Was trying to extract about 50k rows from a database to .xlsx where one column is formatted as Date and noticed that after 32767 rows Date format disappears. 
It does not matter if you start with rownum 0 or rownum 500, after 32767 rows formatting disappears. 

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Code:
package orat_reports;

import java.sql.DriverManager;
import java.sql.Connection;
import java.sql.SQLException;
import java.sql.ResultSet;
import java.sql.PreparedStatement;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.FileNotFoundException;

import org.apache.poi.ss.usermodel.Cell;
import org.apache.poi.ss.usermodel.CellStyle;
import org.apache.poi.ss.usermodel.Row;
import org.apache.poi.ss.usermodel.Sheet;
import org.apache.poi.xssf.streaming.SXSSFWorkbook;
import org.apache.poi.xssf.usermodel.XSSFDataFormat;

public class SQL_SH_to_XLSX {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		
		String url = "jdbc:oracle:thin:@//localhost:1521/orcl";
		String username = "User";
		String password = "Password";
		
		String sqlQuerry = "Select * from customers";
		
		// Create new workbook
		SXSSFWorkbook wb = new SXSSFWorkbook();
		Sheet sh = wb.createSheet();
		wb.setSheetName(0, "SQL Test");
		int rownum = 0;
		
		try{
			Connection con = DriverManager.getConnection(url, username, password);
			PreparedStatement st = con.prepareStatement(sqlQuerry);
			ResultSet rs = st.executeQuery();
			
			while(rs.next()) {

				Row row = sh.createRow(rownum);
				
				
					Cell c = row.createCell(0);
					c.setCellValue(rs.getDouble(1));
					
					c = row.createCell(1);
					c.setCellValue(rs.getString(2));
					
					c = row.createCell(2);
					c.setCellValue(rs.getDate(21));
					// Date format for cell
					XSSFDataFormat df = (XSSFDataFormat)wb.createDataFormat();
					CellStyle cs = wb.createCellStyle();
					cs.setDataFormat(df.getFormat("dd-mm-yyyy"));
					c.setCellStyle(cs);
					
				rownum++;
			}			
			
		} catch (SQLException e) {
			System.out.println(e.getErrorCode());
		} 
		
		//Write file
		try {
			FileOutputStream out = new FileOutputStream("SQL Test.xlsx");
			try {
				wb.write(out);
				out.close();
				wb.close();
			} catch (IOException ioe) {
				System.out.println(ioe.getMessage());
			}

		} catch (FileNotFoundException fnfe) {
			System.out.println(fnfe.getMessage());
		}
		
		System.out.println("Happy Days");
	}

}