Class CompositeELResolver
ELResolver
s.
Though only a single ELResolver
is associated with an
ELContext
, there are usually multiple resolvers considered
for any given variable or property resolution. ELResolver
s
are combined together using a CompositeELResolver
, to define
rich semantics for evaluating an expression.
For the getValue(javax.el.ELContext, java.lang.Object, java.lang.Object)
, getType(javax.el.ELContext, java.lang.Object, java.lang.Object)
, setValue(javax.el.ELContext, java.lang.Object, java.lang.Object, java.lang.Object)
and
isReadOnly(javax.el.ELContext, java.lang.Object, java.lang.Object)
methods, an ELResolver
is not
responsible for resolving all possible (base, property) pairs. In fact,
most resolvers will only handle a base
of a single type.
To indicate that a resolver has successfully resolved a particular
(base, property) pair, it must set the propertyResolved
property of the ELContext
to true
. If it could
not handle the given pair, it must leave this property alone. The caller
must ignore the return value of the method if propertyResolved
is false
.
The CompositeELResolver
initializes the
ELContext.propertyResolved
flag to false
, and uses
it as a stop condition for iterating through its component resolvers.
The ELContext.propertyResolved
flag is not used for the
design-time methods getFeatureDescriptors(javax.el.ELContext, java.lang.Object)
and
getCommonPropertyType(javax.el.ELContext, java.lang.Object)
. Instead, results are collected and
combined from all child ELResolver
s for these methods.
- Since:
- JSP 2.1
- See Also:
-
Field Summary
Fields inherited from class javax.el.ELResolver
RESOLVABLE_AT_DESIGN_TIME, TYPE
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Constructor Summary
-
Method Summary
Modifier and TypeMethodDescriptionvoid
add
(ELResolver elResolver) Adds the given resolver to the list of component resolvers.convertToType
(ELContext context, Object obj, Class<?> targetType) Converts an object to a specific type.Class<?>
getCommonPropertyType
(ELContext context, Object base) Returns the most general type that this resolver accepts for theproperty
argument, given abase
object.getFeatureDescriptors
(ELContext context, Object base) Returns information about the set of variables or properties that can be resolved for the givenbase
object.Class<?>
For a givenbase
andproperty
, attempts to identify the most general type that is acceptable for an object to be passed as thevalue
parameter in a future call to thesetValue(javax.el.ELContext, java.lang.Object, java.lang.Object, java.lang.Object)
method.Attempts to resolve the givenproperty
object on the givenbase
object by querying all component resolvers.Attemps to resolve and invoke the givenmethod
on the givenbase
object by querying all component resolvers.boolean
isReadOnly
(ELContext context, Object base, Object property) For a givenbase
andproperty
, attempts to determine whether a call tosetValue(javax.el.ELContext, java.lang.Object, java.lang.Object, java.lang.Object)
will always fail.void
Attempts to set the value of the givenproperty
object on the givenbase
object.
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Constructor Details
-
CompositeELResolver
public CompositeELResolver()
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Method Details
-
add
Adds the given resolver to the list of component resolvers.Resolvers are consulted in the order in which they are added.
- Parameters:
elResolver
- The component resolver to add.- Throws:
NullPointerException
- If the provided resolver isnull
.
-
getValue
Attempts to resolve the givenproperty
object on the givenbase
object by querying all component resolvers.If this resolver handles the given (base, property) pair, the
propertyResolved
property of theELContext
object must be set totrue
by the resolver, before returning. If this property is nottrue
after this method is called, the caller should ignore the return value.First,
propertyResolved
is set tofalse
on the providedELContext
.Next, for each component resolver in this composite:
- The
getValue()
method is called, passing in the providedcontext
,base
andproperty
. - If the
ELContext
'spropertyResolved
flag isfalse
then iteration continues. - Otherwise, iteration stops and no more component resolvers are
considered. The value returned by
getValue()
is returned by this method.
If none of the component resolvers were able to perform this operation, the value
.null
is returned and thepropertyResolved
flag remains set tofalse
Any exception thrown by component resolvers during the iteration is propagated to the caller of this method.
