The Spring Expression Language (SpEL) is an object graph navigation language provided with Spring 3, which can be used to construct predicates and expressions in a route. A notable feature of SpEL is the ease with which you can access beans from the registry.
The SpEL expressions must use the placeholder syntax,
#{, so that they can be embedded in
a plain text string (in other words, SpEL has expression templating enabled).SpelExpression}
SpEL can also look up beans in the registry (typically, the Spring registry), using the
@ syntax. For example, given a bean with the
ID, BeanIDheaderUtils, and the method, count() (which counts the number of
headers on the current message), you could use the headerUtils bean in an SpEL
predicate, as follows:
#{@headerUtils.count > 4}To use SpEL in your routes you need to add a dependency on camel-spring
to your project as shown in Example 18.1.
Example 18.1. Adding the camel-spring dependency
<!-- Maven POM File -->
<properties>
<camel-version>2.8.0-fuse-00-08</camel-version>
...
</properties>
<dependencies>
...
<dependency>
<groupId>org.apache.camel</groupId>
<artifactId>camel-spring</artifactId>
<version>${camel-version}</version>
</dependency>
...
</dependencies>Table 18.1 lists the variables that are accessible when using SpEL.
Table 18.1. SpEL variables
| Variable | Type | Description |
|---|---|---|
this | Exchange | The current exchange is the root object. |
exchange | Exchange | The current exchange. |
exchangeId | String | The current exchange's ID. |
exception | Throwable | The exchange exception (if any). |
fault | Message | The fault message (if any). |
request | Message | The exchange's In message. |
response | Message | The exchange's Out message (if any). |
properties | Map | The exchange properties. |
property( | Object | The exchange property keyed by Name. |
property( | Type | The exchange property keyed by Name, converted to the
type, Type. |
 |  | |
 |
