Request Handling

Implement the logic to handle requests to WebServer in a Handler, which is a FunctionalInterface. Handlers:

Process the request and send a response.
Act as a filter and forward requests to downstream handlers using the request.next() method.
Throw an exception or call request.next(exception) to begin error handling.

Process Request and Produce Response

Each Handler has two parameters. ServerRequest and ServerResponse.

Request provides access to the request method, URI, path, query parameters, headers and entity.
Response provides an ability to set response code, headers, and entity.

Handler as a Filter

The handler forwards the request to the downstream handlers by nexting. There are two options:

call req.next()
```
.any("/hello", (req, res) -> { 
    // filtering logic  
    req.next(); 
})
```
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- handler for any HTTP method using the /hello path
- business logic implementation
- forward the current request to the downstream handler

call req.next(throwable) to forward the handling to the error handlers

.any("/hello", (req, res) -> { 
    // filtering logic (e.g., validating parameters) 
    if (userParametersOk()) {
        req.next(); 
    } else {
        req.next(new IllegalArgumentException("Invalid parameters."); 
    }
})

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handler for any HTTP method using the /hello path
custom logic
forward the current request to the downstream handler
forward the request to the error handler

The handling logic can explicitly forward the execution to a different thread. This is the reason why returning from the handler can’t automatically trigger calling the next handler.

Sending a response

To complete the request handling, you must send a response by calling the res.send() method.

.get("/hello", (req, res) -> { 
    // terminating logic
    res.status(Http.Status.ACCEPTED_201);
    res.send("Saved!"); 
})

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handler that terminates the request handling for any HTTP method using the /hello path
send the response