之前所用的下載檔案方法總是出現下載檔案未知大小的問題，百思不得其解，最後使用該方法後，問題解決。

　　// 根目錄為resources

　　private static final String filePath = "/excel/xxx.xlsx";

 　　/**
     * 下載EXCEL模板檔案
     * 
     * @param response
     */
    @ApiOperation(value = "下載EXCEL模板檔案", notes = "下載EXCEL模板檔案", httpMethod = "GET", produces = "application/vnd.ms-excel", protocols = "HTTP/1.1")
    @RequestMapping(value 
 
= "/download-excel-model", method = RequestMethod.GET)
    public void downloadImportTemplate(HttpServletResponse response) {
        try {

            ResourcePatternResolver resolver = new PathMatchingResourcePatternResolver();
            // 獲取所有匹配的檔案
            org.springframework.core.io.Resource[] resources = resolver.getResources(filePath);
            InputStream stream 
 
= resources[0].getInputStream();
            response.setContentType("application/vnd.ms-excel");
            response.setHeader("Content-Disposition", "attachment;filename=xxx.xlsx");
            IOUtils.copy(stream, response.getOutputStream());
            response.flushBuffer();

        } catch (IOException ex) {
            ex.printStackTrace();
        }
    }

==============================================================================================================

 

import org.apache.commons.io.IOUtils;
import org.springframework.core.io.support.PathMatchingResourcePatternResolver;
import org.springframework.core.io.support.ResourcePatternResolver;

import javax.servlet.http.HttpServletResponse;
import java.io.InputStream;
import java.nio.charset.StandardCharsets;

public class DownloadExcelModel {

    // 下載檔案路徑
    private String filePath;

    // 生成檔名稱
    private String fileName;

    public DownloadExcelModel() {

    }

    public DownloadExcelModel(String filePath, String fileName) {
        this.filePath = filePath;
        this.fileName = fileName;
    }

    /**
     * <p>
     * 通用Excel匯出方法,利用反射機制遍歷物件的所有欄位，將資料寫入Excel檔案中 <br>
     * 此版本生成2007以上版本的檔案 (檔案字尾：xlsx)
     * </p>
     */
    public void downloadExcelModel(HttpServletResponse response) throws Exception {

        ResourcePatternResolver resolver = new PathMatchingResourcePatternResolver();
        // 獲取所有匹配的檔案
        org.springframework.core.io.Resource[] resources = resolver.getResources(filePath);
        InputStream inputStream = resources[0].getInputStream();

        // response緩衝區重置
        response.reset();
        // 支援下載引數
        response.setContentType("application/vnd.ms-excel");
        // 設定瀏覽器響應頭對應的Content-disposition
        response.setHeader("Content-Disposition", "attachment;filename=" + new String(fileName.getBytes(), StandardCharsets.ISO_8859_1) + ".xlsx");
        // 設定響應編碼
        response.setCharacterEncoding("UTF-8");

        IOUtils.copy(inputStream, response.getOutputStream());
        response.flushBuffer();
    }

}