INT-1516 added docs for service-activator and SpEL

docs/src/reference/docbook/service-activator.xml

@@ -66,6 +66,35 @@
     configuration is not allowed, as it creates an ambiguous condition and will result in an Exception being thrown.
     </para>
     </note>
+    
+    <para>
+    	<emphasis>Service Activators and Spring Expression Language (SpEL)</emphasis>
+    </para>
+    
+    <para>
+    Since Spring Integration 2.0 Service Activators can also benefit from SpEL ()http://static.springsource.org/spring/docs/3.0.x/spring-framework-reference/html/expressions.html
+    in several ways.
+	</para>
+	<para>
+	First, you may now invoke any bean method without pointing to this bean via <code>ref</code> attribute or including it as an 
+	inner definition. For example:
+	
+	<programlisting language="xml"><![CDATA[<int:service-activator input-channel="in" output-channel="out" 
+	expression="@accountService.processAccount(payload)"/>
+	
+	<bean id="accountService" class="foo.bar.Account"/>]]></programlisting>
+	
+	In the above configuration instead of injecting 'accountService' using <code>ref</code> or as inner bean we are simply using <code>@beanId</code> 
+	notation and invoking a method which takes the type compatible with Message payload.
+
+    For simple scenarios your <emphasis>Service Activators</emphasis> do not even have to reference a bean if all logic can be encapsulated 
+    by such expression.
+    
+    <programlisting language="xml"><![CDATA[<int:service-activator input-channel="in" output-channel="out" expression="payload * 2"/>]]></programlisting>
+    In the above configuration our service logic is to simply multiply the payload value by 2 and SpEL lets us handle it relatively easy.
+    
+    </para>
+    
   </section>
 
 </section>