郎寰福地

在开发一个MIS系统中,部分页面中有需要上传文件的字段,相信大家在开发中也经常遇到这样的情况.因为要上传文件，所以FORM标记中的ENCTYPE="multipart/form-data",可是这样的话，当你在servlet里面用request.getParameter()方法无论如何都只是获得null值，没有办法只好在网上搜索一下,其中收集到了不同的方法,贴出来以备查询.
方法一
用jspsmartupload组件实现文件上传的
这个方法是我使用的方法,所以把主要代码贴了出来

SmartUpload upload = new SmartUpload();
     try{
	upload.initialize(config, request, response);
	// 允许上传的文件类型
	upload.setAllowedFilesList("doc,xls,");
	// 拒绝上传的文件类型
	upload.setDeniedFilesList("exe,bat,jsp");
	// 允许上传文件的单个最大大小
	upload.setMaxFileSize(1024 * 1024 * 20);
	// 允许上传文件的最大大小总和
	// upload.setTotalMaxFileSize(1024*1024*10);
	//上传数据
	upload.upload();
	}
	catch (SmartUploadException e){
		e.printStackTrace();
		return;
	}

	Request req = upload.getRequest();
	String spid=(String)req.getParameter("teacherId");
         //.....
         //To do something

这样就可以取得对应的值了.
方法二
这个是在Google中搜索的
I cannot read the submitter using request.getParameter("submitter") (it returns null). ]

Situation:

javax.servlet.HttpServletRequest.getParameter(String) returns null when the ContentType is multipart/form-data

Solutions:

Solution A:

1. download http://www.servlets.com/cos/index.html
2. invoke getParameters() on com.oreilly.servlet.MultipartRequest

Solution B:

1. download http://jakarta.apache.org/commons/sandbox/fileupload/
2. invoke readHeaders() in
org.apache.commons.fileupload.MultipartStream

Solution C:

1. download http://users.boone.net/wbrameld/multipartformdata/
2. invoke getParameter on
com.bigfoot.bugar.servlet.http.MultipartFormData

Solution D:

Use Struts. Struts 1.1 handles this automatically.

Solution B:
1. download > http://jakarta.apache.org/commons/sandbox/fileupload/ 2. invoke readHeaders()
in > org.apache.commons.fileupload.MultipartStream
The Solution B as given by my dear friend is a bit hectic and
a bit complex :
(We can try the following solution which I found much simpler (at least in usage).
1.Download one of the versions of UploadFile from
http://jakarta.apache.org/commons/fileupload/
2. Invoke parseRequest(request)
on org.apache.commons.fileupload.FileUploadBase which returns
list of
org.apache.commons.fileupload.FileItem objects.
3. Invoke isFormField() on each of the FileItem objects.
This determines whether the file item is a form paramater or stream of uploaded file.
4. Invoke getFieldName() to get parameter name and getString() to get parameter value on FileItem if it's a form parameter.
Invoke write(java.io.File) on FileItem to save the uploaded file stream to a file if the FileItem is not a form parameter.
主要是getFieldName和getString，判断加工一下，还是可以获取到的.

方法三
使用jspsmartupload组件的
只需要在servlet中添加

//中文和日文时使用
    request.setCharacterEncoding("UTF-8");    
//***************************************************************
          JspFactory _jspxFactory = null;
          PageContext pageContext = null;
          JspWriter out = null;
             _jspxFactory = JspFactory.getDefaultFactory();
             pageContext = _jspxFactory.getPageContext(this, 
                         request, response,"", true, 8192, true);
             out = pageContext.getOut(); 
    //smartupload   
    SmartUpload su = new SmartUpload();
    su.initialize(pageContext);    
    su.upload();    
    Request requestSu = su.getRequest();

    //getParameter
    //普通的
              int id = Integer.parseInt(
                      requestSu.getParameter("id"));            
            String languages = requestSu.getParameter("languages");
            String flag = requestSu.getParameter("flag");
//*******************************************************
 //中文和日文时使用
     Description = request.getParameter("Description"); 
//******************************************************
另外在jsp中要传中文和日文得使用
    document.form_SuccessfulCase.action=
           "/homepage/SuccessfulCase?title=" + 
           encodeURI(document.form_SuccessfulCase.title.value)+
           "&Description="+
           encodeURI(document.form_SuccessfulCase.Description.value);
//***********************************

boolean isMultipart = ServletFileUpload.isMultipartContent(request);