javax.el.MapELResolver Maven / Gradle / Ivy
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package javax.el;
import java.beans.FeatureDescriptor;
import java.util.Map;
import java.util.Iterator;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.ArrayList;
/**
* 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 JSP 2.1
*/
public class MapELResolver extends ELResolver {
/**
* Creates a new read/write MapELResolver.
*/
public MapELResolver() {
this.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.
*/
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.
*/
public Object getValue(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 map.get(property);
}
return null;
}
static private Class theUnmodifiableMapClass =
Collections.unmodifiableMap(new HashMap()).getClass();
/**
* 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.
*/
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(true);
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.
*/
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.
*/
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);
descriptor.setValue("type", key==null? null: key.getClass());
descriptor.setValue("resolvableAtDesignTime", Boolean.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.
*/
public Class getCommonPropertyType(ELContext context,
Object base) {
if (base != null && base instanceof Map) {
return Object.class;
}
return null;
}
private boolean isReadOnly;
}