关于添加菜品会重复添加的问题

package foodServlet;

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;

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.FileItem;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;

import utils.FoodDaoImpl;
import utils.UploadUtils;

/*
 * 菜品添加的servlet
 */
@WebServlet("/FoodAddServlet")
public class FoodAddServlet extends HttpServlet {

 protected void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  Map map;
  try {
   map = UploadUtils.UploadFile(request, "/upload");
   // 判断菜品ID是否存在
   for (Map<String, Object> food : FoodDaoImpl.getDb()) {
    if (food.get("id").equals(map.get("id"))) {
     request.setAttribute("msg", "该菜品已经存在，请重新添加");
     request.getRequestDispatcher("/myFile.jsp/addFood.jsp").forward(request, response);

    }

   }
   FoodDaoImpl.addFood(map);
  } catch (FileUploadException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  }

  // 添加成功，跳转到展示页面
  response.sendRedirect(request.getContextPath() + "/myFile.jsp/showFoodList.jsp");
 }

 protected void doPost(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {

  doGet(request, response);
 }

}