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java.lang.Objectjavax.el.ELResolver
javax.el.CompositeELResolver
public class CompositeELResolver
Maintains an ordered composite list of child ELResolvers.
Though only a single ELResolver is associated with an
ELContext, there are usually multiple resolvers considered
for any given variable or property resolution. ELResolvers
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 ELResolvers for these methods.
ELContext,
ELResolver| Field Summary |
|---|
| Fields inherited from class javax.el.ELResolver |
|---|
RESOLVABLE_AT_DESIGN_TIME, TYPE |
| Constructor Summary | |
|---|---|
CompositeELResolver()
|
|
| Method Summary | |
|---|---|
void |
add(ELResolver elResolver)
Adds the given resolver to the list of component resolvers. |
Class<?> |
getCommonPropertyType(ELContext context,
Object base)
Returns the most general type that this resolver accepts for the property argument, given a base object. |
Iterator<FeatureDescriptor> |
getFeatureDescriptors(ELContext context,
Object base)
Returns information about the set of variables or properties that can be resolved for the given base object. |
Class<?> |
getType(ELContext context,
Object base,
Object property)
For a given base and property, attempts to
identify the most general type that is acceptable for an object to be
passed as the value parameter in a future call
to the setValue(javax.el.ELContext, java.lang.Object, java.lang.Object, java.lang.Object) method. |
Object |
getValue(ELContext context,
Object base,
Object property)
Attempts to resolve the given property object on the given
base object by querying all component resolvers. |
boolean |
isReadOnly(ELContext context,
Object base,
Object property)
For a given base and property, attempts to
determine whether a call to setValue(javax.el.ELContext, java.lang.Object, java.lang.Object, java.lang.Object) will always fail. |
void |
setValue(ELContext context,
Object base,
Object property,
Object val)
Attempts to set the value of the given property
object on the given base object. |
| Methods inherited from class java.lang.Object |
|---|
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
| Constructor Detail |
|---|
public CompositeELResolver()
| Method Detail |
|---|
public void add(ELResolver elResolver)
Resolvers are consulted in the order in which they are added.
elResolver - The component resolver to add.
NullPointerException - If the provided resolver is
null.
public Object getValue(ELContext context,
Object base,
Object property)
property object on the given
base object by querying all component resolvers.
If this resolver handles the given (base, property) pair,
the propertyResolved property of the
ELContext object must be set to true
by the resolver, before returning. If this property is not
true after this method is called, the caller should ignore
the return value.
First, propertyResolved is set to false on
the provided ELContext.
Next, for each component resolver in this composite:
getValue() method is called, passing in
the provided context, base and
property.ELContext's propertyResolved
flag is false then iteration continues.getValue() is
returned by this method.If none of the component resolvers were able to perform this
operation, the value null is returned and the
propertyResolved flag remains set to
false
Any exception thrown by component resolvers during the iteration is propagated to the caller of this method.
getValue in class ELResolvercontext - The context of this evaluation.base - The base object whose property value is to be returned,
or null to resolve a top-level variable.property - The property or variable to be resolved.
propertyResolved property of
ELContext was set to true, then
the result of the variable or property resolution; otherwise
undefined.
NullPointerException - if context is null
PropertyNotFoundException - if the given (base, property) pair
is handled by this ELResolver 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.
public Class<?> getType(ELContext context,
Object base,
Object property)
base and property, attempts to
identify the most general type that is acceptable for an object to be
passed as the value parameter in a future call
to the setValue(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 the
ELContext object must be set to true
by the resolver, before returning. If this property is not
true after this method is called, the caller should ignore
the return value.
First, propertyResolved is set to false on
the provided ELContext.
