Uppercase of "URL" worked for me to resolve the first problem i.e.,
<spring:property name="URL" value="jdbc:oracle:thin:@localhost:1521:xe" />
And the second problem was resolved by placing the "xa-transaction" element before the query as below.
<jdbc-ee:outbound-endpoint exchange-pattern="request-response" queryKey="testQuery" queryTimeout="-1" connector-ref="Database" doc:name="Database">
<xa-transaction action="NONE" />
<jdbc-ee:query key="testQuery" value="select * from test" />