Tukukkk

I am exporting a List of virtual servers to a CSV file. The users submits filters and the applications generates FilterDTOs containing a map of the attribute and the corresponding value. The idea was to 'undock' the filter and the simple DTOs that contained all the variables from the export, so the export does not need to know the concrete filter (actually he knows but only to let the FilterDTOs be generated). All values in the map are Optional<String>.
Here is the exporter, the getFileEnding and getMediaType are given by the interface to dynamically handle the return of a byte in a REST-controller (I need the file ending to parse the file and the media type for setting the HTTP headers).
I would appreciate any critic and tips

public class FilteredCsvExporter implements Exporter {

    private ExportFilter filter;



    public FilteredCsvLbExporter(ExportFilter filter) {

        this.filter = filter;

    }



    @Override

    public void exportData() throws IOException, DocumentException {

        List<VirtualServerFilterDTO> servers = PoolRepository.getInstance().getVirtualServerFilterDTOs(filter);

        PrintWriter pw = new PrintWriter(new File(getBaseTempDir() + "/filteredExport.csv"));

        writeDataToFile(pw, new StringBuilder(), servers);

    }



    private void writeDataToFile(PrintWriter printWriter, StringBuilder builder, List<VirtualServerFilterDTO> servers) {

        generateHeadline(builder, servers);

        servers = servers.stream().filter(i -> i.getAttributes().get("Pool").isPresent() != false).collect(Collectors.toList());

        servers.forEach(server -> {

            addMapToCsv(builder, server.getAttributes());

            if (server.getAssignedPool().get().getAttributes().size() <= 0) {

                return;

            }

            addMapToCsv(builder, server.getAssignedPool().get().getAttributes());

            server.getAssignedPool().get().getMembers().forEach(member -> {

                addMapToCsv(builder, member.getAttributes());

            });

            builder.append("n");

        });

        builder.append("n");

        builder.append("n");

        builder.append("Pools that are not assigned to any virtual server");

        builder.append("n");

        appendPoolsWithoutServerHeader(builder, servers);

        builder.append("n");

        getPoolsWithoutServer().forEach(pool -> {

            addMapToCsv(builder, pool.getAttributes());

            builder.append("n");

        });

        printWriter.write(builder.toString());

        printWriter.close();

        System.out.println("Done");

        getPoolsWithoutServer();

    }



    private void appendPoolsWithoutServerHeader(StringBuilder builder, List<VirtualServerFilterDTO> servers) {

        servers.get(0).getAssignedPool().get().getAttributes().forEach((k, v) -> {

            builder.append(k);

            builder.append(",");

        });

    }



    private void addMapToCsv(StringBuilder builder, Map<String, Optional<String>> map) {

        for (Map.Entry<String, Optional<String>> entry : map.entrySet()) {

            if (entry.getValue().orElse("-").contains(",")) {

                builder.append(escapeStringForCSV(entry.getValue()));

                builder.append(",");

            } else {

                builder.append(entry.getValue().orElse("-"));

                builder.append(",");

            }

        }

    }



    private List<PoolFilterDto> getPoolsWithoutServer() {

        List<VirtualServerFilterDTO> servers = PoolRepository.getInstance().getVirtualServerFilterDTOs(filter);

        List<PoolFilterDto> pools = new ArrayList<>();

        List<PoolDTO> poolDTOS = PoolRepository.getInstance().getPools().getPools();

        List<PoolDTO> temp = new ArrayList<>();



        for (int i = 0; i < servers.size(); i++) {

            for (int j = 0; j < poolDTOS.size(); j++) {

                VirtualServerFilterDTO server = servers.get(i);

                PoolDTO pool = poolDTOS.get(j);

                if (server.getAssignedPool().isPresent()) {

                    if (server.getAssignedPool().get().getAttributes().size() > 0) {

                        if (server.getAssignedPool().get().getAttributes().get("Full path").get().equalsIgnoreCase(pool.getFullPath())) {

                            temp.add(pool);

                        }

                    }

                }

            }

        }

        poolDTOS.removeAll(temp);

        poolDTOS.forEach(p -> {

            pools.add(new PoolFilterDto(p, filter));

        });

        return pools;

    }



    private String escapeStringForCSV(Optional<String> value) {

        if (!value.isPresent()) {

            return "-";

        }

        return """ + value.get() + """;

    }



    private void generateHeadline(StringBuilder builder, List<VirtualServerFilterDTO> servers) {

        servers.get(0).getAttributes().forEach((k, v) -> {

            builder.append(k);

            builder.append(",");

        });

        servers.get(0).getAssignedPool().get().getAttributes().forEach((k, v) -> {

            builder.append(k);

            builder.append(",");

        });



        int size = servers.stream().mapToInt(m -> m.getAssignedPool().get().getMembers().size()).max().getAsInt();



        Map<String, Optional<String>> map = servers.get(0).getAssignedPool().get().getMembers().get(0).getAttributes();

        for (int i = 0; i < size; i++) {

            for (Map.Entry<String, Optional<String>> entry : map.entrySet()) {

                builder.append(entry.getKey());

                builder.append(",");

            }

        }

        builder.append("n");

    }



    @Override

    public File getBaseTempDir() {

        return new File(System.getProperty("java.io.tmpdir"));

    }



    @Override

    public String getFileEnding() {

        return ".csv";

    }



    @Override

    public String getMediaType() {

        return "text/csv";

    }

}