api/src/main/java/javax/el/ResourceBundleELResolver.java

/*
 * Copyright (c) 1997-2018 Oracle and/or its affiliates. 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 javax.el;

import java.beans.FeatureDescriptor;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.List;
import java.util.MissingResourceException;
import java.util.ResourceBundle;

/**
 * Defines property resolution behavior on instances of {@link java.util.ResourceBundle}.
 *
 * <p>
 * This resolver handles base objects of type <code>java.util.ResourceBundle</code>. It accepts any object as a property
 * and coerces it to a <code>java.lang.String</code> for invoking
 * {@link java.util.ResourceBundle#getObject(java.lang.String)}.
 * </p>
 *
 * <p>
 * This resolver is read only and will throw a {@link PropertyNotWritableException} if <code>setValue</code> is called.
 * </p>
 *
 * <p>
 * <code>ELResolver</code>s are combined together using {@link CompositeELResolver}s, to define rich semantics for
 * evaluating an expression. See the javadocs for {@link ELResolver} for details.
 * </p>
 *
 * @see CompositeELResolver
 * @see ELResolver
 * @see java.util.ResourceBundle
 * @since JSP 2.1
 */
public class ResourceBundleELResolver extends ELResolver {

    /**
     * If the base object is an instance of <code>ResourceBundle</code>, the provided property will first be coerced to a
     * <code>String</code>. The <code>Object</code> returned by <code>getObject</code> on the base
     * <code>ResourceBundle</code> will be returned.
     *
     * <p>
     * If the base is <code>ResourceBundle</code>, the <code>propertyResolved</code> property of the <code>ELContext</code>
     * object must be set to <code>true</code> by this resolver, before returning. If this property is not <code>true</code>
     * after this method is called, the caller should ignore the return value.
     *
     * @param context The context of this evaluation.
     * @param base The ResourceBundle to analyze.
     * @param property The name of the property to analyze. Will be coerced to a <code>String</code>.
     * @return If the <code>propertyResolved</code> property of <code>ELContext</code> was set to <code>true</code>, then
     * <code>null</code> if property is <code>null</code>; otherwise the <code>Object</code> for the given key (property
     * coerced to <code>String</code>) from the <code>ResourceBundle</code>. If no object for the given key can be found,
     * then the <code>String</code> "???" + key + "???".
     * @throws NullPointerException if context is <code>null</code>
     * @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 instanceof ResourceBundle) {
            context.setPropertyResolved(true);
            if (property != null) {
                try {
                    return ((ResourceBundle) base).getObject(property.toString());
                } catch (MissingResourceException e) {
                    return "???" + property + "???";
                }
            }
        }
        return null;
    }

    /**
     * If the base object is an instance of <code>ResourceBundle</code>, return <code>null</code>, since the resolver is
     * read only.
     *
     * <p>
     * If the base is <code>ResourceBundle</code>, the <code>propertyResolved</code> property of the <code>ELContext</code>
     * object must be set to <code>true</code> by this resolver, before returning. If this property is not <code>true</code>
     * after this method is called, the caller should ignore the return value.
     * </p>
     *
     * @param context The context of this evaluation.
     * @param base The ResourceBundle to analyze.
     * @param property The name of the property to analyze.
     * @return If the <code>propertyResolved</code> property of <code>ELContext</code> was set to <code>true</code>, then
     * <code>null</code>; otherwise undefined.
     * @throws NullPointerException if context is <code>null</code>
     */
    @Override
    public Class<?> getType(ELContext context, Object base, Object property) {
        if (context == null) {
            throw new NullPointerException();
        }

        if (base instanceof ResourceBundle) {
            context.setPropertyResolved(true);
        }
        return null;
    }

    /**
     * If the base object is a ResourceBundle, throw a {@link PropertyNotWritableException}.
     *
     * @param context The context of this evaluation.
     * @param base The ResourceBundle to be modified. Only bases that are of type ResourceBundle are handled.
     * @param property The String property to use.
     * @param value The value to be set.
     * @throws NullPointerException if context is <code>null</code>.
     * @throws PropertyNotWritableException Always thrown if base is an instance of ReasourceBundle.
     */
    @Override
    public void setValue(ELContext context, Object base, Object property, Object value) {
        if (context == null) {
            throw new NullPointerException();
        }

        if (base instanceof ResourceBundle) {
            context.setPropertyResolved(true);
            throw new PropertyNotWritableException("ResourceBundles are immutable");
        }
    }

