Request Mapping Annotation in Spring Boot

The @RequestMapping is a class level (also called type level) and method level annotation, it is used to process HTTP requests with specified URL patterns. It is used in and along with both @Controller and @RestController.

Table of Contents

• Request Mapping Annotation in Spring Boot
  • 1. How @RequestMapping annotation it is used?
  • 2. Optional Elements of @RequestMapping
    • 2.1 name, value and path
    • 2.2 headers, consumes and produces
  • 3. Specialization of @RequestMapping

1. How @RequestMapping annotation it is used?

@Controller
@RequestMapping("/student")
public class StudentController{

  @RequestMapping("/dashboard")
  public String dashboard(){
  return "dashboard";
  }

 @RequestMapping("result")
 public String result(){
 return "result";
 }
}

We can see in above code sample "/student" , "/dashboard" and "result" passed with annotation are called request value/path present in the URL patterns.

The class StudentController will handle all the requests like example.com/students

And the member functions(methods) inside the class will handle the requests followed by the example.com/students/**

    dashboard() method will handle the request coming to example.com/students/dashboard

    result() method will handle the request coming to example.com/students/result

2. Optional Elements of @RequestMapping

All fields are public and abstract

Modifier and Type	Optional Element and Description
String[]	consumes Narrows the primary mapping by media types that can be consumed by the mapped handler.
String[]	headers The headers of the mapped request, narrowing the primary mapping.
RequestMethod[]	method The HTTP request methods to map to, narrowing the primary mapping: GET, POST, HEAD, OPTIONS, PUT, PATCH, DELETE, TRACE.
String	name Assign a name to this mapping.
String[]	params The parameters of the mapped request, narrowing the primary mapping.
String[]	path The path mapping URIs
String[]	produces Narrows the primary mapping by media types that can be produced by the mapped handler.
String[]	value The primary mapping expressed by this annotation.

 

2.1 name, value and path

These elements are quit confusing, seems they are same.

• name - As in servlet mapping we assing name to the servlet class and url pattern and later it used in web.xml, in spring we can also assign name to the mapping. 
• value & path - according to official documentation both are alias of each other, both accept string array (see in table) ,both works similar, we can conversely use any of them. But the question arises, if they are doing same work then why they exist?

Remember!

Spring Boot is built on the top of Spring framework, Boot is focused to reduce configuration overheads, other things work same as Spring.

2.2 headers, consumes and produces

• headers - Headers are the meta data or extra message attached to HTTP requests. If we want to filter the request mappings on the basis of headers we need to specify that. It narrows down the mapping e.g. 

   @RequestMapping(value = "/something", headers = "content-type=text/*")

  it will accept all content types like "text/html", "text/plain", etc. Also we can see it contains expression "content-type=text" we can also negate that with != i.e "content-type!=text/" which means it will accept all "/something" having headers with content-type "application/json", "application/xml" , "image/png", "image/, etc except "text/". Here * is wild card used for all.

2.3 params

 

2.4 method

3. Specialization of @RequestMapping

@RequestMapping specialiszations are created on basis of HTTP request methods, the other elements provided in the above table are used similarly as per the requirement.

1. @GetMapping
2. @PutMapping
3. @PostMapping
4. @DeleteMapping
5. @PatchMapping

3.1 @GetMapping