make ComplexColumn an interface and ExtensionPoint (#7633)

* make ComplexColumn an interface and ExtensionPoint

* incorporate review comments

* make ColumnValueSelector @ExtensionPoint

* more java docs

* add close() method to ComplexColumn interface

processing/src/main/java/org/apache/druid/segment/BaseDoubleColumnValueSelector.java

@@ -19,7 +19,7 @@
 
 package org.apache.druid.segment;
 
-import org.apache.druid.guice.annotations.PublicApi;
+import org.apache.druid.guice.annotations.ExtensionPoint;
 import org.apache.druid.query.monomorphicprocessing.CalledFromHotLoop;
 import org.apache.druid.query.monomorphicprocessing.HotLoopCallee;
 
@@ -30,7 +30,7 @@ import org.apache.druid.query.monomorphicprocessing.HotLoopCallee;
  *
  * All implementations of this interface MUST also implement {@link ColumnValueSelector}.
  */
-@PublicApi
+@ExtensionPoint
 public interface BaseDoubleColumnValueSelector extends HotLoopCallee, BaseNullableColumnValueSelector
 {
   @CalledFromHotLoop

processing/src/main/java/org/apache/druid/segment/BaseFloatColumnValueSelector.java

@@ -19,7 +19,7 @@
 
 package org.apache.druid.segment;
 
-import org.apache.druid.guice.annotations.PublicApi;
+import org.apache.druid.guice.annotations.ExtensionPoint;
 import org.apache.druid.query.monomorphicprocessing.CalledFromHotLoop;
 import org.apache.druid.query.monomorphicprocessing.HotLoopCallee;
 
@@ -30,7 +30,7 @@ import org.apache.druid.query.monomorphicprocessing.HotLoopCallee;
  *
  * All implementations of this interface MUST also implement {@link ColumnValueSelector}.
  */
-@PublicApi
+@ExtensionPoint
 public interface BaseFloatColumnValueSelector extends HotLoopCallee, BaseNullableColumnValueSelector
 {
   @CalledFromHotLoop

processing/src/main/java/org/apache/druid/segment/BaseLongColumnValueSelector.java

@@ -19,7 +19,7 @@
 
 package org.apache.druid.segment;
 
-import org.apache.druid.guice.annotations.PublicApi;
+import org.apache.druid.guice.annotations.ExtensionPoint;
 import org.apache.druid.query.monomorphicprocessing.CalledFromHotLoop;
 import org.apache.druid.query.monomorphicprocessing.HotLoopCallee;
 
@@ -30,7 +30,7 @@ import org.apache.druid.query.monomorphicprocessing.HotLoopCallee;
  *
  * All implementations of this interface MUST also implement {@link ColumnValueSelector}.
  */
-@PublicApi
+@ExtensionPoint
 public interface BaseLongColumnValueSelector extends HotLoopCallee, BaseNullableColumnValueSelector
 {
   @CalledFromHotLoop

processing/src/main/java/org/apache/druid/segment/BaseObjectColumnValueSelector.java

@@ -19,7 +19,7 @@
 
 package org.apache.druid.segment;
 
-import org.apache.druid.guice.annotations.PublicApi;
+import org.apache.druid.guice.annotations.ExtensionPoint;
 
 import javax.annotation.Nullable;
 
@@ -30,7 +30,7 @@ import javax.annotation.Nullable;
  *
  * All implementations of this interface MUST also implement {@link ColumnValueSelector}.
  */
-@PublicApi
+@ExtensionPoint
 public interface BaseObjectColumnValueSelector<T> extends BaseNullableColumnValueSelector
 {
   @Nullable

processing/src/main/java/org/apache/druid/segment/ColumnValueSelector.java

@@ -19,7 +19,7 @@
 
 package org.apache.druid.segment;
 
-import org.apache.druid.guice.annotations.PublicApi;
+import org.apache.druid.guice.annotations.ExtensionPoint;
 
 /**
  * Base type for interfaces that manage column value selection, e.g. {@link DimensionSelector}, {@link
@@ -33,7 +33,7 @@ import org.apache.druid.guice.annotations.PublicApi;
  * methods and null from {@link #getObject()}, should always be an instance of {@link NilColumnValueSelector}.
  * `selector instanceof NilColumnValueSelector` is the recommended way to check for this condition.
  */
-@PublicApi
+@ExtensionPoint
 public interface ColumnValueSelector<T> extends BaseLongColumnValueSelector, BaseDoubleColumnValueSelector,
     BaseFloatColumnValueSelector, BaseObjectColumnValueSelector<T>
 {

processing/src/main/java/org/apache/druid/segment/column/ComplexColumn.java

@@ -19,45 +19,60 @@
 
 package org.apache.druid.segment.column;
 
+import org.apache.druid.guice.annotations.ExtensionPoint;
 import org.apache.druid.query.monomorphicprocessing.RuntimeShapeInspector;
 import org.apache.druid.segment.ColumnValueSelector;
 import org.apache.druid.segment.ObjectColumnSelector;
-import org.apache.druid.segment.data.GenericIndexed;
 import org.apache.druid.segment.data.ReadableOffset;
 
 import javax.annotation.Nullable;
 
