how to read http headers in esb - wso2

Question

How do I set a property to the value of an incoming http request header? I tried a few things (see following), but my log values are all null, so I'm clearly not reading the header values correctly. The header value I really care about is X-EMPID. Using wso2esb 4.8.1.
Here are a couple of posts that led me to believe this would work, but I'm not having any luck yet.
<proxy xmlns="http://ws.apache.org/ns/synapse"
name="getaccount2"
transports="https,http"
statistics="disable"
trace="disable"
startOnLoad="true">
<target>
<inSequence>
<property name="empid"
expression="get-property('transport', 'X-EMPID')"
scope="default"
type="STRING"/>
<log level="custom">
<property name="emp_id" expression="get-property('empid')"/>
</log>
<log level="custom">
<property name="content_length"
expression="get-property('transport', 'Content-Length')"/>
</log>
<log level="custom">
<property name="TRANSPORT_HEADERS" expression="get-property('TRANSPORT_HEADERS')"/>
</log>

Answer 1

You can conveniently access HTTP headers, which technically are transport headers in WSO2 ESB, by using XPath variables. The easiest way to read an HTTP header named X-EMPID is by using the following XPath: $trp:X-EMPID, where the $trp prefix indicates that the part following the colon is the name of a transport property. To log the header value you could use the following log mediator:
<log level="custom">
<property name="X-EMPID value" expression="$trp:X-EMPID" />
</log>
To set the property myProperty to the value of X-EMPID HTTP header (which is already stored in a transport property) you would use the property mediator:
<property name="myProperty" expression="$trp:X-EMPID" />
The functionality is documented on the WSO2 site.