Implement Java extension type

java/adapter/jdbc/src/main/java/org/apache/arrow/adapter/jdbc/JdbcToArrowConfigBuilder.java

@@ -211,6 +211,8 @@ public JdbcToArrowConfigBuilder setTargetBatchSize(int targetBatchSize) {
    *
    * <p>Defaults to wrapping {@link JdbcToArrowUtils#getArrowTypeFromJdbcType(JdbcFieldInfo,
    * Calendar)}.
+   *
+   * @see JdbcToArrowUtils#reportUnsupportedTypesAsUnknown(Function)
    */
   public JdbcToArrowConfigBuilder setJdbcToArrowTypeConverter(
       Function<JdbcFieldInfo, ArrowType> jdbcToArrowTypeConverter) {

java/adapter/jdbc/src/main/java/org/apache/arrow/adapter/jdbc/JdbcToArrowUtils.java

@@ -18,6 +18,7 @@
 
 import static org.apache.arrow.vector.types.FloatingPointPrecision.DOUBLE;
 import static org.apache.arrow.vector.types.FloatingPointPrecision.SINGLE;
+import static org.apache.arrow.vector.types.Types.MinorType;
 
 import java.io.IOException;
 import java.math.RoundingMode;
@@ -37,6 +38,7 @@
 import java.util.Locale;
 import java.util.Map;
 import java.util.TimeZone;
+import java.util.function.Function;
 import org.apache.arrow.adapter.jdbc.consumer.ArrayConsumer;
 import org.apache.arrow.adapter.jdbc.consumer.BigIntConsumer;
 import org.apache.arrow.adapter.jdbc.consumer.BinaryConsumer;
@@ -80,6 +82,7 @@
 import org.apache.arrow.vector.VectorSchemaRoot;
 import org.apache.arrow.vector.complex.ListVector;
 import org.apache.arrow.vector.complex.MapVector;
+import org.apache.arrow.vector.extension.UnknownType;
 import org.apache.arrow.vector.types.DateUnit;
 import org.apache.arrow.vector.types.TimeUnit;
 import org.apache.arrow.vector.types.pojo.ArrowType;
@@ -216,11 +219,28 @@ public static ArrowType getArrowTypeFromJdbcType(
       case Types.STRUCT:
         return new ArrowType.Struct();
       default:
-        // no-op, shouldn't get here
         throw new UnsupportedOperationException("Unmapped JDBC type: " + fieldInfo.getJdbcType());
     }
   }
 
+  /**
+   * Wrap a JDBC to Arrow type converter such that {@link UnsupportedOperationException} becomes
+   * {@link org.apache.arrow.vector.extension.UnknownType}.
+   *
+   * @param typeConverter The type converter to wrap.
+   * @param vendorName The database name to report as the Unknown type's vendor name.
+   */
+  public static Function<JdbcFieldInfo, ArrowType> reportUnsupportedTypesAsUnknown(
+      Function<JdbcFieldInfo, ArrowType> typeConverter, String vendorName) {
+    return (final JdbcFieldInfo fieldInfo) -> {
+      try {
+        return typeConverter.apply(fieldInfo);
+      } catch (UnsupportedOperationException e) {
+        return new UnknownType(MinorType.NULL.getType(), fieldInfo.getTypeName(), vendorName);
+      }
+    };
+  }
+
   /**
    * Create Arrow {@link Schema} object for the given JDBC {@link java.sql.ResultSetMetaData}.
    *

java/adapter/jdbc/src/test/java/org/apache/arrow/adapter/jdbc/h2/JdbcToArrowDataTypesTest.java

