初学ajax，实现用户名重复提示、二级/三级联动下拉框

初学ajax，实现异步操作！

源代码下载链接：http://download.csdn.net/detail/yan13507001470/9911744

               

以下为三级联动下拉框部分代码

jsp页面部分代码

   			

   				
下拉框:
	   			

				   	
				   		请选择省份
						   
						  		${list.name }
						   
				   	
			   		    
			   		
			   			请选择城市
			   		
			   		    
			   		
			   			请选择县区
			   		
			   		    
		   		
				

	   		
   		

servlet代码

@WebServlet("/ProvinceCityCountyServlet")
public class ProvinceCityCountyServlet extends HttpServlet {
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		request.setCharacterEncoding("utf-8");
		String method = request.getParameter("method");
		
		if(method.equals("ajaxone")){
			
			response.setContentType("text/xml;charset=utf-8");
			String provinceId = request.getParameter("provinceId");
			
			CityService cityService = new CityService();
			List allCities = cityService.findByFKId(Integer.parseInt(provinceId));
			
			PrintWriter pw = response.getWriter();
			pw.write("");
			pw.write("");
			
			for(int i=0;i"+city.getName()+"");
			}
			
			pw.write("");
			pw.flush();
			pw.close();
			
		}else if (method.equals("ajaxtwo")) {
			response.setContentType("text/xml;charset=utf-8");
			String cityId = request.getParameter("cityId");
			
			CountyService countyService = new CountyService();
			List allCounties = countyService.findByFKId(Integer.parseInt(cityId));
			
			PrintWriter pw = response.getWriter();
			pw.write("");
			pw.write("");
			
			for(int i=0;i"+county.getName()+"");
			}
			
			pw.write("");
			pw.flush();
			pw.close();
			
		}else if (method.equals("fromSubmit")) {	//提交获取数据
			
			String countId = request.getParameter("countyId");
			
			CountyService countyService = new CountyService();
			County county = countyService.findById(Integer.parseInt(countId));
			System.out.println("县："+county.getName());
			
			CityService cityService = new CityService();
			City city = cityService.findById(county.getCity_id());
			System.out.println("城市："+city.getName());
			
			ProvinceServince provinceServince = new ProvinceServince();
			Province province = provinceServince.findById(city.getProvince_id());
			System.out.println("省："+province.getName());
			
			System.out.println(province.getName()+"-"+city.getName()+"-"+county.getName());
			
		}else {
			ProvinceServince provinceServince = new ProvinceServince();
			List allProvinces = provinceServince.findAll();
			
			request.setAttribute("allProvinces", allProvinces);
			request.getRequestDispatcher("/Province_city_county.jsp").forward(request, response);
			
		}
		
	}

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

注：有什么写的不对的地方，请提出来，感谢