Instance.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.inject;

import java.lang.annotation.Annotation;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;

import javax.enterprise.util.TypeLiteral;
import javax.inject.Provider;

/**
 * <p>
 * Allows the application to dynamically obtain instances of beans with a specified combination of required type and qualifiers.
 * </p>
 * 
 * <p>
 * In certain situations, injection is not the most convenient way to obtain a contextual reference. For example, it may not be
 * used when:
 * </p>
 * 
 * <ul>
 * <li>the bean type or qualifiers vary dynamically at runtime, or</li>
 * <li>depending upon the deployment, there may be no bean which satisfies the type and qualifiers, or</li>
 * <li>we would like to iterate over all beans of a certain type.</li>
 * </ul>
 * 
 * <p>
 * In these situations, an instance of the <tt>Instance</tt> may be injected:
 * </p>
 * 
 * <pre>
 * @Inject
 * Instance<PaymentProcessor> paymentProcessor;
 * </pre>
 * 
 * <p>
 * Any combination of qualifiers may be specified at the injection point:
 * </p>
 * 
 * <pre>
 * @Inject
 * @PayBy(CHEQUE)
 * Instance<PaymentProcessor> chequePaymentProcessor;
 * </pre>
 * 
 * <p>
 * Or, the {@link javax.enterprise.inject.Any @Any} qualifier may be used, allowing the application to specify qualifiers
 * dynamically:
 * </p>
 * 
 * <pre>
 * @Inject
 * @Any
 * Instance<PaymentProcessor> anyPaymentProcessor;
 * </pre>
 * 
 * <p>
 * Finally, the {@link javax.enterprise.inject.New @New} qualifier may be used, allowing the application to obtain a
 * {@link javax.enterprise.inject.New @New} qualified bean:
 * </p>
 * 
 * <pre>
 * @Inject
 * @New(ChequePaymentProcessor.class)
 * Instance<PaymentProcessor> chequePaymentProcessor;
 * </pre>
 * 
 * <p>
 * For an injected <tt>Instance</tt>:
 * </p>
 * 
 * <ul>
 * <li>the <em>required type</em> is the type parameter specified at the injection point, and</li>
 * <li>the <em>required qualifiers</em> are the qualifiers specified at the injection point.</li>
 * </ul>
 * 
 * <p>
 * The inherited {@link javax.inject.Provider#get()} method returns a contextual references for the unique bean that matches the
 * required type and required qualifiers and is eligible for injection into the class into which the parent <tt>Instance</tt>
 * was injected, or throws an {@link javax.enterprise.inject.UnsatisfiedResolutionException} or
 * {@link javax.enterprise.inject.AmbiguousResolutionException}.
 * </p>
 * 
 * <pre>
 * PaymentProcessor pp = chequePaymentProcessor.get();
 * </pre>
 * 
 * <p>
 * The inherited {@link java.lang.Iterable#iterator()} method returns an iterator over contextual references for beans that
 * match the required type and required qualifiers and are eligible for injection into the class into which the parent
 * <tt>Instance</tt> was injected.
 * </p>
 * 
 * <pre>
 * for (PaymentProcessor pp : anyPaymentProcessor)
 *     pp.test();
 * </pre>
 * 
 * @see javax.inject.Provider#get()
 * @see java.lang.Iterable#iterator()
 * @see javax.enterprise.util.AnnotationLiteral
 * @see javax.enterprise.util.TypeLiteral
 * 
 * @author Gavin King
 * @author John Ament
 * @author Martin Kouba
 * 
 * @param <T> the required bean type
 */

public interface Instance<T> extends Iterable<T>, Provider<T> {

    /**
     * <p>
     * Obtains a child <tt>Instance</tt> for the given additional required qualifiers.
     * </p>
     * 
     * @param qualifiers the additional required qualifiers
     * @return the child <tt>Instance</tt>
     * @throws IllegalArgumentException if passed two instances of the same non repeating qualifier type, or an instance of an annotation that
     *         is not a qualifier type
     * @throws IllegalStateException if the container is already shutdown
     */
    Instance<T> select(Annotation... qualifiers);

