Spring Web MVC

Front Controller : 

the concept of the Front Controller in the typical Spring Model View Controller architecture

At a very high level, here are the main responsibilities we're looking at:

• Intercepts incoming requests
• Converts the payload of the request to the internal structure of the data
• Sends the data to Model for further processing
• Gets processed data from the Model and advances that data to the View for rendering

• DispatcherServlet plays the role of the Front Controller in the architecture.
• The diagram is applicable both to typical MVC controllers as well as RESTful controllers
• MVC applications are not service-oriented hence there is a View Resolver that renders final views based on data received from a Controller
• RESTful applications are designed to be service-oriented and return raw data (JSON/XML typically). Since these applications do not do any view rendering, there are no View Resolvers – the Controller is generally expected to send data directly via the HTTP response

MVC Controller : 

@Controller

@RequestMapping(value="Test")

public class TestController{

.....

}

Rest Controller :

Maven Dependencies :  spring-web,  spring-webmvc,  jackson-databind

@Controller

public class TestController{

   @GetMapping(value = "/student/{studentId}")

    public @ResponseBody Student getTestData(@PathVariable Integer studentId) {

        Student student = new Student();

        student.setName("Peter");

        student.setId(studentId);

        return student;

    } 

}

@ResponseBody annotation on the method – which instructs Spring to bypass the view resolver and essentially write out the output directly to the body of the HTTP response.

Spring Boot - @RestController

@RestController

public class RestAnnotatedController {

    @GetMapping(value = "/annotated/student/{studentId}")

    public Student getData(@PathVariable Integer studentId) {

        Student student = new Student();

        student.setName("Peter");

        student.setId(studentId);

        return student;

    }

}

@RestController annotation from Spring Boot is basically a quick shortcut that saves us from always having to define @ResponseBody. Help by pass view rendering stage and directly writing response to HTTP response body

@RequestMapping
the annotation is used to map web requests to Spring Controller methods

Example 1 : Request Mapping with by path and HTTP method

@RequestMapping(value = "/ex/foos", method = POST)

@ResponseBody

public String postFoos() {

    return "Post some Foos";

}

Example 2 : Request Mapping and HTTP header

@RequestMapping(

  value = "/ex/foos", 

  headers = { "key1=val1", "key2=val2" }, method = GET)

@ResponseBody

public String getFoosWithHeaders() {

    return "Get some Foos with Header";

}

Example 3 : Mapping media types produced and consumed by controller

@RequestMapping(value="/method6",

produces={"application/json","application/xml"},

consumes="text/html")

@ResponseBody

public String method6(){

return "method6";

}

Above method can consume message only with Content-Type as text/html and is able to produce messages of type application/json and application/xml.

Example 4 : Request Mapping with Path Variable

@RequestMapping(value = "/ex/foos/{fooid}/bar/{barid}", method = GET)

@ResponseBody

public String getFoosBySimplePathWithPathVariables

  (@PathVariable long fooid, @PathVariable long barid) {

    return "Get a specific Bar with id=" + barid + 

      " from a Foo with id=" + fooid;

}

Example 5 : Request Mapping with Request Parameters

@RequestMapping(value = "/ex/bars", method = GET)

@ResponseBody

public String getBarBySimplePathWithRequestParam( @RequestParam("id") long id) {

    return "Get a specific Bar with id=" + id;

}

http://localhost:8080/spring-rest/ex/bars?id=100

Example 6 :  Request Mapping with Fallback

@RequestMapping(

  value = "*", 

  method = { RequestMethod.GET, RequestMethod.POST ... })

@ResponseBody

public String allFallback() {

    return "Fallback for All Requests";

}

@RequestMapping New Shortcut Annotations

• @GetMapping
• @PostMapping
• @PutMapping
• @DeleteMapping
• @PatchMapping
  
  

Reference 1 :  Baeldung
Reference 2 :  Journal Dev