Question

I’m working on a project where the user is supposed to fill the criteria he wants in a form and then accordingly to these criteria a servlet returns the appropriate results from the the database; I’m using mysql server.
My problem is that the Prepared Statement I used for that (because the user can search with a variable number of criteria) always return null, so I get an

Exception: null java.lang.NullPointerException at    
Servlet_GrowerResults.doGet(Servlet_GrowerResults.java:102)

Here’s the method fetchGrowers in class GetData which returns the ResultSet to the Servlet_GrowerResults

private PreparedStatement stmt_growers=null;
private ResultSet rs_growers;
private final String getGrowersQuery="select * from grower where name like ? and surname like ? and area like ? and partnership like ?;";

public ResultSet fetchGrowers(String criteria_name,String criteria_surname,String criteria_area, String criteria_partnership){
    try{
        stmt_growers=dbcon.getConnection().prepareStatement(getGrowersQuery);
        stmt_growers.setString(1, criteria_name);
        stmt_growers.setString(3, criteria_surname);
        stmt_growers.setString(5, criteria_area);
        stmt_growers.setString(7, criteria_partnership);

        rs_growers=stmt_growers.executeQuery();
        return rs_growers;
    }
    catch(Exception e9){
        errorMessage = "Error while getting all growers from database!<br>" + e9.getMessage();
        return null;
    }

here’s the lines where ResultSets are initialized. There are also other else if to cover all the cases of criteria submited

   try{
        getData.getDBcon().open();
        ResultSet rsAreas=getData.fetchGrowerAreas();
        ResultSet rsPartnership=getData.fetchGrowerPartnership();
        ResultSet rsGrowersReturned;

        String sqlWildcard="%";

        //Cases of criteria submited by the user,
        //in order to send the apropriate parameters
        //to the PreparedStatement

        //1st case: searching without names criteria
        if( (criteriaNames.length()>0) && (!(criteriaAreas.length()>0)) && (!(criteriaPartnerships.length()>0)) ){
            rsGrowersReturned=getData.fetchGrowers(sqlWildcard,sqlWildcard,criteriaAreas,criteriaPartnerships);
        }

and here’s the lines where the Exception points. And more specificly line 102 is: while(rsGrowersReturned.next())

 if((sorting.equals("περιοχή"))){
        while(rsAreas.next()){
                out.println("<table>");
                String area=rsAreas.getString("area");
                area = new String(area.getBytes("ISO-8859-1"), "ISO-8859-7");
                out.println("<tr><th>"+rsAreas.getString("area")+"</th></tr>");

    /*line 102*/ while(rsGrowersReturned.next()){
                    if(rsGrowersReturned.getString("area").equals(rsAreas.getString("area"))){
                        String name=rsGrowersReturned.getString("name");
                        name = new String(name.getBytes("ISO-8859-1"), "ISO-8859-7");
                        String surname=rsGrowersReturned.getString("surname");
                        surname = new String(surname.getBytes("ISO-8859-1"), "ISO-8859-7");
                        String partnership=rsGrowersReturned.getString("partnership");
                        partnership = new String(partnership.getBytes("ISO-8859-1"), "ISO-8859-7");

                        out.println("<tr><td>"+name+" "+surname+"</td>");
                        out.println("<td>"+partnership+"</td></tr>");
                    }//end of neaced if
                }//end of second while
            }//end of first while
            out.println("</table>");
        }//end of if

I can see that there occurs indeed the problem because before getting to the second while it prints the first area as it is supposed to do and then Exception!!!

I tried the sql query directly to the mysql server and it works, I just can’t find the problem! Every answer will be appreciated, thank you.

Answer 1

You need to set the input parameters for your PrepareStatement in sequential order:

stmt_growers.setString(1, criteria_name);
stmt_growers.setString(2, criteria_surname);
stmt_growers.setString(3, criteria_area);
stmt_growers.setString(4, criteria_partnership);