Convert jsonb postgres column data to String

Could you please clarify what exactly you want to do?
If you need to remove whitespaces in Java you can try something like this.

        try (final Connection connection = embeddedPostgres.getTestDatabase().getConnection();
         final Statement statement = connection.createStatement();
         final PreparedStatement updateStatement = connection.prepareStatement("update your_table set your_column = ? where id = ?")) {
        connection.setAutoCommit(false);
        try (final ResultSet resultSet = statement.executeQuery("select * from your_table order by id limit 10")) {
            while (resultSet.next()) {
                final long id = resultSet.getLong("id");
                final String infoAsString = resultSet.getString("info");

                final String withoutWhitespaces = StringUtils.deleteWhitespace(infoAsString);
                final PGobject fixedInfoObject = new PGobject();
                fixedInfoObject.setType("jsonb");
                fixedInfoObject.setValue(withoutWhitespaces);
                updateStatement.setObject(1, fixedInfoObject);
                updateStatement.setLong(2, id);
                updateStatement.executeUpdate();
            }
        }
        connection.commit();
    }