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java.lang.Object javax.servlet.jsp.el.ExpressionEvaluator
public abstract class ExpressionEvaluator
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 Summary | |
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ExpressionEvaluator()
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Method Summary | |
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abstract Object |
evaluate(String expression,
Class expectedType,
VariableResolver vResolver,
FunctionMapper fMapper)
Evaluates an expression. |
abstract Expression |
parseExpression(String expression,
Class expectedType,
FunctionMapper fMapper)
Prepare an expression for later evaluation. |
Methods inherited from class java.lang.Object |
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clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Constructor Detail |
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public ExpressionEvaluator()
Method Detail |
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public abstract Expression parseExpression(String expression, 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 Object evaluate(String expression, 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.
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