Export csv file by opencsv lib

ExportCsvUtil

import com.opencsv.CSVWriter;
import lombok.extern.slf4j.Slf4j;
import org.apache.commons.lang3.StringUtils;

import javax.servlet.http.HttpServletResponse;
import java.io.Writer;
import java.lang.reflect.Field;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;

@Slf4j
public class ExportCsvUtil {


    private final static SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");


    public static <T> void export(String csvName, List<T> list, LinkedHashMap<String, String> fieldMap,
                                  HttpServletResponse response) {

        if (StringUtils.isBlank(csvName)) {
            csvName = sdf.format(new Date());
        } else {
            csvName = csvName + sdf.format(new Date());
        }

        response.reset();
        response.setContentType("APPLICATION/OCTET-STREAM");
        response.setHeader("Content-disposition", "attachment;  filename=" + csvName + ".csv");


        try (Writer writer = response.getWriter()) {
            //BOM
            writer.write(new String(new byte[]{(byte) 0xEF, (byte) 0xBB, (byte) 0xBF}));
            CSVWriter cw = new CSVWriter(writer);
            fillCsv(cw, list, fieldMap);
            cw.flush();
            cw.close();
        } catch (Exception e) {
            log.error(e.getMessage());
        }
    }

    private static Field getFieldByName(String fieldName, Class<?> clazz) {
        Field[] selfFields = clazz.getDeclaredFields();

        for (Field field : selfFields) {
            if (field.getName().equals(fieldName)) {
                return field;
            }
        }

        Class<?> superClazz = clazz.getSuperclass();
        if (superClazz != null && superClazz != Object.class) {
            // Recursion
            return getFieldByName(fieldName, superClazz);
        }

        return null;
    }


    private static Object getFieldValueByName(String fieldName, Object o) {

        Object value = null;
        Field field = getFieldByName(fieldName, o.getClass());

        if (field != null) {
            try {
                field.setAccessible(true);

                value = field.get(o);
            } catch (IllegalAccessException e) {
                log.error(e.getMessage(), e);
            }
        }
        return value;
    }


    /**
     * Get "name" value or "department.name" value
     *
     * @param fieldNameSequence
     * @param o
     * @return
     * @throws Exception
     */
    private static Object getFieldValueByNameSequence(String fieldNameSequence, Object o) throws Exception {
        Object value;

        String[] attributes = fieldNameSequence.split("\\.");
        if (attributes.length == 1) {
            value = getFieldValueByName(fieldNameSequence, o);
        } else {
            Object fieldObj = getFieldValueByName(attributes[0], o);
            String subFieldNameSequence = fieldNameSequence.substring(fieldNameSequence.indexOf(".") + 1);
            value = getFieldValueByNameSequence(subFieldNameSequence, fieldObj);
        }
        return value;

    }

    private static <T> void fillCsv(CSVWriter writer, List<T> list, LinkedHashMap<String, String> fieldMap) throws Exception {
        String[] enFields = new String[fieldMap.size()];
        String[] cnFields = new String[fieldMap.size()];

        int count = 0;
        for (Map.Entry<String, String> entry : fieldMap.entrySet()) {
            enFields[count] = entry.getKey();
            cnFields[count] = entry.getValue();
            count++;
        }

        // Header
        String[] headers = new String[count];
        for (int i = 0; i < cnFields.length; i++) {
            headers[i] = cnFields[i];
        }
        writer.writeNext(headers);


        // content
        String[] data = new String[count];
        for (int index = 0; index < list.size(); index++) {
            T item = list.get(index);
            for (int i = 0; i < enFields.length; i++) {
                Object value = getFieldValueByNameSequence(enFields[i], item);
                String str;
                if (value == null) {
                    str = "";
                } else if (value instanceof Date) {
                    str = sdf.format(value);
                } else {
                    str = String.valueOf(value);
                }
                data[i] = str;
            }
            writer.writeNext(data);
        }

    }

}