Literal Expressions
A literal expression is evaluated to the text of the expression, which is of type String. A literal expression does not use the ${} or #{} delimiters.
If you have a literal expression that includes the reserved ${} or #{} syntax, you need to escape these characters as follows:
By creating a composite expression as shown here:
${'${'}exprA}#{'#{'}exprB}The resulting values would then be the strings ${exprA} and #{exprB}.
By using the escape characters \$ and \# to escape what would otherwise be treated as an eval-expression:
\${exprA}\#{exprB}The resulting values would again be the strings ${exprA} and #{exprB}.
When a literal expression is evaluated, it can be converted to another type. Table 6-2 shows examples of various literal expressions and their expected types and resulting values.
Table 6-2 Literal Expressions
Expression |
Expected Type |
Result |
|---|---|---|
Hi |
String |
Hi |
true |
Boolean |
Boolean.TRUE |
42 |
int |
42 |
Literal expressions can be evaluated immediately or deferred and can be either value or method expressions. At what point a literal expression is evaluated depends on where it is being used. If the tag attribute that uses the literal expression is defined to accept a deferred value expression, when referencing a value, the literal expression is evaluated at a point in the lifecycle that is determined by other factors, such as where the expression is being used and to what it is referring.
In the case of a method expression, the method that is referenced is invoked and returns the specified String literal. For example, the h:commandButton tag of the guessnumber application uses a literal method expression as a logical outcome to tell the JavaServer Faces navigation system which page to display next.