Spring MVC Auto-configuration
// Spring Boot为Spring MVC提供了自动配置，它可以很好地与大多数应用程序一起工作。
Spring Boot provides auto-configuration for Spring MVC that works well with most applications.
// 自动配置在Spring默认设置的基础上添加了以下功能：
The auto-configuration adds the following features on top of Spring’s defaults:
// 包含视图解析器
Inclusion of ContentNegotiatingViewResolver and BeanNameViewResolver beans.
// 支持静态资源文件夹的路径，以及webjars
Support for serving static resources, including support for WebJars 
// 自动注册了Converter：
// 转换器，这就是我们网页提交数据到后台自动封装成为对象的东西，比如把"1"字符串自动转换为int类型
// Formatter：【格式化器，比如页面给我们了一个2019-8-10，它会给我们自动格式化为Date对象】
Automatic registration of Converter, GenericConverter, and Formatter beans.
// HttpMessageConverters
// SpringMVC用来转换Http请求和响应的的，比如我们要把一个User对象转换为JSON字符串，可以去看官网文档解释；
Support for HttpMessageConverters (covered later in this document).
// 定义错误代码生成规则的
Automatic registration of MessageCodesResolver (covered later in this document).
// 首页定制
Static index.html support.
// 图标定制
Custom Favicon support (covered later in this document).
// 初始化数据绑定器：帮我们把请求数据绑定到JavaBean中！
Automatic use of a ConfigurableWebBindingInitializer bean (covered later in this document).

/*
如果您希望保留Spring Boot MVC功能，并且希望添加其他MVC配置（拦截器、格式化程序、视图控制器和其他功能），则可以添加自己
的@configuration类，类型为webmvcconfiguer，但不添加@EnableWebMvc。如果希望提供
RequestMappingHandlerMapping、RequestMappingHandlerAdapter或ExceptionHandlerExceptionResolver的自定义
实例，则可以声明WebMVCregistrationAdapter实例来提供此类组件。
*/
If you want to keep Spring Boot MVC features and you want to add additional MVC configuration 
(interceptors, formatters, view controllers, and other features), you can add your own 
@Configuration class of type WebMvcConfigurer but without @EnableWebMvc. If you wish to provide 
custom instances of RequestMappingHandlerMapping, RequestMappingHandlerAdapter, or 
ExceptionHandlerExceptionResolver, you can declare a WebMvcRegistrationsAdapter instance to provide such components.

// 如果您想完全控制Spring MVC，可以添加自己的@Configuration，并用@EnableWebMvc进行注释。
If you want to take complete control of Spring MVC, you can add your own @Configuration annotated with @EnableWebMvc.

@Bean
@ConditionalOnBean(ViewResolver.class)
@ConditionalOnMissingBean(name = "viewResolver", value = ContentNegotiatingViewResolver.class)
public ContentNegotiatingViewResolver viewResolver(BeanFactory beanFactory) {
    ContentNegotiatingViewResolver resolver = new ContentNegotiatingViewResolver();
    resolver.setContentNegotiationManager(beanFactory.getBean(ContentNegotiationManager.class));
    // ContentNegotiatingViewResolver使用所有其他视图解析器来定位视图，因此它应该具有较高的优先级
    resolver.setOrder(Ordered.HIGHEST_PRECEDENCE);
    return resolver;
}

@Nullable // 注解说明：@Nullable 即参数可为null
public View resolveViewName(String viewName, Locale locale) throws Exception {
    RequestAttributes attrs = RequestContextHolder.getRequestAttributes();
    Assert.state(attrs instanceof ServletRequestAttributes, "No current ServletRequestAttributes");
    List<MediaType> requestedMediaTypes = this.getMediaTypes(((ServletRequestAttributes)attrs).getRequest());
    if (requestedMediaTypes != null) {
        // 获取候选的视图对象
        List<View> candidateViews = this.getCandidateViews(viewName, locale, requestedMediaTypes);
        // 选择一个最适合的视图对象，然后把这个对象返回
        View bestView = this.getBestView(candidateViews, requestedMediaTypes, attrs);
        if (bestView != null) {
            return bestView;
        }
    }
    // .....
}

Iterator var5 = this.viewResolvers.iterator();

