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java.lang.Objectjavax.el.Expression
javax.el.ValueExpression
public abstract class ValueExpression
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(ELContext, String, 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(ELContext)
,
setValue(ELContext, Object)
, isReadOnly(ELContext)
and
getType(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(ELContext, Object, 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(ELContext, Object,
Object)
, ELResolver.setValue(ELContext, Object, Object, Object)
, ELResolver.isReadOnly(ELContext, Object, Object)
or ELResolver.getType(ELContext, Object,
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
,
Serialized FormConstructor Summary | |
---|---|
ValueExpression()
|
Method Summary | |
---|---|
abstract java.lang.Class<?> |
getExpectedType()
Returns the type the result of the expression will be coerced to after evaluation. |
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 the value parameter in a future call to the setValue(ELContext, 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 returns true if a call to setValue(ELContext, Object) will always fail. |
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 javax.el.Expression |
---|
equals, getExpressionString, hashCode, isLiteralText |
Methods inherited from class java.lang.Object |
---|
clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait |
Constructor Detail |
---|
public ValueExpression()
Method Detail |
---|
public abstract java.lang.Class<?> getExpectedType()
public abstract java.lang.Class<?> getType(ELContext context)
setValue(ELContext, Object)
method. This is not always the same as
getValue().getClass(). For example, in the case of an expression that references an array
element, the getType 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.
context
- The context of this evaluation.
java.lang.NullPointerException
- if context is null.
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.public abstract java.lang.Object getValue(ELContext context)
context
- The context of this evaluation.
java.lang.NullPointerException
- if context is null.
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.public abstract boolean isReadOnly(ELContext context)
setValue(ELContext, Object)
will always fail.
context
- The context of this evaluation.
java.lang.NullPointerException
- if context is null.
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.public abstract void setValue(ELContext context, java.lang.Object value)
context
- The context of this evaluation.value
- The new value to be set.
java.lang.NullPointerException
- if context is null.
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.
|
Copyright © 2006-2009 Odysseus Software GmbH. | ||||||||
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