public abstract class TypeConverter extends ELResolver
For example, to convert a String to an instance of MyDate, one can write
ELProcessor elp = new ELProcessor();
elp.getELManager().addELResolver(new TypeConverter() {
Object convertToType(ELContext context, Object obj, Class<?> type) {
if ((obj instanceof String) && type == MyDate.class) {
context.setPropertyResolved(obj, type);
return (obj == null)? null: new MyDate(obj.toString());
}
return null;
}
};
RESOLVABLE_AT_DESIGN_TIME, TYPE
Constructor and Description |
---|
TypeConverter() |
Modifier and Type | Method and Description |
---|---|
abstract Object |
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 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 ELResolver.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. |
boolean |
isReadOnly(ELContext context,
Object base,
Object property)
For a given
base and property , attempts to determine whether a call to ELResolver.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 value)
Attempts to set the value of the given
property object on the given base object. |
invoke
public Object getValue(ELContext context, Object base, Object property)
ELResolver
property
object on the given base
object.
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.
getValue
in class ELResolver
context
- 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.public Class<?> getType(ELContext context, Object base, Object property)
ELResolver
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 ELResolver.setValue(javax.el.ELContext, java.lang.Object, java.lang.Object, java.lang.Object)
method.
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.
This is not always the same as getValue().getClass()
. For example, in the case of an
ArrayELResolver
, 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.
getType
in class ELResolver
context
- 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.public void setValue(ELContext context, Object base, Object property, Object value)
ELResolver
property
object on the given base
object.
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.
setValue
in class ELResolver
context
- 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.value
- The value to set the property or variable to.public boolean isReadOnly(ELContext context, Object base, Object property)
ELResolver
base
and property
, attempts to determine whether a call to ELResolver.setValue(javax.el.ELContext, java.lang.Object, java.lang.Object, java.lang.Object)
will always fail.
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.
isReadOnly
in class ELResolver
context
- 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.public Iterator<FeatureDescriptor> getFeatureDescriptors(ELContext context, Object base)
ELResolver
base
object. One use for this method is to assist tools in auto-completion.
If the base
parameter is null
, the resolver must enumerate the list of top-level variables
it can resolve.
The Iterator
returned must contain zero or more instances of FeatureDescriptor
, in no
guaranteed order. In the case of primitive types such as int
, the value null
must be
returned. This is to prevent the useless iteration through all possible primitive values. A return value of
null
indicates that this resolver does not handle the given base
object or that the results
are too complex to represent with this method and the ELResolver.getCommonPropertyType(javax.el.ELContext, java.lang.Object)
method should be used instead.
Each FeatureDescriptor
will contain information about a single variable or property. In addition to the
standard properties, the FeatureDescriptor
must have two named attributes (as set by the
setValue
method):
ELResolver.TYPE
- The value of this named attribute must be an instance of java.lang.Class
and specify
the runtime type of the variable or property.ELResolver.RESOLVABLE_AT_DESIGN_TIME
- The value of this named attribute must be an instance of
java.lang.Boolean
and indicates whether it is safe to attempt to resolve this property at design-time.
For instance, it may be unsafe to attempt a resolution at design time if the ELResolver
needs access to
a resource that is only available at runtime and no acceptable simulated value can be provided.
The caller should be aware that the Iterator
returned might iterate through a very large or even
infinitely large set of properties. Care should be taken by the caller to not get stuck in an infinite loop.
This is a "best-effort" list. Not all ELResolver
s will return completely accurate results, but all must
be callable at both design-time and runtime (i.e. whether or not Beans.isDesignTime()
returns
true
), without causing errors.
The propertyResolved
property of the ELContext
is not relevant to this method. The results
of all ELResolver
s are concatenated in the case of composite resolvers.
getFeatureDescriptors
in class ELResolver
context
- 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)
ELResolver
property
argument, given a
base
object. One use for this method is to assist tools in auto-completion.
This assists tools in auto-completion and also provides a way to express that the resolver accepts a primitive value,
such as an integer index into an array. For example, the ArrayELResolver
will accept any int
as
a property
, so the return value would be Integer.class
.
getCommonPropertyType
in class ELResolver
context
- 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
.public abstract Object convertToType(ELContext context, Object obj, Class<?> targetType)
An ELException
is thrown if an error occurs during the conversion.
convertToType
in class ELResolver
context
- The context of this evaluation.obj
- The object to convert.targetType
- The target type for the conversion.targetType
ELException
- thrown if errors occur.Comments to: el-dev@eclipse.org.
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Use is subject to license terms.