File upload and download

1, File upload

Dependent jar packages:

comments-fileupload.jar comments-io.jar

1. Form attribute enctype = "multipart / form data" method = "post";

2. Request code and response code settings;

3. 3 steps to parse request object

Create factory class: FileItemFactory factory=DisFileItemFactory();

Create parser: servletfileupload = new servletfileupload (factory);

Use the parser to parse the request object: List < fileitem > items = upload parseRequest(request);

4. Restriction element (before parser parsing)

①upload.setFileSizeMax(1024*n); Limit the size of all file uploads

②upload.setSizeMax(1024*n); Limit the size of a single file upload

③upload.setHeaderEncoding("utf-8"); Set the uploaded Chinese format

5. FileItem object related methods

①String itemName = item.getFieldName() ； Gets the name value of the form item

②boolean isFormField() ； Judge whether it is an ordinary form field (true/false) -- that is, the difference between ordinary fields such as text and file

③ String getString("code setting"); Get field content, normal field -- value value file field -- file content

④ String getContextType(): gets the upload file type text/image. If it is a normal field, null will be returned. You can also limit the upload file type through the suffix in the file name string;

⑥ long getSize(1024*n): get the field content size, in byte s

⑦ InputStream getInputStream(): get the input stream of the file content. If it is a normal field, return the input value of value

6. Get form data (text, file...)

① Define receive variables

② Iterator / for loop variable item value

Items usage: items Next() returns boolean

whie(items.next()){

    FileItem item = items.next();
    String itemName = item.getFieldName();// Get name
    var var = -1/null/...
    if(item.isFormField()){
if(equals name){
            var = item.getString("utf-8");// Accept value matching name
        }else if(...){
            ...
        }eles{
Other fields
        }
    }else{
        String fileName = item.getName(); Get file name
File related operations
    }
}

7. File related operations

(1) Get path string
①String path = "xxxx"; / / specify the path statically
②String path = request.getSession().getServletContext().getRealPath("upload") / / dynamically obtain the project path under tomcat
③ File dir = new File("path + project name (" d:/upload ")")// Create your own directory
if(!dir.exists()){
dir.mkdirs(); // Create if not present
}
(2) Get file name (including suffix)
String fileName = item.getName();
Handle the overwriting problem caused by file name duplication - UUID class
UUID uuid = UUID.randomUUID();
String uuidName = uuid.toString()+fileName.substring(fileName.lastIndexOf("."));
③ How to store files (path location and file name)
File file = new file path: path/dir file name: fileName/uuidName;
④ File upload (item is actually the file content obtained)
item.write(file);

Simple example:

<form action="uploadServlet" enctype="multipart/form-data" method="post">
		Document number:<input type="text" name="fno"/>
		file:<input type="file" name="file"/>
</form>

    //Set encoding format        
    request.setCharacterEncoding("utf-8");
    response.setCharacterEncoding("utf-8");
    response.setContentType("text/html; charset=UTF-8");

	Iterator<FileItem> iter = items.iterator();// List elements via iterators
				while (iter.hasNext()) {
					FileItem item = iter.next();
					if (item.isFormField()) {
						// type = form attribute
						String itemName = item.getFieldName();
						String fno = "";
						if (itemName.equals("fno")) {
							fno = item.getString();//Get the attribute value with name fno
							System.out.println("fno Attribute value:" + fno);
						} else {
							System.out.println("Other attribute fields...");
						}

					} else {
						// type=file
						System.out.println("xxx");
						String fileName = item.getName();// Get file name
						File dir = new File("D:/testDir");// File storage directory, create if none
						if (!(dir.exists())) {
							dir.mkdirs();
						}
						File file = new File(dir, fileName);
						item.write(file);

					}

				}
			} catch (FileUploadException e) {
				e.printStackTrace();
			} catch (Exception e) {
				e.printStackTrace();
			}
		} else {
			// Not a file form
			System.out.println("Non file form...");
		}

2, File download

Dependent jar package: None

1. Download the file through < a href = "" > < / a > or form form - get the download file name

	<form action="downloadServlet" method="post">
		file name:<input type="text" name="fname"/><br>
		<input type="submit" value="download"/><br>
	</form>
	<a href="downloadServlet?fname=1234.docx">The download file name is 1234.docx File</a>

2. Configure the response header in the downloadServlet

response.addHeader("content-Type", "application/octet-stream");
response.addHeader("content-Disposition", "attachment;filename=" + fname);

Garbled file names downloaded by different browsers:

However, I tested it, even if it is set to urlencoder Encode (fname, "UTF-8"), and it will not be garbled when downloaded on Firefox.

String agent = request.getHeader("User-Agent");
		if (agent.toLowerCase().indexOf("firefox") != -1) {
			System.out.println("Firefox settings");
			response.addHeader("content-Disposition", "attachment;filename==?UTF-8?B?"
					+ new String(Base64.encodeBase64(fname.getBytes("utf-8")) + "?="));
		} else {
			System.out.println("Non Firefox settings:" + agent);
			response.addHeader("content-Disposition", "attachment;filename=" + URLEncoder.encode(fname, "utf-8"));
		}

3. Gets the path to the downloaded file

String path = "D:/testDir/" + fname;

4. Convert files to input / output streams through IO operations

    InputStream in = new FileInputStream(path);//Convert the corresponding directory file into an input stream
/*
  * The file is in the project directory
  *  InputStream in = getServletContext().getResourceAsStream("/ServletDir/" + fname);   
*/
  
	ServletOutputStream out = response.getOutputStream();
		byte[] chs = new byte[100];
		int len = -1;
		while ((len = in.read(chs)) != -1) {
			out.write(chs, 0, len);
		}

    //Close flow
		out.close();
		in.close();