public abstract class ValueExpression extends Expression
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 and Description |
---|
ValueExpression() |
Modifier and Type | Method and Description |
---|---|
abstract Class<?> |
getExpectedType()
Returns the type the result of the expression will be coerced to after evaluation.
|
abstract 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 Object |
getValue(ELContext context)
Evaluates the expression relative to the provided context, and returns the resulting value.
|
ValueReference |
getValueReference(ELContext context)
Returns a
ValueReference for this expression instance. |
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,
Object value)
Evaluates the expression relative to the provided context, and sets the result to the provided value.
|
equals, getExpressionString, hashCode, isLiteralText
public abstract Class<?> getExpectedType()
public abstract 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.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 Object getValue(ELContext context)
context
- The context of this evaluation.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.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, Object value)
context
- The context of this evaluation.value
- The new value to be set.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.public ValueReference getValueReference(ELContext context)
ValueReference
for this expression instance.context
- the context of this evaluationValueReference
for this ValueExpression
, or null
if this ValueExpression
is not a reference to a base (null or non-null) and a
property. If the base is null, and the property is a EL variable, return the ValueReference
for the ValueExpression
associated with this EL variable.Copyright © 2015 Alfresco. All rights reserved.