使用javax.servlet.http.Part类上传文件

使用的是Servlet 3.0 新的特征标注（Annotaion）类描述部署，一些低版本的服务器需要使用标准依赖部署描述文件（web.xml）来部署，另外Part也是Java EE 6.0新增的类，Part是一个接口继承于javax.servlet.http，代表一部分表单项目接收来自multipart/form-data的POST的请求。

!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
    <head>
        <title>上传文件</title>

    </head>
    <body>
        <div class="container">
            <form action="upload.do" method="post" enctype="multipart/form-data">
                <table>
                    <tr>
                        <td><label for="file">上传文件：</label></td>
                        <td><input type="file" id="file" name="picture" value=""/></td>
                    </tr>
                    <tr>
                        <td colspan="2"><input type="submit" value="提交"/></td>
                    </tr>
                </table>
            </form>
        </div>
    </body>
</html>

@MultipartConfig
@WebServlet(name = "UploadServlet", urlPatterns = {"/upload.do"})
public class UploadServlet extends HttpServlet {
 
    private String contextPath;
 
    @Override
    public void init() throws ServletException {
        contextPath = getServletContext().getRealPath("/");
    }
 
    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        request.setCharacterEncoding("utf-8");
        Part part = request.getPart("picture");
        String fileName = getFileName(part);
        writeTo(fileName, part);
 
        //forward到显示
        request.setAttribute("fileName", fileName);
        request.getRequestDispatcher("show.jsp").forward(request, response);
    }
 
    //取得上传文件名
    private String getFileName(Part part) {
        String header = part.getHeader("Content-Disposition");
        String fileName = header.substring(header.indexOf("filename="") + 10,
                header.lastIndexOf("""));
        return fileName;
    }
 
    //存储文件
    private void writeTo(String fileName, Part part) throws IOException, FileNotFoundException {
        InputStream in = part.getInputStream();
        OutputStream out = new FileOutputStream(contextPath + fileName);
        byte[] buffer = new byte[1024];
        int length = -1;
        while ((length = in.read(buffer)) != -1) {
            out.write(buffer, 0, length);
        }
        in.close();
        out.close();
    }
}

<!DOCTYPE html>
<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
        <title>JSP Page</title>
    </head>
    <body>
        <h1>图片显示</h1>
        <a href="${fileName}">${fileName}</a>
    </body>
</html>