封装Servlet使用自定义注解进行参数接收

前言

先说项目背景，本项目是本人在校期间老师布置的作业（就一个CRUD），课程是后端应用程序设计，其实就是servlet和jsp那一套，要求使用jsp+servlet完成一个天气查询系统，如果直接使用HttpServlet的话，业务代码中会有大量的if-else,所以本人将servlet进行了再封装，并使用自定义注解接收前端的参数，主要是利用反射去完成的。

一、前后对比

前后对比

封装前

重写doGet和doPost方法，在其中使用action这个参数来完成业务实现的区分。

package com.servlet;
​
import com.entity.WeatherInfo;
import com.service.ManageService;
import com.service.impl.ManageServiceImpl;
​
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 java.io.IOException;
import java.util.Date;
import java.util.HashMap;
import java.util.Map;
​
/**
 * @Author YZK
 * @Date 2023/11/9
 */
@WebServlet(value = "/weather/manage",name = "mangeServlet")
public class MangeServlet extends HttpServlet {
​
    ManageService manageService = new ManageServiceImpl();
​
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("utf-8");
        resp.setContentType("text/html;charset=UTF-8");
        String action = req.getParameter("action");
        //跳转至添加数据界面
        if (action.equals("toAdd")) {
            req.getRequestDispatcher("/addInfo.jsp").forward(req, resp);
            //修改数据并回显当前行数据
        } else if (action.equals("toEdit")) {
            String id = req.getParameter("id");
            try {
                WeatherInfo weatherInfo = manageService.queryWeatherInfoById(id);
                req.getSession().setAttribute("weatherInfo", weatherInfo);
                req.getRequestDispatcher("/editInfo.jsp").forward(req, resp);
            } catch (Exception e) {
                throw new RuntimeException(e);
            }
        }
    }
​
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //todo 封装更新、添加操作
        req.setCharacterEncoding("utf-8");
        resp.setContentType("text/html;charset=UTF-8");
        String action = req.getParameter("action");
        //通过id删除数据
        switch (action) {
            case "delete": {
                String id = req.getParameter("id");
                try {
                    manageService.deleteById(id);
                } catch (Exception e) {
                    throw new RuntimeException(e);
                }
​
                break;
            }
            //添加数据
            case "add": {
                //todo 增加数据校验
                Map<String, String> map = this.encapsulationData(req);
                try {
                    manageService.insertWeatherInfo(map.get("province"), map.get("city"), map.get("weather"), map.get("temperature")
                            , map.get("windDirection"), map.get("windPower"), map.get("humidity"), new Date(),
                            Float.toString(Float.parseFloat(map.get("temperature"))), Float.toString(Float.parseFloat(map.get("humidity"))));
                } catch (Exception e) {
                    throw new RuntimeException(e);
                }
                break;
            }
            //更新数据
            case "update": {
                String id = req.getParameter("id");
                Map<String, String> map = this.encapsulationData(req);
                try {
                    manageService.updateWeatherInfo(id, map.get("province"), map.get("city"), map.get("weather"), map.get("temperature")
                            , map.get("windDirection"), map.get("windPower"), map.get("humidity"), new Date(),
                            Float.toString(Float.parseFloat(map.get("temperature"))), Float.toString(Float.parseFloat(map.get("humidity"))));
                } catch (Exception e) {
                    throw new RuntimeException(e);
                }
                break;
            }
        }
    }
​
    public Map<String, String> encapsulationData(HttpServletRequest req) {
        Map<String, String> map = new HashMap<>();
        map.put("province", req.getParameter("province"));
        map.put("city", req.getParameter("city"));
        map.put("weather", req.getParameter("weather"));
        map.put("temperature", req.getParameter("temperature"));
        map.put("windDirection", req.getParameter("windDirection"));
        map.put("windPower", req.getParameter("windPower"));
        map.put("humidity", req.getParameter("humidity"));
        return map;
    }
}
​

