Github user neykov commented on a diff in the pull request:
https://github.com/apache/brooklyn-server/pull/70#discussion_r56623544
--- Diff:
core/src/main/java/org/apache/brooklyn/core/objs/proxy/SpecialBrooklynObjectConstructor.java
---
@@ -0,0 +1,80 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you 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 org.apache.brooklyn.core.objs.proxy;
+
+import org.apache.brooklyn.api.entity.Entity;
+import org.apache.brooklyn.api.internal.AbstractBrooklynObjectSpec;
+import org.apache.brooklyn.api.location.Location;
+import org.apache.brooklyn.api.mgmt.ManagementContext;
+import org.apache.brooklyn.config.ConfigKey;
+import org.apache.brooklyn.core.config.ConfigKeys;
+
+import com.google.common.annotations.Beta;
+import com.google.common.reflect.TypeToken;
+
+/** Marker interface for use when a spec needs something special to create
the object under management.
+ * Set the {@link Config#SPECIAL_CONSTRUCTOR} config key in the spec
pointing to the class;
+ * it will be instantiated and {@link #create(Class,
AbstractBrooklynObjectSpec)} invoked to create the class.
+ * The type of course must be consistent with the spec.
+ * <p>
+ * This entire mechanism is beta; it is introduced for a few special cases
where some type of dynamicism is currently required.
+ * In most cases the {@link AbstractBrooklynObjectSpec} should correspond
directly to the object created.
+ * Some use cases are:
+ * <li>PortForwarderManager, shared global record
+ * <li>Choosing a different entity type smartly based on the location
(e.g. deploying to PaaS vs IaaS)
+ * <li>Referencing an existing location (optionally, and there are MAJOR
issues with this in general; see below)
+ * <li>Clocker (?) - newly defined docker locations (although these may
all point at entities)
+ * <p>
+ * See implementations of this interface.
+ * <p>
+ * Note that the caller may typically do additional configuration on the
resulting object,
+ * such as setting a catalog item ID etc. That behaviour may merit
adjustment and is subject to change.
+ * <p>
+ * Where this returns an existing item we must be VERY careful around
*unmanaging*,
+ * both when this reference is unmanaged (but the original is still in
use)
+ * and when the target is unmanaged (but this reference is still in use).
+ * <p>
+ * Some possible improvements to the simple approach here are:
+ * <li>Return a delegate impl of the {@link Location} or {@link Entity}
interface pointing at the target.
+ * (This would work fine for sensors/effectors but it would fail any
java type checks or casts.
+ * We could switch to a brooklyn-managed type system, which would also
allow for explicit yaml inheritance,
+ * but that's not a small task.)
+ * <li>Return a java reflections proxy impl (we have this for entity
already;
+ * but for many Location types interfaces are not currently defined;
+ * adding them would be nice to make Locations more like Entities)
+ * <li>Require the appropriate {@link Entity} or {@link Location} type, on
a case-by-case basis,
+ * where the lifecycle is as normal, and the logic for initializing
and delegating is done
+ * in the init. (Possibly this is better than the current
implementation!? It is certainly
+ * simpler than allowing multiple links to existing items, and would
be feasible in many
+ * cases, e.g. a `same-machine-as` type (assuming we made
SshMachineEntity an interface);
+ * but it would not allow choosing an entity type smartly based on
location.)
+ */
+@Beta
+public interface SpecialBrooklynObjectConstructor {
--- End diff --
Don't like `Special` in the name. This is essentially a factory for the
BrooklynObject instances - could just call it `BrooklynObjectFactory` (or some
derivate including spec in the name). Same for the key.
Also deserves an entry in the spec builder, similar to `.impl`.
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