SpringBoot上传文件如何返回前端进度条

import javax.servlet.http.HttpSession;
 
import org.apache.commons.fileupload.ProgressListener;
import org.springframework.stereotype.Component;
 
@Component
public class UploadProgressListener implements ProgressListener {
    private HttpSession session;
 
    public void setSession(HttpSession session){
        this.session=session;
        ProgressEntity status = new ProgressEntity();
        session.setAttribute("status", status);
    }
 
    /* pBytesRead  到目前为止读取文件的比特数
     * pContentLength 文件总大小
     * pItems 目前正在读取第几个文件
     */
    public void update(long pBytesRead, long pContentLength, int pItems) {
        ProgressEntity status = (ProgressEntity) session.getAttribute("status");
        status.setPBytesRead(pBytesRead);
        status.setPContentLength(pContentLength);
        status.setPItems(pItems);
        System.out.println("UploadProgressListener update ProgressEntity:  "+status.toString());
    }
}

@Component
public class ProgressEntity {
    // 读取的文件的比特数
    private long pBytesRead = 0L;
    // 文件的总大小
    private long pContentLength = 0L;
    // 目前正在读取第几个文件
    private int pItems;
 
    private long startTime = System.currentTimeMillis();
 
    public ProgressEntity() {
        pBytesRead = 0L;
        pContentLength = 0L;
    }
 
    public long getPBytesRead() {
        return pBytesRead;
    }
 
    public void setPBytesRead(long bytesRead) {
        pBytesRead = bytesRead;
    }
 
    public long getPContentLength() {
        return pContentLength;
    }
 
    public void setPContentLength(long contentLength) {
        pContentLength = contentLength;
    }
 
    public int getPItems() {
        return pItems;
    }
 
    public void setPItems(int items) {
        pItems = items;
    }
 
    @Override
    public String toString() {
        float tmp = (float) pBytesRead;
        float result = tmp / pContentLength * 100;
        return "ProgressEntity [pBytesRead=" + pBytesRead + ", pContentLength="
                + pContentLength + ", percentage=" + result + "% , pItems=" + pItems + "]";
    }
}

import javax.servlet.http.HttpServletRequest;
 
import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileUpload;
import org.apache.commons.fileupload.FileUploadBase;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.multipart.MaxUploadSizeExceededException;
import org.springframework.web.multipart.MultipartException;
import org.springframework.web.multipart.commons.CommonsMultipartResolver;
 
public class CustomMultipartResolver extends CommonsMultipartResolver {
 
    @Autowired
    private UploadProgressListener uploadProgressListener;
 
    @Override
    protected MultipartParsingResult parseRequest(HttpServletRequest request) throws MultipartException {
        String encoding = determineEncoding(request);
        FileUpload fileUpload = prepareFileUpload(encoding);
 
 
        uploadProgressListener.setSession(request.getSession());// 文件上传进度监听器设置session用于存储上传进度
        fileUpload.setProgressListener(uploadProgressListener);// 将文件上传进度监听器加入到 fileUpload 中
        try {
            List<FileItem> fileItems = ((ServletFileUpload) fileUpload).parseRequest(request);
            return parseFileItems(fileItems, encoding);
        } catch (FileUploadBase.SizeLimitExceededException ex) {
            throw new MaxUploadSizeExceededException(fileUpload.getSizeMax(), ex);
        } catch (FileUploadBase.FileSizeLimitExceededException ex) {
            throw new MaxUploadSizeExceededException(fileUpload.getFileSizeMax(), ex);
        } catch (FileUploadException ex) {
            throw new MultipartException("Failed to parse multipart servlet request", ex);
        }
    }
}

import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.multipart.MultipartResolver;
 
import com.baidu.doclabel.biz.listener.CustomMultipartResolver;
 
 

@EnableAutoConfiguration
@Configuration
public class UploadProgressApplication {
    @Bean(name = "multipartResolver")
    public MultipartResolver multipartResolver() {
        CustomMultipartResolver customMultipartResolver = new CustomMultipartResolver();
        return customMultipartResolver;
    }
}