实现同样的功能，地址栏路径不同，出现报错

---------------核心控制器----------------------

package com.imooc.hospital.global;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import javax.servlet.GenericServlet;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

public class DispatcherServlet extends GenericServlet {
    private ApplicationContext context;

    public void init() throws ServletException {
        super.init();
        context=new ClassPathXmlApplicationContext("spring.xml");
    }

    public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {
        HttpServletRequest request= (HttpServletRequest) servletRequest;
        HttpServletResponse response= (HttpServletResponse) servletResponse;

        String beanName=null;
        String methodName=null;

        String path=request.getServletPath().substring(1);
        Integer index=path.indexOf("/");

        if (path.indexOf("/")!=-1){
            beanName=path.substring(0,index)+"Controller";
            methodName=path.substring(index+1,path.indexOf(".do"));
        }else {
            beanName="selfController";
            methodName=path.substring(0,path.indexOf(".do"));
        }

        System.out.println(beanName+":"+methodName);

        Object object=context.getBean(beanName);
        try {
            Method method=object.getClass().getMethod(methodName,HttpServletRequest.class,HttpServletResponse.class);
            method.invoke(object,request,response);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

---------------------------Controller------------------------

package com.imooc.hospital.controller;

import com.imooc.hospital.entity.Category;
import com.imooc.hospital.entity.Department;
import com.imooc.hospital.service.CategoryService;
import com.imooc.hospital.service.DepartmentService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.List;

@Controller("selfController")
public class SelfController {
    @Autowired
    private CategoryService categoryService;

    @Autowired
    private DepartmentService departmentService;

    public void index(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        List<Category> categories=categoryService.getAll();
        List<Department> departments=departmentService.getAll();
        request.setAttribute("CATS",categories);
        request.setAttribute("DEPS",departments);
        request.getRequestDispatcher("../index.jsp").forward(request,response);
    }

}

地址栏输入：http://localhost:8080/front/self/index.do，正常实现功能

地址栏输入地址：http://localhost:8080/front/index.do，无法实现功能，并报错

请老师看看，这是什么原因？按照核心控制器的逻辑，应该两种方式都是可以实现功能的