Java中上传文件的进度显示如何实现 - 问答

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。

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