Support Connection.isValid method

Add ping request to the DB using 'SELECT 1' expression. Timeout requires
the implementation of at least Statement.setQueryTimeout and
Statement.cancel.

Closes: #75
Depends on: #155

src/main/java/org/tarantool/jdbc/SQLConnection.java

@@ -44,6 +44,7 @@
 public class SQLConnection implements Connection {
 
     private static final int UNSET_HOLDABILITY = 0;
+    private static final String PING_QUERY = "SELECT 1";
 
     private final TarantoolConnection connection;
 
@@ -374,9 +375,40 @@ public SQLXML createSQLXML() throws SQLException {
         throw new SQLFeatureNotSupportedException();
     }
 
+    /**
+     * {@inheritDoc}
+     *
+     * @param timeout temporally ignored param
+     *
+     * @return connection activity status
+     */
     @Override
     public boolean isValid(int timeout) throws SQLException {
-        return true;
+        if (timeout < 0) {
+            throw new SQLNonTransientException(
+                    "Timeout cannot be negative",
+                    SQLStates.INVALID_PARAMETER_VALUE.getSqlState()
+            );
+        }
+        if (isClosed()) {
+            return false;
+        }
+        return checkConnection(timeout);
+    }
+
+    private boolean checkConnection(int timeout) {
+        ResultSet resultSet = null;
+        try (Statement pingStatement = createStatement()) {
+            // todo: before use timeout we need to provide query timeout per statement
+
+            resultSet = pingStatement.executeQuery(PING_QUERY);
+            boolean isValid = resultSet.next() && resultSet.getInt(1) == 1;
+            resultSet.close();
+
+            return isValid;
+        } catch (SQLException e) {
+            return false;
+        }
     }
 
     @Override

src/test/java/org/tarantool/jdbc/JdbcConnectionIT.java

@@ -113,6 +113,15 @@ public void execute() throws Throwable {
         assertEquals(5, i);
     }
 
+    @Test
+    void testIsValidCheck() throws SQLException {
+        assertTrue(conn.isValid(2000));
+        assertThrows(SQLException.class, () -> conn.isValid(-1000));
+
+        conn.close();
+        assertFalse(conn.isValid(2000));
+    }
+
     @Test
     public void testConnectionUnwrap() throws SQLException {
         assertEquals(conn, conn.unwrap(SQLConnection.class));