how to do runtime changes in xml file

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XML

Hi,
I am work on generating report through java application.I successful to generate report through java application but now I want to do run time changes in xml file. means firstly I write sql query in xml file like follow

<queryString language="SQL">
             <!--  <![CDATA[SELECT * FROM EMPLOYEES ]]>-->
    </queryString>

and design it as follows
<columnheader><statictext>
<text><<![CDATA[$F{EMPLOYEE_ID}

This is for column on report
<detail>

<band height="20">
    <line>
        <reportElement positionType="FixRelativeToBottom" x="0" y="19" width="555" height="1"/>
    </line>
    <textField isStretchWithOverflow="true">
        <reportElement x="0" y="0" width="92" height="20"/>
        <textElement>
            <font size="10"/>
        </textElement>
        <textFieldExpression><![CDATA[$F{EMPLOYEE_ID}]]></textFieldExpression>
    </textField

>
this is for details of selected column.
Here I want to changes the column name at run time.for this run time changes in xml file what do I am?
please help me.