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java.lang.Object | +--javax.servlet.jsp.el.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.
For JSP EL expressions, an expression string without '${' and '}' tokens is considered to be a static string. One or more occurrences of '${' and '}' can be used in the expression string to delimit dynamic expressions. Examples:
${lastName}
${8 * 8}
Version ${major}.${minor}
${my:reverse('hello')}
Constructor Summary | |
ExpressionEvaluator()
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Method Summary | |
abstract java.lang.Object |
evaluate(java.lang.String expression,
java.lang.Class expectedType,
VariableResolver vResolver,
FunctionMapper fMapper,
java.lang.String defaultPrefix)
Evaluates an expression. |
abstract Expression |
parseExpression(java.lang.String expression,
java.lang.Class expectedType,
FunctionMapper fMapper,
java.lang.String defaultPrefix)
Prepare an expression for later evaluation. |
Methods inherited from class java.lang.Object |
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Constructor Detail |
public ExpressionEvaluator()
Method Detail |
public abstract Expression parseExpression(java.lang.String expression, java.lang.Class expectedType, FunctionMapper fMapper, java.lang.String defaultPrefix) 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 FunctionMapper will be
invoked one or more times between parsing the expression and
evaluating it, and must return a consistent value each time
it is invoked.defaultPrefix
- The default prefix to use when a function is
encountered with no prefix, or "" if the default is no prefix.
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, java.lang.String defaultPrefix) 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. The FunctionMapper will be
invoked one or more times between parsing the expression and
evaluating it, and must return a consistent value each time
it is invoked.defaultPrefix
- The default prefix to use when a function is
encountered with no prefix, or "" if the default is no prefix.
ELException
- Thrown if the expression evaluation failed.
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