Dinesh on Java

In this article, we are going discuss about one of the main annotation in Spring MVC @RequestMapping – used to mapping a web request to Spring Controller’s handler methods.

All incoming requests are handled by the Dispatcher Servlet and it route them through Spring. When it receives a web request, it determines which controllers should handle the incoming request.

Dispatcher Servlet initially scans all the classes that are annotated with the @Controller annotation. The dispatching process depends on the various @RequestMapping annotations declared in a controller class and its handler methods.

There are three levels of request mapping in Spring MVC

• @RequestMapping annotations at only method level
• @RequestMapping annotations at class level
• Mapping requests by request type

@RequestMapping

It can be applied to the controller class as well as methods. This annotation for mapping web requests onto specific handler classes and/or handler methods.

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@RequestMapping annotations at only method level

In this case we are using @RequestMapping annotations is to declare the handler methods directly. The handler method is annotated with @RequestMapping annotation containing a URL pattern. If this pattern of a handler @RequestMapping annotation matches the request URL, DispatcherServlet it dispatches the request to this handler for it to process the request.

1. @RequestMapping Basics

Let’s discuss with a simple example – mapping an HTTP request to a method using some straightforward criteria.

1.1 @RequestMapping – by Path

@RequestMapping(value = "/doj/spring")
 @ResponseBody
 public String getDOJSpringCourse(){
    return "Get DOJ Course for Spring";
 }

For testing hit following URL on browser:

GET http://localhost:8080/SpringApp/doj/spring

— response —
200 OK
Server: Apache-Coyote/1.1
Content-Type: text/html
Content-Length: 25
Date: Fri, 18 Mar 2016 10:38:14 GMT

Get DOJ Course for Spring

1.2  @RequestMapping – the HTTP Method

There is no by default HTTP method mapped by a @RequestMapping – so it maps to any type of HTTP request; we sh to add the method :

@RequestMapping(value = "/doj/spring", method = RequestMethod.POST)
 @ResponseBody
 public String postDOJSpringCourse(){
  return "Post DOJ Course for Spring";
 }

POST http://localhost:8080/SpringApp/doj/spring
Content-Type: application/json

— response —
200 OK
Server: Apache-Coyote/1.1
Content-Type: text/html
Content-Length: 26
Date: Fri, 18 Mar 2016 10:38:22 GMT

Post DOJ Course for Spring

2. RequestMapping with HTTP Headers

2.1. @RequestMapping with the headers attribute

The mapping can be narrowed even further by specifying a header for the request:

@RequestMapping(value = "/doj/spring", headers = "key=val")
 @ResponseBody
 public String getDOJSpringCourseWithHeaders(){
  return "Get DOJ Course for Spring with headers";
 }

And even multiple headers via the header attribute of @RequestMapping:

@RequestMapping(value = "/doj/spring", headers = {"key1=val1", "key2=val2"})
 @ResponseBody
 public String getDOJSpringCourseWithHeaders(){
  return "Get DOJ Course for Spring with headers";
 }

2.2. @RequestMapping Consumes and Produces

Mapping media types produced by a controller method is worth special attention – we can map a request based on its Accept header via the @RequestMapping headers attribute introduced above:

@RequestMapping(value = "/doj/spring", headers = "Accept=application/json")
 @ResponseBody
 public String getDOJSpringCourseJSON(){
  return "Get DOJ Course for Spring as JSON";
 }

GET http://localhost:8080/SpringApp/doj/spring
key: value

— response —
200 OK
Server: Apache-Coyote/1.1
Content-Type: application/json
Content-Length: 33
Date: Fri, 18 Mar 2016 10:57:03 GMT

Get DOJ Course for Spring as JSON

@RequestMapping annotation now has a produces and a consumes attributes, specifically for this purpose:

@RequestMapping(value = "/doj/spring", method = RequestMethod.GET, produces = "application/json")
 @ResponseBody
 public String getDOJSpringCourseJSONFromREST(){
  return "Get DOJ Course for Spring as JSON from REST";
 }

GET http://localhost:8080/SpringApp/doj/spring
key: value

— response —
200 OK
Server: Apache-Coyote/1.1
Content-Type: application/json
Content-Length: 43
Date: Fri, 18 Mar 2016 11:00:28 GMT

Get DOJ Course for Spring as JSON from REST

Additionally, produces support multiple values as well:

@RequestMapping(value = "/doj/spring", produces = { "application/json", "application/xml" })

A final note on the new produces and consumes mechanism – these behave differently from most other annotations: when specified at type level, the method level annotations do not complement but override the type level information.

3. RequestMapping with Path Variables

Parts of the mapping URI can be bound to variables via the @PathVariable annotation.

3.1. Single @PathVariable