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/*
 * Copyright 2013 the original author or authors.
 *
 * 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 ratpack.registry;

import ratpack.api.Nullable;

import java.util.List;

/**
 * An object registry.
 * 

* Registries are primarily used for inter {@link ratpack.handling.Handler} communication in request processing. * The {@link ratpack.handling.Context} object that handlers operate on implements the {@link ratpack.registry.Registry} interface. *

 * import ratpack.handling.Handler;
 * import ratpack.handling.Context;
 * import ratpack.registry.Registry;
 * import static ratpack.registry.Registries.registry;
 *
 * public class Thing {
 *   private final String name
 *   public Thing(String name) { this.name = name; }
 *   public String getName() { return name; }
 * }
 *
 * public class UpstreamHandler implements Handler {
 *   public void handle(Context context) {
 *     context.next(registry(new Thing("foo")));
 *   }
 * }
 *
 * public class DownstreamHandler implements Handler {
 *   public void handle(Context context) {
 *     assert context instanceof Registry;
 *     Thing thing = context.get(Thing.class);
 *     context.render(thing.getName());
 *   }
 * }
 *
 * import ratpack.test.handling.Invocation;
 * import ratpack.test.handling.InvocationBuilder;
 *
 * import static ratpack.test.UnitTest.invoke;
 * import static ratpack.handling.Handlers.chain;
 * import static ratpack.func.Actions.noop;
 *
 * Handler chain = chain(new UpstreamHandler(), new DownstreamHandler());
 * Invocation result = invoke(chain, noop());
 *
 * assert result.rendered(String.class).equals("foo");
 * 
*
Thread safety
*

* Registry objects are assumed to be thread safe. * No external synchronization is performed around registry access. * As registry objects may be used across multiple requests, they should be thread safe. *

* Registries that are created per request however do not need to be thread safe. */ public interface Registry { /** * Provides an object of the specified type, or throws an exception if no object of that type is available. * * @param type The type of the object to provide * @param The type of the object to provide * @return An object of the specified type * @throws NotInRegistryException If no object of this type can be returned */ O get(Class type) throws NotInRegistryException; /** * Does the same thing as {@link #get(Class)}, except returns null instead of throwing an exception. * * @param type The type of the object to provide * @param The type of the object to provide * @return An object of the specified type, or null if no object of this type is available. */ @Nullable O maybeGet(Class type); /** * Returns all of the objects whose declared type is assignment compatible with the given type. * * @param type the type of objects to search for * @param the type of objects to search for * @return All objects of the given type */ List getAll(Class type); }





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