ExpressionFactorypublic abstract class ExpressionEvaluator
extends java.lang.Object
The abstract base class for an expression-language evaluator. Classes that implement an expression language expose their functionality via this abstract class.
An instance of the ExpressionEvaluator can be obtained via the JspContext / PageContext
The parseExpression() and evaluate() methods must be thread-safe. That is, multiple threads may call these methods on the same ExpressionEvaluator object simultaneously. Implementations should synchronize access if they depend on transient state. Implementations should not, however, assume that only one object of each ExpressionEvaluator type will be instantiated; global caching should therefore be static.
Only a single EL expression, starting with '${' and ending with '}', can be parsed or evaluated at a time. EL
expressions cannot be mixed with static text. For example, attempting to parse or evaluate
"abc${1+1}def${1+1}ghi" or even "${1+1}${1+1}" will cause an ELException to be
thrown.
The following are examples of syntactically legal EL expressions:
${person.lastName}${8 * 8}${my:reverse('hello')}| Constructor and Description |
|---|
ExpressionEvaluator()
Deprecated.
|
| Modifier and Type | Method and Description |
|---|---|
abstract java.lang.Object |
evaluate(java.lang.String expression,
java.lang.Class expectedType,
VariableResolver vResolver,
FunctionMapper fMapper)
Deprecated.
Evaluates an expression.
|
abstract Expression |
parseExpression(java.lang.String expression,
java.lang.Class expectedType,
FunctionMapper fMapper)
Deprecated.
Prepare an expression for later evaluation.
|
public abstract Expression parseExpression(java.lang.String expression, java.lang.Class expectedType, FunctionMapper fMapper) throws ELException
expression - The expression to be evaluated.expectedType - The expected type of the result of the evaluationfMapper - A FunctionMapper to resolve functions found in the expression. It can be null, in which case
no functions are supported for this invocation. The ExpressionEvaluator must not hold on to
the FunctionMapper reference after returning from parseExpression(). The
Expression object returned must invoke the same functions regardless of whether
the mappings in the provided FunctionMapper instance change between calling
ExpressionEvaluator.parseExpression() and Expression.evaluate().ELException - Thrown if parsing errors were found.public abstract java.lang.Object evaluate(java.lang.String expression,
java.lang.Class expectedType,
VariableResolver vResolver,
FunctionMapper fMapper)
throws ELException
expression - The expression to be evaluated.expectedType - The expected type of the result of the evaluationvResolver - A VariableResolver instance that can be used at runtime to resolve the name of implicit
objects into Objects.fMapper - A FunctionMapper to resolve functions found in the expression. It can be null, in which case
no functions are supported for this invocation.ELException - Thrown if the expression evaluation failed.