[OLINGO-856] Added OlingoExtension interface

lib/server-api/src/main/java/org/apache/olingo/server/api/ODataHandler.java

@@ -18,9 +18,7 @@
  */
 package org.apache.olingo.server.api;
 
-import org.apache.olingo.server.api.etag.CustomETagSupport;
 import org.apache.olingo.server.api.processor.Processor;
-import org.apache.olingo.server.api.serializer.CustomContentTypeSupport;
 
 /**
  * <p>Handles requests as OData requests.</p>
@@ -49,15 +47,10 @@ public interface ODataHandler {
   void register(Processor processor);
 
   /**
-   * Registers a service implementation for modifying the standard list of supported
-   * content types.
-   * @see CustomContentTypeSupport
+   * <p>Registers additional extensions for handling OData requests.</p>
+   * <p>This method is used for registration of all possible extensions
+   * and provide the extensibility for further extensions and
+   * different ODataHandler implementations/extensions.</p>
    */
-  void register(CustomContentTypeSupport customContentTypeSupport);
-
-  /**
-   * Registers support for concurrency control for certain entity sets.
-   * @param customETagSupport handler to register
-   */
-  void register(CustomETagSupport customETagSupport);
+  void register(OlingoExtension extension);
 }

lib/server-api/src/main/java/org/apache/olingo/server/api/ODataHttpHandler.java

@@ -22,6 +22,8 @@ import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 
 import org.apache.olingo.server.api.debug.DebugSupport;
+import org.apache.olingo.server.api.etag.CustomETagSupport;
+import org.apache.olingo.server.api.serializer.CustomContentTypeSupport;
 
 /**
  * Handles HTTP requests as OData requests.
@@ -50,4 +52,17 @@ public interface ODataHttpHandler extends ODataHandler {
    * @param debugSupport handler to register
    */
   void register(DebugSupport debugSupport);
+
+  /**
+   * Registers a service implementation for modifying the standard list of supported
+   * content types.
+   * @see CustomContentTypeSupport
+   */
+  void register(CustomContentTypeSupport customContentTypeSupport);
+
+  /**
+   * Registers support for concurrency control for certain entity sets.
+   * @param customETagSupport handler to register
+   */
+  void register(CustomETagSupport customETagSupport);
 }

lib/server-api/src/main/java/org/apache/olingo/server/api/OlingoExtension.java

@@ -0,0 +1,25 @@
+/*
+ * 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.olingo.server.api;
+
+/**
+ * Marker interface for all possible Olingo extensions.
+ */
+public interface OlingoExtension {
+}

lib/server-api/src/main/java/org/apache/olingo/server/api/debug/DebugSupport.java

@@ -20,16 +20,17 @@ package org.apache.olingo.server.api.debug;
 
 import org.apache.olingo.server.api.OData;
 import org.apache.olingo.server.api.ODataResponse;
+import org.apache.olingo.server.api.OlingoExtension;
 
 /**
  * Register this interface to add debug support to your service.
  */
-public interface DebugSupport {
+public interface DebugSupport extends OlingoExtension {
 
-  public static final String ODATA_DEBUG_QUERY_PARAMETER = "odata-debug";
-  public static final String ODATA_DEBUG_JSON = "json";
-  public static final String ODATA_DEBUG_HTML = "html";
-  public static final String ODATA_DEBUG_DOWNLOAD = "download";
+  String ODATA_DEBUG_QUERY_PARAMETER = "odata-debug";
+  String ODATA_DEBUG_JSON = "json";
+  String ODATA_DEBUG_HTML = "html";
+  String ODATA_DEBUG_DOWNLOAD = "download";
 
   /**
    * Initializes the debug support implementation.

lib/server-api/src/main/java/org/apache/olingo/server/api/etag/CustomETagSupport.java

@@ -19,6 +19,7 @@
 package org.apache.olingo.server.api.etag;
 
 import org.apache.olingo.commons.api.edm.EdmBindingTarget;
+import org.apache.olingo.server.api.OlingoExtension;
 
 /**
  * <p>Processors that would like to support etags for certain entity sets can implement this
@@ -27,7 +28,7 @@ import org.apache.olingo.commons.api.edm.EdmBindingTarget;
  * require an if-match/if-none-match or an if-modified-since/if-unmodified-since header. Otherwise the request will
  * result in a "Precondition Required" response</p>
  */
-public interface CustomETagSupport {
+public interface CustomETagSupport extends OlingoExtension {
 
