③、ProcityController
前端介绍完了，我们回到后端进行介绍，当然了，你也可以忽略本节，因为不是所用的关联数据都通过springMVC这种方法获取，那么先预览一下代码吧！
package com.honzh.spring.controller; import java.util.ArrayList; import java.util.List; import javax.servlet.http.HttpServletResponse; import org.apache.log4j.Logger; import org.springframework.stereotype.Controller; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.bind.annotation.RequestParam; import com.honzh.biz.database.entity.City; import com.honzh.biz.database.entity.Option; import com.honzh.biz.database.entity.Provincial; import com.honzh.common.util.JsonUtil; import com.honzh.spring.service.CityService; import com.honzh.spring.service.ProvincialService; @Controller @RequestMapping(value = "/procity") public class ProcityController extends BaseController { private static Logger logger = Logger.getLogger(ProcityController.class); /** * 当传递city_code，则表明下拉框要被选中，否则不选中 */ @RequestMapping("") public void index(@RequestParam(value = "city_code", required = false) String city_code, @RequestParam(value = "pro_code", required = false) String pro_code, HttpServletResponse response) { try { logger.debug("获取所在地区" + city_code + ", 省" + pro_code); // 如果pro_code为””，则表明要获取城市菜单，否则获取市级菜单 if (!pro_code.equals("")) { Integer pro_id = ProvincialService.getInstance().getByProvincialcode(pro_code).getId(); List<City> citys = CityService.getInstance().getCitysByProvincialId(pro_id); List<Option> coptions = new ArrayList<Option>(citys.size()); for (City city : citys) { Option coption = new Option(); coption.setId(city.getId()); coption.setName(city.getCname()); coption.setValue(city.getCode()); // 市级菜单被选中 if (city_code != null && !city_code.equals("")) { if (city.getCode().equals(city_code)) { coption.setSelected("selected"); } } coptions.add(coption); } renderJson(response, coptions); } else { List<Provincial> provincials = ProvincialService.getInstance().getProvincials(); // 转换成标准的option属性（name,value,selected） List<Option> options = new ArrayList<Option>(provincials.size()); // 被选中的省市 // 则说明是展示页面，此时需要为省级菜单和市级菜单设置选择项 if (city_code != null && !city_code.equals("")) { Provincial selected_provincial = ProvincialService.getInstance().getProvincialByCitycode(city_code); pro_code = selected_provincial.getProcode(); } else { pro_code = provincials.get(0) == null ? "" : provincials.get(0).getProcode(); } for (Provincial provincial : provincials) { Option option = new Option(); option.setId(provincial.getId()); option.setName(provincial.getProname()); option.setValue(provincial.getProcode()); if (!pro_code.equals("") && provincial.getProcode().equals(pro_code)) { option.setSelected("selected"); } options.add(option); } renderJson(response, JsonUtil.toJson(options)); } } catch (Exception e) { logger.error(e.getMessage()); logger.error(e.getMessage(), e); renderJson(response, null); } } }
@RequestParam(value = "city_code", required = false) String city_code，对于RequestParam注解，其实非常好用，这里就不多做解释，只是推广一下，固定个数的参数，用该注解更易于代码的维护。
ProvincialService类、CityService类就是两个单例，尽量把数据放置在内存当中，减少查询数据库的次数，稍候贴出来一个例子。
Option类就是单纯的封装前端option组件的关键属性，便于组件的通用化。
renderJson(response, JsonUtil.toJson(options));将数据json化后返回，稍候贴上详细代码。
④、ProvincialService.java
只贴出来代码例子，不做详细解释，毕竟不是本章重点。
package com.honzh.spring.service; import java.util.ArrayList; import java.util.List; import com.honzh.biz.database.entity.City; import com.honzh.biz.database.entity.Provincial; import com.honzh.biz.database.mapper.ProvincialMapper; import com.honzh.common.spring.SpringContextHolder; public class ProvincialService { private static Object lock = new Object(); private static ProvincialService config = null; private ProvincialService() { provincials = new ArrayList<Provincial>(); ProvincialMapper mapper = SpringContextHolder.getBean(ProvincialMapper.class); provincials.addAll(mapper.getProvincials()); } public static ProvincialService getInstance() { synchronized (lock) { if (null == config) { config = new ProvincialService(); } } return (config); } public Provincial getByProvincialcode(String provincial_code) { for (Provincial provincial : provincials) { if (provincial.getProcode().equals(provincial_code)) { return provincial; } } return null; } private List<Provincial> provincials = null; public List<Provincial> getProvincials() { return provincials; } public Provincial getProvincialByCitycode(String city_code) { City city = CityService.getInstance().getCityByCode(city_code); for (Provincial provincial : provincials) { if (provincial.getId().intValue() == city.getProid().intValue()) { return provincial; } } return null; } public Provincial getProvincialByCode(String province_code) { for (Provincial provincial : provincials) { if (provincial.getProcode().equals(province_code)) { return provincial; } } return null; } }
⑤、renderJson方法
/** * 如果出错的话，response直接返回404 */ protected void renderJson(HttpServletResponse response, Object responseObject) { PrintWriter out = null; try { if (responseObject == null) { response.sendError(404); return; } // 将实体对象转换为JSON Object转换 String responseStr = JsonUtil.toJson(responseObject); response.setCharacterEncoding("UTF-8"); response.setContentType("application/json; charset=utf-8"); out = response.getWriter(); out.append(responseStr); logger.debug("返回是：" + responseStr); } catch (IOException e) { logger.error(e.getMessage()); logger.error(e.getMessage(), e); } finally { if (out != null) { out.close(); } } }
