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(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.
ELResolver,
Expression,
ExpressionFactory,
ValueExpression,
Serialized Form| Constructor and Description |
|---|
ValueExpressionImpl() |
ValueExpressionImpl(String expr,
Node node,
FunctionMapper fnMapper,
VariableMapper varMapper,
Class<?> expectedType) |
| Modifier and Type | Method and Description |
|---|---|
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) |
ValueReference |
getValueReference(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) |
public ValueExpressionImpl()
public ValueExpressionImpl(String expr, Node node, FunctionMapper fnMapper, VariableMapper varMapper, Class<?> expectedType)
public boolean equals(Object obj)
equals in class Expressionpublic Class<?> getExpectedType()
getExpectedType in class ValueExpressionpublic String getExpressionString()
getExpressionString in class ExpressionexpectedType passed to the
ExpressionFactory.createValueExpression method
that created this ValueExpression.Expression.getExpressionString()public Class<?> getType(ELContext context) throws PropertyNotFoundException, ELException
getType in class ValueExpressioncontext - The EL context for this evaluationPropertyNotFoundException - 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
variablepublic Object getValue(ELContext context) throws PropertyNotFoundException, ELException
getValue in class ValueExpressioncontext - The EL context for this evaluationPropertyNotFoundException - 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
variablepublic int hashCode()
hashCode in class Expressionpublic boolean isLiteralText()
isLiteralText in class Expressionpublic boolean isReadOnly(ELContext context) throws PropertyNotFoundException, ELException
isReadOnly in class ValueExpressioncontext - The EL context for this evaluationtrue if this expression is read only otherwise
falsePropertyNotFoundException - 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
variablepublic void readExternal(ObjectInput in) throws IOException, ClassNotFoundException
readExternal in interface ExternalizableIOExceptionClassNotFoundExceptionpublic void setValue(ELContext context, Object value) throws PropertyNotFoundException, PropertyNotWritableException, ELException
setValue in class ValueExpressioncontext - The EL context for this evaluationvalue - The value to set the property to which this value
expression refersPropertyNotFoundException - 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
variablepublic void writeExternal(ObjectOutput out) throws IOException
writeExternal in interface ExternalizableIOExceptionpublic ValueReference getValueReference(ELContext context)
getValueReference in class ValueExpressioncontext - The EL context for this evaluationnullCopyright © 2000-2021 Apache Software Foundation. All Rights Reserved.