import com.alibaba.excel.EasyExcel;
import com.alibaba.excel.read.listener.ReadListener;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.poi.ss.formula.functions.T;
import org.springframework.web.multipart.MultipartFile;

import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletResponse;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.UnsupportedEncodingException;
import java.net.URLEncoder;
import java.util.List;

/**
 * 基于EasyExcel的导入导出工具类， 在使用时需要先将excel实体类中的字段使用@ExcelProperty来指定表头
 * {@link com.alibaba.excel.annotation.ExcelProperty}
 * {@link com.alibaba.excel.annotation.write.style.ColumnWidth}
 * {@link com.alibaba.excel.annotation.format.DateTimeFormat}
 */
public class EasyExcelAlibabaUtil {

    private static Log logger = LogFactory.getLog("EasyExcelAlibabaUtil");

    /**
     * 将excel文件转化成javaList集合，
     * 需要在传入的class的字段中加入EasyExcel的专用注解来指定表名
     * @param excelFile
     * @param clazz
     * @param <T>
     * @return
     */
    public static <T> List<T> excelToList(MultipartFile excelFile, Class<T> clazz) {
        List<T> objects = null;
        try {
            InputStream inputStream = excelFile.getInputStream();
            objects = EasyExcel.read(inputStream).head(clazz).sheet().doReadSync();
        } catch (Exception e) {
            logger.error("excelToList-exception", e);
        } finally {
            return objects;
        }
    }

    /**
     * 读取excel，这个相当于一个高性能模式。
     * 比上面的方法多了一个readListener接口， 需要传一个实现这个接口的实现类
     * 其中invoke方法是每读取一行都会调用， 所以可以读取一行处理一行， 性能比较高。
     * @param excelFile
     * @param clazz
     * @param readListener
     */
    public static void readExcelHighSpeed(MultipartFile excelFile, Class<T> clazz, ReadListener readListener) {
        try {
            InputStream inputStream = excelFile.getInputStream();
            EasyExcel.read(inputStream, clazz, readListener).sheet().doRead();
        } catch (Exception e) {
            logger.error("excelToList-readExcelHighSpeed", e);
        }
    }

    /**
     * 下载excel
     * @param response
     * @param clazz
     * @param list
     * @param excelName
     */
    public static void download(HttpServletResponse response, Class<?> clazz, List<?> list, String excelName) {
        try {
            ServletOutputStream outputStream = response.getOutputStream();
            response.setCharacterEncoding("UTF-8");
            response.setHeader("content-Type", "application/vnd.ms-excel");
            response.setHeader("Content-Disposition",
                    "attachment;filename=" + URLEncoder.encode(excelName, "UTF-8"));
            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            EasyExcel.write(baos, clazz).sheet("sheet1").doWrite(list);
            response.setHeader("Content-Length", String.valueOf(baos.size()));
            outputStream.write(baos.toByteArray());
            response.flushBuffer();
        } catch(Exception e){
            logger.error("excelToList-download", e);
        }
    }

}