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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.

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from("jms:queue:order")
   .choice()
      .when().header("type").isEqualTo("widget")).to("bean:widgetOrder")
      .when().header("type").isEqualTo("wombat")).to("bean:wombatOrder")
   .otherwise()
      .to("bean:miscOrder")
   .end();  

...

Predicate isWidget = header("type").isEqualTo("widget");

And then you can refer to it in the route as:

from("jms:queue:order")
   .choice()
      .when(isWidget).to("bean:widgetOrder")
      .when(isWombat).to("bean:wombatOrder")
   .otherwise()
      .to("bean:miscOrder")
   .end();  

Negating a Predicate

You can use the not method on the PredicateBuilder to negate a predicate.

First we import the not static, so it makes our route nice and easy to read:

import static org.apache.camel.builder.PredicateBuilder.not

And then we can use it to enclose an existing predicate and negate it as the example shows:

{snippet:id=e1|lang=java|url=camel/trunk/camel-core/src/test/java/org/apache/camel/processor/ChoiceWhenNotPredicateTest.java}

Compound Predicates

You can also create compound predicates using boolean operators such as and, or, not and many others.

Currently this feature is only available in the Java-based DSLs, but not in the Spring nor Blueprint DSLs.

Using the PredicateBuilder class, you can combine predicates from different Expression Languages based on logical operators and comparison operators:

• not, and, or
• isNull, isNotNull
• isEqualTo, isGreaterThan, isLessThan
• startsWith, endsWith
• in ("any of X predicates stands true")

Additionally, with PredicateBuilder you can create Regular Expressions and use them as predicates, applying them to the result of an expression, e.g. PredicateBuilder.regex(header("foo"), "\d{4}") applies the regular expression to the header = foo.

Combining different Expression Languages is also possible, e.g.:

PredicateBuilder.and(XPathBuilder.xpath("/bookings/flights"), simple("${property.country = 'Spain'}"))

The sample below demonstrates this:
TODO: Snippetfurther use cases:

{snippet:id=e1|lang=java|url=camel/trunk/camel-core/src/test/java/org/apache/camel/processor/ChoiceCompoundPredicateTest.java}

Extensible Predicates

Camel supports extensible Predicates using multiple Languages; the following languages are supported out of the box

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 IDE

See Also

• Expression