/*
* Copyright (C) 2007 Sun Microsystems, Inc. All rights reserved. Use is
* subject to license terms.
*/
package org.jdesktop.el;
import java.util.ArrayList;
import java.util.Iterator;
import java.beans.FeatureDescriptor;
/**
* Maintains an ordered composite list of child <code>ELResolver</code>s.
*
* <p>Though only a single <code>ELResolver</code> is associated with an
* <code>ELContext</code>, there are usually multiple resolvers considered
* for any given variable or property resolution. <code>ELResolver</code>s
* are combined together using a <code>CompositeELResolver</code>, to define
* rich semantics for evaluating an expression.</p>
*
* <p>For the {@link #getValue}, {@link #getType}, {@link #setValue} and
* {@link #isReadOnly} methods, an <code>ELResolver</code> is not
* responsible for resolving all possible (base, property) pairs. In fact,
* most resolvers will only handle a <code>base</code> of a single type.
* To indicate that a resolver has successfully resolved a particular
* (base, property) pair, it must set the <code>propertyResolved</code>
* property of the <code>ELContext</code> to <code>true</code>. If it could
* not handle the given pair, it must leave this property alone. The caller
* must ignore the return value of the method if <code>propertyResolved</code>
* is <code>false</code>.</p>
*
* <p>The <code>CompositeELResolver</code> initializes the
* <code>ELContext.propertyResolved</code> flag to <code>false</code>, and uses
* it as a stop condition for iterating through its component resolvers.</p>
*
* <p>The <code>ELContext.propertyResolved</code> flag is not used for the
* design-time methods {@link #getFeatureDescriptors} and
* {@link #getCommonPropertyType}. Instead, results are collected and
* combined from all child <code>ELResolver</code>s for these methods.</p>
*
* @see ELContext
* @see ELResolver
* @since JSP 2.1
*/
public class CompositeELResolver extends ELResolver {
/**
* Adds the given resolver to the list of component resolvers.
*
* <p>Resolvers are consulted in the order in which they are added.</p>
*
* @param elResolver The component resolver to add.
* @throws NullPointerException If the provided resolver is
* <code>null</code>.
*/
public void add(ELResolver elResolver) {
if (elResolver == null) {
throw new NullPointerException();
}
elResolvers.add(elResolver);
}
/**
* Attempts to resolve the given <code>property</code> object on the given
* <code>base</code> object by querying all component resolvers.
*
* <p>If this resolver handles the given (base, property) pair,
* the <code>propertyResolved</code> property of the
* <code>ELContext</code> object must be set to <code>true</code>
* by the resolver, before returning. If this property is not
* <code>true</code> after this method is called, the caller should ignore
* the return value.</p>
*
* <p>First, <code>propertyResolved</code> is set to <code>false</code> on
* the provided <code>ELContext</code>.</p>
*
* <p>Next, for each component resolver in this composite:
* <ol>
* <li>The <code>getValue()</code> method is called, passing in
* the provided <code>context</code>, <code>base</code> and
* <code>property</code>.</li>
* <li>If the <code>ELContext</code>'s <code>propertyResolved</code>
* flag is <code>false</code> then iteration continues.</li>
* <li>Otherwise, iteration stops and no more component resolvers are
* considered. The value returned by <code>getValue()</code> is
* returned by this method.</li>
* </ol></p>
*
* <p>If none of the component resolvers were able to perform this
* operation, the value <code>null</code> is returned and the
* <code>propertyResolved</code> flag remains set to
* <code>false</code></p>.
*
* <p>Any exception thrown by component resolvers during the iteration
* is propagated to the caller of this method.</p>
*
* @param context The context of this evaluation.
* @param base The base object whose property value is to be returned,
* or <code>null</code> to resolve a top-level variable.
* @param property The property or variable to be resolved.
* @return If the <code>propertyResolved</code> property of
* <code>ELContext</code> was set to <code>true</code>, then
* the result of the variable or property resolution; otherwise
* undefined.