//如果你想自定义一些功能，只要写这个组件，就可以将他交给springboot，springboot就会帮我们自动装配
//扩展springmvc
@Configuration
public class MyMvcConfig implements WebMvcConfigurer {

    //viewResolver 实现了视图解析器接口的类，我们就可以把它看作视图解析器

    @Bean
    public ViewResolver myViewResolver(){
        return new MyViewResoler();
    }

    //定义一个自己的视图解析器MyViewResoler
    public static class MyViewResoler implements ViewResolver{
        @Override
        public View resolveViewName(String s, Locale locale) throws Exception {
            return null;
        }
    }
}

//如果你想自定义一些功能，只要写这个组件，就可以将他交给springboot，springboot就会帮我们自动装配
//扩展springmvc
@Configuration
public class MyMvcConfig implements WebMvcConfigurer {

    //viewResolver 实现了视图解析器接口的类，我们就可以把它看作视图解析器

    @Bean
    public ViewResolver myViewResolver(){
        return new MyViewResoler();
    }

    //定义一个自己的视图解析器MyViewResoler
    public static class MyViewResoler implements ViewResolver{
        @Override
        public View resolveViewName(String s, Locale locale) throws Exception {
            return null;
        }
    }
}

//应为类型要求为WebMvcConfigurer，所以我们实现其接口
//可以使用自定义类扩展MVC的功能
@Configuration
public class MyMvcConfig implements WebMvcConfigurer {

    @Override
    public void addViewControllers(ViewControllerRegistry registry) {
        // 浏览器发送/test ， 就会跳转到test页面；
        registry.addViewController("/toTest").setViewName("test");
    }
}

public class DelegatingWebMvcConfiguration extends WebMvcConfigurationSupport {
    private final WebMvcConfigurerComposite configurers = new WebMvcConfigurerComposite();
    
  // 从容器中获取所有的webmvcConfigurer
    @Autowired(required = false)
    public void setConfigurers(List<WebMvcConfigurer> configurers) {
        if (!CollectionUtils.isEmpty(configurers)) {
            this.configurers.addWebMvcConfigurers(configurers);
        }
    }
}

protected void addViewControllers(ViewControllerRegistry registry) {
    this.configurers.addViewControllers(registry);
}

public void addViewControllers(ViewControllerRegistry registry) {
    Iterator var2 = this.delegates.iterator();

    while(var2.hasNext()) {
        // 将所有的WebMvcConfigurer相关配置来一起调用！包括我们自己配置的和Spring给我们配置的
        WebMvcConfigurer delegate = (WebMvcConfigurer)var2.next();
        delegate.addViewControllers(registry);
    }

}

@Import({DelegatingWebMvcConfiguration.class})
public @interface EnableWebMvc {
}

public class DelegatingWebMvcConfiguration extends WebMvcConfigurationSupport {  
    // ......
}

@Configuration(proxyBeanMethods = false)
@ConditionalOnWebApplication(type = Type.SERVLET)
@ConditionalOnClass({ Servlet.class, DispatcherServlet.class, WebMvcConfigurer.class })
// 这个注解的意思就是：容器中没有这个组件的时候，这个自动配置类才生效
@ConditionalOnMissingBean(WebMvcConfigurationSupport.class)
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE + 10)
@AutoConfigureAfter({ DispatcherServletAutoConfiguration.class, TaskExecutionAutoConfiguration.class,
    ValidationAutoConfiguration.class })
public class WebMvcAutoConfiguration {
    
}

@Configuration
//@EnableWebMvc
public class MyMvcConfig implements WebMvcConfigurer {

    @Override
    public void addViewControllers(ViewControllerRegistry registry) {
        registry.addViewController("/").setViewName("index");
        registry.addViewController("/index.html").setViewName("index");
    }
}

public class MyLocaleResolver implements LocaleResolver {

    //解析请求
    @Override
    public Locale resolveLocale(HttpServletRequest request) {
        //获取请求中的语言参数
        String language = request.getParameter("l");

        Locale locale = Locale.getDefault();//如果没有就使用默认的
        //如果请求的链接携带了国际化的参数
        if(!StringUtils.isEmpty(language)){
            //分割参数
            String[] split = language.split("_");
            //国家，地区
            locale = new Locale(split[0],split[1]);
        }

        return locale;
    }

    @Override
    public void setLocale(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Locale locale) {