 /**
-*/
+ * This interface represents a complex column and can be implemented by druid extension writer of a custom column
-public class ComplexColumn implements BaseColumn
+ * with arbitrary serialization instead of a custom column that serializes rows of objects serialized using
+ * {@link org.apache.druid.segment.data.GenericIndexed} class which is default implementation of "writeToXXX" methods in
+ * {@link org.apache.druid.segment.serde.ComplexColumnSerializer}. In that case {@link GenericIndexedBasedComplexColumn}
+ * should be used.
+ */
+@ExtensionPoint
+public interface ComplexColumn extends BaseColumn
 {
-  private final GenericIndexed<?> index;
+  /**
-  private final String typeName;
+   * @return Class of objects returned on calls to {@link ComplexColumn#getRowValue(int)} .
+   */
+  Class<?> getClazz();
 
-  public ComplexColumn(String typeName, GenericIndexed<?> index)
+  /**
-  {
+   * @return Typename associated with this column.
-    this.index = index;
+   */
-    this.typeName = typeName;
+  String getTypeName();
-  }
 
-  public String getTypeName()
+  /**
-  {
+   * Return rows in the column.
-    return typeName;
+   * @param rowNum the row number
-  }
+   * @return row object of type same as {@link ComplexColumn#getClazz()}  } at row number "rowNum" .
+   */
+  Object getRowValue(int rowNum);
 
-  @Nullable
+  /**
-  public Object getRowValue(int rowNum)
+   * @return serialized size (in bytes) of this column.
-  {
+   */
-    return index.get(rowNum);
+  int getLength();
-  }
-
-  public int getLength()
-  {
-    return index.size();
-  }
 
+  /**
+   * Close and release any resources associated with this column.
+   */
   @Override
-  public ColumnValueSelector<?> makeColumnValueSelector(ReadableOffset offset)
+  void close();
+
+  /**
+   * Optionally overridden when complex column serialization is not based on default serialization based
+   * on {@link org.apache.druid.segment.data.GenericIndexed} in {@link org.apache.druid.segment.serde.ComplexColumnSerializer}.
+   * @param offset object to retrieve row number
+   * @return the {@link ColumnValueSelector} object
+   */
+  @Override
+  default ColumnValueSelector<?> makeColumnValueSelector(ReadableOffset offset)
   {
     return new ObjectColumnSelector()
     {
@@ -71,7 +86,7 @@ public class ComplexColumn implements BaseColumn
       @Override
       public Class classOfObject()
       {
-        return index.getClazz();
+        return getClazz();
       }
 
       @Override
@@ -81,10 +96,4 @@ public class ComplexColumn implements BaseColumn
       }
     };
   }
-
-  @Override
-  public void close()
-  {
-    // nothing to close
-  }
 }

processing/src/main/java/org/apache/druid/segment/column/GenericIndexedBasedComplexColumn.java

@@ -0,0 +1,68 @@
+/*
+ * 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.druid.segment.column;
+
+import org.apache.druid.segment.data.GenericIndexed;
+
+/**
+ * Implementation of {@link ComplexColumn} to be used when complex column serialization is done by using
+ * {@link GenericIndexed} by using default implementations of "writeToXXX" methods in
+ * {@link org.apache.druid.segment.serde.ComplexColumnSerializer}
+*/
+public class GenericIndexedBasedComplexColumn implements ComplexColumn
+{
+  private final GenericIndexed<?> index;
+  private final String typeName;
+
+  public GenericIndexedBasedComplexColumn(String typeName, GenericIndexed<?> index)
+  {
+    this.index = index;
+    this.typeName = typeName;
+  }
+
+  @Override
+  public Class<?> getClazz()
+  {
+    return index.getClazz();
+  }
+
+  @Override
+  public String getTypeName()
+  {
+    return typeName;
+  }
+
+  @Override
+  public Object getRowValue(int rowNum)
+  {
+    return index.get(rowNum);
+  }
+
+  @Override
+  public int getLength()
+  {
+    return index.size();
+  }
+
+  @Override
+  public void close()
+  {
+  }
+}

processing/src/main/java/org/apache/druid/segment/serde/ComplexColumnPartSupplier.java

@@ -21,6 +21,7 @@ package org.apache.druid.segment.serde;
 
 import com.google.common.base.Supplier;
 import org.apache.druid.segment.column.ComplexColumn;
+import org.apache.druid.segment.column.GenericIndexedBasedComplexColumn;
 import org.apache.druid.segment.data.GenericIndexed;
 
 /**
@@ -39,6 +40,6 @@ public class ComplexColumnPartSupplier implements Supplier<ComplexColumn>
   @Override
   public ComplexColumn get()
   {
-    return new ComplexColumn(typeName, complexType);
+    return new GenericIndexedBasedComplexColumn(typeName, complexType);
   }
 }