通过映射方式，继承BaseServlet来继承HttpServlet并完成方法分发

package cn.itcast.travel.web.servlet;

import com.fasterxml.jackson.databind.ObjectMapper;

import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.annotation.*;
import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;


public class BaseServlet extends HttpServlet {
    private  ObjectMapper mapper = new ObjectMapper();
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //完成方法分发
        //1.获取请求路径
        String uri = req.getRequestURI();
        System.out.println("请求uri:"+uri);//  /travel/user/add
        //2.获取方法名称
        String methodName = uri.substring(uri.lastIndexOf("/") + 1);
        System.out.println("方法名称："+methodName);
        //3.获取方法对象Method
        //谁调用我？我代表谁
        System.out.println(this);//UserServlet的对象cn.itcast.travel.web.servlet.UserServlet@4903d97e
        try {
            //忽略修饰符获取
            //getDeclaredMethod
            Method method = this.getClass().getMethod(methodName, HttpServletRequest.class, HttpServletResponse.class);
            //4.执行方法
            //暴力反射
            //method.setAccessible(true);
            method.invoke(this,req,resp);
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        }
    }

    /**
     * 直接将传入的对象序列化为json，并且写回客户端
     * @param obj
     * @param response
     * @throws IOException
     */
    public void writeValue(Object obj,HttpServletResponse response) throws IOException {
        response.setContentType("application/json;charset=UTF-8");
        mapper.writeValue(response.getOutputStream(),obj);
    }
    public String writeValue(Object obj) throws IOException {
       return mapper.writeValueAsString(obj);
    }
        //声明UserServlet业务方法
    //对象序列化为json 并写回客户端
    public void jsonWrite(HttpServletRequest request,HttpServletResponse response ,Object info) throws IOException {
        //将info对象序列化为json

        String json = mapper.writeValueAsString(info);

        //将json数据写回客户端
//        设置content-type
        response.setContentType("application/json;charset=utf-8");
//        response.getWriter().write(json);
        response.getOutputStream().write(json.getBytes());

    }
    //三元运算
    public int triadic(String num,int noNum){
        return num != null && num.length() >0 ? Integer.parseInt(num) :noNum;
    };
}