jakarta.el

Class TypeConverter

java.lang.Object

jakarta.el.ELResolver

jakarta.el.TypeConverter

public abstract class TypeConverter
extends ELResolver

A convenient class for writing an ELResolver to do custom type conversions.

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;
         }
      };
 
 

Since:

Jakarta Expression Language 3.0

Field Summary

Fields inherited from class jakarta.el.ELResolver

RESOLVABLE_AT_DESIGN_TIME, TYPE

Constructor Summary

Constructors

Constructor and Description
TypeConverter()

Method Summary

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(jakarta.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(jakarta.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.

Methods inherited from class jakarta.el.ELResolver

invoke

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

TypeConverter

public TypeConverter()

Method Detail

getValue

public Object getValue(ELContext context,
                       Object base,
                       Object property)

Description copied from class: ELResolver

Attempts to resolve the given 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.

Specified by:

getValue in class ELResolver

Parameters:

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.

Returns:

If the propertyResolved property of ELContext was set to true, then the result of the variable or property resolution; otherwise undefined.

getType

public Class<?> getType(ELContext context,
                        Object base,
                        Object property)

Description copied from class: ELResolver

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.

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.

Specified by:

getType in class ELResolver

Parameters:

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.

Returns:

If the propertyResolved property of ELContext was set to true, then the most general acceptable type; otherwise undefined.

setValue

public void setValue(ELContext context,
                     Object base,
                     Object property,
                     Object value)

Description copied from class: ELResolver

Attempts to set the value of the given 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.

Specified by:

setValue in class ELResolver

Parameters:

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.

isReadOnly

public boolean isReadOnly(ELContext context,
                          Object base,
                          Object property)

Description copied from class: ELResolver

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.

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.

Specified by:

isReadOnly in class ELResolver

Parameters:

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.

Returns:

If the propertyResolved property of ELContext was set to true, then true if the property is read-only or false if not; otherwise undefined.

getFeatureDescriptors

public Iterator<FeatureDescriptor> getFeatureDescriptors(ELContext context,
                                                         Object base)

Description copied from class: ELResolver

Returns information about the set of variables or properties that can be resolved for the given 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(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.

Specified by:

getFeatureDescriptors in class ELResolver

Parameters:

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.

Returns:

An 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 method

See Also:

FeatureDescriptor

getCommonPropertyType

public Class<?> getCommonPropertyType(ELContext context,
                                      Object base)

Description copied from class: ELResolver

Returns the most general type that this resolver accepts for the 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.

Specified by:

getCommonPropertyType in class ELResolver

Parameters:

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.

Returns:

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.

convertToType

public abstract Object convertToType(ELContext context,
                                     Object obj,
                                     Class<?> targetType)

Converts an object to a specific type.

An ELException is thrown if an error occurs during the conversion.

Overrides:

convertToType in class ELResolver

Parameters:

context - The context of this evaluation.

obj - The object to convert.

targetType - The target type for the conversion.

Returns:

object converted to targetType

Throws:

ELException - thrown if errors occur.