29.2. XML DSL

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Simple expressions in XML DSL

In the XML DSL, you can use a simple expression by putting the expression inside a simple element. For example, to define a route that performs filtering based on the contents of the foo header:
<route id="simpleExample">
  <from uri="seda:orders"/>
    <to uri="mock:fooOrders"/>

Alternative placeholder syntax

Sometimes—for example, if you have enabled Spring property placeholders or OSGi blueprint property placeholders—you might find that the ${Expression} syntax clashes with another property placeholder syntax. In this case, you can disambiguate the placeholder using the alternative syntax, $simple{Expression}, for the simple expression. For example:
<simple>Hello $simple{}, how are you?</simple>

Customizing the start and end tokens

From XML configuration, you can customize the start and end tokens ({ and }, by default) by overriding the SimpleLanguage instance. For example, to change the start and end tokens to [ and ], define a new SimpleLanguage bean in your XML configuration file, as follows:
<bean id="simple" class="org.apache.camel.language.simple.SimpleLanguage">
  <constructor-arg name="functionStartToken" value="["/>
  <constructor-arg name="functionEndToken" value="]"/>
Customizing the start and end tokens affects all Apache Camel applications that share the same camel-core library on their classpath. For example, in an OSGi server this might affect many applications; whereas in a Web application (WAR file) it would affect only the Web application itself.

Whitespace and auto-trim in XML DSL

By default, whitespace preceding and following a simple expression is automatically trimmed in XML DSL. So this expression with surrounding whitespace:
is automatically trimmed, so that it is equivalent to this expression (no surrounding whitespace):
If you want to include newlines before or after the expression, you can either explicitly add a newline character, as follows:
or you can switch off auto-trimming, by setting the trim attribute to false, as follows:
<transform trim="false"> 
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