用Struts2实现文件上传时显示进度条功能

最近在做一个资源共享的项目中，采用了Struts2.1.8+Spring2.5.6+hibernate3.32的框架整合方式进行开发。在文件上传这块，因为需要实现文件上传时显示进度条的功能，所以尝试了一下。怕以后忘记，先贴出来分享下。
  
要在上传文件时能显示进度条，首先需要实时的获知web服务端接收了多少字节，以及文件总大小，这里我们在页面上使用AJAX技术每一秒向服务器发送一次请求来获得需要的实时上传信息。但是当我们使用struts2后怎么在服务端获得实时的上传大小呢？这里需要用到commons-fileupload中的progressListener接口,实现这个接口，然后再实现一个自己的解析器，并在解析器中添加自己实现的那个progressListener;然后再替换struts2自带的解析器（struts2自带的解析器类没有添加progressListener），然后就可以了。下面看看主要的代码(技术有限，如有不对之处，望不吝点解):
 
监听器：
import
javax.servlet.http.HttpServletRequest;
import
javax.servlet.http.HttpSession;
import
org.apache.commons.fileupload.ProgressListener;
 
public class
ResourceProgressListener implements ProgressListener {
   
private HttpSession session;
 
    public
ResourceProgressListener(HttpServletRequest request)
{
       session =
request.getSession();
      
ResourceFileUploadStatus newUploadStatus = new
ResourceFileUploadStatus();
      
session.setAttribute("currentUploadStatus",
newUploadStatus);
    }
 
    public
void update(long readedBytes, long totalBytes, int currentItem)
{
       ResourceFileUploadStatus status =
(ResourceFileUploadStatus)
session.getAttribute("currentUploadStatus");
      
status.setReadedBytes(readedBytes);
      
status.setTotalBytes(totalBytes);
      
status.setCurrentItem(currentItem);
   
}
}
上传状态类：
public class ResourceFileUploadStatus
{
    private long readedBytes = 0L;
   
private long totalBytes = 0L;
    private int currentItem =
0;
  
    public long getReadedBytes()
{
       return
readedBytes;
    }
    public void
setReadedBytes(long bytes) {
       readedBytes
= bytes;
    }
    public long
getTotalBytes() {
       return
totalBytes;
    }
    public void
setTotalBytes(long bytes) {
       totalBytes =
bytes;
    }
    public int getCurrentItem()
{
       return
currentItem;
    }
    public void
setCurrentItem(int item) {
       currentItem =
item;
   
}
}
实现自己的解析器类：方法比较简单，找到struts2实现的解析器类，把代码拷贝过来然后添加上监听器即可。这个类代码较多就不整个文件拷了，主要是在parse方法里添加。Parse方法代码如下：红色标注部分即是需要自己添加的progressListener.
public
void parse(HttpServletRequest servletRequest, String
saveDir)
           
throws IOException {
   
System.out.println("执行自定义MultiPartRequest");
       
DiskFileItemFactory fac = new
DiskFileItemFactory();
        // Make
sure that the data is written to
file
       
fac.setSizeThreshold(0);
        if
(saveDir != null)
{
           
fac.setRepository(new
File(saveDir));
       
}
 
        // Parse the
request
        try
{
           
ServletFileUpload upload = new
ServletFileUpload(fac);
           
upload.setSizeMax(maxSize);
         

           
ResourceProgressListener progressListener = new
ResourceProgressListener(servletRequest);//新建一个监听器
           
upload.setProgressListener(progressListener);//添加自己的监听器
          

            List
items =
upload.parseRequest(createRequestContext(servletRequest));
 
           
for (Object item1 : items)
{
               
FileItem item = (FileItem)
item1;
               
if (LOG.isDebugEnabled()) LOG.debug("Found item " +
item.getFieldName());
               
if (item.isFormField())
{
                   
LOG.debug("Item is a normal form
field");
                   
List<String>
values;
                   
if (params.get(item.getFieldName()) != null)
{
                       
values =
params.get(item.getFieldName());
                   
} else
{
                       
values = new
ArrayList<String>();
                   
}
                   
String charset =
servletRequest.getCharacterEncoding();
                   
if (charset != null)
{
                       
values.add(item.getString(charset));
                   
} else
{
                       
values.add(item.getString());
                   
}
                   
params.put(item.getFieldName(),
values);
               
} else
{
                   
LOG.debug("Item is a file
upload");
 
                   
// Skip file uploads that don‘t have a file name - meaning that no file was
selected.
                   
if (item.getName() == null || item.getName().trim().length() < 1)
{
                       
LOG.debug("No file has been uploaded for the field: " +
item.getFieldName());
                       
continue;
                   
}
 
                   
List<FileItem>
values;
                   
if (files.get(item.getFieldName()) != null)
{
                       
values =
files.get(item.getFieldName());
                   
} else
{
                       
values = new
ArrayList<FileItem>();
                   
}
 
                   
values.add(item);
                   
files.put(item.getFieldName(),
values);
               
}
           
}
        } catch (FileUploadException e)
{
           
LOG.warn("Unable to parse request",
e);
           
errors.add(e.getMessage());
       
}
}
 
上面的类建立完成后，还需要做一项工作：在struts.xml中添加如下内容：
<bean
type="org.apache.struts2.dispatcher.multipart.MultiPartRequest"
name="requestParser"
   
class="com.zeige.ResourceMultiPartRequest" scope="default" optional="true"
/>
<constant name="struts.multipart.handler" value="requestParser"
/>
 
下面就可以正常使用了，建立两个action，一个用来接收上传文件，以及对接收的文件作相应处理，处理完成后，在return
SUCCESS之前去除session中currentUploadStatus属性，一个用来为页面读取实时上传进度服务，这个类中只要将session中的currentUploadStatus对象拿出来按照相应格式返回给客户端即可。