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29.2. XML DSL

Simple expressions in XML DSL
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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"/>
  <filter>
    <simple>${in.header.foo}</simple>
    <to uri="mock:fooOrders"/>
  </filter>
</route>

Alternative placeholder syntax
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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{in.header.name}, how are you?</simple>

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