Java Prepared Statement using List and how to return values in list

Question

I have multiple values in list and now I want to get data from the database on the bases of these values but I am getting null in return.

List<String> tptTnx = new ArrayList<String>();
//tptTnx have these values  [101,102,103,104]

//convert list into array
String[] item = tptTnx.toArray(new String[tptTnx.size()]);  

On the bases of the above values, I am using below query and methods.

private static final String SQL_TPT_ACCOUNT = "select customer_id from 
customer_reference where back_office IN (select upper(bo_cust_number) 
from gtp_account where account_no IN ? )";

//passing array in method
public String getCompanyID(String[] item)
{
    Connection con = null;
    PreparedStatement pstmt = null;
    ResultSet rset = null;
    String companyID = null;
    List<String> cid = null;
    try
    {
        con = PoolBrokerService.getConnection();
        pstmt = con.prepareStatement(SQL_TPT_ACCOUNT);

        pstmt.setArray(1, item);


        rset = pstmt.executeQuery();

        while (rset.next())
        {
            //companyID = rset.getString(1);
            cid.add(rset.getString(1));

        }

        rset.close();
    }
    catch (Exception e)
    {
        GTPException.log("account_id - getAccountID event ", e);
    }

    return cid; 
}

the output should be: 401,402,403 but i am getting null values. Please advise how can i pass the list in prepared statement and get result in list or array