jakarta.el

Class ListELResolver

java.lang.Object

jakarta.el.ELResolver

jakarta.el.ListELResolver

public class ListELResolver
extends ELResolver

Defines property resolution behavior on instances of List.

This resolver handles base objects of type java.util.List. It accepts any object as a property and coerces that object into an integer index into the list. The resulting value is the value in the list at that index.

This resolver can be constructed in read-only mode, which means that isReadOnly will always return true and setValue(jakarta.el.ELContext, java.lang.Object, java.lang.Object, java.lang.Object) will always throw PropertyNotWritableException.

ELResolvers are combined together using CompositeELResolvers, to define rich semantics for evaluating an expression. See the javadocs for ELResolver for details.

Since:

Jakarta Server Pages 2.1

See Also:

CompositeELResolver, ELResolver, List

Field Summary

Fields inherited from class jakarta.el.ELResolver

RESOLVABLE_AT_DESIGN_TIME, TYPE

Constructor Summary

Constructors

Constructor and Description
ListELResolver() Creates a new read/write ListELResolver.
ListELResolver(boolean isReadOnly) Creates a new ListELResolver whose read-only status is determined by the given parameter.

Method Summary

Modifier and Type	Method and Description
Class<?>	getCommonPropertyType(ELContext context, Object base) If the base object is a list, returns the most general type that this resolver accepts for the property argument.
Iterator<FeatureDescriptor>	getFeatureDescriptors(ELContext context, Object base) Always returns null, since there is no reason to iterate through set set of all integers.
Class<?>	getType(ELContext context, Object base, Object property) If the base object is a list, returns the most general acceptable type for a value in this list.
Object	getValue(ELContext context, Object base, Object property) If the base object is a list, returns the value at the given index.
boolean	isReadOnly(ELContext context, Object base, Object property) If the base object is a list, returns whether a call to 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 val) If the base object is a list, attempts to set the value at the given index with the given value.

Methods inherited from class jakarta.el.ELResolver

convertToType, invoke

Methods inherited from class java.lang.Object

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

Constructor Detail

ListELResolver

public ListELResolver()

Creates a new read/write ListELResolver.

ListELResolver

public ListELResolver(boolean isReadOnly)

Creates a new ListELResolver whose read-only status is determined by the given parameter.

Parameters:

isReadOnly - true if this resolver cannot modify lists; false otherwise.

Method Detail

getType

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

If the base object is a list, returns the most general acceptable type for a value in this list.

If the base is a List, the propertyResolved property of the ELContext object must be set to true by this resolver, before returning. If this property is not true after this method is called, the caller should ignore the return value.

Assuming the base is a List, this method will always return Object.class. This is because Lists accept any object as an element.

Specified by:

getType in class ELResolver

Parameters:

context - The context of this evaluation.

base - The list to analyze. Only bases of type List are handled by this resolver.

property - The index of the element in the list to return the acceptable type for. Will be coerced into an integer, but otherwise ignored by this resolver.

Returns:

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

Throws:

PropertyNotFoundException - if the given index is out of bounds for this list.

NullPointerException - if context is null

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.

getValue

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

If the base object is a list, returns the value at the given index. The index is specified by the property argument, and coerced into an integer. If the coercion could not be performed, an IllegalArgumentException is thrown. If the index is out of bounds, null is returned.

If the base is a List, the propertyResolved property of the ELContext object must be set to true by this 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 list to be analyzed. Only bases of type List are handled by this resolver.

property - The index of the value to be returned. Will be coerced into an integer.

Returns:

If the propertyResolved property of ELContext was set to true, then the value at the given index or null if the index was out of bounds. Otherwise, undefined.

Throws:

IllegalArgumentException - if the property could not be coerced into an integer.

NullPointerException - if context is null.

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.

setValue

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

If the base object is a list, attempts to set the value at the given index with the given value. The index is specified by the property argument, and coerced into an integer. If the coercion could not be performed, an IllegalArgumentException is thrown. If the index is out of bounds, a PropertyNotFoundException is thrown.

If the base is a List, the propertyResolved property of the ELContext object must be set to true by this resolver, before returning. If this property is not true after this method is called, the caller can safely assume no value was set.

If this resolver was constructed in read-only mode, this method will always throw PropertyNotWritableException.

If a List was created using Collections.unmodifiableList(java.util.List<? extends T>), this method must throw PropertyNotWritableException. Unfortunately, there is no Collections API method to detect this. However, an implementation can create a prototype unmodifiable List and query its runtime type to see if it matches the runtime type of the base object as a workaround.

Specified by:

setValue in class ELResolver

Parameters:

context - The context of this evaluation.

base - The list to be modified. Only bases of type List are handled by this resolver.

property - The index of the value to be set. Will be coerced into an integer.

val - The value to be set at the given index.

Throws:

ClassCastException - if the class of the specified element prevents it from being added to this list.

NullPointerException - if context is null, or if the value is null and this List does not support null elements.

IllegalArgumentException - if the property could not be coerced into an integer, or if some aspect of the specified element prevents it from being added to this list.

PropertyNotWritableException - if this resolver was constructed in read-only mode, or if the set operation is not supported by the underlying list.

PropertyNotFoundException - if the given index is out of bounds for this list.

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.

isReadOnly

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

If the base object is a list, returns whether a call to setValue(jakarta.el.ELContext, java.lang.Object, java.lang.Object, java.lang.Object) will always fail.

If the base is a List, the propertyResolved property of the ELContext object must be set to true by this resolver, before returning. If this property is not true after this method is called, the caller should ignore the return value.

If this resolver was constructed in read-only mode, this method will always return true.

If a List was created using Collections.unmodifiableList(java.util.List<? extends T>), this method must return true. Unfortunately, there is no Collections API method to detect this. However, an implementation can create a prototype unmodifiable List and query its runtime type to see if it matches the runtime type of the base object as a workaround.

Specified by:

isReadOnly in class ELResolver

Parameters:

context - The context of this evaluation.

base - The list to analyze. Only bases of type List are handled by this resolver.

property - The index of the element in the list to return the acceptable type for. Will be coerced into an integer, but otherwise ignored by this resolver.

Returns:

If the propertyResolved property of ELContext was set to true, then true if calling the setValue method will always fail or false if it is possible that such a call may succeed; otherwise undefined.

Throws:

PropertyNotFoundException - if the given index is out of bounds for this list.

NullPointerException - if context is null

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.

getFeatureDescriptors

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

Always returns null, since there is no reason to iterate through set set of all integers.

The getCommonPropertyType(jakarta.el.ELContext, java.lang.Object) method returns sufficient information about what properties this resolver accepts.

Specified by:

getFeatureDescriptors in class ELResolver

Parameters:

context - The context of this evaluation.

base - The list. Only bases of type List are handled by this resolver.

Returns:

null.

See Also:

FeatureDescriptor

getCommonPropertyType

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

If the base object is a list, returns the most general type that this resolver accepts for the property argument. Otherwise, returns null.

Assuming the base is a List, this method will always return Integer.class. This is because Lists accept integers as their index.

Specified by:

getCommonPropertyType in class ELResolver

Parameters:

context - The context of this evaluation.

base - The list to analyze. Only bases of type List are handled by this resolver.

Returns:

null if base is not a List; otherwise Integer.class.