/*
 * The contents of this file are subject to the terms
 * of the Common Development and Distribution License
 * (the "License").  You may not use this file except
 * in compliance with the License.
 * 
 * You can obtain a copy of the license at
 * http://www.opensource.org/licenses/cddl1.php
 * See the License for the specific language governing
 * permissions and limitations under the License.
 */

package javax.ws.rs.core;

import java.util.Collections;
import java.util.Set;

/**
 * Defines the components of a JAX-RS application and supplies additional
 * metadata. A JAX-RS application or implementation supplies a concrete
 * subclass of this abstract class.
 * 
 */
public abstract class Application {
    private static final Set<Object> emptySet = Collections.emptySet();
    
    /**
     * Get a set of root resource and provider classes. The default lifecycle
     * for resource class instances is per-request. The default lifecycle for
     * providers is singleton.
     * 
     * <p>Implementations should warn about and ignore classes that do not 
     * conform to the requirements of root resource or provider classes.
     * Implementations should warn about and ignore classes for which
     * {@link #getSingletons()} returns an instance. Implementations MUST
     * NOT modify the returned set.</p>
     * 
     * @return a set of root resource and provider classes. Returning null
     * is equivalent to returning an empty set.
     */
    public abstract Set<Class<?>> getClasses();
    
    /**
     * Get a set of root resource and provider instances. Fields and properties
     * of returned instances are injected with their declared dependencies
     * (see {@link Context}) by the runtime prior to use.
     * 
     * <p>Implementations should warn about and ignore classes that do not
     * conform to the requirements of root resource or provider classes.
     * Implementations should flag an error if the returned set includes
     * more than one instance of the same class. Implementations MUST
     * NOT modify the returned set.</p>
     * 
     * <p>The default implementation returns an empty set.</p>
     * 
     * @return a set of root resource and provider instances. Returning null
     * is equivalent to returning an empty set.
     */
    public Set<Object> getSingletons() {
        return emptySet;
    }
    
}