How @ModelAttribute Annotation works in Spring?

package com.customer.controller;

import java.sql.Date;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;

import org.springframework.beans.propertyeditors.CustomDateEditor;
import org.springframework.stereotype.Controller;
import org.springframework.ui.ModelMap;
import org.springframework.validation.BindingResult;
import org.springframework.web.bind.WebDataBinder;
import org.springframework.web.bind.annotation.InitBinder;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.support.SessionStatus;

import com.customer.model.Customer;

@Controller
@RequestMapping("/customer.htm")
public class CustomerController{
 
 @RequestMapping(method = RequestMethod.POST)
 public String processSubmit(@ModelAttribute("customer") Customer customer,
   BindingResult result, SessionStatus status) {
  System.out.println("Parameter Level ModelAttriute is executed");
  if (result.hasErrors()) {
   return "CustomerForm";
  } else {
   status.setComplete();
   return "CustomerSuccess";
  }
 }
 
 @RequestMapping(method = RequestMethod.GET)
 public String initForm(ModelMap model){
  System.out.println("initForm method is executed (GET)");
  Customer cust = new Customer();
  cust.setFavFramework(new String []{"Spring MVC"});
  cust.setSex("M");
  cust.setJavaSkills("Hibernate");
  cust.setSecretValue("I‘m hidden value");
  model.addAttribute("customer", cust);
  return "CustomerForm";
 }
 
 
 @ModelAttribute("webFrameworkList")
 public List<String> populateWebFrameworkList() {
  System.out.println("Method Level ModelAttriute is executed (populateWebFrameworkList)");
  List<String> webFrameworkList = new ArrayList<String>();
  webFrameworkList.add("Spring MVC");
  webFrameworkList.add("Struts 1");
  webFrameworkList.add("Struts 2");
  webFrameworkList.add("JSF");
  webFrameworkList.add("Apache Wicket");
  return webFrameworkList;
 }
 
 @InitBinder
 public void initBinder(WebDataBinder binder) {
  System.out.println("initBinder method is executed");
  SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
  binder.registerCustomEditor(Date.class, new CustomDateEditor(dateFormat, true));
 }
 
 @ModelAttribute("numberList")
 public List<String> populateNumberList() {
  System.out.println("Method Level ModelAttriute is executed (populateNumberList)");
  List<String> numberList = new ArrayList<String>();
  numberList.add("Number 1");
  numberList.add("Number 2");
  numberList.add("Number 3");
  numberList.add("Number 4");
  numberList.add("Number 5");
  return numberList;
 }
 
 @ModelAttribute("javaSkillsList")
 public Map<String,String> populateJavaSkillList() {
  System.out.println("Method Level ModelAttriute is executed (populateJavaSkillList)");
  Map<String,String> javaSkill = new LinkedHashMap<String,String>();
  javaSkill.put("Hibernate", "Hibernate");
  javaSkill.put("Spring", "Spring");
  javaSkill.put("Apache Wicket", "Apache Wicket");
  javaSkill.put("Struts", "Struts");
  return javaSkill;
 }

 @ModelAttribute("countryList")
 public Map<String,String> populateCountryList() {
  System.out.println("Method Level ModelAttriute is executed (populateCountryList)");
  Map<String,String> country = new LinkedHashMap<String,String>();
  country.put("US", "United Stated");
  country.put("CHINA", "China");
  country.put("SG", "Singapore");
  country.put("MY", "Malaysia");
  return country;
 }
 
}