org.apache.el
public final class ValueExpressionImpl extends ValueExpression implements Externalizable
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, ValueExpressionImpl, ValueExpressionImpl and
ValueExpressionImpl 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.
Version: $Change: 181177 $$DateTime: 2001/06/26 08:45:09 $$Author: markt $
See Also: javax.el.ELResolver javax.el.Expression javax.el.ExpressionFactory javax.el.ValueExpression
Constructor Summary | |
---|---|
ValueExpressionImpl() | |
ValueExpressionImpl(String expr, Node node, FunctionMapper fnMapper, VariableMapper varMapper, Class expectedType) |
Method Summary | |
---|---|
boolean | equals(Object obj) |
Class | getExpectedType() |
String | getExpressionString()
Returns the type the result of the expression will be coerced to after
evaluation.
|
Class | getType(ELContext context) |
Object | getValue(ELContext context) |
int | hashCode() |
boolean | isLiteralText() |
boolean | isReadOnly(ELContext context) |
void | readExternal(ObjectInput in) |
void | setValue(ELContext context, Object value) |
String | toString() |
void | writeExternal(ObjectOutput out) |
Returns: the expectedType
passed to the
ExpressionFactory.createValueExpression
method
that created this ValueExpression
.
See Also: javax.el.Expression#getExpressionString()