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java实现上传进度条 JavaWeb项目实现文件上传动态显示进度实例

DongXv 人气:0
想了解JavaWeb项目实现文件上传动态显示进度实例的相关内容吗,DongXv在本文为您仔细讲解java实现上传进度条的相关知识和一些Code实例,欢迎阅读和指正,我们先划重点:java实现上传进度条,java上传文件带进度条,java文件上传进度条,下面大家一起来学习吧。

很久没有更新博客了,这段时间实在的忙的不可开交,项目马上就要上线了,要修补的东西太多了。当我在学习JavaWeb文件上传的时候,我就一直有一个疑问,网站上那些博客的图片是怎么上传的,因为当提交了表单之后网页就跳转了。后来我学习到了Ajax,我知道了浏览器可以异步的发送响应,这时我又有新的疑问,那就是在我上传一些文件的时候,那些网站的上传进度是怎么做到的,因为servlet直到上传完成之后才完成响应。

最近我们的项目中有一个地方中需要用到一个功能,当用户点击一个处理按钮时,前台会实时的显示后台处理动态,由于servlet一次只能接受一个请求,而且在servlet的生命周期结束时才会把响应数据发送到前台(这一点大家可以做个这样的测试:

 response.getWriter().print("hello");
 Thread.sleep(10000);
 response.getWriter().print("world");

你们会发现前台在等待了约10s后收到了"helloworld")。所以我想到了一个方法:使用单例保存实时信息。具体的实现方法就是,当用户点击了处理按钮时,在后台开启一个线程进行处理,并且每进行到一步,就向单例中写入当前状态信息。然后编写一个servlet,用于返回单例中的信息,前台循环发送请求,这样就能实现实时显示进度的效果。

好了,啰嗦了这么多,下面进入正题,如何实现上传文件动态显示进度,其实思想和上面的功能是一致的,我将这个功能分为三个点:

1.单例:用于保存进度信息;

2.上传servlet:用于上传文件并实时写入进度;

3.进度servlet:用于读取实时进度信息;

上代码,前台:

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
<style type="text/css">
  #progress:after {
    content: '%';
  }
</style>
</head>
<body>
  <h3>File upload demo</h3>
  <form action="TestServlet" method="post" enctype="multipart/form-data" id="dataForm">
    <input type="file" name="file" id="fileInput"> <br>
    <input type="submit" value="submit" id="submit">
  </form>
  <div id="progress"></div>
  <script type="text/javascript" src="scripts/jquery-1.9.1.min.js"></script>
  <script type="text/javascript">
  (function () {
    var form = document.getElementById("dataForm");
    var progress = document.getElementById("progress");
    
    $("#submit").click(function(event) {
      //阻止默认事件
      event.preventDefault();
      //循环查看状态
      var t = setInterval(function(){
        $.ajax({
          url: 'ProgressServlet',
          type: 'POST',
          dataType: 'text',
          data: {
            filename: fileInput.files[0].name,
          },
          success: function (responseText) {
            var data = JSON.parse(responseText);
            //前台更新进度
            progress.innerText = parseInt((data.progress / data.size) * 100);
          },
          error: function(){
            console.log("error");
          }
        });
      }, 500);
      //上传文件
      $.ajax({
        url: 'UploadServlet',
        type: 'POST',
        dataType: 'text',
        data: new FormData(form),
        processData: false,
        contentType: false,
        success: function (responseText) {
          //上传完成,清除循环事件
          clearInterval(t);
          //将进度更新至100%
          progress.innerText = 100;
        },
        error: function(){
          console.log("error");
        }
      });
      return false;
    });
  })();
  </script>
</body>
</html>

后台,单例:

import java.util.Hashtable;

public class ProgressSingleton {
  //为了防止多用户并发,使用线程安全的Hashtable
  private static Hashtable<Object, Object> table = new Hashtable<>();
  
  public static void put(Object key, Object value){
    table.put(key, value);
  }
  
  public static Object get(Object key){
    return table.get(key);
  }
  
  public static Object remove(Object key){
    return table.remove(key);
  }
}

上传servlet:

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

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

import org.apache.tomcat.util.http.fileupload.FileItem;
import org.apache.tomcat.util.http.fileupload.FileUploadException;
import org.apache.tomcat.util.http.fileupload.disk.DiskFileItemFactory;
import org.apache.tomcat.util.http.fileupload.servlet.ServletFileUpload;
import org.apache.tomcat.util.http.fileupload.servlet.ServletRequestContext;

import singleton.ProgressSingleton;

@WebServlet("/UploadServlet")
public class UploadServlet extends HttpServlet {
  private static final long serialVersionUID = 1L;

  public UploadServlet() {
  }

  protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    DiskFileItemFactory factory = new DiskFileItemFactory();
    factory.setSizeThreshold(4*1024);
    
    ServletFileUpload upload = new ServletFileUpload(factory);
    
    List<FileItem> fileItems;
    try {
      fileItems = upload.parseRequest(new ServletRequestContext(request));
      //获取文件域
      FileItem fileItem = fileItems.get(0);
      //使用sessionid + 文件名生成文件号
      String id = request.getSession().getId() + fileItem.getName();
      //向单例哈希表写入文件长度和初始进度
      ProgressSingleton.put(id + "Size", fileItem.getSize());
      //文件进度长度
      long progress = 0;
      //用流的方式读取文件,以便可以实时的获取进度
      InputStream in = fileItem.getInputStream();
      File file = new File("D:/test");
      file.createNewFile();
      FileOutputStream out = new FileOutputStream(file);
      byte[] buffer = new byte[1024];
      int readNumber = 0;
      while((readNumber = in.read(buffer)) != -1){
        //每读取一次,更新一次进度大小
        progress = progress + readNumber;
        //向单例哈希表写入进度
        ProgressSingleton.put(id + "Progress", progress);
        out.write(buffer);
      }
      //当文件上传完成之后,从单例中移除此次上传的状态信息
      ProgressSingleton.remove(id + "Size");
      ProgressSingleton.remove(id + "Progress");
      in.close();
      out.close();
    } catch (FileUploadException e) {
      e.printStackTrace();
    }
    
    response.getWriter().print("done");
  }

  protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    doGet(request, response);
  }

}

进度servlet:

import java.io.IOException;

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

import net.sf.json.JSONObject;
import singleton.ProgressSingleton;

@WebServlet("/ProgressServlet")
public class ProgressServlet extends HttpServlet {
  private static final long serialVersionUID = 1L;
    
  public ProgressServlet() {
    super();
    // TODO Auto-generated constructor stub
  }

  protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    String id = request.getSession().getId();
    String filename = request.getParameter("filename");
    //使用sessionid + 文件名生成文件号,与上传的文件保持一致
    id = id + filename;
    Object size = ProgressSingleton.get(id + "Size");
    size = size == null ? 100 : size;
    Object progress = ProgressSingleton.get(id + "Progress");
    progress = progress == null ? 0 : progress; 
    JSONObject json = new JSONObject();
    json.put("size", size);
    json.put("progress", progress);
    response.getWriter().print(json.toString());
  }

  protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    doGet(request, response);
  }

}

效果图:

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