Add `@RequestType` annotation and common config supplier registry

- Add a `@RequestType` annotation for common use (e.g. request handler, encoder or decoder)
- Add a registry for universal config supplier (e.g. namespace of client)

Signed-off-by: Eric Zhao <sczyh16@gmail.com>

sentinel-cluster/sentinel-cluster-common-default/pom.xml

@@ -13,7 +13,10 @@
     <packaging>jar</packaging>
 
     <dependencies>
-
+        <dependency>
+            <groupId>com.alibaba.csp</groupId>
+            <artifactId>sentinel-core</artifactId>
+        </dependency>
     </dependencies>
 
 </project>

sentinel-cluster/sentinel-cluster-common-default/src/main/java/com/alibaba/csp/sentinel/cluster/annotation/RequestType.java

@@ -0,0 +1,41 @@
+/*
+ * Copyright 1999-2018 Alibaba Group Holding Ltd.
+ *
+ * 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 com.alibaba.csp.sentinel.cluster.annotation;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/**
+ * Request type annotation for handlers, codes, etc.
+ *
+ * @author Eric Zhao
+ * @since 1.4.0
+ */
+@Retention(RetentionPolicy.RUNTIME)
+@Target({ElementType.TYPE})
+@Documented
+public @interface RequestType {
+
+    /**
+     * Type of the request to handle.
+     *
+     * @return type of the request
+     */
+    int value();
+}

sentinel-cluster/sentinel-cluster-common-default/src/main/java/com/alibaba/csp/sentinel/cluster/registry/ConfigSupplierRegistry.java

@@ -0,0 +1,60 @@
+/*
+ * Copyright 1999-2018 Alibaba Group Holding Ltd.
+ *
+ * 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 com.alibaba.csp.sentinel.cluster.registry;
+
+import com.alibaba.csp.sentinel.log.RecordLog;
+import com.alibaba.csp.sentinel.util.AppNameUtil;
+import com.alibaba.csp.sentinel.util.AssertUtil;
+import com.alibaba.csp.sentinel.util.function.Supplier;
+
+/**
+ * @author Eric Zhao
+ * @since 1.4.0
+ */
+public final class ConfigSupplierRegistry {
+
+    /**
+     * The default namespace supplier provides appName as namespace.
+     */
+    private static final Supplier<String> DEFAULT_APP_NAME_SUPPLIER = new Supplier<String>() {
+        @Override
+        public String get() {
+            return AppNameUtil.getAppName();
+        }
+    };
+    /**
+     * Registered namespace supplier.
+     */
+    private static Supplier<String> namespaceSupplier = DEFAULT_APP_NAME_SUPPLIER;
+
+    /**
+     * Get the registered namespace supplier.
+     *
+     * @return the registered namespace supplier
+     */
+    public static Supplier<String> getNamespaceSupplier() {
+        return namespaceSupplier;
+    }
+
+    public static void setNamespaceSupplier(Supplier<String> namespaceSupplier) {
+        AssertUtil.notNull(namespaceSupplier, "namespaceSupplier cannot be null");
+        ConfigSupplierRegistry.namespaceSupplier = namespaceSupplier;
+        RecordLog.info("[ConfigSupplierRegistry] New namespace supplier provided, current supplied: "
+            + namespaceSupplier.get());
+    }
+
+    private ConfigSupplierRegistry() {}
+}