package HRCproject;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.google.gson.Gson;

import HRCproject.pojo.*;

import HRCproject.JDBC_Connection ;
@WebServlet("/fetch")
public class fetch_sevelet extends HttpServlet {
/**
 * 
 */
private static final long serialVersionUID = 1L;

public void doGet(HttpServletRequest req, HttpServletResponse res) throws IOException, ServletException 
{   
    res.setContentType("application/json");
    res.setCharacterEncoding("UTF-8");
    int max_rows = 500;
    PrintWriter out = res.getWriter();
    ArrayList<Invoice> data = new ArrayList<>();
    //get connection
    try {
    Class.forName(JDBC_Connection.JDBC_DRIVER);
    }
    catch (ClassNotFoundException e) {
        e.printStackTrace();
    }
    try {
        Connection con = DriverManager.getConnection(JDBC_Connection.URL,JDBC_Connection.USER,JDBC_Connection.PASS);
        System.out.println("Connection Succesful");
        
        String pageInURL = req.getParameter("page");
        int page = Integer.parseInt(pageInURL) * max_rows;
        

        // executing queries
        Statement stmt = con.createStatement();  
        ResultSet rs = stmt.executeQuery("SELECT * FROM winter_internship ORDER BY sl_no LIMIT "   page); 
         
        while (rs.next()) 
        {  
 Invoice s = new Invoice();
            
            s.setSl_no(rs.getInt("sl_no"));
            s.setBusiness_code(rs.getString("business_code"));
            s.setCust_number(rs.getString("cust_number"));
            s.setClear_date(rs.getString("clear_date"));
            s.setBuisness_year(rs.getInt("buisness_year"));
            String doc_id = rs.getString("doc_id");
            doc_id.replace("0","");
            s.setDoc_id(doc_id);
            s.setPosting_date(rs.getDate("posting_date"));
            s.setDue_in_date(rs.getDate("due_in_date"));
            s.setBaseline_create_date(rs.getDate("baseline_create_date"));
            s.setCust_payment_terms(rs.getString("cust_payment_terms"));
            s.setInvoice_currency(rs.getString("invoice_currency"));
            s.setDocument_type(rs.getString("document_type"));
            s.setPosting_id(rs.getString("posting_id"));
            s.setInvoice_id(rs.getInt("invoice_id"));
            s.setTotal_open_amount(rs.getDouble("total_open_amount"));
            
            data.add(s);
        } 
        Gson gson = new Gson();
        String invoices = gson.toJson(data);
        out.print(invoices);
        
        out.flush();
        
    }
    catch(SQLException e) {
        e.printStackTrace();
    }
    catch(Exception e) {
        e.printStackTrace();
    }
    
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // TODO Auto-generated method stub
    doGet(request, response);
}
}

Why am I getting this error? I am trying to get data from the database and then get the as json file.

I don't know where the error is there in the code if someone could help and figure out how to solve the problem. I have tried to replace the code in while clause with a different code which was working earlier so it seems there is not the problem in the while clause

CodePudding user response：

it must be because "gson.toJson(data);" this statement returning a null object and you're trying to store it in string format. that is why it giving you an error. try investigate it.

CodePudding user response：

It has to throws exception at Integer.parseInt() method, try to find why req.getParameter("page") returns null to String object.