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 <T> T |
convertToType(ELContext context,
java.lang.Object obj,
java.lang.Class<T> targetType)
Converts an object to a specific type.
|
java.lang.Class<?> |
getCommonPropertyType(ELContext context,
java.lang.Object base)
Returns the most general type that this resolver accepts for the
property argument, given a
base object. |
java.util.Iterator<java.beans.FeatureDescriptor> |
getFeatureDescriptors(ELContext context,
java.lang.Object base)
Deprecated.
|
java.lang.Class<?> |
getType(ELContext context,
java.lang.Object base,
java.lang.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(jakarta.el.ELContext, java.lang.Object, java.lang.Object, java.lang.Object)
method. |
java.lang.Object |
getValue(ELContext context,
java.lang.Object base,
java.lang.Object property)
Attempts to resolve the given
property object on the given base object. |
boolean |
isReadOnly(ELContext context,
java.lang.Object base,
java.lang.Object property)
For a given
base and property, attempts to determine whether a call to ELResolver.setValue(jakarta.el.ELContext, java.lang.Object, java.lang.Object, java.lang.Object)
will always fail. |
void |
setValue(ELContext context,
java.lang.Object base,
java.lang.Object property,
java.lang.Object value)
Attempts to set the value of the given
property object on the given base object. |
invokepublic java.lang.Object getValue(ELContext context, java.lang.Object base, java.lang.Object property)
ELResolverproperty 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 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.public java.lang.Class<?> getType(ELContext context, java.lang.Object base, java.lang.Object property)
ELResolverbase 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(jakarta.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.
If the resolver or the property is read-only, this method must return null.
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,
the most general acceptable type which must be null if the either the property or the resolver is
read-only; otherwise undefinedpublic void setValue(ELContext context, java.lang.Object base, java.lang.Object property, java.lang.Object value)
ELResolverproperty 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 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.value - The value to set the property or variable to.public boolean isReadOnly(ELContext context, java.lang.Object base, java.lang.Object property)
ELResolverbase and property, attempts to determine whether a call to ELResolver.setValue(jakarta.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 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.@Deprecated public java.util.Iterator<java.beans.FeatureDescriptor> getFeatureDescriptors(ELContext context, java.lang.Object base)
ELResolverbase
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(jakarta.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 ELResolvers 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 ELResolvers are concatenated in the case of composite resolvers.
The default implementation in ELResolver returns null. Sub-classes may wish to over-ride this
method.
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 methodFeatureDescriptorpublic java.lang.Class<?> getCommonPropertyType(ELContext context, java.lang.Object base)
ELResolverproperty 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 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.public abstract <T> T convertToType(ELContext context, java.lang.Object obj, java.lang.Class<T> targetType)
An ELException is thrown if an error occurs during the conversion.
convertToType in class ELResolvercontext - The context of this evaluation.obj - The object to convert.targetType - The target type for the conversion.targetTypeELException - thrown if errors occur.