Class ValueExpressionImpl
- All Implemented Interfaces:
Externalizable
,Serializable
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(javax.el.ELContext, java.lang.String, java.lang.Class<?>)
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 getValue(javax.el.ELContext)
, setValue(javax.el.ELContext, java.lang.Object)
, isReadOnly(javax.el.ELContext)
and
getType(javax.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(javax.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(javax.el.ELContext, java.lang.Object, java.lang.Object)
, ELResolver.setValue(javax.el.ELContext, java.lang.Object, java.lang.Object, java.lang.Object)
,
ELResolver.isReadOnly(javax.el.ELContext, java.lang.Object, java.lang.Object)
or ELResolver.getType(javax.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.
- Author:
- Jacob Hookom [jacob@hookom.net]
- See Also:
-
Constructor Summary
ConstructorDescriptionValueExpressionImpl
(String expr, org.apache.el.parser.Node node, FunctionMapper fnMapper, VariableMapper varMapper, Class<?> expectedType) -
Method Summary
Modifier and TypeMethodDescriptionboolean
Class<?>
Returns the type the result of the expression will be coerced to after evaluation.Class<?>
getValueReference
(ELContext context) int
hashCode()
boolean
boolean
isReadOnly
(ELContext context) void
void
toString()
void
-
Constructor Details
-
ValueExpressionImpl
public ValueExpressionImpl() -
ValueExpressionImpl
public ValueExpressionImpl(String expr, org.apache.el.parser.Node node, FunctionMapper fnMapper, VariableMapper varMapper, Class<?> expectedType)
-
-
Method Details
-
equals
- Specified by:
equals
in classExpression
-
getExpectedType
- Specified by:
getExpectedType
in classValueExpression
-
getExpressionString
Returns the type the result of the expression will be coerced to after evaluation.- Specified by:
getExpressionString
in classExpression
- Returns:
- the
expectedType
passed to theExpressionFactory.createValueExpression
method that created thisValueExpression
. - See Also:
-
getType
- Specified by:
getType
in classValueExpression
- Parameters:
context
- The EL context for this evaluation- Returns:
- The type of the result of this value expression
- Throws:
PropertyNotFoundException
- If a property/variable resolution failed because no match was found or a match was found but was not readableELException
- Wraps any exception throw whilst resolving a property or variable
-
getValue
- Specified by:
getValue
in classValueExpression
- Parameters:
context
- The EL context for this evaluation- Returns:
- The result of evaluating this value expression
- Throws:
PropertyNotFoundException
- If a property/variable resolution failed because no match was found or a match was found but was not readableELException
- Wraps any exception throw whilst resolving a property or variable
-
hashCode
public int hashCode()- Specified by:
hashCode
in classExpression
-
isLiteralText
public boolean isLiteralText()- Specified by:
isLiteralText
in classExpression
-
isReadOnly
- Specified by:
isReadOnly
in classValueExpression
- Parameters:
context
- The EL context for this evaluation- Returns:
true
if this expression is read only otherwisefalse
- Throws:
PropertyNotFoundException
- If a property/variable resolution failed because no match was found or a match was found but was not readableELException
- Wraps any exception throw whilst resolving a property or variable
-
readExternal
- Specified by:
readExternal
in interfaceExternalizable
- Throws:
IOException
ClassNotFoundException
-
setValue
public void setValue(ELContext context, Object value) throws PropertyNotFoundException, PropertyNotWritableException, ELException - Specified by:
setValue
in classValueExpression
- Parameters:
context
- The EL context for this evaluationvalue
- The value to set the property to which this value expression refers- Throws:
PropertyNotFoundException
- If a property/variable resolution failed because no match was foundPropertyNotWritableException
- If a property/variable resolution failed because a match was found but was not writableELException
- Wraps any exception throw whilst resolving a property or variable
-
writeExternal
- Specified by:
writeExternal
in interfaceExternalizable
- Throws:
IOException
-
toString
-
getValueReference
- Overrides:
getValueReference
in classValueExpression
- Parameters:
context
- The EL context for this evaluation- Returns:
- This default implementation always returns
null
- Since:
- EL 2.2
-