docs/user-manual/en/annotation-based-expression-language.adoc

[[AnnotationBasedExpressionLanguage-AnnotationBasedExpressionLanguage]]
=== Annotation Based Expression Language

You can also use any of the link:languages.adoc[Languages] supported in
Camel to bind expressions to method parameters when using
link:bean-integration.adoc[Bean Integration]. For example you can use
any of these annotations:

[width="100%",cols="50%,50%",options="header",]
|=======================================================================
|Annotation |Description
|http://camel.apache.org/maven/current/camel-core/apidocs/org/apache/camel/language/Bean.html[@Bean]
|Inject a <<bean-language,Bean>> expression

|http://camel.apache.org/maven/current/camel-script/apidocs/org/apache/camel/builder/script/BeanShell.html[@BeanShell]
|Inject a <<beanshell-language,BeanShell>> expression

|http://camel.apache.org/maven/current/camel-core/apidocs/org/apache/camel/language/Constant.html[@Constant]
|Inject a <<constant-language,Constant>> expression

|http://camel.apache.org/maven/current/camel-juel/apidocs/org/apache/camel/language/juel/EL.html[@EL]
|Inject an <<el-language,EL>> expression

|http://camel.apache.org/maven/current/camel-script/apidocs/org/apache/camel/builder/script/Groovy.html[@Groovy]
|Inject a <<groovy-language,Groovy>> expression

|http://camel.apache.org/maven/current/maven/camel-core/apidocs/org/apache/camel/Header.html[@Header]
|Inject a <<header-language,Header>> expression

|http://camel.apache.org/maven/current/camel-script/apidocs/org/apache/camel/builder/script/JavaScript.html[@JavaScript]
|Inject a <<javascript-language,JavaScript>> expression

|http://camel.apache.org/maven/current/camel-mvel/apidocs/org/apache/camel/language/mvel/MVEL.html[@MVEL]
|Inject a <<mvel-language,MVEL>> expression

|http://camel.apache.org/maven/current/camel-ognl/apidocs/org/apache/camel/language/ognl/OGNL.html[@OGNL]
|Inject an <<ognl-language,OGNL>> expression

|http://camel.apache.org/maven/current/camel-script/apidocs/org/apache/camel/builder/script/PHP.html[@PHP]
|Inject a <<php-language,PHP>> expression

|http://camel.apache.org/maven/current/camel-script/apidocs/org/apache/camel/builder/script/Python.html[@Python]
|Inject a <<python-language,Python>> expression

|http://camel.apache.org/maven/current/camel-script/apidocs/org/apache/camel/builder/script/Ruby.html[@Ruby]
|Inject a <<ruby-language,Ruby>> expression

|http://camel.apache.org/maven/current/camel-core/apidocs/org/apache/camel/language/Simple.html[@Simple]
|Inject an <<simple-language,Simple>> expression

|http://camel.apache.org/maven/current/camel-core/apidocs/org/apache/camel/language/XPath.html[@XPath]
|Inject an <<xpath-language,XPath>> expression

|http://camel.apache.org/maven/current/camel-saxon/apidocs/org/apache/camel/component/xquery/XQuery.html[@XQuery]
|Inject an <<xquery-language,XQuery>> expression
|=======================================================================

[[AnnotationBasedExpressionLanguage-Example]]
===== Example

[source,java]
----
public class Foo {
    
    @MessageDriven(uri = "activemq:my.queue")
    public void doSomething(@XPath("/foo/bar/text()") String correlationID, @Body String body) {
        // process the inbound message here
    }
}
----

[[AnnotationBasedExpressionLanguage-AdvancedexampleusingBean]]
===== Advanced example using @Bean

And an example of using the the
http://camel.apache.org/maven/current/camel-core/apidocs/org/apache/camel/language/Bean.html[@Bean]
binding annotation, where you can use a <<bean-component,POJO>> where you
can do whatever java code you like:

[source,java]
----
public class Foo {
    
    @MessageDriven(uri = "activemq:my.queue")
    public void doSomething(@Bean("myCorrelationIdGenerator") String correlationID, @Body String body) {
        // process the inbound message here
    }
}
----

And then we can have a spring bean with the id
`myCorrelationIdGenerator` where we can compute the id.

[source,java]
----
public class MyIdGenerator {

    private UserManager userManager;

    public String generate(@Header(name = "user") String user, @Body String payload) throws Exception {
       User user = userManager.lookupUser(user);
       String userId = user.getPrimaryId();
       String id = userId + generateHashCodeForPayload(payload);
       return id;
   }
}
----

The <<bean-component,POJO>> `MyIdGenerator` has one public method that
accepts two parameters. However we have also annotated this one with the
`@Header` and `@Body` annotation to help Camel know what to bind here from
the Message from the Exchange being processed.

Of course this could be simplified a lot if you for instance just have a
simple id generator. But we wanted to demonstrate that you can use the
link:bean-binding.adoc[Bean Binding] annotations anywhere.

[source,java]
----
public class MySimpleIdGenerator {

    public static int generate()  {
       // generate a unique id
       return 123;
   }
}
----

And finally we just need to remember to have our bean registered in the
Spring link:registry.adoc[Registry]:

[source,xml]
----
   <bean id="myCorrelationIdGenerator" class="com.mycompany.MySimpleIdGenerator"/>
----

[[AnnotationBasedExpressionLanguage-ExampleusingGroovy]]
===== Example using <<groovy-language,Groovy>>

In this example we have an Exchange that has a User object stored in the
in header. This User object has methods to get some user information. We
want to use <<groovy.adoc[Groovy] to inject an expression that
extracts and concats the fullname of the user into the fullName
parameter.

[source,java]
----
    public void doSomething(@Groovy("$request.header['user'].firstName $request.header['user'].familyName) String fullName, @Body String body) {
        // process the inbound message here
    }
----

Groovy supports GStrings that is like a template where we can insert $
placeholders that will be evaluated by Groovy.