Introduction to WebMvc.fn

Confidential │ ©2020 VMware, Inc.
Introduction to
WebMvc.fn
Functional Servlet Endpoints
Arjen Poutsma (@poutsma)
Sr. Staff Engineer at VMware
3rd September 2020

Agenda
2
Handler Functions
Router Functions
Filter Functions
Final Comparison

Confidential │ ©2020 VMware, Inc. 3
WebMvc.fn was introduced
in Spring 5.2 and is fully
compatible with Spring Boot

Handler Functions
Map from ServerRequest to ServerResponse
4

Handler Functions
@Controller
class PersonController {
PersonRepository repository;
ResponseEntity<Person> getPerson(@PathVariable String id) {
Person person = repository.findById(id);
return ResponseEntity.ok()
.contentType(APPLICATION_JSON)
.body(person);
}
ResponseEntity<List<Person>> getPeople() {
List<Person> people = repository.findAll();
.body(people);
}
}
Web MVC

Handler Functions
@Controller
class PersonHandler {
ServerResponse getPerson(ServerRequest request) {
String id = request.pathVariable("id");
return ServerResponse.ok()
.body(person);
}
ServerResponse getPeople(ServerRequest request) {
.body(people);
}
}
WebMvc.fn

Web MVC WebMvc.fn
6
Handler Function Comparison
@Controller
.body(person);
}
.body(people);
}
}
@Controller
String id = request.pathVariable("id");
.body(person);
}
.body(people);
}
}

Handler Functions map from
ServerRequest to ServerResponse
• both are immutable
• create response with builder

Router Functions
Map from ServerRequest to HandlerFunction
8

Router Functions
@Controller
@RequestMapping("/people")
@RequestMapping(value = "/{id}", method = GET)
...
}
@RequestMapping(method = GET)
...
}
}
Web MVC

Router Functions
@Controller
...
}
...
}
@Bean
static RouterFunction router(PersonHandler handler) {
return route()
.GET("/people/{id}", handler::getPerson)
.GET(“/people", handler::getPeople)
.build();
}
}
WebMvc.fn

Router Functions
@Controller
...
}
...
}
@Bean
return route()
.path(“/people", builder -> builder
.GET("/{id}", handler::getPerson)
.GET("/", handler::getPeople));
.build();
}
}
WebMvc.fn

Web MVC WebMvc.fn
10
Router Function Comparison
@Controller
...
}
...
}
@Bean
return route()
.path(“/people", builder -> builder
.GET("/", handler::getPeople));
.build();
}
}
@Controller
@RequestMapping(“/people")
@RequestMapping(value = "/{id}", method = GET)
...
}
@RequestMapping(method = GET)
...
}
}

Router Functions created using builder
• GET, POST, PUT, etc.
• resources
• nesting
• more powerful abstraction underneath:
RequestPredicate

Request Predicates
Evaluate on a ServerRequest
12

Request Predicates
RequestPredicate get = RequestPredicates.method(HttpMethod.GET);
RequestPredicate people = RequestPredicates.path("/people");
RequestPredicate getPeople = get.and(people); // or RequestPredicates.GET("/people")
RequestPredicate acceptJson = RequestPredicates.accept(APPLICATION_JSON);
RequestPredicate extensionJson = RequestPredicates.pathExtension("json");
RequestPredicate paramTypeJson = RequestPredicates.param("type", "json");
RequestPredicate json = acceptJson.or(extensionJson).or(paramTypeJson);

Request Predicates
@Controller
...
ServerResponse createPerson(ServerRequest request) {
Person person = request.body(Person.class);
repository.savePerson(person);
.build();
}
@Bean
return route()
.path("/people", b -> b
.GET("/{id}", accept(APPLICATION_JSON), handler::getPerson)
.GET("/", accept(APPLICATION_JSON), handler::getPeople)
.POST("/", contentType(APPLICATION_JSON), handler::createPerson))
.build();
}
}

Request Predicates
@Controller
...
ServerResponse createPerson(ServerRequest request) {
Person person = request.body(Person.class);
this.repository.savePerson(person);
.build();
}
@Bean
static RouterFunction<ServerResponse> routerFunction(PersonHandler handler) {
return route()
.path(“/people", b -> b
.nest(accept(APPLICATION_JSON), b1 -> b1
.GET("/", handler::getPeople)
)
.build();
}
}

Web MVC WebMvc.fn
15
Request Predicates Comparison
@Controller
@RequestMapping(“/people”)
@RequestMapping(value = "/{id}",
method = GET,
produces = APPLICATION_JSON_VALUE)
...
}
@RequestMapping(method = GET,
produces = APPLICATION_JSON_VALUE)
ResponseEntity<List<Person>> showPeople() {
...
}
@RequestMapping(method = POST,
consumes = APPLICATION_JSON_VALUE)
void createPerson(RequestEntity<Person> person) {
...
}
}
@Controller
...
@Bean
return route()
.GET("/{id}", accept(APPLICATION_JSON), handler::getP
.GET("/", accept(APPLICATION_JSON), handler::getPeopl
.POST("/", contentType(APPLICATION_JSON), handler::cr
.build();
}
}

Web MVC WebMvc.fn
16
@Controller
...
@Bean
static RouterFunction<ServerResponse> routerFunction(Person
return route()
.path("/person", b -> b
)
.POST("/", contentType(APPLICATION_JSON), handler::cr
.build();
}
}
?

Handler Filter Functions
Maps ServerRequest and HandlerFunction
to ServerResponse
17

Maps ServerRequest and HandlerFunction to ServerResponse
@Controller
...
@ExceptionHandler(NotFoundException.class)
ResponseEntity notFound() {
return ResponseEntity.notFound().build()
}
}
Web MVC

@Controller
...
ServerResponse notFound(Throwable throwable, ServerRequest request) {
return ServerResponse.notFound().build();
}
@Bean
return route()
)
.onError(NotFoundException.class, handler::notFound)
.build();
}
}
WebMvc.fn

@Controller
...
}
@Bean
return route()
)
.build();
}
}
WebMvc.fn

Web MVC WebMvc.fn
19
Handler Filter Function Comparison
@Controller
...
@ExceptionHandler(NotFoundException.class)
ResponseEntity notFound() {
return ResponseEntity.notFound().build()
}
}
@Controller
...
}
@Bean
return route()
.path("/person", b -> b
)
.build();
}
}

Final Comparison
20

• Functions
• Code
• Rigid handler methods
(ServerRequest→ServerResponse)
• Flexible routing
• Annotations
• Meta-data
• Flexible handler methods
(parameters & return type)
• Limited routing
Web MVC WebMvc.fn
21

Thank You

Introduction to WebMvc.fn

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