Tag Handler Manipulates the Body

If the tag handler needs to manipulate the body, the tag handler must capture the body in a StringWriter. The invoke method directs all output to a supplied writer. Then the modified body is written to the JspWriter returned by the getOut method of the JspContext. Thus, a tag that converts its body to uppercase could be written as follows:

public class SimpleWriter extends SimpleTagSupport {
    public void doTag() throws JspException, IOException {
        StringWriter sw = new StringWriter();
        jspBody.invoke(sw);
        jspContext().
            getOut().println(sw.toString().toUpperCase());
    }
}