Spring JDBC ResultSetMetaData“ getColumnName（）”方法返回一个空字符串

Question

I have the following section of code to implement a drop-down menu. Based on the two parameters selected from the menu, I run the corresponding query by replacing the selected column with the mapped column name.

String sql = "SELECT ?, ? FROM <table_name>";

ArrayList<Some_POJO> res = this.jdbcTemplate.query(sql, new ResultSetExtractor<Some_POJO>()
    {//logic goes here.},
    user_inputs_as_object_array);

Now, in the logic section, I'm using the following command to map the returned values:

while(rs.next()) {
    Some_POJO = new SOME_POJO();
    Some_POJO.setParam1(rs.getString("SOME_COLUMN_NAME")); //ERROR
}

Now, the marked line fails when I refer to column by name. But what is surprising is, the following workaround works:

while(rs.next()) {
    Some_POJO = new SOME_POJO();
    int i = 1;
    Some_POJO.setParam1(rs.getString(i)); //Works(?!)
}

I tried to modify the JDBC template call to return the ResultSetMetaData object instead of an ArrayList of Some_POJO:

String sql = "SELECT ?, ? FROM <table_name>";

ResultSetMetaData res = this.jdbcTemplate.query(sql, new ResultSetExtractor<ResultSetMetaData>()
    {//extractData now returns rs.getMetaData()},
    user_inputs_as_object_array);

try
    {
        System.out.println("Column cout: " + res.getColumnCount());
        for(int i = 1; i <= res.getColumnCount(); i++)
            System.out.println("Label: " + res.getColumnLabel(i) +  "\nName: " + res.getColumnName(i));
    }
    catch(SQLException sqle)

Only to get:

Column cout: 2
Label: :1
Name: 
Label: :2
Name:

Could someone please shed some light into what is happening and (except for suggestions suggesting a complete redesign) what would be the most optimal way to achieve the expected functionality? I would prefer not to use column indexes since order changes would break the functionality.

Answer 1

Just for refactoring code, get values as:

    ArrayList result = new ArrayList(0);
    result.addAll(this.jdbcTemplate.query(sql, (RowMapper) (rs, rowNum) -> {
        POJO out = new POJO();
        out.setProperty1(rs.getString("prop1"));
        out.setProperty2(rs.getString("prop2"));
        ...
        return out;
    }));

For me it works fine, passing field name in method, don't think that there are some troubles with spring jdbc. Maybe is something wrong in your sql query.