httpServlet
layout: default
title: HttpServletRequest and HttpServletResponse
HttpServletRequest and HttpServletResponse are Java object representations of the requests received by your servlet and the subsequent response.
They give us access to a number of methods we can use to manipulate these packets.
HttpServletRequest¶
getHeader(name)- returns the value of the specified header.
HttpServletResponse¶
setHeader(key, value)- adds a response header in a key/value format.setStatus(value)- sets the status code of the response.
Response Handling and Dependency Injection¶
Accessing the HttpServletResponse object from a Spring controller route is possible thanks to Spring's dependency injection.
When a request is received by the Tomcat server, it is mapped to a dispatcher servlet.
- In turn, the dispatcher servlet determines if there is a controller route with a
@RequestMappingcapable of handling the request.
Along the way, the servlet creates several objects that will be needed for the request to be handled (notably a HttpServletRequest and a HttpServletResponse object), and injects these dependencies into the controller method which is responsible for handling the request.
As a result of this dependency injection, EVERY Spring MVC controller method has access to the HttpServletRequest and HttpServletResponse objects (if you chose to use them).
Examples¶
Example 1:
* The following route is 100% valid in Spring, and will respond with the String "pong", and a HTTP Status Code of 200 by default:
@RestController
public class ExampleController {
@GetMapping("/ping")
public String ping() {
return "pong";
}
}
Example 2:
* It is possible to write the same controller method and gain access to the injected HttpServletRequest and HttpServletResponse by parameterizing them in the method signature.
* This method produces the exact same result as the previous method.
@RestController
public class ExampleController {
@GetMapping("/ping")
public String ping(HttpServletRequest request, HttpServletResponse response) {
return "pong";
}
}
Example 3: * With access to the request and response objects, it is possible to extract/modify information from these objects.
- This method still responds with the
String"pong", but we have changed the response's status code to202('Accepted'), and includes a"Location"header, indicating where this information can be found again.
@RestController
public class ExampleController {
@GetMapping("/ping")
public String ping(HttpServletRequest request, HttpServletResponse response) {
response.setStatus(202);
response.setHeader("Location","http://localhost:8080/ping");
return "pong";
}
}
Example 4:
* Similarly, it is possible to gain additional information about a request from the HttpServletRequest object.
In the following method, we will only respond with "pong", status 202 and the "Location" header IF* the request has a "say-please" header. Otherwise, the method will send back a 401 ('Unauthorized'), and the text "you didn't say the magic word":
@RestController
public class ExampleController {
@GetMapping("/ping")
public String ping(HttpServletRequest request, HttpServletResponse response) {
if (request.getHeader("say-please") != null) {
response.setStatus(202);
response.setHeader("Location","http://localhost:8080/ping");
return "pong";
}
response.setStatus(401);
return "you didn't say the magic word";
}
}
Some of your controller methods will not need to modify the request or response at all. In these cases you won't need to create a parameter for either of the injected objects.
- The key takeaway is that if you require access to either, they are both made available to you by SpringMVC's dependency injection.
Drill¶
In the VideoStoreREST application, change the status code of the AddressController's create method to 201 with an appropriate Location header if the creation was successful. If the object failed insertion into the database return a 400.