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1 files changed, 51 insertions, 0 deletions

diff --git a/config-model/src/main/java/com/yahoo/config/model/ConfigModelRegistry.java b/config-model/src/main/java/com/yahoo/config/model/ConfigModelRegistry.java
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+++ b/config-model/src/main/java/com/yahoo/config/model/ConfigModelRegistry.java
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+// Copyright 2016 Yahoo Inc. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package com.yahoo.config.model;
+
+import com.yahoo.config.model.builder.xml.ConfigModelBuilder;
+import com.yahoo.config.model.builder.xml.ConfigModelId;
+
+import java.util.Collection;
+import java.util.Collections;
+
+/**
+ * A resolver of implementations of named config models.
+ * Registries may be chained in a chain of command.
+ *
+ * @author bratseth
+ */
+public abstract class ConfigModelRegistry {
+
+    private final ConfigModelRegistry chained;
+
+    public ConfigModelRegistry() {
+        this(new EmptyTerminalRegistry());
+    }
+
+    /** Creates a config model class registry which forwards unresolved requests to the argument instance */
+    public ConfigModelRegistry(ConfigModelRegistry chained) {
+        this.chained=chained;
+    }
+
+    /**
+     * Returns the builders this id resolves to both in this and any chained registry.
+     *
+     * @return the resolved config model builders, or an empty list (never null) if none
+     */
+    public abstract Collection<ConfigModelBuilder> resolve(ConfigModelId id);
+
+    public ConfigModelRegistry chained() { return chained; }
+
+    /** An empty registry which does not support chaining */
+    private static class EmptyTerminalRegistry extends ConfigModelRegistry {
+
+        public EmptyTerminalRegistry() {
+            super(null);
+        }
+
+        @Override
+        public Collection<ConfigModelBuilder> resolve(ConfigModelId id) {
+            return Collections.emptyList();
+        }
+    }
+
+}