In this example, we will discuss how to use @MultipartConfig annotation to handle file upload through a servlet.

The @MultipartConfig annotation, when specified on a Servlet, indicates that the request it expects is of type multipart/form-data. The HttpServletRequest object of the corresponding servlet must make available the MIME attachments via the getParts and getPart methods to iterate over the various MIME attachments.

The @MultipartConfig annotation attributes

The below diagram shows that class diagram of @MultipartConfig annotation:

The @MultipartConfig annotation supports the following optional attributes:

fileSizeThreshold: We can specify the size threshold after which the file will be written to disk. The size value is in bytes, so 1024*1024*10 is 10 MB.
location: Directory where files will be stored by default, it’s default value is “”.
maxFileSize: Maximum size allowed to upload a file, it’s value is provided in bytes. Its default value is -1L means unlimited.
maxRequestSize: Maximum size allowed for multipart/form-data request. The default value is -1L that means unlimited.

@MultipartConfig annotation example

The following example illustrates how to configure a servlet to handle file upload using @MultipartConfig annotation:

import java.io.File;
import java.io.IOException;
 
import javax.servlet.ServletException;
import javax.servlet.annotation.MultipartConfig;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.Part;
 
@WebServlet("/FileUploadServlet")
@MultipartConfig(fileSizeThreshold=1024*1024*10,  // 10 MB 
                 maxFileSize=1024*1024*50,       // 50 MB
                 maxRequestSize=1024*1024*100)    // 100 MB
public class FileUploadServlet extends HttpServlet {
 
    private static final long serialVersionUID = 205242440643911308L;
 
    /**
     * Directory where uploaded files will be saved, its relative to
     * the web application directory.
     */
    private static final String UPLOAD_DIR = "uploads";
     
    protected void doPost(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        // gets absolute path of the web application
        String applicationPath = request.getServletContext().getRealPath("");
        // constructs path of the directory to save uploaded file
        String uploadFilePath = applicationPath + File.separator + UPLOAD_DIR;
         
        // creates the save directory if it does not exists
        File fileSaveDir = new File(uploadFilePath);
        if (!fileSaveDir.exists()) {
            fileSaveDir.mkdirs();
        }
        System.out.println("Upload File Directory="+fileSaveDir.getAbsolutePath());
        
        String fileName = null;
        //Get all the parts from request and write it to the file on server
        for (Part part : request.getParts()) {
            fileName = getFileName(part);
            part.write(uploadFilePath + File.separator + fileName);
        }
 
        request.setAttribute("message", fileName + " File uploaded successfully!");
        getServletContext().getRequestDispatcher("/response.jsp").forward(
                request, response);
    }
 
    /**
     * Utility method to get file name from HTTP header content-disposition
     */
    private String getFileName(Part part) {
        String contentDisp = part.getHeader("content-disposition");
        System.out.println("content-disposition header= "+contentDisp);
        String[] tokens = contentDisp.split(";");
        for (String token : tokens) {
            if (token.trim().startsWith("filename")) {
                return token.substring(token.indexOf("=") + 2, token.length()-1);
            }
        }
        return "";
    }
}

Note: Instead of using the @MultipartConfig annotation to hard-code these attributes in your file upload servlet, you could add the following as a child element of the servlet configuration element in the web.xml file.

<multipart-config>
    <location>/tmp</location>
    <max-file-size>20848820</max-file-size>
    <max-request-size>418018841</max-request-size>
    <file-size-threshold>1048576</file-size-threshold>
</multipart-config>