Implementing Request Handlers
Request handlers are the functions that handle the client request and construct a response. The servlet base classes define the request handler functions. A derived servlet implements the function or functions that handle the client request.
rwsf::HttpServlet contains default implementations of the handlers for standard HTTP requests.
For HTTP/1.1, the default implementation of most methods return the HTTP Method Not Allowed status code (405) with an appropriate message. The method doHead() first defaults to doGet() before returning status code 405.
For HTTP/1.0, requests return a Bad Request Response status code (400).
An HTTP servlet implements the functions for the methods the servlet accepts and relies on the default implementations for methods the servlet does not accept.
Table 1 – Request handlers by HTTP method
HTTP Method | rwsf::HttpServlet function | Description |
|---|
DELETE | doDelete | Removes the resource from the Agent. |
GET | doGet | Returns a document. |
HEAD | doHead | Returns the headers for a document. |
POST | doPost | Sends information to the Agent. |
PUT | doPut | Uploads a file to the Agent. |
TRACE | doTrace | Returns the request to the client |
Each of the above functions takes a
rwsf::HttpServletRequest and a
rwsf::HttpServletResponse as parameters. To respond to a request, a servlet overrides the functions that correspond to the request methods the servlet accepts. For example, an HTTP servlet that accepts the HTTP
GET method implements the
doGet() function.
Since the HelloWorldExample servlet only responds to HTTP GET requests, the servlet only declares doGet(). The sample below shows an excerpt from the header file for the HelloWorldExample servlet:
// HelloWorldExample.h
#include <rw/rwsf/servlet/http/HttpServlet.h>
class HelloWorldExample : public rwsf::HttpServlet
{
public:
void doGet(rwsf::HttpServletRequest& request,
rwsf::HttpServletResponse& response);
};
The HelloWorldExample servlet does not dynamically allocate resources, so the servlet needs no init() method or destroy() method.
The implementation of the servlet simply returns an HTTP response without inspecting the request. The sample below shows the servlet implementation:
// HelloWorldExample.cpp
#include "HelloWorldExample.h"
// Define the servlet for the container.
RWSF_DEFINE_SERVLET(HelloWorldExample) // 1
// Implement a response to the HTTP GET method.
void
HelloWorldExample::doGet(rwsf::HttpServletRequest& request,
rwsf::HttpServletResponse& response)
{
// Tell the client that the response is an HTML document.
response.setContentType("text/html"); // 2
// Get a reference to the response output stream.
rwsf::ServletOutputStream& out = response.getOutputStream(); // 3
// Send a canned response to the client.
log("Hello World Example: begin"); // 4
log("Hello World Example: Starting HTML output...");
out.println("<html>");
out.println("<head>");
log("Hello World Example: Printing title...");
out.println("<title>HelloWorldExample</title>");
out.println("</head>");
out.println("<body bgcolor=\"white\">");
out.println("<h1>HelloWorldExample</h1>");
out.println("</body>");
out.println("</html>");
log("Hello World Example: Finished HTML output");
log("Hello World Example: end");
}