    /**
     * <p>
     * Obtains a child <tt>Instance</tt> for the given required type and additional required qualifiers.
     * </p>
     * 
     * @param <U> the required type
     * @param subtype a {@link java.lang.Class} representing the required type
     * @param qualifiers the additional required qualifiers
     * @return the child <tt>Instance</tt>
     * @throws IllegalArgumentException if passed two instances of the same non repeating qualifier type, or an instance of an annotation that
     *         is not a qualifier type
     * @throws IllegalStateException if the container is already shutdown
     */
    <U extends T> Instance<U> select(Class<U> subtype, Annotation... qualifiers);

    /**
     * <p>
     * Obtains a child <tt>Instance</tt> for the given required type and additional required qualifiers.
     * </p>
     * 
     * @param <U> the required type
     * @param subtype a {@link javax.enterprise.util.TypeLiteral} representing the required type
     * @param qualifiers the additional required qualifiers
     * @return the child <tt>Instance</tt>
     * @throws IllegalArgumentException if passed two instances of the same non repeating qualifier type, or an instance of an annotation that
     *         is not a qualifier type
     * @throws IllegalStateException if the container is already shutdown
     */
    <U extends T> Instance<U> select(TypeLiteral<U> subtype, Annotation... qualifiers);

    /**
     * <p>
     * When called, provides back a Stream of the beans available in this Instance. If no beans are found, it returns an empty
     * stream.
     * </p>
     *
     * @since 2.0
     * @return a <tt>Stream</tt> representing the beans associated with this {@link Instance} object
     */
    default Stream<T> stream() {
        return StreamSupport.stream(this.spliterator(), false);
    }

    /**
     * <p>
     * Determines if there is no bean that matches the required type and qualifiers and is eligible for injection into the class
     * into which the parent <tt>Instance</tt> was injected.
     * </p>
     * 
     * @return <tt>true</tt> if there is no bean that matches the required type and qualifiers and is eligible for injection
     *         into the class into which the parent <tt>Instance</tt> was injected, or <tt>false</tt> otherwise.
     */
    boolean isUnsatisfied();

    /**
     * <p>
     * Determines if there is more than one bean that matches the required type and qualifiers and is eligible for injection
     * into the class into which the parent <tt>Instance</tt> was injected.
     * </p>
     * 
     * @return <tt>true</tt> if there is more than one bean that matches the required type and qualifiers and is eligible for
     *         injection into the class into which the parent <tt>Instance</tt> was injected, or <tt>false</tt> otherwise.
     */
    boolean isAmbiguous();

    /**
     * <p>
     * Determines if there is exactly one bean that matches the required type and qualifiers and is eligible for injection
     * into the class into which the parent <tt>Instance</tt> was injected.
     * </p>
     *
     * @since 2.0
     * @return <tt>true</tt> if there is exactly one bean that matches the required type and qualifiers and is eligible for
     *         injection into the class into which the parent <tt>Instance</tt> was injected, or <tt>false</tt> otherwise.
     */
    default boolean isResolvable() {
        return !isUnsatisfied() && !isAmbiguous();
    }

    /**
     * <p>
     * When called, the container destroys the instance if the active context object for the scope type of the bean supports
     * destroying bean instances. All normal scoped built-in contexts support destroying bean instances.
     * </p>
     * 
     * <p>
     * The instance passed should either be a dependent scoped bean instance obtained from the same {@link Instance} object, or
     * the client proxy for a normal scoped bean instance.
     * </p>
     * 
     * 
     * @since 1.1
     * @param instance the instance to destroy
     * @throws UnsupportedOperationException if the active context object for the scope type of the bean does not support
     *         destroying bean instances
     */
    void destroy(T instance);

}