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MapELResolver (Java EE 5 SDK) - Java Platform, Enterprise Edition v5.0 API Specifications

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javax.el
Class MapELResolver

java.lang.Object
  extended by javax.el.ELResolver
      extended by javax.el.MapELResolver

public class MapELResolver
extends ELResolver

Defines property resolution behavior on instances of Map.

This resolver handles base objects of type java.util.Map. It accepts any object as a property and uses that object as a key in the map. The resulting value is the value in the map that is associated with that key.

This resolver can be constructed in read-only mode, which means that isReadOnly will always return true and setValue(javax.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:
JSP 2.1
See Also:
CompositeELResolver, ELResolver, Map

Field Summary
 
Fields inherited from class javax.el.ELResolver
RESOLVABLE_AT_DESIGN_TIME, TYPE
 
Constructor Summary
MapELResolver()
          Creates a new read/write MapELResolver.
MapELResolver(boolean isReadOnly)
          Creates a new MapELResolver whose read-only status is determined by the given parameter.
 
Method Summary
 Class<?> getCommonPropertyType(ELContext context, Object base)
          If the base object is a map, returns the most general type that this resolver accepts for the property argument.
 Iterator<FeatureDescriptor> getFeatureDescriptors(ELContext context, Object base)
          If the base object is a map, returns an Iterator containing the set of keys available in the Map.
 Class<?> getType(ELContext context, Object base, Object property)
          If the base object is a map, returns the most general acceptable type for a value in this map.
 Object getValue(ELContext context, Object base, Object property)
          If the base object is a map, returns the value associated with the given key, as specified by the property argument.
 boolean isReadOnly(ELContext context, Object base, Object property)
          If the base object is a map, returns whether a call to 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 val)
          If the base object is a map, attempts to set the value associated with the given key, as specified by the property argument.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

MapELResolver

public MapELResolver()
Creates a new read/write MapELResolver.

MapELResolver

public MapELResolver(boolean isReadOnly)
Creates a new MapELResolver whose read-only status is determined by the given parameter.

Parameters:
isReadOnly - true if this resolver cannot modify maps; false otherwise.
Method Detail

getType

public Class<?> getType(ELContext context,
                        Object base,
                        Object property)
If the base object is a map, returns the most general acceptable type for a value in this map.

If the base is a Map, 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 Map, this method will always return Object.class. This is because Maps accept any object as the value for a given key.

Specified by:
getType in class ELResolver
Parameters:
context - The context of this evaluation.
base - The map to analyze. Only bases of type Map are handled by this resolver.
property - The key to return the acceptable type for. Ignored by this resolver.
Returns:
If the propertyResolved property of ELContext was set to true, then the most general acceptable type; otherwise undefined.
Throws:
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 map, returns the value associated with the given key, as specified by the property argument. If the key was not found, null is returned.

If the base is a Map, 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.

Just as in Map.get(java.lang.Object), just because null is returned doesn't mean there is no mapping for the key; it's also possible that the Map explicitly maps the key to null.

Specified by:
getValue in class ELResolver
Parameters:
context - The context of this evaluation.
base - The map to be analyzed. Only bases of type Map are handled by this resolver.
property - The key whose associated value is to be returned.
Returns:
If the propertyResolved property of ELContext was set to true, then the value associated with the given key or null if the key was not found. Otherwise, undefined.
Throws:
ClassCastException - if the key is of an inappropriate type for this map (optionally thrown by the underlying Map).
NullPointerException - if context is null, or if the key is null and this map does not permit null keys (the latter is optionally thrown by the underlying Map).
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 map, attempts to set the value associated with the given key, as specified by the property argument.

If the base is a Map, 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 Map was created using Collections.unmodifiableMap(java.util.Map), this method must throw PropertyNotWritableException. Unfortunately, there is no Collections API method to detect this. However, an implementation can create a prototype unmodifiable Map 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 map to be modified. Only bases of type Map are handled by this resolver.
property - The key with which the specified value is to be associated.
val - The value to be associated with the specified key.
Throws:
ClassCastException - if the class of the specified key or value prevents it from being stored in this map.
NullPointerException - if context is null, or if this map does not permit null keys or values, and the specified key or value is null.
IllegalArgumentException - if some aspect of this key or value prevents it from being stored in this map.
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.
PropertyNotWritableException - if this resolver was constructed in read-only mode, or if the put operation is not supported by the underlying map.

isReadOnly

public boolean isReadOnly(ELContext context,
                          Object base,
                          Object property)
If the base object is a map, returns whether a call to setValue(javax.el.ELContext, java.lang.Object, java.lang.Object, java.lang.Object) will always fail.

If the base is a Map, 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 Map was created using Collections.unmodifiableMap(java.util.Map), this method must return true. Unfortunately, there is no Collections API method to detect this. However, an implementation can create a prototype unmodifiable Map 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 map to analyze. Only bases of type Map are handled by this resolver.
property - The key to return the read-only status for. 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:
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)
If the base object is a map, returns an Iterator containing the set of keys available in the Map. Otherwise, returns null.

The Iterator returned must contain zero or more instances of FeatureDescriptor. Each info object contains information about a key in the Map, and is initialized as follows:

  • displayName - The return value of calling the toString method on this key, or "null" if the key is null.
  • name - Same as displayName property.
  • shortDescription - Empty string
  • expert - false
  • hidden - false
  • preferred - true
    • In addition, the following named attributes must be set in the returned FeatureDescriptors:
  • ELResolver.TYPE - The return value of calling the getClass() method on this key, or null if the key is null.
  • ELResolver.RESOLVABLE_AT_DESIGN_TIME - true

    • Specified by:
    getFeatureDescriptors in class ELResolver
    Parameters:
    context - The context of this evaluation.
    base - The map whose keys are to be iterated over. Only bases of type Map are handled by this resolver.
    Returns:
    An Iterator containing zero or more (possibly infinitely more) FeatureDescriptor objects, each representing a key in this map, or null if the base object is not a map.
    See Also:
    FeatureDescriptor

    getCommonPropertyType

    public Class<?> getCommonPropertyType(ELContext context,
                                      Object base)
    If the base object is a map, returns the most general type that this resolver accepts for the property argument. Otherwise, returns null.

    Assuming the base is a Map, this method will always return Object.class. This is because Maps accept any object as a key.

    Specified by:
    getCommonPropertyType in class ELResolver
    Parameters:
    context - The context of this evaluation.
    base - The map to analyze. Only bases of type Map are handled by this resolver.
    Returns:
    null if base is not a Map; otherwise Object.class.
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