Ext4.2结合Spring MVC实现文件上传显示进度

1.实现原理：

　　在大文件上传时显示上传进度是很有必要的，不能让用户感觉到陷入无穷的等待中，或感觉程序已经卡死。为此我们可以在session中存一个上传进度的变量，在文件上传的过程中实时的去修改这个值，这就需要在后台重写Spring MVC自带的上传解析类，每上传一定的字节数就修改一下session中的进度，在前台通个AJAX请求每隔一定的时间去获取这个值显示给用户，这样就达到了显示上传进度的需求，不过这样频繁的请求服务器无疑是增加了服务器的压力，在没有使用任何第三方上传组件的情况下只能如此。

2.测试结果：

   没有出现任何内存溢出或奔溃的情况。

   前台效果和后台打印日志:

   

 3.代码

 ①CustomMultipartResolver.java,Spring默认的文件上传类是CommonsMultipartResolver,我们需要自定义一个类CustomMultipartResolver继承它.

package com.upload;

import java.util.List;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;

import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileItemFactory;
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.web.multipart.MaxUploadSizeExceededException;
import org.springframework.web.multipart.MultipartException;
import org.springframework.web.multipart.MultipartHttpServletRequest;
import org.springframework.web.multipart.commons.CommonsMultipartResolver;

public class CustomMultipartResolver extends CommonsMultipartResolver {
    
    private HttpServletRequest request;
    protected FileUpload newFileUpload(FileItemFactory fileItemFactory) {
        ServletFileUpload upload = new ServletFileUpload(fileItemFactory);
        if (request != null) {
            HttpSession session = request.getSession();
            MyProgressListener uploadProgressListener = new MyProgressListener(session);
            upload.setProgressListener(uploadProgressListener);
        }
        return upload;
    }
     
    public MultipartHttpServletRequest resolveMultipart(
            HttpServletRequest request) throws MultipartException {
        this.request = request;// 获取到request,要用到session
        return super.resolveMultipart(request);
    }
     
    @Override
    public MultipartParsingResult parseRequest(HttpServletRequest request)
            throws MultipartException {
        String encoding = determineEncoding(request);
        FileUpload fileUpload = prepareFileUpload(encoding);
        //设置监听器
        MyProgressListener progressListener = new MyProgressListener(request.getSession());
        fileUpload.setProgressListener(progressListener);
        try {
            List<FileItem> fileItems = ((ServletFileUpload) fileUpload).parseRequest(request);
            return parseFileItems(fileItems, encoding);
        }
        catch (FileUploadBase.SizeLimitExceededException ex) {
            throw new MaxUploadSizeExceededException(fileUpload.getSizeMax(), ex);
        }
        catch (FileUploadException ex) {
            throw new MultipartException("Could not parse multipart servlet request", ex);
        }
    }
 
}

 ②spring-servlet.xml,XML配置

<!-- 文件上传配置 -->
    <!-- <bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver">  
         <property name="maxUploadSize" value="1048576000"/>  
         <property name="maxInMemorySize" value="4096"/>  
         <property name="defaultEncoding" value="UTF-8"></property>
    </bean>  
   -->
    <bean id="multipartResolver" class="com.upload.CustomMultipartResolver">  
         <property name="maxUploadSize" value="1048576000"/>  
         <property name="maxInMemorySize" value="4096"/>  
         <property name="defaultEncoding" value="UTF-8"></property>
    </bean> 

③MyProgressListener.java,文件上传监听器,需要实现ProgressListener接口

package com.upload;

import javax.servlet.http.HttpSession;

import org.apache.commons.fileupload.ProgressListener;

public class MyProgressListener implements ProgressListener {
    
    private HttpSession session;  
     
    public MyProgressListener() {
         
    }
    public MyProgressListener(HttpSession session) {
        this.session = session;
        ProgressEntity ps = new ProgressEntity();
        session.setAttribute("upload_ps", ps);
    }
 
    public void setSession(HttpSession session){
        this.session = session;
    }
    @Override
    public void update(long pBytesRead, long pContentLength, int pItems) {
        ProgressEntity ps = (ProgressEntity) session.getAttribute("upload_ps");
        ps.setpBytesRead(pBytesRead);
        ps.setpContentLength(pContentLength);
        ps.setpItems(pItems);    
        //更新
        session.setAttribute("upload_ps", ps);
       // System.out.println("当前进度:"+ps.getpBytesRead());
    }
}

 ④ProgressEntity.java 包含上传信息的实体

package com.upload;

public class ProgressEntity {
    private long pBytesRead = 0L;   //到目前为止读取文件的比特数 
    private long pContentLength = 0L;    //文件总大小 
    private int pItems;                //目前正在读取第几个文件 
    public long getpBytesRead() {
        return pBytesRead;
    }
    public void setpBytesRead(long pBytesRead) {
        this.pBytesRead = pBytesRead;
    }
    public long getpContentLength() {
        return pContentLength;
    }
    public void setpContentLength(long pContentLength) {
        this.pContentLength = pContentLength;
    }
    public int getpItems() {
        return pItems;
    }
    public void setpItems(int pItems) {
        this.pItems = pItems;
    }
    @Override
    public String toString() {
        return "ProgressEntity [pBytesRead=" + pBytesRead + ", pContentLength="
                + pContentLength + ", pItems=" + pItems + "]";
    }
}

⑤Action中的方法,上传方法任然不用变，还是原来的Spring上传方法，只需修改XML中的上传解析器.改成前面自定义的即可，增加一个获取上传进度的方法。SuccessBean是封装了返回前台的信息：包含success和msg两个字段。

@ResponseBody
    @RequestMapping(value = "/getProgress", method = RequestMethod.GET)
    public SuccessBean getProgress(HttpServletRequest request, HttpServletResponse response){
        if(request.getSession().getAttribute("upload_ps")==null){
             return new SuccessBean(true,"0");
        }
        ProgressEntity ps = (ProgressEntity)request.getSession().getAttribute("upload_ps");
        Double percent = 0d;
        if(ps.getpContentLength() != 0L){
            percent = (double)ps.getpBytesRead()/(double)ps.getpContentLength()*1.0d;  //百分比
            if(percent != 0d){
                DecimalFormat df = new DecimalFormat("0.00");
                percent = Double.parseDouble(df.format(percent));
            }
        }
       logger.info("当前上传进度:" + percent.toString());
       return new SuccessBean(true, percent.toString());
    }

 ⑥前台就更简单了，只需一个FormPanel添加一个filefield组件,在表单提交后同时启动定时任务，每隔1秒从后台获取一下进度显示出来即可。