Red Hat Summit Red Hat SummitSupportConsoleDevelopersStart a trialContact

29.4. Expressions

Overview
Copy link

The simple language provides various elementary expressions that return different parts of a message exchange. For example, the expression, simple("${header.timeOfDay}"), would return the contents of a header called timeOfDay from the incoming message.
Note
Since Apache Camel 2.9, you must always use the placeholder syntax, ${Expression}, to return a variable value. It is never permissible to omit the enclosing tokens (${ and }).

Contents of a single variable
Copy link

You can use the simple language to define string expressions, based on the variables provided. For example, you can use a variable of the form, in.header.HeaderName, to obtain the value of the HeaderName header, as follows: 
simple("${in.header.foo}")
Copy to Clipboard Toggle word wrap

Variables embedded in a string
Copy link

You can embed simple variables in a string expression—for example: 
simple("Received a message from ${in.header.user} on ${date:in.header.date:yyyyMMdd}.")
Copy to Clipboard Toggle word wrap

date and bean variables
Copy link

As well as providing variables that access all of the different parts of an exchange (see Table 29.1, “Variables for the Simple Language”), the simple language also provides special variables for formatting dates, date:command:pattern, and for calling bean methods, bean:beanRef. For example, you can use the date and the bean variables as follows: 
simple("Todays date is ${date:now:yyyyMMdd}")
simple("The order type is ${bean:orderService?method=getOrderType}")
Copy to Clipboard Toggle word wrap

Specifying the result type
Copy link

You can specify the result type of an expression explicitly. This is mainly useful for converting the result type to a boolean or numerical type.
In the Java DSL, specify the result type as an extra argument to simple(). For example, to return an integer result, you could evaluate a simple expression as follows: 
...
.setHeader("five", simple("5", Integer.class))
Copy to Clipboard Toggle word wrap
In the XML DSL, specify the result type using the resultType attribute. For example: 
<setHeader headerName="five">
  <!-- use resultType to indicate that the type should be a java.lang.Integer --> 
  <simple resultType="java.lang.Integer">5</simple>
</setHeader>
Copy to Clipboard Toggle word wrap

Nested expressions
Copy link

Simple expressions can be nested—for example: 
simple("${header.${bean:headerChooser?method=whichHeader}}")
Copy to Clipboard Toggle word wrap

Accessing constants or enums
Copy link

You can access a bean's constant or enum fields using the following syntax: 
type:ClassName.Field
Copy to Clipboard Toggle word wrap
For example, consider the following Java enum type: 
package org.apache.camel.processor;
...
public enum Customer {
    GOLD, SILVER, BRONZE
}
Copy to Clipboard Toggle word wrap
You can access the Customer enum fields, as follows: 
 from("direct:start")
    .choice()
        .when().simple("${header.customer} ==
          ${type:org.apache.camel.processor.Customer.GOLD}")
            .to("mock:gold")
        .when().simple("${header.customer} ==
          ${type:org.apache.camel.processor.Customer.SILVER}")
            .to("mock:silver")
        .otherwise()
            .to("mock:other");
Copy to Clipboard Toggle word wrap

OGNL expressions
Copy link

The Object Graph Navigation Language (OGNL) is a notation for invoking bean methods in a chain-like fashion. If a message body contains a Java bean, you can easily access its bean properties using OGNL notation. For example, if the message body is a Java object with a getAddress() accessor, you can access the Address object and the Address object's properties as follows: 
simple("${body.address}")
simple("${body.address.street}")
simple("${body.address.zip}")
simple("${body.address.city}")
Copy to Clipboard Toggle word wrap
Where the notation, ${body.address.street}, is shorthand for ${body.getAddress.getStreet}.

OGNL null-safe operator
Copy link

You can use the null-safe operator, ?., to avoid encountering null-pointer exceptions, in case the body does not have an address. For example: 
simple("${body?.address?.street}")
Copy to Clipboard Toggle word wrap
If the body is a java.util.Map type, you can look up a value in the map with the key, foo, using the following notation: 
simple("${body[foo]?.name}")
Copy to Clipboard Toggle word wrap

OGNL list element access
Copy link

You can also use square brackets notation, [k], to access the elements of a list. For example: 
simple("${body.address.lines[0]}")
simple("${body.address.lines[1]}")
simple("${body.address.lines[2]}")
Copy to Clipboard Toggle word wrap
The last keyword returns the index of the last element of a list. For example, you can access the second last element of a list, as follows: 
simple("${body.address.lines[last-1]}")
Copy to Clipboard Toggle word wrap
You can use the size method to query the size of a list, as follows: 
simple("${body.address.lines.size}")
Copy to Clipboard Toggle word wrap

OGNL array length access
Copy link

You can access the length of a Java array through the length method, as follows: 
String[] lines = new String[]{"foo", "bar", "cat"};
exchange.getIn().setBody(lines);

simple("There are ${body.length} lines")
Copy to Clipboard Toggle word wrap
Back to top
Red Hat logoGithubredditYoutubeTwitter

Learn

Try, buy, & sell

Communities

About Red Hat Documentation

We help Red Hat users innovate and achieve their goals with our products and services with content they can trust. Explore our recent updates.

Making open source more inclusive

Red Hat is committed to replacing problematic language in our code, documentation, and web properties. For more details, see the Red Hat Blog.

About Red Hat

We deliver hardened solutions that make it easier for enterprises to work across platforms and environments, from the core datacenter to the network edge.

Theme

© 2025 Red Hat