封装后

package com.servlet;
​
import cn.hutool.http.HttpUtil;
import com.annotation.Action;
import com.entity.WeatherInfo;
import com.service.IndexService;
import com.service.impl.IndexServiceImpl;
​
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.util.List;
​
/**
 * @Author YZK
 * @Date 2023/11/9
 */
@WebServlet(value = "/weather/index", name = "indexServlet")
public class IndexServlet extends BaseServlet {
​
    IndexService indexService = new IndexServiceImpl();
​
    @Action(actionName = "queryWeather")
    public void queryWeather(HttpServletRequest req, HttpServletResponse resp) throws Exception {
        List<WeatherInfo> weatherInfoList = indexService.queryWeather();
        req.getSession().setAttribute("weatherInfoList", weatherInfoList);
        req.getRequestDispatcher("/weatherInfo.jsp").forward(req, resp);
    }
​
​
    @Action(actionName = "init")
    public void init(HttpServletRequest req, HttpServletResponse resp) {
        List<WeatherInfo> weatherInfoList = null;
        try {
            weatherInfoList = indexService.queryWeather();
            req.getSession().setAttribute("weatherInfoList", weatherInfoList);
            req.getRequestDispatcher("/init.jsp").forward(req, resp);
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }
​
    @Action(actionName = "toLogin")
    public void toLogin(HttpServletRequest req, HttpServletResponse resp) throws Exception {
        req.getRequestDispatcher("/login.jsp").forward(req, resp);
    }
​
    @Action(actionName = "login")
    public void login(HttpServletRequest req, HttpServletResponse resp) throws Exception {
        String username = req.getParameter("username");
        String password = req.getParameter("password");
        if (username.equals("admin") && password.equals("123")) {
            List<WeatherInfo> weatherInfoList = indexService.queryWeather();
            req.getSession().setAttribute("weatherInfoList", weatherInfoList);
            req.getRequestDispatcher("/weatherInfo.jsp").forward(req, resp);
        } else {
            resp.sendRedirect("/login.jsp");
        }
    }
}
​

将每一个业务行为都抽成了一个方法，前端发起一个带有action的参数，后端使用同样的@Action(actionName="")进行接收，如果相同，则执行该方法。

二、具体实现

在HttpServlet中，service()方法是用来处理客户端请求的主要方法。它接收一个HttpServletRequest对象和一个HttpServletResponse对象作为参数，并根据请求的类型（GET、POST、PUT等）调用对应的doGet()、doPost()、doPut()等方法来处理请求。如果没有覆盖service()方法，它会自动调用doGet()或doPost()方法，具体取决于客户端请求的类型。开发人员可以覆盖service()方法来自定义处理请求的逻辑。

BaseServlet

package com.servlet;
​
import com.annotation.Action;
​
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.lang.reflect.Method;
​
/**
 * @Author YZK
 * @Date 2023/12/2
 * @Desc
 */
public class BaseServlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("utf-8");
        resp.setContentType("text/html;charset=UTF-8");
        String servletName = req.getHttpServletMapping().getServletName();
        String className = req.getServletContext().getServletRegistration(servletName).getClassName();
        //通过全类名获取servlet实例来执行其中的方法
        try {
            Class<?> clazz = Class.forName(className);
            Method[] methods = clazz.getMethods();
            for (Method m : methods) {
                if (m.isAnnotationPresent(Action.class)) {
                    String s = m.getAnnotation(Action.class).actionName();
                    m.setAccessible(true);
                    if (req.getParameter("action").equals(s)) {
                        m.invoke(this, req, resp);
                    }
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
            throw new RuntimeException(e);
        }
    }
}
​

代码步骤解释：

0. 在用户发起请求时，从请求中获取当前请求的servlet的名字，
1. 通过req.getServletContext().getServletRegistration(servletName)获取当前请求的servlet的全类名
2. 通过全类名获取Class对象，再通过getMethods()方法获取该类所有的方法
3. 遍历所有方法，如果带有@Action注解，再判断传入的action参数是否与注解中的actionName参数相同
4. 相同的话就执行该方法（前提是一定要传入req和resp两个参数）

完成以上所有便对servlet进行了简单的封装，这个封装还是很不完善，比如没有判断action为空和同名的情况。

三、效果展示

调用相应接口，返回正常页面