    }
}

@Configuration
//@EnableWebMvc
public class MyMvcConfig implements WebMvcConfigurer {

    @Override
    public void addViewControllers(ViewControllerRegistry registry) {
        registry.addViewController("/").setViewName("index");
        registry.addViewController("/index.html").setViewName("index");
    }

    //自定义的国际化组件
    @Bean
    public LocaleResolver localeResolver(){
        return new MyLocaleResolver();
    }
}

@Controller
public class LoginController {

    @RequestMapping("/user/login")
    public String login(@RequestParam("username") String username, @RequestParam("password") String password, Model model){

        if(!StringUtils.isEmpty(username) && "123456".equals(password)){
            return "redirect:/main.html";
        }else{
            //告诉用户登陆失败
            model.addAttribute("msg","用户名或密码错误！");
            return "index";
        }
    }
}

@Override
public void addViewControllers(ViewControllerRegistry registry) {
    registry.addViewController("/").setViewName("index");
    registry.addViewController("/index.html").setViewName("index");
    registry.addViewController("/main.html").setViewName("dashboard");
}

public class LoginHandlerInterceptor implements HandlerInterceptor {

    //拦截器，拦截是否登录后进入主页
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {

        //登陆成功之后，应该有用户的session
        Object loginUser = request.getSession().getAttribute("loginUser");
        if(loginUser==null){//session为空，没有登录
            request.setAttribute("msg","没有权限，请先登录！");
            request.getRequestDispatcher("/index.html").forward(request,response);
            return false;
        }
        return true;
    }
}

@Controller
public class LoginController {

    @RequestMapping("/user/login")
    public String login(@RequestParam("username") String username, @RequestParam("password") String password, Model model, HttpSession session){

        if(!StringUtils.isEmpty(username) && "123456".equals(password)){
            session.setAttribute("loginUser",username);
            return "redirect:/main.html";
        }else{
            //告诉用户登陆失败
            model.addAttribute("msg","用户名或密码错误！");
            return "index";
        }
    }
}

@Configuration
public class MyMvcConfig implements WebMvcConfigurer {

    @Override
    public void addViewControllers(ViewControllerRegistry registry) {
        registry.addViewController("/").setViewName("index");
        registry.addViewController("/index.html").setViewName("index");
        registry.addViewController("/main.html").setViewName("dashboard");
    }

    //自定义的国际化组件生效
    @Bean
    public LocaleResolver localeResolver(){
        return new MyLocaleResolver();
    }

    //配置拦截器
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new LoginHandlerInterceptor())
                .addPathPatterns("/**")//拦截所有请求
                .excludePathPatterns("/index.html","/","/user/login","/css/**","/js/**","/img/**");//不拦截那些页面
    }
}

//注销用户
@RequestMapping("/user/logout")
public String out(HttpSession session){
    session.invalidate();
    return "redirect:index.html";
}

@Controller
public class EmployeeController {

    @Autowired
    EmployeeDao employeeDao;

    @RequestMapping("/emps")
    public String list(Model model){
        Collection<Employee> employees = employeeDao.getAll();
        model.addAttribute("emps",employees);
        return "emp/list";
    }
}

    @GetMapping("/emp")
    public String toAddpage(Model model){
        //获取所有部门
        Collection<Department> departments = departmentDao.getDepartments();
        model.addAttribute("departments",departments);
        return "emp/add";
    }

    @PostMapping("/emp")
    public String addEmp(Employee employee){
//        添加操作
        employeeDao.save(employee);//调用业务方法，保存员工信息
        return "redirect:/emps";
    }

//跳转修改页面
@GetMapping("/emp/{id}")
public String toUpdateEmp(@PathVariable("id") Integer id,Model model){
    //查出的数据
    Employee employee = employeeDao.get(id);
    model.addAttribute("employee",employee);
    //获取所有部门
    Collection<Department> departments = departmentDao.getDepartments();
    model.addAttribute("departments",departments);
    return "emp/update";
}

@RequestMapping("/updateEmp")
public String updateEmp(Employee employee){
    //修改员工
    employeeDao.save(employee);
    return "redirect:/emps";
}

//删除操作
@GetMapping("/deleteEmp/{id}")
public String deleteEmp(@PathVariable("id") int id){
    employeeDao.delete(id);
    return "redirect:/emps";
}