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(jakarta.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(jakarta.el.ELContext), setValue(jakarta.el.ELContext, java.lang.Object), isReadOnly(jakarta.el.ELContext) and getType(jakarta.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(jakarta.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(jakarta.el.ELContext, java.lang.Object, java.lang.Object),
ELResolver.setValue(jakarta.el.ELContext, java.lang.Object, java.lang.Object, java.lang.Object), ELResolver.isReadOnly(jakarta.el.ELContext, java.lang.Object, java.lang.Object) or
ELResolver.getType(jakarta.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:
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Constructor Summary
ConstructorsConstructorDescriptionValueExpressionImpl(String expr, org.apache.el.parser.Node node, FunctionMapper fnMapper, VariableMapper varMapper, Class<?> expectedType) -
Method Summary
Modifier and TypeMethodDescriptionbooleanClass<?> Returns the type the result of the expression will be coerced to after evaluation.Class<?> <T> TgetValueReference(ELContext context) inthashCode()booleanbooleanisReadOnly(ELContext context) voidvoidtoString()void
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Constructor Details
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ValueExpressionImpl
public ValueExpressionImpl() -
ValueExpressionImpl
public ValueExpressionImpl(String expr, org.apache.el.parser.Node node, FunctionMapper fnMapper, VariableMapper varMapper, Class<?> expectedType)
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Method Details
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equals
- Specified by:
equalsin classExpression
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getExpectedType
- Specified by:
getExpectedTypein classValueExpression
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getExpressionString
Returns the type the result of the expression will be coerced to after evaluation.- Specified by:
getExpressionStringin classExpression- Returns:
- the
expectedTypepassed to theExpressionFactory.createValueExpressionmethod that created thisValueExpression. - See Also:
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getType
- Specified by:
getTypein 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
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getValue
- Specified by:
getValuein classValueExpression- Type Parameters:
T- The expected type for the result of evaluating this value expression- 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
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hashCode
public int hashCode()- Specified by:
hashCodein classExpression
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isLiteralText
public boolean isLiteralText()- Specified by:
isLiteralTextin classExpression
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isReadOnly
- Specified by:
isReadOnlyin classValueExpression- Parameters:
context- The EL context for this evaluation- Returns:
trueif 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
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readExternal
- Specified by:
readExternalin interfaceExternalizable- Throws:
IOExceptionClassNotFoundException
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setValue
public void setValue(ELContext context, Object value) throws PropertyNotFoundException, PropertyNotWritableException, ELException - Specified by:
setValuein 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
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writeExternal
- Specified by:
writeExternalin interfaceExternalizable- Throws:
IOException
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toString
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getValueReference
- Overrides:
getValueReferencein classValueExpression- Parameters:
context- The EL context for this evaluation- Returns:
- This default implementation always returns
null
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