Global Variables in PI

Hi All,
I need some help in understanding the use of global variables in SAP PI.

My scenario is as follows:
Source Message structure
<SMS>
<SMSParameters>
<User/>
<Password/>
<RequestID/>
</SMSParameters>
<SMSMessage>
<DestinationAddr/>
<Text/>
<TransactionId/>
<Priority/>
<SourceAddr/>
</SMSMessage>
</SMS>

Target Message Structure:
User=ABC&Password=DEF&RequestID=90342
<SMSMessage>
<DestinationAddr>ABC&XYZ</DestinationAddr>
<Text>testing</Text>
<TransactionId>4534534</TransactionId>
<Priority>2</Priority>
<SourceAddr>QWE@ZXC</SourceAddr>
</SMSMessage>

Is it possible to read the SMSParameters(User, Password, RequestID) from the Source message as global variables and use them in java mapping to achieve the above target message?

I dont want to use the UDF for this.
Hope im making sense.

Regards,
J