org.apache.el

Class ValueExpressionImpl

java.lang.Object

javax.el.Expression

javax.el.ValueExpression

org.apache.el.ValueExpressionImpl

All Implemented Interfaces:

Externalizable, Serializable

public final class ValueExpressionImpl
extends ValueExpression
implements 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(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:

ELResolver, Expression, ExpressionFactory, ValueExpression, Serialized Form

Constructor Summary

Constructors

Constructor and Description
ValueExpressionImpl()
ValueExpressionImpl(String expr, Node node, FunctionMapper fnMapper, VariableMapper varMapper, Class<?> expectedType)

Method Summary

Methods

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)

Methods inherited from class java.lang.Object

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

Constructor Detail

ValueExpressionImpl

public ValueExpressionImpl()

ValueExpressionImpl

public ValueExpressionImpl(String expr,
                   Node node,
                   FunctionMapper fnMapper,
                   VariableMapper varMapper,
                   Class<?> expectedType)

Method Detail

equals

public boolean equals(Object obj)

Specified by:

equals in class Expression

getExpectedType

public Class<?> getExpectedType()

Specified by:

getExpectedType in class ValueExpression

getExpressionString

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

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 Object getValue(ELContext context)
                throws PropertyNotFoundException,
                       ELException

Specified by:

getValue in class ValueExpression

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()

Specified by:

isLiteralText in class Expression

isReadOnly

public boolean isReadOnly(ELContext context)
                   throws PropertyNotFoundException,
                          ELException

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(ObjectInput in)
                  throws IOException,
                         ClassNotFoundException

Specified by:

readExternal in interface Externalizable

Throws:

IOException

ClassNotFoundException

setValue

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

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(ObjectOutput out)
                   throws IOException

Specified by:

writeExternal in interface Externalizable

Throws:

IOException

toString

public String toString()

Overrides:

toString in class Object

getValueReference

public ValueReference getValueReference(ELContext context)

Overrides:

getValueReference in class ValueExpression

Parameters:

context - The EL context for this evaluation

Returns:

This default implementation always returns null

Since:

EL 2.2