2019
https://www.linkedin.com/learning/spring-spring-mvc-2
    Incoming HTTP Request is Processed by
        DispatcherServlet->HandlerMapping->Controller (Front Controller DP)
        ->Controller->...processing...->back-to-DispatcherServlet
        ->ViewResolver
        
    Instead of String method at Controller we can use
        ModelAndView
            .setViewName
            .setStatus
            .addObject(name, value)
    SearchController {
        @GetMapping("/search")
        public String search(@RequestParam("search") String search, Model model) {
            ...
            List<Product> products = searchRepository.searchByName(search);
            model.addAttribute("products", products);
            ...
        }
    }
    RegistrationController {
        @PostMapping("/registeruser")
        public String registerUser(@ModelAttribute("newuser") User user) { // <form method="post" modelAttribute="newuser" ...>
            
        }
    }
    HomeController {
        ...
        @ModelAttribute("newuser")
        public User getDefaultUser() { return new User(); }
        @ModelAttribute("genderItems")
        public List<String> getGenderItems() { return List.of("Male", "Female", "Other"); }
    }

    javax.validation -> hibernate validator
    annotate with @Valid our beans at controller and add BindingResult param right after the annotated one
    and add <form:errors path="someAttr".../> to our form elements
    in order to localize error messages, add resources/ValidationMessages.properties, add msg.key=msg.value
    and use ... message="{msg.key}"

    binders extend ModelAttribute-s
    User {
         
        private Date dateOfBirth; // <form:input path="dateOfBirth" type="date" .../>
    }
    RegistrationController {
        @InitBinder
        public void initBinder(WebDataBinder binder) {
            binder.registerCustomEditor(Date.class, "dateOfBirth", new CustomDateEditor(new SimpleDateFormat("yyyy-MM-dd")));
        }
    }

    converters extend binders concept, transform request data to desired types
    built in converters present, but we can provide custom ones

    public enum Gender { MALE, FEMALE, OTHER }
    User { 
        @Enumerated(EnumType.STRING)
        private Gender gender;
    }

    public class StringToEnumConverter implements .core.convert.Converter<String, Gender> {
        @Override
        public Gender convert(String s) {
            ... regurn Gender.GGG ...;
        }
    }

    ApplicationConfig {
        ...
        @Override
        protected void addFormatters(FormatterRegistry registry) {
            registry.addConverter(new StringToEnumConverter());
        }
    }

    HandlerMapping - maps request to handler
    HandlerAdapter - invokes the handler
    ViewResolver - helps resolve views
    LocaleResolver - helps with l10n and i18n support
    ThemeResolver
    HandlerExceptionResolver - helps with exception handling
        ExceptionHandlerExceptionResolver - define ex-handling methods in controllers (annotated by @ExceptionHandler)
        SimpleMappingExceptionResolver - maps each ex-n class with an error page
        DefaultHandlerExceptionResolver - default, maps exceptions to error codes 
        ResponseStatusExceptionResolver - resolves custom exceptions using status code defined in @ResponseStatus (for ex-ns)
        to disable standard error resolver, we need to add property
        spring.autoconfigure.exclude=ord.springframework.boot.autoconfigure.web.servlet.error.ErrorMvcAutoConfiguration

    public class Login {
        private String login;
        private String password;
    }
    HomeController {
        ... @ModelAttribute("login") public Login getDefaultLogin() { return new Login(); }
    }

    public class ApplicationException extends RuntimeException { ... }

    LoginController {
        @PostMapping("/login")
        public String login(@ModelAttribute("login") Login login) {
            User user = userRepository.searchByName(login.getUsername());
            if (user == null) {
                throw new ApplicationException("User not found");
            }
        }
        @ExceptionHandler(ApplicationException.class)
        public String handleException(ApplicationException ex, WebRequest request) {
            return "error";
        }
    }
    for global handler
    @ControllerAdvice
    public class ApplicationExceptionHandler {
        
