Chapter 30. SpEL
Overview
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.
Syntax
The SpEL expressions must use the placeholder syntax,
#{SpelExpression}, so that they can be embedded in a plain text string (in other words, SpEL has expression templating enabled).
SpEL can also look up beans in the registry (typically, the Spring registry), using the
@BeanID syntax. For example, given a bean with the ID, headerUtils, 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}Adding SpEL package
To use SpEL in your routes you need to add a dependency on
camel-spring to your project as shown in Example 30.1, “Adding the camel-spring dependency”.
Example 30.1. Adding the camel-spring dependency
<!-- Maven POM File -->
<properties>
<camel-version>2.15.1.redhat-620133</camel-version>
...
</properties>
<dependencies>
...
<dependency>
<groupId>org.apache.camel</groupId>
<artifactId>camel-spring</artifactId>
<version>${camel-version}</version>
</dependency>
...
</dependencies>Variables
Table 30.1, “SpEL variables” lists the variables that are accessible when using SpEL.
| 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(Name) | Object | The exchange property keyed by Name. |
property(Name, Type) | Type | The exchange property keyed by Name, converted to the type, Type. |
XML example
For example, to select only those messages whose
Country header has the value USA, you can use the following SpEL expression:
<route>
<from uri="SourceURL"/>
<filter>
<spel>#{request.headers['Country'] == 'USA'}}</spel>
<to uri="TargetURL"/>
</filter>
</route>Java example
You can define the same route in the Java DSL, as follows:
from("SourceURL")
.filter().spel("#{request.headers['Country'] == 'USA'}")
.to("TargetURL");
The following example shows how to embed SpEL expressions within a plain text string:
from("SourceURL")
.setBody(spel("Hello #{request.body}! What a beautiful #{request.headers['dayOrNight']}"))
.to("TargetURL");