<dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-thymeleaf</artifactId>
    </dependency>

package com.example.demo;

public class User {
  String name;
  Integer age;

  public String getName() {
    return name;
  }
  public void setName(String name) {
    this.name = name;
  }
  public Integer getAge() {
    return age;
  }
  public void setAge(Integer age) {
    this.age = age;
  }

  @Override
  public String toString() {
    return "User{" +
        "name='" + name + '\'' +
        ", age=" + age +
        '}';
  }
}

package com.example.demo;

import org.springframework.format.Formatter;

import java.text.ParseException;
import java.util.Locale;

public class UserFormatter implements Formatter<User> {

  /**
   * 字符串转换为对象
  */
  @Override
  public User parse(String s, Locale locale) throws ParseException {
    return null;
  }

  /**
   * 对象转换为字符串
   */
  @Override
  public String print(User user, Locale locale) {
    return "name:" + user.getName();
  }
}

package com.example.demo;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class MyConfig {
  @Bean
  public UserFormatter userFormatter(){
    return new UserFormatter();
  }
}

package com.example.demo;

import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestMapping;

@Controller
public class TestController {
  @RequestMapping("/")
  public String test(Model model){
    User user = new User();
    user.setName("lc");
    user.setAge(30);
    model.addAttribute("user", user);
    return "test";
  }
}