The Java EE 5 Tutorial

Setting Value Expressions on Component Properties

When the attribute value is a value expression, setProperties first checks if it is not a literal expression. If the expression is not a literal, setProperties stores the expression into a collection, from which the component class can retrieve it and resolve it at the appropriate time. If the expression is a literal, setProperties performs any required type conversion and then does one of the following:

The following piece of the MapTag handler’s setProperties method sets the renderer-dependent property, styleClass, and the renderer-independent property, immediate:

if (styleClass != null) {
    if (!styleClass.isLiteralText()) {
        map.setValueExpression("styleClass", styleClass);
    } else {
if (immediate != null) {
    if (!immediate.isLiteralText()) {
        map.setValueExpression("immediate", immediate);
    } else {