Class ValueExpression
- java.lang.Object
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- org.jdesktop.el.Expression
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- org.jdesktop.el.ValueExpression
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- All Implemented Interfaces:
java.io.Serializable
- Direct Known Subclasses:
ValueExpressionImpl
,ValueExpressionLiteral
public abstract class ValueExpression extends Expression
AnExpression
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 returntrue
fromisReadOnly()
.The
method can be used to parse an expression string and return a concrete instance ofExpressionFactory.createValueExpression(org.jdesktop.el.ELContext, java.lang.String, java.lang.Class<?>)
ValueExpression
that encapsulates the parsed expression. TheFunctionMapper
is used at parse time, not evaluation time, so one is not needed to evaluate an expression using this class. However, theELContext
is needed at evaluation time.The
getValue(org.jdesktop.el.ELContext)
,setValue(org.jdesktop.el.ELContext, java.lang.Object)
,isReadOnly(org.jdesktop.el.ELContext)
andgetType(org.jdesktop.el.ELContext)
methods will evaluate the expression each time they are called. TheELResolver
in theELContext
is used to resolve the top-level variables and to determine the behavior of the.
and[]
operators. For any of the four methods, theELResolver.getValue(org.jdesktop.el.ELContext, java.lang.Object, java.lang.Object)
method is used to resolve all properties up to but excluding the last one. This provides thebase
object. At the last resolution, theValueExpression
will call the correspondingELResolver.getValue(org.jdesktop.el.ELContext, java.lang.Object, java.lang.Object)
,ELResolver.setValue(org.jdesktop.el.ELContext, java.lang.Object, java.lang.Object, java.lang.Object)
,ELResolver.isReadOnly(org.jdesktop.el.ELContext, java.lang.Object, java.lang.Object)
orELResolver.getType(org.jdesktop.el.ELContext, java.lang.Object, java.lang.Object)
method, depending on which was called on theValueExpression
.See the notes about comparison, serialization and immutability in the
Expression
javadocs.- Since:
- JSP 2.1
- See Also:
ELResolver
,Expression
,ExpressionFactory
, Serialized Form
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Nested Class Summary
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Nested classes/interfaces inherited from class org.jdesktop.el.Expression
Expression.ResolvedProperty, Expression.Result
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Constructor Summary
Constructors Constructor Description ValueExpression()
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Method Summary
All Methods Instance Methods Abstract Methods Concrete Methods Modifier and Type Method Description abstract java.lang.Class<?>
getExpectedType()
Returns the type the result of the expression will be coerced to after evaluation.Expression.Result
getResult(ELContext context, boolean trackResolvedObjects)
java.lang.Object
getSource()
Returns the source of the expression.abstract java.lang.Class<?>
getType(ELContext context)
Evaluates the expression relative to the provided context, and returns the most general type that is acceptable for an object to be passed as thevalue
parameter in a future call to thesetValue(org.jdesktop.el.ELContext, java.lang.Object)
method.abstract java.lang.Object
getValue(ELContext context)
Evaluates the expression relative to the provided context, and returns the resulting value.abstract boolean
isReadOnly(ELContext context)
Evaluates the expression relative to the provided context, and returnstrue
if a call tosetValue(org.jdesktop.el.ELContext, java.lang.Object)
will always fail.void
setSource(java.lang.Object source)
Sets the source of the expression.abstract void
setValue(ELContext context, java.lang.Object value)
Evaluates the expression relative to the provided context, and sets the result to the provided value.-
Methods inherited from class org.jdesktop.el.Expression
equals, getExpressionString, hashCode, isLiteralText
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Method Detail
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setSource
public void setSource(java.lang.Object source)
Sets the source of the expression. For ValueExpressions that have a source, any identifiers are evaluated relative to the source. For example, if the expression"${first.name}"
has a source, then"first"
is evaluated relative to the source.- Parameters:
source
- the initial source for identifiers; may benull
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getSource
public java.lang.Object getSource()
Returns the source of the expression.- Returns:
- the source of the expression
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getValue
public abstract java.lang.Object getValue(ELContext context)
Evaluates the expression relative to the provided context, and returns the resulting value.The resulting value is automatically coerced to the type returned by
getExpectedType()
, which was provided to theExpressionFactory
when this expression was created.- Parameters:
context
- The context of this evaluation.- Returns:
- The result of the expression evaluation.
- Throws:
java.lang.NullPointerException
- if context isnull
.PropertyNotFoundException
- if one of the property resolutions failed because a specified variable or property does not exist or is not readable.ELException
- if an exception was thrown while performing property or variable resolution. The thrown exception must be included as the cause property of this exception, if available.
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getResult
public Expression.Result getResult(ELContext context, boolean trackResolvedObjects) throws PropertyNotFoundException, ELException
- Throws:
PropertyNotFoundException
ELException
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setValue
public abstract void setValue(ELContext context, java.lang.Object value)
Evaluates the expression relative to the provided context, and sets the result to the provided value.- Parameters:
context
- The context of this evaluation.value
- The new value to be set.- Throws:
java.lang.NullPointerException
- if context isnull
.PropertyNotFoundException
- if one of the property resolutions failed because a specified variable or property does not exist or is not readable.PropertyNotWritableException
- if the final variable or property resolution failed because the specified variable or property is not writable.ELException
- if an exception was thrown while attempting to set the property or variable. The thrown exception must be included as the cause property of this exception, if available.
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isReadOnly
public abstract boolean isReadOnly(ELContext context)
Evaluates the expression relative to the provided context, and returnstrue
if a call tosetValue(org.jdesktop.el.ELContext, java.lang.Object)
will always fail.- Parameters:
context
- The context of this evaluation.- Returns:
true
if the expression is read-only orfalse
if not.- Throws:
java.lang.NullPointerException
- if context isnull
.PropertyNotFoundException
- if one of the property resolutions failed because a specified variable or property does not exist or is not readable.ELException
- if an exception was thrown while performing property or variable resolution. The thrown exception must be included as the cause property of this exception, if available. * @throws NullPointerException if context isnull
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getType
public abstract java.lang.Class<?> getType(ELContext context)
Evaluates the expression relative to the provided context, and returns the most general type that is acceptable for an object to be passed as thevalue
parameter in a future call to thesetValue(org.jdesktop.el.ELContext, java.lang.Object)
method.This is not always the same as
getValue().getClass()
. For example, in the case of an expression that references an array element, thegetType
method will return the element type of the array, which might be a superclass of the type of the actual element that is currently in the specified array element.- Parameters:
context
- The context of this evaluation.- Returns:
- the most general acceptable type; otherwise undefined.
- Throws:
java.lang.NullPointerException
- if context isnull
.PropertyNotFoundException
- if one of the property resolutions failed because a specified variable or property does not exist or is not readable.ELException
- if an exception was thrown while performing property or variable resolution. The thrown exception must be included as the cause property of this exception, if available.
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getExpectedType
public abstract java.lang.Class<?> getExpectedType()
Returns the type the result of the expression will be coerced to after evaluation.- Returns:
- the
expectedType
passed to theExpressionFactory.createValueExpression
method that created thisValueExpression
.
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