Class ValueExpression
- All Implemented Interfaces:
Serializable
- Direct Known Subclasses:
ValueExpressionImpl
,ValueExpressionLiteral
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
method
can be used to parse an expression string and return a concrete instance
of ExpressionFactory.createValueExpression(org.jdesktop.el.ELContext, java.lang.String, java.lang.Class<?>)
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 getValue(org.jdesktop.el.ELContext)
, setValue(org.jdesktop.el.ELContext, java.lang.Object)
, isReadOnly(org.jdesktop.el.ELContext)
and
getType(org.jdesktop.el.ELContext)
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(org.jdesktop.el.ELContext, java.lang.Object, java.lang.Object)
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(org.jdesktop.el.ELContext, java.lang.Object, java.lang.Object)
,
ELResolver.setValue(org.jdesktop.el.ELContext, java.lang.Object, java.lang.Object, java.lang.Object)
, ELResolver.isReadOnly(org.jdesktop.el.ELContext, java.lang.Object, java.lang.Object)
or
ELResolver.getType(org.jdesktop.el.ELContext, java.lang.Object, java.lang.Object)
method, depending on which was called on
the ValueExpression
.
See the notes about comparison, serialization and immutability in
the Expression
javadocs.
- Since:
- JSP 2.1
- See Also:
-
Nested Class Summary
Nested classes/interfaces inherited from class org.jdesktop.el.Expression
Expression.ResolvedProperty, Expression.Result
-
Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionabstract Class
<?> Returns the type the result of the expression will be coerced to after evaluation.Returns the source of the expression.abstract Class
<?> Evaluates the expression relative to the provided context, and returns the most general type that is acceptable for an object to be passed as thevalue
parameter in a future call to thesetValue(org.jdesktop.el.ELContext, java.lang.Object)
method.abstract Object
Evaluates the expression relative to the provided context, and returns the resulting value.abstract boolean
isReadOnly
(ELContext context) Evaluates the expression relative to the provided context, and returnstrue
if a call tosetValue(org.jdesktop.el.ELContext, java.lang.Object)
will always fail.void
Sets the source of the expression.abstract void
Evaluates the expression relative to the provided context, and sets the result to the provided value.Methods inherited from class org.jdesktop.el.Expression
equals, getExpressionString, hashCode, isLiteralText
-
Constructor Details
-
ValueExpression
public ValueExpression()
-
-
Method Details
-
setSource
Sets the source of the expression. For ValueExpressions that have a source, any identifiers are evaluated relative to the source. For example, if the expression"${first.name}"
has a source, then"first"
is evaluated relative to the source.- Parameters:
source
- the initial source for identifiers; may benull
-
getSource
Returns the source of the expression.- Returns:
- the source of the expression
-
getValue
Evaluates the expression relative to the provided context, and returns the resulting value.The resulting value is automatically coerced to the type returned by
getExpectedType()
, which was provided to theExpressionFactory
when this expression was created.- Parameters:
context
- The context of this evaluation.- Returns:
- The result of the expression evaluation.
- Throws:
NullPointerException
- if context isnull
.PropertyNotFoundException
- if one of the property resolutions failed because a specified variable or property does not exist or is not readable.ELException
- if an exception was thrown while performing property or variable resolution. The thrown exception must be included as the cause property of this exception, if available.
-
getResult
public Expression.Result getResult(ELContext context, boolean trackResolvedObjects) throws PropertyNotFoundException, ELException - Throws:
PropertyNotFoundException
ELException
-
setValue
Evaluates the expression relative to the provided context, and sets the result to the provided value.- Parameters:
context
- The context of this evaluation.value
- The new value to be set.- Throws:
NullPointerException
- if context isnull
.PropertyNotFoundException
- if one of the property resolutions failed because a specified variable or property does not exist or is not readable.PropertyNotWritableException
- if the final variable or property resolution failed because the specified variable or property is not writable.ELException
- if an exception was thrown while attempting to set the property or variable. The thrown exception must be included as the cause property of this exception, if available.
-
isReadOnly
Evaluates the expression relative to the provided context, and returnstrue
if a call tosetValue(org.jdesktop.el.ELContext, java.lang.Object)
will always fail.- Parameters:
context
- The context of this evaluation.- Returns:
true
if the expression is read-only orfalse
if not.- Throws:
NullPointerException
- if context isnull
.PropertyNotFoundException
- if one of the property resolutions failed because a specified variable or property does not exist or is not readable.ELException
- if an exception was thrown while performing property or variable resolution. The thrown exception must be included as the cause property of this exception, if available. * @throws NullPointerException if context isnull
-
getType
Evaluates the expression relative to the provided context, and returns the most general type that is acceptable for an object to be passed as thevalue
parameter in a future call to thesetValue(org.jdesktop.el.ELContext, java.lang.Object)
method.This is not always the same as
getValue().getClass()
. For example, in the case of an expression that references an array element, thegetType
method will return the element type of the array, which might be a superclass of the type of the actual element that is currently in the specified array element.- Parameters:
context
- The context of this evaluation.- Returns:
- the most general acceptable type; otherwise undefined.
- Throws:
NullPointerException
- if context isnull
.PropertyNotFoundException
- if one of the property resolutions failed because a specified variable or property does not exist or is not readable.ELException
- if an exception was thrown while performing property or variable resolution. The thrown exception must be included as the cause property of this exception, if available.
-
getExpectedType
Returns the type the result of the expression will be coerced to after evaluation.- Returns:
- the
expectedType
passed to theExpressionFactory.createValueExpression
method that created thisValueExpression
.
-