Context.java

/*
 * JBoss, Home of Professional Open Source
 * Copyright 2010, Red Hat, Inc., and individual contributors
 * by the @authors tag. See the copyright.txt in the distribution for a
 * full listing of individual contributors.
 *
 * 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.enterprise.context.spi;

import java.lang.annotation.Annotation;

import javax.enterprise.context.ContextNotActiveException;

/**
 * <p>
 * Provides an operation for obtaining contextual instances with a particular scope of any contextual type. Any instance of
 * {@code Context} is called a context object.
 * </p>
 * 
 * <p>
 * {@link AlterableContext} was introduced in CDI 1.1 to allow bean instances to be destroyed by the application. Extensions
 * should implement {@link AlterableContext} instead of {@link Context}.
 * </p>
 * 
 * <p>
 * The context object is responsible for creating and destroying contextual instances by calling operations of
 * {@link javax.enterprise.context.spi.Contextual}. In particular, the context object is responsible for destroying any
 * contextual instance it creates by passing the instance to
 * {@link javax.enterprise.context.spi.Contextual#destroy(Object, CreationalContext)} . A destroyed instance must not
 * subsequently be returned by {@code get()}. The context object must pass the same instance of
 * {@link javax.enterprise.context.spi.CreationalContext} to {@code Contextual.destroy()} that it passed to
 * {@code Contextual.create()} when it created the instance.
 * </p>
 * 
 * <p>
 * A custom context object may be registered with the container using
 * {@link javax.enterprise.inject.spi.AfterBeanDiscovery#addContext(Context)}.
 * </p>
 * 
 * @author Gavin King
 * @author Pete Muir
 */

public interface Context {

    /**
     * Get the scope type of the context object.
     * 
     * @return the scope
     */
    public Class<? extends Annotation> getScope();

    /**
     * Return an existing instance of certain contextual type or create a new instance by calling
     * {@link javax.enterprise.context.spi.Contextual#create(CreationalContext)} and return the new instance.
     * 
     * @param <T> the type of contextual type
     * @param contextual the contextual type
     * @param creationalContext the context in which the new instance will be created
     * @return the contextual instance
     * 
     * @throws ContextNotActiveException if the context is not active
     */
    public <T> T get(Contextual<T> contextual, CreationalContext<T> creationalContext);

    /**
     * Return an existing instance of a certain contextual type or a null value.
     * 
     * @param <T> the type of the contextual type
     * @param contextual the contextual type
     * @return the contextual instance, or a null value
     * 
     * @throws ContextNotActiveException if the context is not active
     */
    public <T> T get(Contextual<T> contextual);

    /**
     * Determines if the context object is active.
     * 
     * @return <tt>true</tt> if the context is active, or <tt>false</tt> otherwise.
     */
    public boolean isActive();

}