@@ -32,19 +32,28 @@
 import static org.apache.arrow.adapter.jdbc.JdbcToArrowTestHelper.assertTinyIntVectorValues;
 import static org.apache.arrow.adapter.jdbc.JdbcToArrowTestHelper.assertVarBinaryVectorValues;
 import static org.apache.arrow.adapter.jdbc.JdbcToArrowTestHelper.assertVarcharVectorValues;
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertEquals;
 
 import java.io.IOException;
+import java.sql.DriverManager;
+import java.sql.ResultSet;
 import java.sql.ResultSetMetaData;
 import java.sql.SQLException;
+import java.sql.Statement;
 import java.util.Arrays;
 import java.util.Calendar;
+import java.util.List;
+import java.util.function.Function;
 import java.util.stream.Stream;
 import org.apache.arrow.adapter.jdbc.AbstractJdbcToArrowTest;
+import org.apache.arrow.adapter.jdbc.JdbcFieldInfo;
 import org.apache.arrow.adapter.jdbc.JdbcToArrowConfig;
 import org.apache.arrow.adapter.jdbc.JdbcToArrowConfigBuilder;
 import org.apache.arrow.adapter.jdbc.JdbcToArrowTestHelper;
 import org.apache.arrow.adapter.jdbc.JdbcToArrowUtils;
 import org.apache.arrow.adapter.jdbc.Table;
+import org.apache.arrow.memory.BufferAllocator;
 import org.apache.arrow.memory.RootAllocator;
 import org.apache.arrow.vector.BigIntVector;
 import org.apache.arrow.vector.BitVector;
@@ -62,7 +71,12 @@
 import org.apache.arrow.vector.VarCharVector;
 import org.apache.arrow.vector.VectorSchemaRoot;
 import org.apache.arrow.vector.complex.ListVector;
+import org.apache.arrow.vector.extension.UnknownType;
+import org.apache.arrow.vector.types.Types;
+import org.apache.arrow.vector.types.pojo.ArrowType;
+import org.apache.arrow.vector.types.pojo.Field;
 import org.apache.arrow.vector.types.pojo.Schema;
+import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.Arguments;
 import org.junit.jupiter.params.provider.MethodSource;
@@ -189,6 +203,44 @@ public void testJdbcSchemaMetadata(Table table) throws SQLException, ClassNotFou
     JdbcToArrowTestHelper.assertFieldMetadataMatchesResultSetMetadata(rsmd, schema);
   }
 
+  @Test
+  void testUnknownType() throws SQLException, ClassNotFoundException {
+    try (BufferAllocator allocator = new RootAllocator()) {
+      String url = "jdbc:h2:mem:JdbcToArrowTest";
+      String driver = "org.h2.Driver";
+      Class.forName(driver);
+      conn = DriverManager.getConnection(url);
+      try (Statement stmt = conn.createStatement()) {
+        stmt.executeUpdate("CREATE TABLE unknowntype (a GEOMETRY, b INT)");
+      }
+
+      String query = "SELECT * FROM unknowntype";
+      Calendar calendar = Calendar.getInstance();
+      Function<JdbcFieldInfo, ArrowType> typeConverter =
+          (field) -> JdbcToArrowUtils.getArrowTypeFromJdbcType(field, calendar);
+      JdbcToArrowConfig config =
+          new JdbcToArrowConfigBuilder()
+              .setAllocator(allocator)
+              .setJdbcToArrowTypeConverter(
+                  JdbcToArrowUtils.reportUnsupportedTypesAsUnknown(typeConverter, "H2"))
+              .build();
+      Schema schema;
+      try (Statement stmt = conn.createStatement();
+          ResultSet rs = stmt.executeQuery(query)) {
+        schema =
+            assertDoesNotThrow(() -> JdbcToArrowUtils.jdbcToArrowSchema(rs.getMetaData(), config));
+      }
+
+      Schema expected =
+          new Schema(
+              List.of(
+                  Field.nullable(
+                      "A", new UnknownType(Types.MinorType.NULL.getType(), "GEOMETRY", "H2")),
+                  Field.nullable("B", Types.MinorType.INT.getType())));
+      assertEquals(expected, schema);
+    }
+  }
+
   /**
    * This method calls the assert methods for various DataSets.
    *

java/vector/src/main/java/org/apache/arrow/vector/extension/InvalidExtensionMetadataException.java

@@ -0,0 +1,28 @@
+/*
+ * 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.arrow.vector.extension;
+
+/** */
+public class InvalidExtensionMetadataException extends RuntimeException {
+  public InvalidExtensionMetadataException(String message) {
+    super(message);
+  }
+
+  public InvalidExtensionMetadataException(String message, Throwable cause) {
+    super(message, cause);
+  }
+}