Next, for each component resolver in this composite:
getType() method is called, passing in
the provided context, base and
property.ELContext's propertyResolved
flag is false then iteration continues.getType() is
returned by this method.If none of the component resolvers were able to perform this
operation, the value null is returned and the
propertyResolved flag remains set to
false
Any exception thrown by component resolvers during the iteration is propagated to the caller of this method.
getType in class ELResolvercontext - The context of this evaluation.base - The base object whose property value is to be analyzed,
or null to analyze a top-level variable.property - The property or variable to return the acceptable
type for.
propertyResolved property of
ELContext was set to true, then
the most general acceptable type; otherwise undefined.
NullPointerException - if context is null
PropertyNotFoundException - if the given (base, property) pair
is handled by this ELResolver 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.
public void setValue(ELContext context,
Object base,
Object property,
Object val)
property
object on the given base 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 the
ELContext object must be set to true
by the resolver, before returning. If this property is not
true after this method is called, the caller can
safely assume no value has been set.
First, propertyResolved is set to false on
the provided ELContext.
Next, for each component resolver in this composite:
setValue() method is called, passing in
the provided context, base,
property and value.ELContext's propertyResolved
flag is false then iteration continues.If none of the component resolvers were able to perform this
operation, the propertyResolved flag remains set to
false
Any exception thrown by component resolvers during the iteration is propagated to the caller of this method.
setValue in class ELResolvercontext - The context of this evaluation.base - The base object whose property value is to be set,
or null to set a top-level variable.property - The property or variable to be set.val - The value to set the property or variable to.
NullPointerException - if context is null
PropertyNotFoundException - if the given (base, property) pair
is handled by this ELResolver but the specified
variable or property does not exist.
PropertyNotWritableException - if the given (base, property)
pair is handled by this ELResolver 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.
public boolean isReadOnly(ELContext context,
Object base,
Object property)
base and property, attempts to
determine whether a call to setValue(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 the
ELContext object must be set to true
by the resolver, before returning. If this property is not
true after this method is called, the caller should ignore
the return value.
First, propertyResolved is set to false on
the provided ELContext.
Next, for each component resolver in this composite:
isReadOnly() method is called, passing in
the provided context, base and
property.ELContext's propertyResolved
flag is false then iteration continues.isReadOnly() is
returned by this method.If none of the component resolvers were able to perform this
operation, the value false is returned and the
propertyResolved flag remains set to
false
Any exception thrown by component resolvers during the iteration is propagated to the caller of this method.
isReadOnly in class ELResolvercontext - The context of this evaluation.base - The base object whose property value is to be analyzed,
or null to analyze a top-level variable.property - The property or variable to return the read-only status
for.
propertyResolved property of
ELContext was set to true, then
true if the property is read-only or
false if not; otherwise undefined.
NullPointerException - if context is null
PropertyNotFoundException - if the given (base, property) pair
is handled by this ELResolver 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.
public Iterator<FeatureDescriptor> getFeatureDescriptors(ELContext context,
Object base)
base 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 the
ELContext is not relevant to this method.
The results of all ELResolvers are concatenated.
The Iterator returned is an iterator over the
collection of FeatureDescriptor objects returned by
the iterators returned by each component resolver's
getFeatureDescriptors method. If null is
returned by a resolver, it is skipped.
getFeatureDescriptors in class ELResolvercontext - The context of this evaluation.base - The base object whose set of valid properties is to
be enumerated, or null to enumerate the set of
top-level variables that this resolver can evaluate.
Iterator containing zero or more (possibly
infinitely more) FeatureDescriptor objects, or
null if this resolver does not handle the given
base object or that the results are too complex to
represent with this methodFeatureDescriptor
public Class<?> getCommonPropertyType(ELContext context,
Object base)
property argument, given a base 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's getCommonPropertyType method. If
null is returned by a resolver, it is skipped.
getCommonPropertyType in class ELResolvercontext - The context of this evaluation.base - The base object to return the most general property
type for, or null to enumerate the set of
top-level variables that this resolver can evaluate.
null if this ELResolver does not
know how to handle the given base object; otherwise
Object.class if any type of property
is accepted; otherwise the most general property
type accepted for the given base.
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Copyright 2006 Sun Microsystems, Inc. All rights reserved.