Add removal strategy for dynamic cluster using predicates

Author: grkvlt

core/src/main/java/org/apache/brooklyn/entity/group/EntityPredicateRemovalStrategy.java

@@ -0,0 +1,52 @@
+/*
+ * 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.entity.group;
+
+import java.util.Collection;
+
+import javax.annotation.Nullable;
+
+import org.apache.brooklyn.api.entity.Entity;
+import org.apache.brooklyn.config.ConfigKey;
+import org.apache.brooklyn.core.config.ConfigKeys;
+import org.apache.brooklyn.core.entity.EntityPredicates;
+
+import com.google.common.base.Optional;
+import com.google.common.base.Predicate;
+import com.google.common.base.Predicates;
+import com.google.common.collect.Iterables;
+import com.google.common.reflect.TypeToken;
+
+public class EntityPredicateRemovalStrategy<T> extends RemovalStrategy {
+
+    public static final ConfigKey<Predicate<Entity>> ENTITY_PREDICATE = ConfigKeys.builder(new TypeToken<Predicate<Entity>>() { })
+            .name("predicate")
+            .description("A predicate that will match the entities to be removed")
+            .constraint(Predicates.notNull())
+            .defaultValue(Predicates.not(EntityPredicates.isServiceUp()))
+            .build();
+
+    @Nullable
+    @Override
+    public Entity apply(@Nullable Collection<Entity> input) {
+        Predicate<Entity> predicate = config().get(ENTITY_PREDICATE);
+        Optional<Entity> entity = Iterables.tryFind(input, predicate);
+        return entity.orNull();
+    }
+}