| java.lang.Object
 javax.el.Expression
javax.el.ValueExpression
org.apache.el.ValueExpressionImpl
| ValueExpressionImpl | | final public class ValueExpressionImpl extends ValueExpression implements Externalizable(Code) | | An Expression that can get or set a value.
In previous incarnations of this API, expressions could only be read.
ValueExpression objects can now be used both to retrieve a
value and to set a value. Expressions that can have a value set on them are
referred to as l-value expressions. Those that cannot are referred to as
r-value expressions. Not all r-value expressions can be used as l-value
expressions (e.g. "${1+1}" or
"${firstName} ${lastName}"). See the EL Specification for
details. Expressions that cannot be used as l-values must always return
true from isReadOnly().
The
ExpressionFactory.createValueExpression method
can be used to parse an expression string and return a concrete instance
of ValueExpression that encapsulates the parsed expression.
The
FunctionMapper is used at parse time, not evaluation time,
so one is not needed to evaluate an expression using this class.
However, the
ELContext is needed at evaluation time.
The
ValueExpressionImpl.getValue ,
ValueExpressionImpl.setValue ,
ValueExpressionImpl.isReadOnly and
ValueExpressionImpl.getType methods will evaluate the expression each time they are
called. The
ELResolver in the ELContext is used to
resolve the top-level variables and to determine the behavior of the
. and [] operators. For any of the four methods,
the
ELResolver.getValue method is used to resolve all properties
up to but excluding the last one. This provides the base
object. At the last resolution, the ValueExpression will
call the corresponding
ELResolver.getValue ,
ELResolver.setValue ,
ELResolver.isReadOnly or
ELResolver.getType method, depending on which was called on
the ValueExpression.
See the notes about comparison, serialization and immutability in
the
Expression javadocs.
See Also: javax.el.ELResolver
See Also: javax.el.Expression
See Also: javax.el.ExpressionFactory
See Also: javax.el.ValueExpression
author:
Jacob Hookom [jacob@hookom.net]
version:
$Change: 181177 $$DateTime: 2001/06/26 08:45:09 $$Author: markt $ |
| ValueExpressionImpl | | public ValueExpressionImpl()(Code) | | |
| getExpressionString | | public String getExpressionString()(Code) | | Returns the type the result of the expression will be coerced to after
evaluation.
the expectedType passed to theExpressionFactory.createValueExpression methodthat created this ValueExpression.
See Also: javax.el.Expression.getExpressionString |
| hashCode | | public int hashCode()(Code) | | |
| isLiteralText | | public boolean isLiteralText()(Code) | | |
| Methods inherited from javax.el.ValueExpression | abstract public Class getExpectedType()(Code)(Java Doc)
abstract public Class getType(ELContext context) throws NullPointerException, PropertyNotFoundException, ELException(Code)(Java Doc)
abstract public Object getValue(ELContext context) throws NullPointerException, PropertyNotFoundException, ELException(Code)(Java Doc)
abstract public boolean isReadOnly(ELContext context) throws NullPointerException, PropertyNotFoundException, ELException(Code)(Java Doc)
abstract public void setValue(ELContext context, Object value) throws NullPointerException, PropertyNotFoundException, PropertyNotWritableException, ELException(Code)(Java Doc)
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