Module jakarta.el

Package 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

Constructor Summary

Constructors

Constructor	Description
TypeConverter()

Method Summary

Modifier and Type	Method	Description
abstract <T> T	convertToType(ELContext context, Object obj, Class<T> 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.
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 Details

TypeConverter

public TypeConverter()

Method Details

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.

If the resolver or the property is read-only, this method must return null.

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, the most general acceptable type which must be null if the either the property or the resolver is read-only; 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.

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 <T> T convertToType(ELContext context,
 Object obj,
 Class<T> 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.