serialization of underscorre(_) characters does not happen correctly

I have a difficulty in converting java object to XML.

I would like to convert a Java object to XML somthing like this

<S_Transaction_Set_Header>
<E_Transaction_Set_Identifier_Code>856</E_Transaction_Set_Identifier_Code>
<E_Transaction_Set_Control_Number>0001</E_Transaction_Set_Control_Number>
</S_Transaction_Set_Header>

I have Java object defined like this

public class TransactionHeader
{
private String E_Transaction_Set_Identifier_Code;
private String E_Transaction_Set_Control_Number;
}

I could able to do the transformation but there is one issue with serializing of the underscore character (_)
The resultant XML is coming like thisi

<S_TransactionSet_Header>
<S_TransactionSetHeader>856</STransactionSet_Header>
<E_TransactionSetControlNumber>0001</ETransactionSetControl_Number>
</S_TransactionSet_Header>

HOW DO i ENSURE THAT _ CHARACTER IS SERIALIZE CORRECTLY

THANKS