based Expression Language.
You can easily write your own plugin predicate by implementing the Predicate interface.
There are also a number of helper builders available such as the PredicateBuilder class
Using Predicates in your IDETo use different expression and predicates in your IDE you need to perform a static import of the builder class for the language(s) you wish to use.