Cách upload file bằng JSP

JSP kết hợp HTML form tag cho phép user upload file lên server. File có thể là text, binary, image hoặc tài liệu bất kỳ.

Tạo Form Upload

Lưu ý quan trọng:

• Form method = POST (không dùng GET).
• Form enctype = multipart/form-data.
• Form action trỏ đến JSP xử lý backend (ví dụ uploadFile.jsp).
• Upload đơn: một <input type="file">. Upload nhiều: nhiều input với name khác nhau.

Ví dụ Form

<html>
  <head> <title>File Uploading Form</title> </head>
  <body>
    <h3>File Upload:</h3>
    Select a file to upload: <br />
    <form action="UploadServlet" method="post" enctype="multipart/form-data">
      <input type="file" name="file" size="50" />
      <br />
      <input type="submit" value="Upload File" />
    </form>
  </body>
</html>

Lưu ý: Form demo, cần triển khai backend để chạy.

JSP Backend (UploadFile.jsp)

Định nghĩa thư mục lưu file. Có thể hard-code hoặc dùng context-param trong web.xml:

<web-app>
  <context-param>
    <description>Location to store uploaded file</description>
    <param-name>file-upload</param-name>
    <param-value>c:\apache-tomcat-5.5.29\webapps\data\</param-value>
  </context-param>
</web-app>

Code UploadFile.jsp (xử lý multiple files):

<%@ page import = "java.io.*,java.util.*, javax.servlet.*" %>
<%@ page import = "javax.servlet.http.*" %>
<%@ page import = "org.apache.commons.fileupload.*" %>
<%@ page import = "org.apache.commons.fileupload.disk.*" %>
<%@ page import = "org.apache.commons.fileupload.servlet.*" %>
<%@ page import = "org.apache.commons.io.output.*" %>
<%
  File file;
  int maxFileSize = 5000 * 1024;
  int maxMemSize = 5000 * 1024;
  ServletContext context = pageContext.getServletContext();
  String filePath = context.getInitParameter("file-upload");
  String contentType = request.getContentType();
  if ((contentType.indexOf("multipart/form-data") >= 0)) {
    DiskFileItemFactory factory = new DiskFileItemFactory();
    factory.setSizeThreshold(maxMemSize);
    factory.setRepository(new File("c:\\temp"));
    ServletFileUpload upload = new ServletFileUpload(factory);
    upload.setSizeMax(maxFileSize);
    try {
      List fileItems = upload.parseRequest(request);
      Iterator i = fileItems.iterator();
      out.println("<html><head><title>JSP File upload</title></head><body>");
      while (i.hasNext()) {
        FileItem fi = (FileItem)i.next();
        if (!fi.isFormField()) {
          String fieldName = fi.getFieldName();
          String fileName = fi.getName();
          boolean isInMemory = fi.isInMemory();
          long sizeInBytes = fi.getSize();
          if (fileName.lastIndexOf("\\") >= 0) {
            file = new File(filePath + fileName.substring(fileName.lastIndexOf("\\")));
          } else {
            file = new File(filePath + fileName.substring(fileName.lastIndexOf("\\")+1));
          }
          fi.write(file);
          out.println("Uploaded Filename: " + filePath + fileName + "<br>");
        }
      }
      out.println("</body></html>");
    } catch(Exception ex) { System.out.println(ex); }
  } else {
    out.println("<html><head><title>Servlet upload</title></head><body><p>No file uploaded</p></body></html>");
  }
%>

Thư viện cần: commons-fileupload.jar, commons-io.jar. Tạo thư mục c:\temp và c:\apache-tomcat5.5.29\webapps\data trước.

File upload thành công lưu tại c:\apache-tomcat5.5.29\webapps\data\.