How to put data into Excel sheet by using Apache POI

package ext;

import java.io.File;

import java.io.FileOutputStream;

import java.io.IOException;

import java.lang.reflect.Field;

import java.lang.reflect.InvocationTargetException;

import java.lang.reflect.Method;

import java.util.*;

import org.apache.commons.io.FileUtils;

import org.apache.poi.openxml4j.exceptions.InvalidFormatException;

import org.apache.poi.openxml4j.opc.OPCPackage;

import org.apache.poi.ss.usermodel.Cell;

import org.apache.poi.ss.usermodel.Row;

import org.apache.poi.ss.usermodel.Workbook;

import org.apache.poi.xssf.streaming.SXSSFSheet;

import org.apache.poi.xssf.streaming.SXSSFWorkbook;

import org.apache.poi.xssf.usermodel.XSSFSheet;

import org.apache.poi.xssf.usermodel.XSSFWorkbook;

import org.joda.time.DateTime;

import org.joda.time.format.DateTimeFormat;

import wt.epm.EPMDocument;

import wt.epm.EPMDocumentMaster;

import wt.fc.PersistenceHelper;

import wt.fc.QueryResult;

import wt.pds.StatementSpec;

import wt.query.QuerySpec;

import wt.util.WTException;

import wt.doc.*;

publicclass Test2 {

    staticint count=2;

    publicstaticvoid main(String[] args) throws WTException {

        QuerySpec qs =new QuerySpec(wt.doc.WTDocument.class);

        QueryResult qr = PersistenceHelper.manager.find((StatementSpec) qs);

        System.out.println("Number of WTDocument Masters: "+ qr.size() +"\n\n");

        WTDocument master =null;      

        XSSFWorkbook workbook =new XSSFWorkbook();    

        XSSFSheet sheet = workbook.createSheet("WTDocument Sheet");

        Map<String, Object[]> data =new TreeMap<String, Object[]>();

        data.put("1", new Object[] {"DOC NAME", "DOC NUMBER"});

        while (qr.hasMoreElements()) {

            master = (WTDocument) qr.nextElement();

            data.put(String.valueOf(count), new Object[] {master.getName(), master.getNumber()});           

            count++;   

        }

        //Iterate over data and write to sheet

        Set<String> keyset = data.keySet();

        int rownum =0;

        for (String key : keyset)

        {

            Row row = sheet.createRow(rownum++);

            Object [] objArr = data.get(key);

            int cellnum =0;

            for (Object obj : objArr) 

            {

               Cell cell = row.createCell(cellnum++);

               if(obj instanceofString)

                    cell.setCellValue((String)obj);

                elseif(obj instanceof Integer)

                    cell.setCellValue((Integer)obj);

            }

        }

        try      

        {

            //Write the workbook in file system

            FileOutputStream out=new FileOutputStream(new File("My_WTDocument.xlsx"));

            workbook.write(out);

            out.close();

            System.out.println("it is written successfully on disk.");

        }

        catch (Exception e)

        {

            e.printStackTrace();

        }

    }

}