* @throws NullPointerException if context is <code>null</code>
* @throws PropertyNotFoundException if the given (base, property) pair
* is handled by this <code>ELResolver</code> but the specified
* variable or property does not exist or is not readable.
* @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) {
context.setPropertyResolved(false);
int i = 0, len = this.elResolvers.size();
ELResolver elResolver;
Object value;
while (i < len) {
elResolver = this.elResolvers.get(i);
value = elResolver.getValue(context, base, property);
if (context.isPropertyResolved()) {
return value;
}
i++;
}
return ELContext.UNRESOLVABLE_RESULT;
}
/**
* For a given <code>base</code> and <code>property</code>, attempts to
* identify the most general type that is acceptable for an object to be
* passed as the <code>value</code> parameter in a future call
* to the {@link #setValue} method. The result is obtained by
* querying all component resolvers.
*
* <p>If this resolver handles the given (base, property) pair,
* the <code>propertyResolved</code> property of the
* <code>ELContext</code> object must be set to <code>true</code>
* by the resolver, before returning. If this property is not
* <code>true</code> after this method is called, the caller should ignore
* the return value.</p>
*
* <p>First, <code>propertyResolved</code> is set to <code>false</code> on
* the provided <code>ELContext</code>.</p>
*
* <p>Next, for each component resolver in this composite:
* <ol>
* <li>The <code>getType()</code> method is called, passing in
* the provided <code>context</code>, <code>base</code> and
* <code>property</code>.</li>
* <li>If the <code>ELContext</code>'s <code>propertyResolved</code>
* flag is <code>false</code> then iteration continues.</li>
* <li>Otherwise, iteration stops and no more component resolvers are
* considered. The value returned by <code>getType()</code> is
* returned by this method.</li>
* </ol></p>
*
* <p>If none of the component resolvers were able to perform this
* operation, the value <code>null</code> is returned and the
* <code>propertyResolved</code> flag remains set to
* <code>false</code></p>.
*
* <p>Any exception thrown by component resolvers during the iteration
* is propagated to the caller of this method.</p>
*
* @param context The context of this evaluation.
* @param base The base object whose property value is to be analyzed,
* or <code>null</code> to analyze a top-level variable.
* @param property The property or variable to return the acceptable
* type for.
* @return If the <code>propertyResolved</code> property of
* <code>ELContext</code> was set to <code>true</code>, then
* the most general acceptable type; otherwise undefined.
* @throws NullPointerException if context is <code>null</code>
* @throws PropertyNotFoundException if the given (base, property) pair
* is handled by this <code>ELResolver</code> but the specified
* variable or property does not exist or is not readable.
* @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) {
context.setPropertyResolved(false);
int i = 0, len = this.elResolvers.size();
ELResolver elResolver;
Class<?> type;
while (i < len) {
elResolver = this.elResolvers.get(i);
type = elResolver.getType(context, base, property);
if (context.isPropertyResolved()) {
return type;
}
i++;
}
return null;
}
/**
* Attempts to set the value of the given <code>property</code>
* object on the given <code>base</code> object. All component
* resolvers are asked to attempt to set the value.
*
* <p>If this resolver handles the given (base, property) pair,
* the <code>propertyResolved</code> property of the
* <code>ELContext</code> object must be set to <code>true</code>
* by the resolver, before returning. If this property is not
* <code>true</code> after this method is called, the caller can
* safely assume no value has been set.</p>
*
* <p>First, <code>propertyResolved</code> is set to <code>false</code> on
* the provided <code>ELContext</code>.</p>
*
* <p>Next, for each component resolver in this composite:
* <ol>
* <li>The <code>setValue()</code> method is called, passing in
* the provided <code>context</code>, <code>base</code>,
* <code>property</code> and <code>value</code>.</li>
* <li>If the <code>ELContext</code>'s <code>propertyResolved</code>
* flag is <code>false</code> then iteration continues.</li>
* <li>Otherwise, iteration stops and no more component resolvers are
* considered.</li>
* </ol></p>
*
* <p>If none of the component resolvers were able to perform this
* operation, the <code>propertyResolved</code> flag remains set to
* <code>false</code></p>.