    /**
     * If the base object is not null and an <code>instanceof</code> {@link ResourceBundle}, return <code>true</code>.
     *
     * @param context The context of this evaluation.
     * @param base The ResourceBundle to be modified. Only bases that are of type ResourceBundle are handled.
     * @param property The String property to use.
     * @return If the <code>propertyResolved</code> property of <code>ELContext</code> was set to <code>true</code>, then
     * <code>true</code>; otherwise undefined.
     * @throws NullPointerException if context is <code>null</code>
     */
    @Override
    public boolean isReadOnly(ELContext context, Object base, Object property) {
        if (context == null) {
            throw new NullPointerException();
        }
        if (base instanceof ResourceBundle) {
            context.setPropertyResolved(true);
            return true;
        }
        return false;
    }

    /**
     * If the base object is a ResourceBundle, returns an <code>Iterator</code> containing the set of keys available in the
     * <code>ResourceBundle</code>. Otherwise, returns <code>null</code>.
     *
     * <p>
     * The <code>Iterator</code> returned must contain zero or more instances of {@link java.beans.FeatureDescriptor}. Each
     * info object contains information about a key in the ResourceBundle, and is initialized as follows:
     * <ul>
     * <li>displayName - The <code>String</code> key
     * <li>name - Same as displayName property.</li>
     * <li>shortDescription - Empty string</li>
     * <li>expert - <code>false</code></li>
     * <li>hidden - <code>false</code></li>
     * <li>preferred - <code>true</code></li>
     * </ul>
     *
     * In addition, the following named attributes must be set in the returned <code>FeatureDescriptor</code>s:
     * <ul>
     * <li>{@link ELResolver#TYPE} - <code>String.class</code></li>
     * <li>{@link ELResolver#RESOLVABLE_AT_DESIGN_TIME} - <code>true</code></li>
     * </ul>
     *
     *
     * @param context The context of this evaluation.
     * @param base The bundle whose keys are to be iterated over. Only bases of type <code>ResourceBundle</code> are handled
     * by this resolver.
     * @return An <code>Iterator</code> containing zero or more (possibly infinitely more) <code>FeatureDescriptor</code>
     * objects, each representing a key in this bundle, or <code>null</code> if the base object is not a ResourceBundle.
     */
    @Override
    public Iterator<FeatureDescriptor> getFeatureDescriptors(ELContext context, Object base) {
        if (base instanceof ResourceBundle) {
            ResourceBundle bundle = (ResourceBundle) base;
            List<FeatureDescriptor> features = new ArrayList<FeatureDescriptor>();
            String key = null;
            FeatureDescriptor desc = null;
            for (Enumeration<String> e = bundle.getKeys(); e.hasMoreElements();) {
                key = e.nextElement();
                desc = new FeatureDescriptor();
                desc.setDisplayName(key);
                desc.setExpert(false);
                desc.setHidden(false);
                desc.setName(key);
                desc.setPreferred(true);
                desc.setValue(TYPE, String.class);
                desc.setValue(RESOLVABLE_AT_DESIGN_TIME, Boolean.TRUE);
                features.add(desc);
            }
            return features.iterator();
        }
        return null;
    }

    /**
     * If the base object is a ResourceBundle, returns the most general type that this resolver accepts for the
     * <code>property</code> argument. Otherwise, returns <code>null</code>.
     *
     * <p>
     * Assuming the base is a <code>ResourceBundle</code>, this method will always return <code>String.class</code>.
     *
     * @param context The context of this evaluation.
     * @param base The bundle to analyze. Only bases of type <code>ResourceBundle</code> are handled by this resolver.
     * @return <code>null</code> if base is not a <code>ResourceBundle</code>; otherwise <code>String.class</code>.
     */
    @Override
    public Class<?> getCommonPropertyType(ELContext context, Object base) {
        if (base instanceof ResourceBundle) {
            return String.class;
        }
        return null;
    }
}