java中excel文件的导入，限制上传的文件类型，文件的大小，显示上传文件的进度条...

要实现Java中的Excel文件导入，限制上传的文件类型，文件大小以及显示上传文件的进度条，可以借助以下几个技术：

1. Apache POI：用于读取和写入Excel文件
2. Apache Commons FileUpload：用于解析和处理文件上传请求
3. jQuery插件：用于实现显示上传文件的进度条

下面是一个简单的代码示例，演示了如何使用这些技术来实现文件上传和Excel文件导入：

import java.io.File;
import java.io.IOException;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileItemFactory;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
import org.apache.poi.ss.usermodel.Cell;
import org.apache.poi.ss.usermodel.Row;
import org.apache.poi.ss.usermodel.Sheet;
import org.apache.poi.ss.usermodel.Workbook;
import org.apache.poi.ss.usermodel.WorkbookFactory;

public class ExcelImportServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;

    private static final int MAX_FILE_SIZE = 1024 * 1024; // 1MB

    private static final String[] ALLOWED_FILE_TYPES = {"xls", "xlsx"};

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        
        // Check if the request is a multipart/form-data POST request
        boolean isMultipart = ServletFileUpload.isMultipartContent(request);
        if (!isMultipart) {
            response.sendError(HttpServletResponse.SC_BAD_REQUEST, "Invalid request type");
            return;
        }
        
        // Create a factory for disk-based file items
        FileItemFactory factory = new DiskFileItemFactory();
        
        // Create a new file upload handler
        ServletFileUpload upload = new ServletFileUpload(factory);
        
        // Set maximum file size
        upload.setFileSizeMax(MAX_FILE_SIZE);
        
        try {
            // Parse the request
            List<FileItem> items = upload.parseRequest(request);
            for (FileItem item : items) {
                // Process only file upload request
                if (!item.isFormField()) {
                    // Check file type
                    String fileName = item.getName();
                    String fileType = fileName.substring(fileName.lastIndexOf(".") + 1).toLowerCase();
                    boolean isAllowedType = false;
                    for (String allowedType : ALLOWED_FILE_TYPES) {
                        if (fileType.equals(allowedType)) {
                            isAllowedType = true;
                            break;
                        }
                    }
                    if (!isAllowedType) {
                        response.sendError(HttpServletResponse.SC_BAD_REQUEST, "Invalid file type");
                        return;
                    }
                    
                    // Create a temporary file to store the uploaded file
                    File tempFile = File.createTempFile("excel-import-", "." + fileType);
                    item.write(tempFile);
                    
                    // Read the uploaded Excel file
                    Workbook workbook = WorkbookFactory.create(tempFile);
                    Sheet sheet = workbook.getSheetAt(0);
                    for (Row row : sheet) {
                        for (Cell cell : row) {
                            // Process cell data
                        }
                    }
                    
                    // Delete the temporary file
                    tempFile.delete();
                    
                    // Send success response
                    response.getWriter().write("File uploaded and processed successfully!");
                }
            }
        } catch (Exception e) {
            response.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR, "Error processing file upload");
            e.printStackTrace();
        }
    }

}

此外，还需要在前端页面中使用jQuery插件来实现上传文件进度条的显示。可以使用一些流行的jQuery插件，例如 jQuery File Upload 或 Dropzone.js。

希望以上内容能够对你有所帮助！