Blank CSV file generated,need to write data stored inside List<List<Object> - spring-mvc

Question

I need to create and download the CSV file, and for this I am using OpenCSV with Spring MVC, the data need to be written is holding by my class name CsvDataDto.
public class CsvDataDto {
private String fileName;
List<String> header=new ArrayList<>();;
private String heading;
List<List<Object>> data=new ArrayList<>();
//getters and setters
}
The main data contains file header (eg: userid,fname,lastname,rollno) and actual data (eg. 1,101,john,doe,1001).
File header is hold by List<String> header
and The file data is hold by List<List<Object>> data
and here is the controller method which set all the required data
#RequestMapping(value = "/export_data")
public void downloadDataInCsv(
#RequestParam("type") String type,
#RequestParam("tID") String tableId,
HttpServletRequest request,
HttpServletResponse response) throws IOException {
if (type.equals("csv")) {
CsvDataDto dataDTO = new CsvDataDto();
dataDTO.setFileName("Table_Data");
dataDTO.getHeader().add("User Id");
dataDTO.getHeader().add("First Name");
dataDTO.getHeader().add("Last Name");
dataDTO.getHeader().add("Roll No");
dataDTO.getHeader().add("Email ID");
dataDTO.getHeader().add("Gender");
List<UserInfo> list = userInfoDao.findById(tableId);
for (UserInfo infoList : list) {
List<Object> newList = new ArrayList<>();
newList.add(infoList.getUserId());
newList.add(infoList.getFirstName());
newList.add(infoList.getLastName());
newList.add(infoList.getRollNo());
newList.add(infoList.getEmail());
newList.add(infoList.getGender());
dataDTO.getData().add(newList);
}
ExportCsvUtil.downloadCsv(request, response, dataDTO);
}
Now the downloadCsv() implementation
public static void downloadCsv(HttpServletRequest request, HttpServletResponse response, CsvDataDto csvDataDto) throws IOException {
List<String[]> records = new ArrayList<>();
String csvFileName = csvDataDto.getFileName();
String headerKey = "Content-Disposition";
String headerValue = String.format("attachment; filename=" + csvDataDto.getFileName() + ".csv");
response.setContentType("text/csv");
response.setHeader(headerKey, headerValue);
CSVWriter writer = new CSVWriter(new FileWriter(csvFileName));
String[] headerArr = new String[csvDataDto.getHeader().size()];
headerArr = csvDataDto.getHeader().toArray(headerArr);
records.add(headerArr);
for (List<Object> objList : csvDataDto.getData()) {
System.out.println("object list:" + objList);
String[] fileData = new String[objList.size()];
fileData = objList.toArray(fileData);
records.add(fileData);
}
writer.writeAll(records);
writer.close();
System.out.println(writer);
}
}
I am stuck here,as I explore tons of examples where the instructors simple pass the data in writeNext() method.
writer.writeNext(csvDataDto);
But I know that it will not work as i expected.File is successfully downloaded but blank, no data is write over it.
I want to implement the logic in such a way, so I get the CSV like below
userid, fname,lastname,rollno,gender (List<String> header)
1 , john, doe ,1001, M (List<List<Object>> data)
2 , Rose, Mary ,1002, F
3 , Jack, Jill ,1003, M
What is the best way to achieve the same by using writeNext().

Answer 1

#RequestMapping(value = "/export_data")
public void downloadDataInCsv(
#RequestParam("type") String type,
#RequestParam("tID") String tableId,
HttpServletRequest request,
HttpServletResponse response) throws IOException {
if (type.equals("csv")) {
List<UserInfo> list = userInfoDao.findById(tableId);
ExportCsvUtil.downloadCsv(request, response, list);
}
}
private void downloadCsv(HttpServletRequest request, HttpServletResponse response, List<UserInfo> list) throws IOException {
String headerKey = "Content-Disposition";
String headerValue = String.format("attachment; filename=Table_Data.csv");
response.setContentType("text/csv");
response.setHeader(headerKey, headerValue);
try (final CSVWriter writer = new CSVWriter(response.getWriter(), ",")) {
writer.writeNext(new String[]{"User Id", "First Name", "Last Name", "Roll No", "Email ID", "Gender"});
for (UserInfo entry: list) {
// cast/convert to String where needed
writer.writeNext(new String[]{entry.getUserId()+"", entry.getFirstName(), entry.getLastName(),entry.getRollNo(),entry.getEmail(),entry.getGender()});
}
writer.close();
}
}