        @ExceptionHandler(ApplicationException.class)
        public String handleException(ApplicationException ex, WebRequest request) {
            return "error";
        }
    }
    ...
    @ControllerAdvice
    public class DefaultModelAttributeController {
        @ModelAttribute("newuser")
        public User getDefaultUser() { return new User(); }
        @ModelAttribute("genderItems")
        public List<String> getGenderItems() { return List.of("Male", "Female", "Other"); }
        ...
    }

    @EnableAsync
    https://stackoverflow.com/questions/36768234/spring-enableasync-breaks-bean-initialization-order
    https://www.baeldung.com/spring-async
    ...ApplicationAsync {
        @Override
        protected void configureAsyncSupport(AsyncSupportConfigurer configurer)
            configurer.setTaskExecutor(mvcTaskExecutor());
            configurer.setDefaultTimeout(5000);
        }
        @Bean public AsyncTaskExecutor mvcTaskExecutor() { ThreadPoolTaskExecutor... }
    }
    ... SearchController {
        public Callable<String> search(..., HttpServletRequest request) {
            log.info(request.isAsyncSupported(), Thread.currentThread().getName());
            return () -> {
                log.info(Thread.currentThread().getName());
                all the business logic
            }

            we can also use DeferredResult
            @Autowired
            private AsyncTaskExecutor executor;


            public DeferredResult<String> search(..., HttpServletRequest request) {
                DeferredResult<String> defferedResult = new DeferredResult<>();
                ...
                executor.execute(() -> {
                    ...
                    defferedResult.setResult(search);
                });
                return defferedResult;
        }
    }

    View
    ViewResolver - resp by resolving views by names
        InternalResourceViewResolver
        ResourceBundleViewResolver
        XmlViewResolver
        VelocityViewResolver, FreeMakerViewResolver, ...
        ChainedViewResolver

    DispatcherServlet
        HandlerMapping, HandlerAdapter (calls interceptors)
            Pre-process Interceptors 1..n
            and then (iff all are OK) - calls a Controller
            after all business-logic -
            Post-process

    Impl-s of HandlerInterceptorAdapter base class
        preHandle
        postHandle
        afterCompletion - after response is completed to the client
    ThemeChangeInterceptor
    LocaleChangeInterceptor

    public class LoggingInterceptor extends HandlerInterceptorAdapter {
        @Override
        public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
            ...
        }
        public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
            ...
        }
    }
    at ApplicationConfig {
        @Override
        protected void addInterceptors(InterceptorRegistry registry) {
            registry.addInterceptor(new LoggingInterceptor()).addPathPatterns("/*")
        }
    }

    ... @SessionAttributes, @SessionAttribute
        @RequestAttribute

    @Controller
    @SessionAttributes("login") // @ModelAttribute should exist
    public class LoginController {
        
        // already exposed by ControllerAdvice
        // @ModelAttribute("login") public Login getDefaultLogin() { return new Login(); }
    }

    @Controller
    public class UserProfileController {
        @PostMapping("/userprofile")
        public String getUserProfile(@SessionAttribute("login") Login login, Model model) {
            // and similar for @RequestAttribute
            model.setAttribute("username"); // or use ${sessionScope.username} at jsp
            return "profile"; // use login in jsp
        }
    }

    LoginController {
        ...
        @PostMapping("/login")
        {
            session.setMaxInactiveTimeout(...)
            ...
            ... return "forward:/userprofile"
        }
    }

    @Controller
    public class LogoutController {
        @GetMapping("/logout")
        public String logout(HttpSession session) {
            session.invalidate();
            return "login";
        }
    }

    @Controller
    public class RedirectionController {
        @GetMapping("/redirectToLinkedIn")
        public String redirectToLinkedIn() {
            return "redirect:http://www.linkedin.com"; // absolute URL is needed
        }
    }

    ThemeResolver facilitates theme resolution
        ThemeSource and default impl - ResourceBundleThemeSource
        CookieThemeResolver
        SessionThemeResolver
        FixedThemeResolver

    resources/client-theme1.properties
        styleSheet=/css/style1.css
    resources/client-theme2.properties
        styleSheet=/css/style2.css

