KLM A Model-View-Controller desing pattern with Spring framework
MVC in a few words.... Being concise controllers manipulate data in a model that represents information the user is interested in and pass that model on to the view, which renders the model in a way useful to the user. The point is to separate different application layers ie Model as business logic, Controller as a director of the flow process and View as presentation layer.
Package and class hierarchy looks like this:
To dispatch the client to a different URL I use org.springframework.web.servlet.view.RedirectView.
The HomeController has several request handler methods. First is home(Map), where argument Map<String, Object> model stands for Model.
@Controller
public class HomeController
{
@RequestMapping("/")
public View home(Map<String, Object> model)
{
model.put("dashboardUrl", "dashboard");
return new RedirectView("/{dashboardUrl}", true);
}
...
}Obviously I could construct the view using the static URL string( new RedirectView("/dashboard", true)), but I would prefer to utilize the replacement template and pull dynamically attributes from the model. Now when we are transfered to /dashboard we serve it with another request handler method.
@RequestMapping(value = "/dashboard", method = RequestMethod.GET)
public String dashboard(Map<String, Object> model)
{
model.put("text", "This is a model attribute.");
model.put("date", Instant.now());
return "home/dashboard";
}The dashboard(Map) responds to the /dashboard URL, saves into the model text and date attributes and returns the String name home/dashboard of a view. Then Spring resolves it to WEB-INF/jsp/view/home/dashboard.jsp using JstlView resolver that I configured in ServletContextConfiguration :
@Bean
public ViewResolver viewResolver()
{
InternalResourceViewResolver resolver =
new InternalResourceViewResolver();
resolver.setViewClass(JstlView.class);
resolver.setPrefix("/WEB-INF/jsp/view/");
resolver.setSuffix(".jsp");
return resolver;
}So we have two JSP views. ---- View Layer WEB-INF/jsp/view/home/dashboard.jsp
<%--@elvariable id="text" type="java.lang.String"--%>
<%--@elvariable id="date" type="java.time.Instant"--%>
<!DOCTYPE html>
<html>
<head>
<title>Dashboard</title>
</head>
<body>
Text: ${text}<br />
Date: ${date}
</body>
</html>It just puts on view two model attributes that are exposed as EL variables for the JSP thanks to Spring JstlView ViewResolver.
#viewing implicitly model attributes To view implicitly model attributes I use org.springframework.web.servlet.RequestToViewNameTranslator configured in ServletContextConfiguration this way:
@Bean
public RequestToViewNameTranslator viewNameTranslator()
{
return new DefaultRequestToViewNameTranslator();
}I utilize deafult option org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator
The userHome() method of the HomeController, mapped to the /user/home URL constructs and populates a new User object, returns it, and also adds it to the model with the attribute key currentUser thanks to @ModelAttribute annotation.
@RequestMapping(value = "/user/home", method = RequestMethod.GET)
@ModelAttribute("currentUser")
public User userHome()
{
User user = new User();
user.setUserId(1234987234L);
user.setUsername("stefan");
user.setName("Stefan Nowak");
return user;
}Thanks to setting up the view name translation the view name becomes user/home, so I have to have this view in WEB-INF/jsp/view/user/home.jsp, where I can utilize again EL variables with "currentUser" object.
<%--@elvariable id="currentUser" type="klm.pstryk.site.User"--%>
<!DOCTYPE html>
<html>
<head>
<title>User Home</title>
</head>
<body>
ID: ${currentUser.userId}<br />
Username: ${currentUser.username}<br />
Name: ${currentUser.name}<br />
</body>
</html>In the app there is another functionality. I employ content negotiation in Spring that allows to change the content type received back to the client based on a file extension. The configuration resides of course in ServletContextConfiguration.
@Override
public void configureContentNegotiation(
ContentNegotiationConfigurer configurer)
{
configurer.favorPathExtension(true).favorParameter(false)
.parameterName("mediaType").ignoreAcceptHeader(false)
.useJaf(false).defaultContentType(MediaType.APPLICATION_XML)
.mediaType("xml", MediaType.APPLICATION_XML)
.mediaType("json", MediaType.APPLICATION_JSON);
}And I use it in the HomeController with @ResponseBody annotation.
@RequestMapping(value = "/user/{userId}", method = RequestMethod.GET)
@ResponseBody
public User getUser(@PathVariable("userId") long userId)
{
User user = new User();
user.setUserId(userId);
user.setUsername("piotr");
user.setName("Piotr Wysmial");
return user;
}Thanks to this the mapped views eg user/1 and user/1.json properly render with "xml view" and "json view" as relevant.