Package org.apache.el

Class ValueExpressionImpl

java.lang.Object

jakarta.el.Expression

jakarta.el.ValueExpression

org.apache.el.ValueExpressionImpl

All Implemented Interfaces:

java.io.Externalizable, java.io.Serializable

public final class ValueExpressionImpl
extends ValueExpression
implements java.io.Externalizable

An 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.

See Also:

ELResolver, Expression, ExpressionFactory, ValueExpression, Serialized Form

Constructor Summary

Constructors

Constructor	Description
ValueExpressionImpl()	Constructs a new ValueExpressionImpl.
ValueExpressionImpl(java.lang.String expr, org.apache.el.parser.Node node, FunctionMapper fnMapper, VariableMapper varMapper, java.lang.Class<?> expectedType)	Constructs a new ValueExpressionImpl.

Method Summary

Modifier and Type	Method	Description
boolean	equals(java.lang.Object obj)
java.lang.Class<?>	getExpectedType()	Returns the expected type of the result of this expression.
java.lang.String	getExpressionString()	Returns the type the result of the expression will be coerced to after evaluation.
java.lang.Class<?>	getType(ELContext context)	Returns the type of the result produced by evaluating this expression.
<T> T	getValue(ELContext context)	Evaluates this expression and returns the result.
ValueReference	getValueReference(ELContext context)	Returns a reference to the resolved property for this expression.
int	hashCode()
boolean	isLiteralText()	Returns whether this expression is a literal text expression, meaning it does not contain any variables, functions, or operators and evaluates to a constant value.
boolean	isReadOnly(ELContext context)	Determines whether the property referenced by this expression is read-only.
void	readExternal(java.io.ObjectInput in)
void	setValue(ELContext context, java.lang.Object value)	Sets the value of the property referenced by this expression.
java.lang.String	toString()
void	writeExternal(java.io.ObjectOutput out)

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

ValueExpressionImpl

public ValueExpressionImpl()

Constructs a new ValueExpressionImpl.

ValueExpressionImpl

public ValueExpressionImpl(java.lang.String expr,
                           org.apache.el.parser.Node node,
                           FunctionMapper fnMapper,
                           VariableMapper varMapper,
                           java.lang.Class<?> expectedType)

Constructs a new ValueExpressionImpl.

Parameters:

expr - The expression string

node - The AST node

fnMapper - The function mapper

varMapper - The variable mapper

expectedType - The expected return type

Method Detail

equals

public boolean equals(java.lang.Object obj)

Specified by:

equals in class Expression

getExpectedType

public java.lang.Class<?> getExpectedType()

Description copied from class: jakarta.el.ValueExpression

Returns the expected type of the result of this expression.

Specified by:

getExpectedType in class ValueExpression

Returns:

The expected result type, or Object.class if no specific type is expected

getExpressionString

public java.lang.String getExpressionString()

Returns the type the result of the expression will be coerced to after evaluation.

Specified by:

getExpressionString in class Expression

Returns:

the expectedType passed to the ExpressionFactory.createValueExpression method that created this ValueExpression.

See Also:

Expression.getExpressionString()

getType

public java.lang.Class<?> getType(ELContext context)
                           throws PropertyNotFoundException,
                                  ELException

Description copied from class: jakarta.el.ValueExpression

Returns the type of the result produced by evaluating this expression.

Specified by:

getType in class ValueExpression

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 readable

ELException - Wraps any exception throw whilst resolving a property or variable

getValue

public <T> T getValue(ELContext context)
               throws PropertyNotFoundException,
                      ELException

Description copied from class: jakarta.el.ValueExpression

Evaluates this expression and returns the result.

Specified by:

getValue in class ValueExpression

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 readable

ELException - Wraps any exception throw whilst resolving a property or variable

hashCode

public int hashCode()

Specified by:

hashCode in class Expression

isLiteralText

public boolean isLiteralText()

Description copied from class: jakarta.el.Expression

Returns whether this expression is a literal text expression, meaning it does not contain any variables, functions, or operators and evaluates to a constant value.

Specified by:

isLiteralText in class Expression

Returns:

true if this expression is a literal text, false otherwise

isReadOnly

public boolean isReadOnly(ELContext context)
                   throws PropertyNotFoundException,
                          ELException

Description copied from class: jakarta.el.ValueExpression

Determines whether the property referenced by this expression is read-only.

Specified by:

isReadOnly in class ValueExpression

Parameters:

context - The EL context for this evaluation

Returns:

true if this expression is read only otherwise false

Throws:

PropertyNotFoundException - If a property/variable resolution failed because no match was found or a match was found but was not readable

ELException - Wraps any exception throw whilst resolving a property or variable

readExternal

public void readExternal(java.io.ObjectInput in)
                  throws java.io.IOException,
                         java.lang.ClassNotFoundException

Specified by:

readExternal in interface java.io.Externalizable

Throws:

java.io.IOException

java.lang.ClassNotFoundException

setValue

public void setValue(ELContext context,
                     java.lang.Object value)
              throws PropertyNotFoundException,
                     PropertyNotWritableException,
                     ELException

Description copied from class: jakarta.el.ValueExpression

Sets the value of the property referenced by this expression.

Specified by:

setValue in class ValueExpression

Parameters:

context - The EL context for this evaluation

value - The value to set the property to which this value expression refers

Throws:

PropertyNotFoundException - If a property/variable resolution failed because no match was found

PropertyNotWritableException - If a property/variable resolution failed because a match was found but was not writable

ELException - Wraps any exception throw whilst resolving a property or variable

writeExternal

public void writeExternal(java.io.ObjectOutput out)
                   throws java.io.IOException

Specified by:

writeExternal in interface java.io.Externalizable

Throws:

java.io.IOException

toString

public java.lang.String toString()

Overrides:

toString in class java.lang.Object

getValueReference

public ValueReference getValueReference(ELContext context)

Description copied from class: jakarta.el.ValueExpression

Returns a reference to the resolved property for this expression.

This default implementation always returns null. Subclasses should override this method to provide the resolved base object and property.

Overrides:

getValueReference in class ValueExpression

Parameters:

context - The EL context for this evaluation

Returns:

This default implementation always returns null