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在Java中，我们可以使用Servlet和Apache Commons FileUpload库来实现文件上传和进度显示。以下是一个简单的示例：
- 首先，添加Apache Commons FileUpload依赖到你的项目。如果你使用Maven，可以在pom.xml文件中添加以下依赖：
<groupId>commons-fileupload</groupId> <artifactId>commons-fileupload</artifactId> <version>1.4</version> </dependency> - 创建一个Servlet来处理文件上传请求。在这个例子中，我们将创建一个名为
FileUploadServlet的类：
import java.io.IOException; import java.io.InputStream; import java.io.OutputStream; import java.nio.file.Files; import java.nio.file.Paths; 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.FileItemIterator; import org.apache.commons.fileupload.FileItemStream; import org.apache.commons.fileupload.servlet.ServletFileUpload; @WebServlet("/FileUploadServlet") public class FileUploadServlet extends HttpServlet { private static final long serialVersionUID = 1L; protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { if (ServletFileUpload.isMultipartContent(request)) { try { ServletFileUpload upload = new ServletFileUpload(); FileItemIterator iterator = upload.getItemIterator(request); while (iterator.hasNext()) { FileItemStream item = iterator.next(); if (!item.isFormField()) { String fileName = item.getName(); InputStream inputStream = item.openStream(); OutputStream outputStream = Files.newOutputStream(Paths.get("uploads/" + fileName)); byte[] buffer = new byte[1024]; int bytesRead; long totalBytesRead = 0; long fileSize = item.getSize(); while ((bytesRead = inputStream.read(buffer)) != -1) { outputStream.write(buffer, 0, bytesRead); totalBytesRead += bytesRead; // 计算并显示上传进度 int progress = (int) ((totalBytesRead / (float) fileSize) * 100); System.out.println("Upload progress: " + progress + "%"); } inputStream.close(); outputStream.close(); } } } catch (Exception e) { throw new ServletException("Error uploading file", e); } } } } - 在HTML页面中创建一个表单，用于选择要上传的文件：
<!DOCTYPE html> <html> <head> <meta charset="UTF-8"> <title>File Upload</title> </head> <body> <form action="FileUploadServlet" method="post" enctype="multipart/form-data"> <input type="file" name="file" /> <input type="submit" value="Upload" /> </form> </body> </html> 现在，当你运行这个应用并尝试上传一个文件时，控制台将显示文件上传的进度。请注意，这个示例仅在控制台显示上传进度，实际应用中你可能需要将进度信息发送到客户端以在网页上显示。要实现这一点，你可以使用WebSockets或其他技术（如AJAX）来实时更新客户端的进度条。