- Specified by:
getValue
in classELResolver
- Parameters:
context
- The context of this evaluation.base
- The base object whose property value is to be returned, ornull
to resolve a top-level variable.property
- The property or variable to be resolved.- Returns:
- If the
propertyResolved
property ofELContext
was set totrue
, then the result of the variable or property resolution; otherwise undefined. - Throws:
NullPointerException
- if context isnull
PropertyNotFoundException
- if the given (base, property) pair is handled by thisELResolver
but the specified variable or property does not exist or is not readable.ELException
- if an exception was thrown while performing the property or variable resolution. The thrown exception must be included as the cause property of this exception, if available.
- The
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invoke
public Object invoke(ELContext context, Object base, Object method, Class<?>[] paramTypes, Object[] params) Attemps to resolve and invoke the givenmethod
on the givenbase
object by querying all component resolvers.If this resolver handles the given (base, method) pair, the
propertyResolved
property of theELContext
object must be set totrue
by the resolver, before returning. If this property is nottrue
after this method is called, the caller should ignore the return value.First,
propertyResolved
is set tofalse
on the providedELContext
.Next, for each component resolver in this composite:
- The
invoke()
method is called, passing in the providedcontext
,base
,method
,paramTypes
, andparams
. - If the
ELContext
'spropertyResolved
flag isfalse
then iteration continues. - Otherwise, iteration stops and no more component resolvers are
considered. The value returned by
getValue()
is returned by this method.
If none of the component resolvers were able to perform this operation, the value
.null
is returned and thepropertyResolved
flag remains set tofalse
Any exception thrown by component resolvers during the iteration is propagated to the caller of this method.
- Overrides:
invoke
in classELResolver
- Parameters:
context
- The context of this evaluation.base
- The bean on which to invoke the methodmethod
- The simple name of the method to invoke. Will be coerced to aString
.paramTypes
- An array of Class objects identifying the method's formal parameter types, in declared order. Use an empty array if the method has no parameters. Can benull
, in which case the method's formal parameter types are assumed to be unknown.params
- The parameters to pass to the method, ornull
if no parameters.- Returns:
- The result of the method invocation (
null
if the method has avoid
return type). - Since:
- EL 2.2
- The
-
getType
For a givenbase
andproperty
, attempts to identify the most general type that is acceptable for an object to be passed as thevalue
parameter in a future call to thesetValue(javax.el.ELContext, java.lang.Object, java.lang.Object, java.lang.Object)
method. The result is obtained by querying all component resolvers.If this resolver handles the given (base, property) pair, the
propertyResolved
property of theELContext
object must be set totrue
by the resolver, before returning. If this property is nottrue
after this method is called, the caller should ignore the return value.First,
propertyResolved
is set tofalse
on the providedELContext
.Next, for each component resolver in this composite:
- The
getType()
method is called, passing in the providedcontext
,base
andproperty
. - If the
ELContext
'spropertyResolved
flag isfalse
then iteration continues. - Otherwise, iteration stops and no more component resolvers are
considered. The value returned by
getType()
is returned by this method.
If none of the component resolvers were able to perform this operation, the value
.null
is returned and thepropertyResolved
flag remains set tofalse
Any exception thrown by component resolvers during the iteration is propagated to the caller of this method.
- Specified by:
getType
in classELResolver
- Parameters:
context
- The context of this evaluation.base
- The base object whose property value is to be analyzed, ornull
to analyze a top-level variable.property
- The property or variable to return the acceptable type for.- Returns:
- If the
propertyResolved
property ofELContext
was set totrue
, then the most general acceptable type; otherwise undefined. - Throws:
NullPointerException
- if context isnull
PropertyNotFoundException
- if the given (base, property) pair is handled by thisELResolver
but the specified variable or property does not exist or is not readable.ELException
- if an exception was thrown while performing the property or variable resolution. The thrown exception must be included as the cause property of this exception, if available.
- The
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setValue
Attempts to set the value of the givenproperty
object on the givenbase
object. All component resolvers are asked to attempt to set the value.If this resolver handles the given (base, property) pair, the
propertyResolved
property of theELContext
object must be set totrue
by the resolver, before returning. If this property is nottrue
after this method is called, the caller can safely assume no value has been set.First,
propertyResolved
is set tofalse
on the providedELContext
.Next, for each component resolver in this composite:
- The
setValue()
method is called, passing in the providedcontext
,base
,property
andvalue
. - If the
ELContext
'spropertyResolved
flag isfalse
then iteration continues. - Otherwise, iteration stops and no more component resolvers are considered.
