Java WebAPI如何实现文件上传下载

Java WebAPI可以通过使用Servlet来实现文件上传下载。以下是一个简单的示例：

@WebServlet("/upload")@MultipartConfigpublic class FileUploadServlet extends HttpServlet {    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        Part filePart = request.getPart("file");        String fileName = filePart.getSubmittedFileName();        InputStream fileContent = filePart.getInputStream();                // 保存文件到指定目录        File file = new File("C:/upload/" + fileName);        try (OutputStream out = new FileOutputStream(file)) {            IOUtils.copy(fileContent, out);        } catch (IOException e) {            e.printStackTrace();        }                response.getWriter().println("文件上传成功");    }}

@WebServlet("/download")public class FileDownloadServlet extends HttpServlet {    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        String fileName = "example.txt";        File file = new File("C:/upload/" + fileName);                response.setContentType("application/octet-stream");        response.setHeader("Content-Disposition", "attachment; filename=\"" + fileName + "\"");                try (InputStream in = new FileInputStream(file);             OutputStream out = response.getOutputStream()) {            IOUtils.copy(in, out);        } catch (FileNotFoundException e) {            e.printStackTrace();        }    }}

在以上示例中，通过MultipartConfig注解标记文件上传Servlet，并使用Part对象获取上传的文件，然后将文件保存到指定目录。在文件下载Servlet中，设置响应的Content-Type和Content-Disposition头，然后将文件内容写入到输出流中实现文件下载。