2.15. Servlet file upload

发布时间 ： 2025-10-25 13:33:41 UTC      

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Servlet can be used with the HTML form tag to allow users to upload files tothe server. The uploaded file can be a text file or an image file or any document.

The files used in this article are:

  • upload.jsp : File upload form

  • message.jsp : Jump to the page after the upload is successful

  • UploadServlet.java : Upload processing Servlet.

  • The jar file that needs to be introduced: commons-fileupload-1.3.2、commons-io-2.5.jar .

The structure diagram is as follows:

Image0

Note: Servlet3.0 has built-in file upload feature, so developers no longer need to import Commons FileUpload components into the project.

Next, we will introduce it in detail.

2.15.1. Create a file upload form

The following HTML code creates a file upload form. The following points need to be noted:

  • Form method property should be set to the POST method and cannot use the GET method.

  • Form enctype property should be set to multipart/form-data .

  • Form action property should be set to handle Servlet files uploaded by files on the back-end server. The following example uses UploadServlet Servlet to upload files.

  • To upload a single file, you should use a single < input… / > tag with theattribute type= “file”. To allow multiple file uploads, include multiple name tags with different input attribute values. Enter a value for the labelwith a different name attribute. The browser associates a browse button foreach input tag.

upload.jsp : The file code is as follows:

<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>     File Upload Example - Rookie Tutorial   
File Upload Example - Rookie Tutorial
 
 Select a file:

2.15.2. Write background Servlet

The following is the source code of UploadServlet, which is the same as dealing with file upload. Before that, let’s make sure that the dependency package has been introduced into the project’s WEB-INF/lib directory:

You can download the two dependency packages provided by this site directly:

The UploadServlet source code is as follows:

package com.runoob.test; import java.io.File; import java.io.IOException; import java.io.PrintWriter; import java.util.List; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import org.apache.commons.fileupload.FileItem; import org.apache.commons.fileupload.disk.DiskFileItemFactory; import org.apache.commons.fileupload.servlet.ServletFileUpload; /** * Servlet implementation class UploadServlet */ @WebServlet("/UploadServlet") public class UploadServlet extends HttpServlet { private static final long serialVersionUID = 1L; // Upload file storage directory private static final String UPLOAD_DIRECTORY = "upload"; // Upload Configuration private static final int MEMORY_THRESHOLD = 1024 * 1024 * 3; // 3MB private static final int MAX_FILE_SIZE = 1024 * 1024 * 40; // 40MB private static final int MAX_REQUEST_SIZE = 1024 * 1024 * 50; // 50MB /** * Upload data and save files */ protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // Check if it is a multimedia upload if (!ServletFileUpload.isMultipartContent(request)) { // If not, stop PrintWriter writer = response.getWriter(); writer.println("Error: The form must contain enctype=multipart/form-data"); writer.flush(); return; } // Configure upload parameters DiskFileItemFactory factory = new DiskFileItemFactory(); // Set memory threshold - if exceeded, temporary files will be generated and stored in the temporary directory factory.setSizeThreshold(MEMORY_THRESHOLD); // Set temporary storage directory factory.setRepository(new File(System.getProperty("java.io.tmpdir"))); ServletFileUpload upload = new ServletFileUpload(factory); // Set maximum file upload value upload.setFileSizeMax(MAX_FILE_SIZE); // Set maximum request value (including file and form data) upload.setSizeMax(MAX_REQUEST_SIZE); // Chinese Processing upload.setHeaderEncoding("UTF-8"); // Construct a temporary path to store uploaded files // This path is relative to the directory of the current application String uploadPath = request.getServletContext().getRealPath("./") + File.separator + UPLOAD_DIRECTORY; // If the directory does not exist, create it File uploadDir = new File(uploadPath); if (!uploadDir.exists()) { uploadDir.mkdir(); } try { // Parse the requested content and extract file data @SuppressWarnings("unchecked") List formItems = upload.parseRequest(request); if (formItems != null && formItems.size() > 0) { // Iteration represents single data for (FileItem item : formItems) { // Process 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); // Output file upload path in the console System.out.println(filePath); // Save files to hard drive item.write(storeFile); request.setAttribute("message", "File upload successful!"); } } } } catch (Exception ex) { request.setAttribute("message", "error message: " + ex.getMessage()); } // Jump to message.jsp request.getServletContext().getRequestDispatcher("/message.jsp").forward( request, response); } }    
 The   message.jsp   file code is as follows: 
 
 
 
<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>     File upload results   
 
${message}
 
   
 
 
  
 
  2.15.3.  Compile and run Servlet  
 
 Compile the Servlet UploadServlet above, and in the   web.xml   create the required entries in the file, as follows: 
 
 
 
   UploadServlet UploadServlet com.runoob.test.UploadServlet   UploadServlet /TomcatTest/UploadServlet   
 
 
 
 Now try uploading the file using the HTML form you created above. When you visit:  http://localhost:8080/TomcatTest/upload.jsp  in the browser, the demonstration is as follows: 
 
 Image1 
 
  
                
                

                    

                        

                            
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                            2.15. Servlet file upload 
                        

                    

                

            
        
        

            

    
        
        

            

                

                    
                        
                            
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