If none of the component resolvers were able to perform this operation, the
.propertyResolved
flag remains set tofalse
Any exception thrown by component resolvers during the iteration is propagated to the caller of this method.
- Specified by:
setValue
in classELResolver
- Parameters:
context
- The context of this evaluation.base
- The base object whose property value is to be set, ornull
to set a top-level variable.property
- The property or variable to be set.val
- The value to set the property or variable to.- Throws:
NullPointerException
- if context isnull
PropertyNotFoundException
- if the given (base, property) pair is handled by thisELResolver
but the specified variable or property does not exist.PropertyNotWritableException
- if the given (base, property) pair is handled by thisELResolver
but 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.
- The
-
isReadOnly
For a givenbase
andproperty
, attempts to determine whether a call tosetValue(javax.el.ELContext, java.lang.Object, java.lang.Object, java.lang.Object)
will always fail. The result is obtained by querying all component resolvers.If this resolver handles the given (base, property) pair, the
propertyResolved
property of theELContext
object must be set totrue
by the resolver, before returning. If this property is nottrue
after this method is called, the caller should ignore the return value.First,
propertyResolved
is set tofalse
on the providedELContext
.Next, for each component resolver in this composite:
- The
isReadOnly()
method is called, passing in the providedcontext
,base
andproperty
. - If the
ELContext
'spropertyResolved
flag isfalse
then iteration continues. - Otherwise, iteration stops and no more component resolvers are
considered. The value returned by
isReadOnly()
is returned by this method.
If none of the component resolvers were able to perform this operation, the value
.false
is returned and thepropertyResolved
flag remains set tofalse
Any exception thrown by component resolvers during the iteration is propagated to the caller of this method.
- Specified by:
isReadOnly
in classELResolver
- Parameters:
context
- The context of this evaluation.base
- The base object whose property value is to be analyzed, ornull
to analyze a top-level variable.property
- The property or variable to return the read-only status for.- Returns:
- If the
propertyResolved
property ofELContext
was set totrue
, thentrue
if the property is read-only orfalse
if not; otherwise undefined. - Throws:
NullPointerException
- if context isnull
PropertyNotFoundException
- if the given (base, property) pair is handled by thisELResolver
but the specified variable or property does not exist.ELException
- if an exception was thrown while performing the property or variable resolution. The thrown exception must be included as the cause property of this exception, if available.
- The
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getFeatureDescriptors
Returns information about the set of variables or properties that can be resolved for the givenbase
object. One use for this method is to assist tools in auto-completion. The results are collected from all component resolvers.The
propertyResolved
property of theELContext
is not relevant to this method. The results of allELResolver
s are concatenated.The
Iterator
returned is an iterator over the collection ofFeatureDescriptor
objects returned by the iterators returned by each component resolver'sgetFeatureDescriptors
method. Ifnull
is returned by a resolver, it is skipped.- Specified by:
getFeatureDescriptors
in classELResolver
- Parameters:
context
- The context of this evaluation.base
- The base object whose set of valid properties is to be enumerated, ornull
to enumerate the set of top-level variables that this resolver can evaluate.- Returns:
- An
Iterator
containing zero or more (possibly infinitely more)FeatureDescriptor
objects, ornull
if this resolver does not handle the givenbase
object or that the results are too complex to represent with this method - See Also:
-
getCommonPropertyType
Returns the most general type that this resolver accepts for theproperty
argument, given abase
object. One use for this method is to assist tools in auto-completion. The result is obtained by querying all component resolvers.The
Class
returned is the most specific class that is a common superclass of all the classes returned by each component resolver'sgetCommonPropertyType
method. Ifnull
is returned by a resolver, it is skipped.- Specified by:
getCommonPropertyType
in classELResolver
- Parameters:
context
- The context of this evaluation.base
- The base object to return the most general property type for, ornull
to enumerate the set of top-level variables that this resolver can evaluate.- Returns:
null
if thisELResolver
does not know how to handle the givenbase
object; otherwiseObject.class
if any type ofproperty
is accepted; otherwise the most generalproperty
type accepted for the givenbase
.
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convertToType
Converts an object to a specific type.An
ELException
is thrown if an error occurs during the conversion.- Overrides:
convertToType
in classELResolver
- Parameters:
context
- The context of this evaluation.obj
- The object to convert.targetType
- The target type for the convertion.- Throws:
ELException
- thrown if errors occur.- Since:
- EL 3.0
-