*
* <p>Any exception thrown by component resolvers during the iteration
* is propagated to the caller of this method.</p>
*
* @param context The context of this evaluation.
* @param base The base object whose property value is to be set,
* or <code>null</code> to set a top-level variable.
* @param property The property or variable to be set.
* @param val The value to set the property or variable to.
* @throws NullPointerException if context is <code>null</code>
* @throws PropertyNotFoundException if the given (base, property) pair
* is handled by this <code>ELResolver</code> but the specified
* variable or property does not exist.
* @throws PropertyNotWritableException if the given (base, property)
* pair is handled by this <code>ELResolver</code> but the specified
* variable or property is not writable.
* @throws ELException if an exception was thrown while attempting to
* set the property or variable. The thrown exception
* must be included as the cause property of this exception, if
* available.
*/
public void setValue(ELContext context,
Object base,
Object property,
Object val) {
context.setPropertyResolved(false);
int i = 0, len = this.elResolvers.size();
ELResolver elResolver;
while (i < len) {
elResolver = this.elResolvers.get(i);
elResolver.setValue(context, base, property, val);
if (context.isPropertyResolved()) {
return;
}
i++;
}
}
/**
* For a given <code>base</code> and <code>property</code>, attempts to
* determine whether a call to {@link #setValue} will always fail. The
* result is obtained by querying all component resolvers.
*
* <p>If this resolver handles the given (base, property) pair,
* the <code>propertyResolved</code> property of the
* <code>ELContext</code> object must be set to <code>true</code>
* by the resolver, before returning. If this property is not
* <code>true</code> after this method is called, the caller should ignore
* the return value.</p>
*
* <p>First, <code>propertyResolved</code> is set to <code>false</code> on
* the provided <code>ELContext</code>.</p>
*
* <p>Next, for each component resolver in this composite:
* <ol>
* <li>The <code>isReadOnly()</code> method is called, passing in
* the provided <code>context</code>, <code>base</code> and
* <code>property</code>.</li>
* <li>If the <code>ELContext</code>'s <code>propertyResolved</code>
* flag is <code>false</code> then iteration continues.</li>
* <li>Otherwise, iteration stops and no more component resolvers are
* considered. The value returned by <code>isReadOnly()</code> is
* returned by this method.</li>
* </ol></p>
*
* <p>If none of the component resolvers were able to perform this
* operation, the value <code>false</code> is returned and the
* <code>propertyResolved</code> flag remains set to
* <code>false</code></p>.
*
* <p>Any exception thrown by component resolvers during the iteration
* is propagated to the caller of this method.</p>
*
* @param context The context of this evaluation.
* @param base The base object whose property value is to be analyzed,
* or <code>null</code> to analyze a top-level variable.
* @param property The property or variable to return the read-only status
* for.
* @return If the <code>propertyResolved</code> property of
* <code>ELContext</code> was set to <code>true</code>, then
* <code>true</code> if the property is read-only or
* <code>false</code> if not; otherwise undefined.
* @throws NullPointerException if context is <code>null</code>
* @throws PropertyNotFoundException if the given (base, property) pair
* is handled by this <code>ELResolver</code> but the specified
* variable or property does not exist.
* @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) {
context.setPropertyResolved(false);
int i = 0, len = this.elResolvers.size();
ELResolver elResolver;
boolean readOnly;
while (i < len) {
elResolver = this.elResolvers.get(i);
readOnly = elResolver.isReadOnly(context, base, property);
if (context.isPropertyResolved()) {
return readOnly;
}
i++;
}
return false; // Does not matter
}
/**
* Returns information about the set of variables or properties that
* can be resolved for the given <code>base</code> object. One use for
* this method is to assist tools in auto-completion. The results are
* collected from all component resolvers.
