如何使用 multipart/form-data 在服务器中上传文件？

Question

我在 jsp 中编写了一个程序，用于将文件上传到在 webcontent 中创建的名为 images 的文件夹中，但我的文件没有上传。请需要一些帮助。

<form action="upload_images_result.jsp" method="post">
    <div align="left">
        Select a file: <input type="file" name="file" size="50"
            enctype="multipart/form-data" placeholder="Upload Your Image" />
    </div>
    <br>
    <div>
        <input type="submit" value="Upload File" />
    </div>
</form>

upload_images_result.jsp

<%
File file;
int maxFileSize = 5000 * 1024;
int maxMemSize = 5000 * 1024;
//ServletContext context = pageContext.getServletContext();
String filePath = "D:\Students_Server\WebContent\Images";
// Verify the content type
String contentType = request.getContentType();
if ((contentType.indexOf("multipart/form-data") >= 0)) {

    DiskFileItemFactory factory = new DiskFileItemFactory();
    // maximum size that will be stored in memory
    factory.setSizeThreshold(maxMemSize);
    // Location to save data that is larger than maxMemSize.
    factory.setRepository(new File(               
    filePath "));
    // Create a new file upload handler
    ServletFileUpload upload = new ServletFileUpload(factory);
    // maximum file size to be uploaded.
    upload.setSizeMax(maxFileSize);
    try {
        // Parse the request to get file items.
        List fileItems = upload.parseRequest(request);
        // Process the uploaded file items
        Iterator i = fileItems.iterator();

        out.println("<html>");
        out.println("<head>");
        out.println("<title>JSP File upload</title>");
        out.println("</head>");
        out.println("<body>");
        while (i.hasNext()) {
            FileItem fi = (FileItem) i.next();
            if (!fi.isFormField()) {
                // Get the uploaded file parameters
                String fieldName = fi.getFieldName();
                String fileName = fi.getName();
                boolean isInMemory = fi.isInMemory();
                long sizeInBytes = fi.getSize();
                // Write the file
                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>");
        out.println("</html>");
    } catch (Exception ex) {
        System.out.println(ex);
    }
} else {
    out.println("<html>");
    out.println("<head>");
    out.println("<title>Servlet upload</title>");
    out.println("</head>");
    out.println("<body>");
    out.println("<p>No file uploaded</p>");
    out.println("</body>");
    out.println("</html>");
}
%>

输出打印为未上传文件

谢谢

Answer 1

您在 html 中使用了错误的属性。属性 enctype="multipart/form-data" 仅在标记 form 中使用，如下所示。

<form action="upload_images_result.jsp"
      method="post" 
      enctype="multipart/form-data">
</form>

或者，您可以在 tag input type="submit" 中使用，如下所示。

<form action="upload_images_result.jsp" 
      method="post">
  <input type="submit" 
         formenctype="multipart/form-data" 
         value="Submit as Multipart/form-data"/>
</form>

Answer 2

当您发出 POST 请求时，您必须以某种方式对构成请求正文的数据进行编码。

HTML表单提供三种编码方式

application/x-www-form-urlencoded（默认）
multipart/form-data
text/plain

当您的表单包含任何 <input type="file"> 元素时使用 enctype=multipart/form-data。

所以使用

<form action="upload_images_result.jsp" method="post" enctype="multipart/form-data">
    <div align="left">
        Select a file: <input type="file" name="file" size="50"
            enctype="multipart/form-data" placeholder="Upload Your Image" />
    </div>
    <br>
    <div>
        <input type="submit" value="Upload File" />
    </div>
</form>

如何使用 multipart/form-data 在服务器中上传文件？

how to upload a file in server using multipart/form-data?

java

jsp

image