JSP should pass parameters to the background while realizing the file upload function

solve JSP The problem of transferring parameters to the background while realizing the file upload function

1. Explain the problem

Jsp When uploading files , It can be done with HTML Medium <form> The form is completed . But the form's ENCTYPE="multipart/form-data", This makes the data of the form No coding Submit in the form of raw data stream . So in Servlet in requeset.getParementer("name"); The values for NULL
1. This blog post is right for ENCTYPE All attribute values of are tested
2. Explanation of principle

2. resolvent

Other business logic in my document code More , So here we are For beginners JSP Upload instance give an example .
This is Servlet About uploading the core code ：

  try {
    
            //  Parse the content of the request, extract the file data 
            @SuppressWarnings("unchecked")
            List<FileItem> formItems = upload.parseRequest(request);
 
            if (formItems != null && formItems.size() > 0) {
    
                //  Stack represents single data 
                for (FileItem item : formItems) {
    
                    //  Handle fields that are not in the form 
                    if (!item.isFormField()) {
    
                        String fileName = new File(item.getName()).getName();
                        String filePath = uploadPath + File.separator + fileName;
                        File storeFile = new File(filePath);
                        //  The upload path of the output file in the console 
                        System.out.println(filePath);
                        //  Save the file to the hard disk 
                        item.write(storeFile);
                        request.setAttribute("message",
                            " File upload succeeded !");
                    }
                }
            }
        } catch (Exception ex) {
    
            request.setAttribute("message",
                    " error message : " + ex.getMessage());
        }

The data of the file is not in the fields in the form , Therefore, the data processing of the file is placed in if(!item.isFormField()) The function of , So the way to get text data is to deal with the fields in the form , That is, add in if(!item.isFormField()) Add else sentence

else{
    
	String fieldName = fi.getFieldName();
	String value = fi.getString("UTF-8");//.getString("encType") The solution of garbled code problem 
	System.out.println("filedName:"+fieldName+"\tvalue: "+value);
}

test ：
front end HTML Relevant codes in the document

<form class="form-inline" role="form" method="POST" enctype="MULTIPART/FORM-DATA" action="UploadServlet">
			<!-- Omitted upload code -->
			<div class="form-group">
				<label for""> Please enter the test </label>
				<input type="text" name="olicytexttest" id="olicytexttest">
			</div>
</form>

Console output ：

filedName:olicytexttest	value: sadfasdfdsaf
filedName:policytext	value: sadfsdafsdf

filedeName Get the control's name attribute ,value Get the input in the control

The file data in the data stream is front , Then there is the order of other controls in the form

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besides , There are many other solutions to this problem , I think the solution mentioned in this article is relatively simple and convenient , Many great gods are CSDN Many other methods have been listed .