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/*
* Copyright 2006-2009 Odysseus Software GmbH
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package javax.el;
import java.beans.FeatureDescriptor;
import java.util.Iterator;
import java.util.Map;
/**
* Defines property resolution behavior on instances of java.util.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 {@link #setValue(ELContext, Object, Object, Object)} will always throw
* PropertyNotWritableException. ELResolvers are combined together using {@link CompositeELResolver}
* s, to define rich semantics for evaluating an expression. See the javadocs for {@link ELResolver}
* for details.
*/
public class MapELResolver extends ELResolver {
private final boolean readOnly;
/**
* Creates a new read/write MapELResolver.
*/
public MapELResolver() {
this(false);
}
/**
* Creates a new MapELResolver whose read-only status is determined by the given parameter.
*/
public MapELResolver(boolean readOnly) {
this.readOnly = readOnly;
}
/**
* 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.
*
* @param context
* The context of this evaluation.
* @param base
* The map to analyze. Only bases of type Map are handled by this resolver.
* @return null if base is not a Map; otherwise Object.class.
*/
@Override
public Class getCommonPropertyType(ELContext context, Object base) {
return isResolvable(base) ? Object.class : null;
}
/**
* 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
* java.beans.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:
*
*
{@link ELResolver#TYPE} - The return value of calling the getClass() method on this key,
* or null if the key is null.
*
* @param context
* The context of this evaluation.
* @param base
* The map to analyze. Only bases of type Map are handled by this resolver.
* @return 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.
*/
@Override
public Iterator getFeatureDescriptors(ELContext context, Object base) {
if (isResolvable(base)) {
Map map = (Map) base;
final Iterator keys = map.keySet().iterator();
return new Iterator() {
public boolean hasNext() {
return keys.hasNext();
}
public FeatureDescriptor next() {
Object key = keys.next();
FeatureDescriptor feature = new FeatureDescriptor();
feature.setDisplayName(key == null ? "null" : key.toString());
feature.setName(feature.getDisplayName());
feature.setShortDescription("");
feature.setExpert(true);
feature.setHidden(false);
feature.setPreferred(true);
feature.setValue(TYPE, key == null ? null : key.getClass());
feature.setValue(RESOLVABLE_AT_DESIGN_TIME, true);
return feature;
}
public void remove() {
throw new UnsupportedOperationException("cannot remove");
}
};
}
return null;
}
/**
* 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.
*
* @param context
* The context of this evaluation.
* @param base
* The map to analyze. Only bases of type Map are handled by this resolver.
* @param property
* The key to return the acceptable type for. Ignored by this resolver.
* @return If the propertyResolved property of ELContext was set to true, then the most general
* acceptable type; otherwise undefined.
* @throws NullPointerException
* if context is null
* @throws 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.
*/
@Override
public Class getType(ELContext context, Object base, Object property) {
if (context == null) {
throw new NullPointerException("context is null");
}
Class result = null;
if (isResolvable(base)) {
result = Object.class;
context.setPropertyResolved(true);
}
return result;
}
/**
* 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 java.util.Map.get(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.
*
* @param context
* The context of this evaluation.
* @param base
* The map to analyze. Only bases of type Map are handled by this resolver.
* @param property
* The key to return the acceptable type for. Ignored by this resolver.
* @return 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).
* @throws 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).
* @throws 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.
*/
@Override
public Object getValue(ELContext context, Object base, Object property) {
if (context == null) {
throw new NullPointerException("context is null");
}
Object result = null;
if (isResolvable(base)) {
result = ((Map) base).get(property);
context.setPropertyResolved(true);
}
return result;
}
/**
* If the base object is a map, returns whether a call to
* {@link #setValue(ELContext, Object, Object, 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 java.util.Collections.unmodifiableMap(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.
*
* @param context
* The context of this evaluation.
* @param base
* The map to analyze. Only bases of type Map are handled by this resolver.
* @param property
* The key to return the acceptable type for. Ignored by this resolver.
* @return 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.
* @throws 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.
*/
@Override
public boolean isReadOnly(ELContext context, Object base, Object property) {
if (context == null) {
throw new NullPointerException("context is null");
}
if (isResolvable(base)) {
context.setPropertyResolved(true);
}
return readOnly;
}
/**
* 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
* java.util.Collections.unmodifiableMap(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.
*
* @param context
* The context of this evaluation.
* @param base
* The map to analyze. Only bases of type Map are handled by this resolver.
* @param property
* The key to return the acceptable type for. Ignored by this resolver.
* @param value
* 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.
* @throws NullPointerException
* if context is null, or if this map does not permit null keys or values, and the
* specified key or value is null.
* @throws IllegalArgumentException
* if some aspect of this key or value prevents it from being stored in this map.
* @throws PropertyNotWritableException
* if this resolver was constructed in read-only mode, or if the put operation is
* not supported by the underlying map.
* @throws 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.
*/
@Override
@SuppressWarnings("unchecked")
public void setValue(ELContext context, Object base, Object property, Object value) {
if (context == null) {
throw new NullPointerException("context is null");
}
if (isResolvable(base)) {
if (readOnly) {
throw new PropertyNotWritableException("resolver is read-only");
}
((Map) base).put(property, value);
context.setPropertyResolved(true);
}
}
/**
* Test whether the given base should be resolved by this ELResolver.
*
* @param base
* The bean to analyze.
* @param property
* The name of the property to analyze. Will be coerced to a String.
* @return base instanceof Map
*/
private final boolean isResolvable(Object base) {
return base instanceof Map;
}
}
