[CONJ-1009] improve performance reading result-set of big size part 3

 * JSON metadata correction

src/main/java/org/mariadb/jdbc/client/DataType.java

@@ -24,7 +24,7 @@ public enum DataType {
   NEWDATE(14, DateColumn::new, DateColumn::new),
   VARCHAR(15, StringColumn::new, StringColumn::new),
   BIT(16, BitColumn::new, BitColumn::new),
-  JSON(245, StringColumn::new, StringColumn::new),
+  JSON(245, JsonColumn::new, JsonColumn::new),
   DECIMAL(246, BigDecimalColumn::new, BigDecimalColumn::new),
   ENUM(247, StringColumn::new, StringColumn::new),
   SET(248, StringColumn::new, StringColumn::new),

src/main/java/org/mariadb/jdbc/client/column/JsonColumn.java

@@ -0,0 +1,41 @@
+// SPDX-License-Identifier: LGPL-2.1-or-later
+// Copyright (c) 2012-2014 Monty Program Ab
+// Copyright (c) 2015-2021 MariaDB Corporation Ab
+
+package org.mariadb.jdbc.client.column;
+
+import org.mariadb.jdbc.Configuration;
+import org.mariadb.jdbc.client.ColumnDecoder;
+import org.mariadb.jdbc.client.DataType;
+import org.mariadb.jdbc.client.ReadableByteBuf;
+import java.sql.*;
+
+/** Column metadata definition */
+public class JsonColumn extends StringColumn implements ColumnDecoder {
+
+  public JsonColumn(
+      ReadableByteBuf buf,
+      int charset,
+      long length,
+      DataType dataType,
+      byte decimals,
+      int flags,
+      int[] stringPos,
+      String extTypeName,
+      String extTypeFormat) {
+    super(buf, charset, length, dataType, decimals, flags, stringPos, extTypeName, extTypeFormat);
+  }
+
+  public String defaultClassname(Configuration conf) {
+    return String.class.getName();
+  }
+
+  public int getColumnType(Configuration conf) {
+    return Types.LONGVARCHAR;
+  }
+
+  public String getColumnTypeName(Configuration conf) {
+      return "JSON";
+  }
+
+}

src/main/java/org/mariadb/jdbc/client/column/StringColumn.java

@@ -398,10 +398,10 @@ public Timestamp decodeTimestampBinary(ReadableByteBuf buf, int length, Calendar
       Timestamp timestamp;
       synchronized (cal) {
         cal.clear();
-        cal.set(year, month - 1, (int) dayOfMonth, hour, minutes, seconds);
+        cal.set(year, month - 1, dayOfMonth, hour, minutes, seconds);
         timestamp = new Timestamp(cal.getTimeInMillis());
       }
-      timestamp.setNanos((int) (microseconds * 1000));
+      timestamp.setNanos(microseconds * 1000);
       return timestamp;
 
     } catch (DateTimeException dte) {

src/main/java/org/mariadb/jdbc/client/column/TimestampColumn.java

@@ -476,7 +476,7 @@ public Timestamp decodeTimestampBinary(ReadableByteBuf buf, int length, Calendar
     Timestamp timestamp;
     synchronized (cal) {
       cal.clear();
-      cal.set(year, month - 1, (int) dayOfMonth, hour, minutes, seconds);
+      cal.set(year, month - 1, dayOfMonth, hour, minutes, seconds);
       timestamp = new Timestamp(cal.getTimeInMillis());
     }
     timestamp.setNanos((int) (microseconds * 1000));