You could specify a binding file like the following and the XJC tool will auto-generate the necessary adapters.
<jxb:bindings
xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns:jxb="http://java.sun.com/xml/ns/jaxb"
version="2.1">
<jxb:bindings>
<jxb:globalBindings>
<jxb:javaType name="java.lang.String" xmlType="xs:int"/>
<jxb:javaType name="java.lang.String" xmlType="xs:decimal"/>
</jxb:globalBindings>
</jxb:bindings>
</jxb:bindings>