In an earlier post, I had written on performing file upload and download using Spring MVC. In that example I used commons-fileupload-1.2.2.jar. This is because Servlets did not have built in support for File upload operation. However Servlets 3.x provides support - as a part of the specs. So no need to include any additional jars. I decided to try an example of the same.
First step was to add an HTML form:
The enctype attribute indicates the encoding used. Its default value is application/x-www-form-urlencoded which is what we use in our simple forms. To process the form I created an upload servlet:
On completion:
The Multipart configuration can also be placed in the XML file - making it easier to increase/decrease
First step was to add an HTML form:
<html> <head></head> <body> <form action="upload.upl" method="post" enctype="multipart/form-data"> Enter Player Name: <input type="text" name="playerName" /> <br /> Select File(s) to Upload: <input type="file" name="file1Name"> <br /> <input type="file" name="file2Name"> <br /> <input type="file" name="file3Name"> <br /> <input type="submit" value="Upload"> </form> </body> </html>The form accepts three files and a text field. The form type is multipart/form-data which indicates a form capable of sending simple data as well as files.
The enctype attribute indicates the encoding used. Its default value is application/x-www-form-urlencoded which is what we use in our simple forms. To process the form I created an upload servlet:
@SuppressWarnings("serial") @WebServlet(displayName = "FileUploadServlet", description = "Servlet for FileUpload Operations", urlPatterns = { "*.upl" }) @MultipartConfig(fileSizeThreshold = 1024 * 1024 * 10, // 10 MB maxFileSize = 1024 * 1024 * 25, // 25 MB maxRequestSize = 1024 * 1024 * 50) // 50 MB public class FileUploadServlet extends HttpServlet {The new annotation introduced here is the MultipartConfig.As described by Java docs:
Annotation that may be specified on a Servlet class, indicating that instances of the Servlet expect requests that conform to the multipart/form-data MIME type.I added the code to process the post request of the form in the doPost method:
/** * Directory where uploaded files will be saved, its relative to the web * application directory. */ private static final File UPLOAD_DIRECTORY = new File("E:\\temp"); protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // Get all the parts from request and write it to the file on server // 1: Return a collection of all uploaded Parts. Collection<Part> allUploadedParts = request.getParts(); int i = 0; for (Part part : allUploadedParts) { // Part: class represents a part as uploaded to the server as part of a // multipart/form-data request body. The part may represent either an // uploaded file or form data. // 2: Retain only file parts and not any form parts // Get name of File String fileName = part.getSubmittedFileName(); if (fileName == null) continue; // 3: Write the file to the disk // convenience method to write an uploaded part to disk. part.write(UPLOAD_DIRECTORY + File.separator + fileName); i++; } String playerName = request.getParameter(""); playerName = playerName != null && !"".equals(playerName.trim()) ? playerName.toUpperCase() : " UNKNOWN "; response.getWriter() .write(playerName + " has " + i + " File(s) uploaded successfully!"); response.getWriter().flush(); }The code can be explained as below:
- The getParts method gets all the Part components of this request, provided that it is of type multipart/form-data. Parts include both files and form inputs.
- The getSubmittedFileName method of Part will be null for file fields.
- The last method I used here is the write method - which will write the file contents to the directory specified as a file.
On completion:
<servlet> <description></description> <display-name>WelcomeServlet</display-name> <servlet-name>WelcomeServlet</servlet-name> <servlet-class>com.servlets.WelcomeServlet</servlet-class> <multipart-config> <location>/tmp</location> <max-file-size>208480</max-file-size> <max-request-size>418841</max-request-size> <file-size-threshold>1066476</file-size-threshold> </multipart-config> </servlet>
great
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