*
* <p>The <code>propertyResolved</code> property of the
* <code>ELContext</code> is not relevant to this method.
* The results of all <code>ELResolver</code>s are concatenated.</p>
*
* <p>The <code>Iterator</code> returned is an iterator over the
* collection of <code>FeatureDescriptor</code> objects returned by
* the iterators returned by each component resolver's
* <code>getFeatureDescriptors</code> method. If <code>null</code> is
* returned by a resolver, it is skipped.</p>
*
* @param context The context of this evaluation.
* @param base The base object whose set of valid properties is to
* be enumerated, or <code>null</code> to enumerate the set of
* top-level variables that this resolver can evaluate.
* @return An <code>Iterator</code> containing zero or more (possibly
* infinitely more) <code>FeatureDescriptor</code> objects, or
* <code>null</code> if this resolver does not handle the given
* <code>base</code> object or that the results are too complex to
* represent with this method
*/
public Iterator<FeatureDescriptor> getFeatureDescriptors(
ELContext context,
Object base) {
return new CompositeIterator(elResolvers.iterator(), context, base);
}
/**
* Returns the most general type that this resolver accepts for the
* <code>property</code> argument, given a <code>base</code> object.
* One use for this method is to assist tools in auto-completion. The
* result is obtained by querying all component resolvers.
*
* <p>The <code>Class</code> returned is the most specific class that is
* a common superclass of all the classes returned by each component
* resolver's <code>getCommonPropertyType</code> method. If
* <code>null</code> is returned by a resolver, it is skipped.</p>
*
* @param context The context of this evaluation.
* @param base The base object to return the most general property
* type for, or <code>null</code> to enumerate the set of
* top-level variables that this resolver can evaluate.
* @return <code>null</code> if this <code>ELResolver</code> does not
* know how to handle the given <code>base</code> object; otherwise
* <code>Object.class</code> if any type of <code>property</code>
* is accepted; otherwise the most general <code>property</code>
* type accepted for the given <code>base</code>.
*/
public Class<?> getCommonPropertyType(ELContext context,
Object base) {
Class<?> commonPropertyType = null;
Iterator<ELResolver> iter = elResolvers.iterator();
while (iter.hasNext()) {
ELResolver elResolver = iter.next();
Class<?> type = elResolver.getCommonPropertyType(context, base);
if (type == null) {
// skip this EL Resolver
continue;
} else if (commonPropertyType == null) {
commonPropertyType = type;
} else if (commonPropertyType.isAssignableFrom(type)) {
continue;
} else if (type.isAssignableFrom(commonPropertyType)) {
commonPropertyType = type;
} else {
// Don't have a commonPropertyType
return null;
}
}
return commonPropertyType;
}
private final ArrayList<ELResolver> elResolvers =
new ArrayList<ELResolver>();
private static class CompositeIterator
implements Iterator<FeatureDescriptor> {
Iterator<ELResolver> compositeIter;
Iterator<FeatureDescriptor> propertyIter;
ELContext context;
Object base;
CompositeIterator(Iterator<ELResolver> iter,
ELContext context,
Object base) {
compositeIter = iter;
this.context = context;
this.base = base;
}
public boolean hasNext() {
if (propertyIter == null || !propertyIter.hasNext()) {
while (compositeIter.hasNext()) {
ELResolver elResolver = compositeIter.next();
propertyIter = elResolver.getFeatureDescriptors(
context, base);
if (propertyIter != null) {
return propertyIter.hasNext();
}
}
return false;
}
return propertyIter.hasNext();
}
public FeatureDescriptor next() {
if (propertyIter == null || !propertyIter.hasNext()) {
while (compositeIter.hasNext()) {
ELResolver elResolver = compositeIter.next();
propertyIter = elResolver.getFeatureDescriptors(
context, base);
if (propertyIter != null) {
return propertyIter.next();
}
}
return null;
}
return propertyIter.next();
}
public void remove() {
throw new UnsupportedOperationException();
}
}
}