Using Spring EL to decide which outbound gateway to use

Using Spring EL to decide which outbound gateway to use

My application can use one of two web services, lets call them WS A and WS
B. Both contain the same interface.
I want to perform some logic on the HTTP headers and request channel. WS B
should only used on certain request channels. To decide which channel is
used I have created a Java class that takes the request channel as a
String parameter.
<http:outbound-gateway request-channel="XXXXX"
url-expression="'${EL EXP}'" http-method="GET"
extract-request-payload="true"
expected-response-type="java.lang.String"
charset="UTF-8" reply-timeout="3000" reply-channel="XXXXX">
</http:outbound-gateway>
I then read that the url-expression is evaluated when the context is
initialised.
source :
http://forum.springsource.org/showthread.php?113446-Usage-of-expressions-in-http-namespace-element-url
<int-http:outbound-gateway request-channel="requestChannel"
url="dummy"
http-method="GET" extract-request-payload="true"
expected-response-type="java.lang.String"
charset="UTF-8" reply-timeout="3000"
reply-channel="sysLoggerRequestChannel">
<int-http:uri-variable name="teststring" expression="test"/>
<int-http:uri-variable name="url"
expression="evalClass.getDestinationForChannel(teststring)"/>
</int-http:outbound-gateway>
The problem with this approach is that the expressions in
int-http:uri-variable do not seem to be evaluation.
All this makes me believe I am taking the wrong approach. Any help would
be very appreciated.