老师，您好，麻烦您看一下我的代码，哪里有问题？

项目路径：（jsp都是引用老师的，css也是）

1，DAO类

package com.imooc.dao;

import com.imooc.entity.Teacher;
import org.springframework.stereotype.Repository;

import java.util.Collection;
import java.util.HashMap;
import java.util.Map;

@Repository("teacherDao")
public class TeacherDAO {
    private Map<Integer, Teacher> map = new HashMap<>();

    public void add(Teacher teacher) {
        map.put(teacher.getId(), teacher);
    }

    public void edit(Teacher teacher) {
        map.put(teacher.getId(), teacher);
    }

    public void delete(Integer id) {
        map.remove(id);
    }

    public Teacher selectByID(Integer id) {
        return map.get(id);
    }

    public Collection<Teacher> selectAll() {
        return map.values();
    }

}

2，entity类

package com.imooc.entity;

public class Teacher {
    private Integer id;
    //教师编号、姓名、性别、主讲课程以及所属学院五个属性。
    private String name;
    private String sex;
    private String course;
    private String school;

    @Override
    public String toString() {
        return "Teacher{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", sex='" + sex + '\'' +
                ", course='" + course + '\'' +
                ", school='" + school + '\'' +
                '}';
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public String getCourse() {
        return course;
    }

    public void setCourse(String course) {
        this.course = course;
    }

    public String getSchool() {
        return school;
    }

    public void setSchool(String school) {
        this.school = school;
    }
}

3，handler

package com.imooc.handler;

import com.imooc.dao.TeacherDAO;
import com.imooc.entity.Teacher;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.*;
import org.springframework.web.servlet.ModelAndView;

import java.util.Collection;

@Controller
public class RestfulHandler {

    @Autowired
    private TeacherDAO teacherDao;

    @RequestMapping("/add")
    public String add(Teacher teacher) {
        teacherDao.add(teacher);
        return "redirect:/getAll";
    }

    @GetMapping("/getById/{id}")
    public ModelAndView getById(@PathVariable(value = "id") Integer id) {
        ModelAndView modelAndView = new ModelAndView();
        Teacher teacher = teacherDao.selectByID(id);
        modelAndView.setViewName("edit");
        modelAndView.addObject("teacher", teacher);
        return modelAndView;
    }

    @GetMapping(value = "/getAll")
    public ModelAndView getAll() {
        ModelAndView modelAndView = new ModelAndView();
        Collection<Teacher> teachers = teacherDao.selectAll();
        modelAndView.setViewName("index");
        modelAndView.addObject("teachers", teachers);
        return modelAndView;
    }

    @PutMapping(value = "/update")
    public String update(Teacher teacher) {
        teacherDao.edit(teacher);
        return "redirect:/getAll";
    }

    @DeleteMapping(value = "/delete/{id}")
    public String delete(@PathVariable(value = "id") Integer id) {
        teacherDao.delete(id);
        return "redirect:/getAll";
    }
}

4, spring.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:mvc="http://www.springframework.org/schema/mvc"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans.xsd
       http://www.springframework.org/schema/context
       http://www.springframework.org/schema/context/spring-context.xsd
       http://www.springframework.org/schema/mvc
       http://www.springframework.org/schema/mvc/spring-mvc-3.2.xsd">

    <context:component-scan base-package="com.imooc"/>

    <!--配置视图解析器-->
    <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix" value="/"/>
        <property name="suffix" value=".jsp"/>
    </bean>

</beans>

6, web.xml

<!DOCTYPE web-app PUBLIC
 "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
 "http://java.sun.com/dtd/web-app_2_3.dtd" >

<web-app>

  <filter>
    <filter-name>encodingFilter</filter-name>
    <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
    <init-param>
      <param-name>encoding</param-name>
      <param-value>UTF-8</param-value>
    </init-param>
    <init-param>
      <param-name>forceEncoding</param-name>
      <param-value>true</param-value>
    </init-param>
  </filter>
  <filter-mapping>
    <filter-name>encodingFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>

  <servlet>
    <servlet-name>SpringMVC</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet </servlet-class>
    <!--配置springmvc.xml的路径-->
    <init-param>
      <param-name>contextConfigLocation</param-name>
      <param-value>classpath:spring.xml</param-value>
    </init-param>
  </servlet>

  <servlet-mapping>
    <servlet-name>SpringMVC</servlet-name>
    <url-pattern>/</url-pattern>
  </servlet-mapping>

  <filter>
    <filter-name>hiddenHttpMethodFilter</filter-name>
    <filter-class>org.springframework.web.filter.HiddenHttpMethodFilter</filter-class>
  </filter>

  <filter-mapping>
    <filter-name>hiddenHttpMethodFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>

  <display-name>Archetype Created Web Application</display-name>
</web-app>