jakarta.el.MapELResolver Maven / Gradle / Ivy
/*
* Copyright (c) 1997, 2019 Oracle and/or its affiliates and others.
* All rights reserved.
* Copyright 2004 The Apache Software Foundation
*
* 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 jakarta.el;
import static java.lang.Boolean.TRUE;
import java.beans.FeatureDescriptor;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
/**
* Defines property resolution behavior on instances of {@link 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 {@link #isReadOnly} will always return
* true and {@link #setValue} 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.
*
*
* @see CompositeELResolver
* @see ELResolver
* @see java.util.Map
* @since Jakarta Server Pages 2.1
*/
public class MapELResolver extends ELResolver {
static private Class theUnmodifiableMapClass = Collections.unmodifiableMap(new HashMap<>()).getClass();
private boolean isReadOnly;
/**
* Creates a new read/write MapELResolver.
*/
public MapELResolver() {
isReadOnly = false;
}
/**
* Creates a new MapELResolver whose read-only status is determined by the given parameter.
*
* @param isReadOnly true if this resolver cannot modify maps; false otherwise.
*/
public MapELResolver(boolean isReadOnly) {
this.isReadOnly = isReadOnly;
}
/**
* 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();
}
if (base != null && base instanceof Map) {
context.setPropertyResolved(true);
return Object.class;
}
return null;
}
/**
* 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 {@link java.util.Map#get}, 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 be analyzed. Only bases of type Map are handled by this resolver.
* @param property The key whose associated value is to be returned.
* @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();
}
if (base != null && base instanceof Map) {
context.setPropertyResolved(base, property);
Map map = (Map) base;
return map.get(property);
}
return null;
}
/**
* 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 {@link java.util.Collections#unmodifiableMap}, 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 be modified. Only bases of type Map are handled by this resolver.
* @param property The key with which the specified value is to be associated.
* @param 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.
* @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 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.
* @throws PropertyNotWritableException if this resolver was constructed in read-only mode, or if the put operation is
* not supported by the underlying map.
*/
@Override
public void setValue(ELContext context, Object base, Object property, Object val) {
if (context == null) {
throw new NullPointerException();
}
if (base != null && base instanceof Map) {
context.setPropertyResolved(base, property);
// The cast is safe
@SuppressWarnings("unchecked")
Map map = (Map) base;
if (isReadOnly || map.getClass() == theUnmodifiableMapClass) {
throw new PropertyNotWritableException();
}
try {
map.put(property, val);
} catch (UnsupportedOperationException ex) {
throw new PropertyNotWritableException();
}
}
}
/**
* If the base object is a map, returns whether a call to {@link #setValue} 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 {@link java.util.Collections#unmodifiableMap}, 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 read-only status 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();
}
if (base != null && base instanceof Map) {
context.setPropertyResolved(true);
Map map = (Map) base;
return isReadOnly || map.getClass() == theUnmodifiableMapClass;
}
return false;
}
/**
* 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 {@link 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.
* - {@link ELResolver#RESOLVABLE_AT_DESIGN_TIME} -
true
*
*
*
* @param context The context of this evaluation.
* @param base The map whose keys are to be iterated over. 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 (base != null && base instanceof Map) {
Map map = (Map) base;
Iterator iter = map.keySet().iterator();
List list = new ArrayList<>();
while (iter.hasNext()) {
Object key = iter.next();
FeatureDescriptor descriptor = new FeatureDescriptor();
String name = key == null ? null : key.toString();
descriptor.setName(name);
descriptor.setDisplayName(name);
descriptor.setShortDescription("");
descriptor.setExpert(false);
descriptor.setHidden(false);
descriptor.setPreferred(true);
if (key != null) {
descriptor.setValue("type", key.getClass());
}
descriptor.setValue("resolvableAtDesignTime", TRUE);
list.add(descriptor);
}
return list.iterator();
}
return null;
}
/**
* 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) {
if (base != null && base instanceof Map) {
return Object.class;
}
return null;
}
}