    ... ApplicationConfig {
        @Bean
        public ThemeResolver themeResolver() {
            CookieThemeResolver cookieThemeResolver = new CookieThemeResolver();
            cookieThemeResolver.setCookieName("theme");
            cookieThemeResolver.setDefaultThemeName("client-theme1");
            return cookieThemeResolver;
        }
        ... // also it's important to add an interceptor
        @Override
        protected void addInterceptors(InterceptorRegistry registry) {
            registry.addInterceptor(new LoggingInterceptor()).addPathPatterns("/*")
            registry.addInterceptor(new ThemeChangeInterceptor());
        }
    }
    // next thing - define at our jsp
    <%@ taglib prefix="spring" uri="http://www.springframework.org/tags" %>
    ...
    <head>
        <link rel="stylesheet" href="<spring:theme code='styleSheet'/>" type="text/css"/>
        ...
    </head>
    // we can check with ...?theme=client-theme2... ... resolver will store this in cookie

    l10n - is to use props for msgs
    i10n - is more than l10n, including locale treatment

    LocaleResolver
        AcceptHeaderLocaleResolver - default one
        CookieLocaleResolver
        SessionLocaleResolver

    resources/messages.properties
        label.home=home
        label.search=search
        label.login=login
        label.linkedin=linkedin
    resources/messages_sv.properties // make sure to have UTF-8
        label.home=hem
        label.search=sok
        label.login=logga in
        label.linkedin=...

    // at jsp - use <spring:message code="label.home"/>
    // default resolver takes locale from client settings of browser

    ... ApplicationConfig {
        @Bean
        public LocaleResolver localeResolver() {
            CookieLocaleResolver cookieLocaleResolver = new CookieLocaleResolver();
            cookieLocaleResolver.setCookieName("locale");
            cookieLocaleResolver.setDefaultLocale(Locale.US);
            return cookieLocaleResolver;
        }
        ... // also it's important to add an interceptor
        @Override
        protected void addInterceptors(InterceptorRegistry registry) {
            registry.addInterceptor(new LoggingInterceptor()).addPathPatterns("/*")
            registry.addInterceptor(new ThemeChangeInterceptor());
            registry.addInterceptor(new LocaleChangeInterceptor()); // can customize with setParamName if need non-default
        }
    }

    REST: spring uses HttpMessageConvertors for JSON (with Jackson), no view name needed


    @Controller
    public class ProductsRestController {
        ...
        @GetMapping("/rest/products") 
        @ResponseBody
        public List<Product> getProducts() {
            return productRepository.findAll();
        }
    }
    @RestController // implies @ResponseBody for every method
    public class ProductsRestController {
        ...
        @GetMapping("/rest/products") 
        public ResponseEntity<List<Product>> getProductsByParam(@RequestParam("name") String name) {
            List<Product> products = productRepository.searchByName(name)
            return new ResponseEntity<>(products, HttpStatus.OK);
        }
        @GetMapping("/rest/products/{id}") 
        public ResponseEntity<List<Product>> getProductsByPathVar(@PathVariable("name") String name) {
            List<Product> products = productRepository.searchByName(name)
            return new ResponseEntity<>(products, HttpStatus.OK);
        }
    }

    public class LoginFailureException extends Exception {
        ...
    }

    @RestController
    public class LoginRestController {
        ...

        @PostMapping("/rest/loginuser") 
        public ResponseEntity<?> loginUser(@RequestBody Login login) {
            User user = userRepository.searchByName(login.getUsername());
            if (user == null) {
                return new ResponseEntity.status(HttpStatus.NOT_FOUND).build();
            }
            if (user.getUsername().equals(login.getUsername)) && ... pwd) {
                return new ResponseEntity<>("Welcome " + user.getUsername(), HttpStatus.OK);
            } else {
                throw new LoginFailureException("username or password is incorrect")
            }
        }

        @ExceptionHandler(LoginFailureException.class)
        public ResponseEntity<?> handle Login(LoginFailureException ex) {
            return ResponseEntity.status(HttpStatus.FORBIDDEN).body(ex.getMessage());
        }
    }