Spring MVC Concepts

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Internal

To Process

TO PROCESS:

Project Directory Layout

src/main/resource/static
src/main/resource/static/images
src/main/resource/templates

Model

The model is an object that ferries data between a controller and whatever view is charged with rendering that data. org.springframework.ui.Model is a holder for model attributes, conceptually a map. Ultimately, data that is placed in the model's attributes will be copied into the servlet response attributes, where the view can find them. @ModelAttribute annotations insure that the corresponding object instances are created in the model.

Controller

A controller is a class that handles requests, fetches and processes data, and then responds with information of some sort. The controller's method handing the requests are named handler methods. Controller classes must be annotated with @Controller stereotype annotation.

In case of a browser-facing application, a controller responds by optionally populating model data and passing the request to a view that produces HTML to be returned to the browser. The view that is supposed to render the response is indicated by its logical name, which is returned by the handler method. 

@Controller
public class HomeController {

    @GetMapping("/")
    public String home() {

        // returns the view name
        return "home";
    }
}

In case of a REST application, the controller writes data directly into the body of the response.

A conventional pattern to designate the responsibilities of the handler methods and to associate them with paths and request types is to use @RequestMapping at class level to configure the base path, and then use @GetMapping, @PostMapping, @PutMapping, @DeleteMapping and @PatchMapping to designate HTTP method-specific handlers: 

@Controller
@RequestMapping("/something")
public class SomeController {

    @GetMapping
    public String read() {
        ...
    }

    @PostMapping
    public String create() {
        ...
    }

    @PutMapping
    public String update() {
        ...
    }
}

Controller Annotations

Common Annotation Configuration Elements

path

@RequestMapping, @GetMapping, etc. accept a "path" data member. The path accepts placeholders: 

"/{id}"

Placeholders are captured with @PathVariable as follows: 

@GetMapping("/{id}")
public ... someMethod(@PathVariable("id") Long id) {
   ...
}

View Controller

A view controller is a controller that is simply enough that it does not populate a model or process input, but simply forward the request to a view. View controller do not require a class on their own, as there is no functionality to populate that class with. Instead, they can be defined by using a specific API in a configuration class. 

@Configuration
public class MyWebConfiguration implements WebMvcConfigurer {
  @Override
  public void addViewControllers(ViewControllerRegistry registry) {
    registry.addViewController("/").setViewName("home");
  }
}

The API allows to associate a GET request path with a view logical name, without the need to write a controller class. ViewControllerRegistry.addViewController() returns a ViewControllerRegistration object on which setViewName() lets you to associate a view with the path.

View

The view renders data into HTML format.

The view is instantiated dynamically, and its implementation depends on the template engine that is available in the classpath. Template libraries are designed to be decoupled by any particular web framework, so they are unaware of Spring's model abstraction and are not able to work with the data the controller places in the model. They can work with servlet request attributes, though, and Spring copies the model data into the request attributes before the request is handed over to the view.

View Logical Name

The template name is derived from the logical name by prefixing it with /templates and postfixing it with .html. Simply placing a <logical-view-name>.html under src/resources/templates makes the template-based view available.

Redirect View

"redirect:/home"

Template Libraries

SIA page 52.

Template Caching

By default, templates are only parsed once, when they’re first used, and the results of that parse are cached for subsequent use. This is desirable or production, as it prevents redundant template parsing on each request and thus improves performance. However, in development we want to be able to modify templates and test results so we need to disable template caching. 

spring.thymeleaf.cache=false
spring.mustache.cache=false
spring.groovy.template.cache=false
spring.freemarker.cache=false

DevTools disable template caching by default.

Configuring MVC Applications

Configuration in this context refers to component configuration.

WebMvcConfigurer

Property Configuration for MVC Applications

TODO: 

export SERVER_PORT=9999

Also see:

Spring Property Injection Concepts - The PropertySource Abstraction

Testing MVC Applications

import org.springframework.test.web.servlet.MockMvc;
import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.content;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.view;
import static org.hamcrest.Matchers.containsString;

@RunWith(SpringRunner.class)
@WebMvcTest(HomeController.class)
public class HomeControllerTest {

    @Autowired
    private MockMvc mockMvc;

    @Test
    public void testHomePage() throws Exception {

        mockMvc.perform(get("/")).
                andExpect(status().isOk()).
                andExpect(view().name("home")).
                andExpect(content().string(containsString("Welcome to ...")));
    }
}

Spring MVC testing implies using @WebMvcTest. MockMvc mocks the mechanics of Spring MVC, instead of starting a full blown web server.

REST

Spring REST Concepts
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