文件上传（3.0 开始支持 3.0 以前需要第三方架包）

import javax.servlet.ServletException;
import javax.servlet.annotation.MultipartConfig;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.Part;
import java.io.File;
import java.io.IOException;
import java.util.UUID;

@WebServlet(name = "UpLoadServlet" ,value="/upload")
@MultipartConfig     //使用MultipartConfig注解标注改servlet能够接受文件上传的请求
public class UpLoadServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        request.setCharacterEncoding("utf-8");
        response.setCharacterEncoding("utf-8");
        response.setContentType("text/html;charset=utf-8");
//           当添加了注解  是  原来怎么获得  就怎么获得
        String studentName = request.getParameter("studentName");
//         获得 文件对象
        Part part = request.getPart("studentPhoto");
//           获得文件名
        String fileName = part.getSubmittedFileName();
//        截取后缀名
        String ext = fileName.substring(fileName.indexOf("."));
//        获得新的文件名
        String uuid = UUID.randomUUID().toString();
        String newfileName = uuid+ext;
//         获得文件存放的地址
        String path = this.getServletContext().getRealPath("/imgs");
//        判断文件夹 imgs 是否存在
        File file =new File(path);
        if (!(file.exists())){
            file.mkdir();
        }
//        得到保存的文件路径
        String save_path = path +File.separator +  newfileName;
        part.write(save_path);

    }
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }
}