In Spring Integration when using http:outbound-gateway if you have to do https communication, you need to do the following trick,

<int-http:outbound-gateway id="my.outbound.gateway"
request-channel="request-channel" reply-channel="reply-channel"
url="https://localhost:8443/myservice/myService"
http-method="POST"
expected-response-type="java.lang.String">
</int-http:outbound-gateway>

Now you need to pass the keystore and trust store of the client and server as follows,

<bean id="trustStore">
<property name="targetObject" value="#{@systemProperties}" />
<property name="targetMethod" value="putAll" />
<property name="arguments">
<props>
<prop key="javax.net.ssl.trustStore"><jks key location></prop>
<prop key="javax.net.ssl.keyStorePassword">password</prop>
</props>
</property>
</bean>

<bean id="keystore">
<property name="targetObject" value="#{@systemProperties}" />
<property name="targetMethod" value="putAll" />
<property name="arguments">
<props>
<prop key="javax.net.ssl.keyStore"><jks key location></prop>
<prop key="javax.net.ssl.keyStorePassword">password</prop>
</props>
</property>
</bean>

There is also another way as mentioned in this article @ http://forum.springsource.org/showthread.php?115198-HTTPS-in-http-outbound-gateway

I hope this blog helped you.