   /**
    * This method will be called for update requests which target an entity or a property of an entity.

lib/server-api/src/main/java/org/apache/olingo/server/api/serializer/CustomContentTypeSupport.java

@@ -21,6 +21,7 @@ package org.apache.olingo.server.api.serializer;
 import java.util.List;
 
 import org.apache.olingo.commons.api.format.ContentType;
+import org.apache.olingo.server.api.OlingoExtension;
 
 /**
  * <p>Processors that supports custom content types can implement this interface.</p>
@@ -33,7 +34,7 @@ import org.apache.olingo.commons.api.format.ContentType;
  * 406 (Not Acceptable); sending content of an unsupported type results in an
  * HTTP error 415 (Unsupported Media Type).</p>
  */
-public interface CustomContentTypeSupport {
+public interface CustomContentTypeSupport extends OlingoExtension {
 
   /**
    * Returns a list of supported content types.
@@ -41,6 +42,6 @@ public interface CustomContentTypeSupport {
    * @param type the current type of representation
    * @return modified list of supported content types
    */
-  public List<ContentType> modifySupportedContentTypes(
+  List<ContentType> modifySupportedContentTypes(
       List<ContentType> defaultContentTypes, RepresentationType type);
 }

lib/server-core/src/main/java/org/apache/olingo/server/core/ODataHandlerImpl.java

@@ -22,6 +22,7 @@ import java.util.LinkedList;
 import java.util.List;
 
 import org.apache.olingo.commons.api.edm.constants.ODataServiceVersion;
+import org.apache.olingo.commons.api.ex.ODataRuntimeException;
 import org.apache.olingo.commons.api.format.ContentType;
 import org.apache.olingo.commons.api.http.HttpHeader;
 import org.apache.olingo.commons.api.http.HttpMethod;
@@ -32,6 +33,7 @@ import org.apache.olingo.server.api.ODataLibraryException;
 import org.apache.olingo.server.api.ODataRequest;
 import org.apache.olingo.server.api.ODataResponse;
 import org.apache.olingo.server.api.ODataServerError;
+import org.apache.olingo.server.api.OlingoExtension;
 import org.apache.olingo.server.api.ServiceMetadata;
 import org.apache.olingo.server.api.deserializer.DeserializerException;
 import org.apache.olingo.server.api.etag.CustomETagSupport;
@@ -207,18 +209,22 @@ public class ODataHandlerImpl implements ODataHandler {
     processors.add(0, processor);
   }
 
-  public void register(final CustomContentTypeSupport customContentTypeSupport) {
-    this.customContentTypeSupport = customContentTypeSupport;
+  @Override
+  public void register(OlingoExtension extension) {
+    if(extension instanceof CustomContentTypeSupport) {
+      this.customContentTypeSupport = (CustomContentTypeSupport) extension;
+    } else if(extension instanceof CustomETagSupport) {
+      this.customETagSupport = (CustomETagSupport) extension;
+    } else {
+      throw new ODataRuntimeException("Got not supported exception with class name " +
+          extension.getClass().getSimpleName());
+    }
   }
 
   public CustomContentTypeSupport getCustomContentTypeSupport() {
     return customContentTypeSupport;
   }
 
-  public void register(final CustomETagSupport customETagSupport) {
-    this.customETagSupport = customETagSupport;
-  }
-
   public CustomETagSupport getCustomETagSupport() {
     return customETagSupport;
   }

lib/server-core/src/main/java/org/apache/olingo/server/core/ODataHttpHandlerImpl.java

@@ -43,6 +43,7 @@ import org.apache.olingo.server.api.ODataLibraryException;
 import org.apache.olingo.server.api.ODataRequest;
 import org.apache.olingo.server.api.ODataResponse;
 import org.apache.olingo.server.api.ODataServerError;
+import org.apache.olingo.server.api.OlingoExtension;
 import org.apache.olingo.server.api.ServiceMetadata;
 import org.apache.olingo.server.api.debug.DebugSupport;
 import org.apache.olingo.server.api.deserializer.DeserializerException;
@@ -296,6 +297,11 @@ public class ODataHttpHandlerImpl implements ODataHttpHandler {
     handler.register(processor);
   }
 
+  @Override
+  public void register(OlingoExtension extension) {
+    handler.register(extension);
+  }
+
   @Override
   public void register(final CustomContentTypeSupport customContentTypeSupport) {
     handler.register(customContentTypeSupport);