servlet.Ajax实现上传文件进度条

待我称王封你为后i 2022-08-18 12:21 256阅读 0赞

这里关于servlet如何上传文件就先不说了,将如何得到已经上传的文件数据的百分比...

首先我们先写一个类这个类要实现ProgressListener这个接口,实现里面的update(...)方法.代码如下

package com.test.servlet;
    
    import java.text.DecimalFormat;
    
    import javax.servlet.http.HttpServletRequest;
    
    import org.apache.commons.fileupload.ProgressListener;
    
    public class UploadProgressListener implements ProgressListener
    {
    	
    	private HttpServletRequest request = null ;
    
    	private DecimalFormat decimalFormat = new DecimalFormat("#00.0");
    	
    	
    	
    	public UploadProgressListener(HttpServletRequest request)
    	{
    		this.request = request;
    	}
    	
    	public void update(long pBytesRead, long pContentLength, int pItems)
    	{
    		
    		 double percent= (double)pBytesRead*100/(double)pContentLength; 
    		 
    		 String hadDownloadPercent = decimalFormat.format(percent).toString();
    	
    		request.getSession().setAttribute("hadDownloadPercent",hadDownloadPercent) ;
    		
    	}
    
    }

这个类写完之后,我们再写一个servlet,这个servlet用于被Ajax在短暂的时间内不断请求数据,比如请求间隔是100ms

上代码

package com.test.servlet;
    
    import java.io.IOException;
    import java.io.PrintWriter;
    
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import javax.servlet.http.HttpSession;
    
    public class ReadProgressInSessionServlet extends HttpServlet
    {
    public void doGet(HttpServletRequest request, HttpServletResponse response)
    			throws ServletException, IOException
    	{
    HttpSession session = request.getSession();
    		
    		String hadDownloadPercent = (String)session.getAttribute("hadDownloadPercent");
    		
    		response.setCharacterEncoding("utf-8");
    		
    		PrintWriter printWriter = response.getWriter();
    		
    		printWriter.write(hadDownloadPercent);
    		
    		printWriter.flush();
    	}
    
    public void doPost(HttpServletRequest request, HttpServletResponse response)
    			throws ServletException, IOException
    	{
    
    	this.doGet(request,response);
    		
    	}
    
    }

还有一个就是上传文件的核心类

ServletFileUpload servletFileUpload = new ServletFileUpload(
    				diskFileItemFactory);
    
    		servletFileUpload.setProgressListener(new UploadProgressListener(req));

其中req是HttpServletRequest对象 UploadProgressListener是ProgressListener接口的实现类...

最后就是通过JavaScript频繁的发起http请求,也就是Ajax...不过这种方式可能对服务器性能造成影响...