531.1 Handling requests (web server frameworks)

Learn how web servers and frameworks manage and respond to client requests on the back end.

Overview

In this topic, we explore how back-end systems handle web requests from users. Students learn how web servers receive requests from the browser and pass them to back-end frameworks, which process the request, run logic, and generate responses. This introduces students to the concept of routing, middleware, and server-side control in a web application.

Targets

In this topic, students learn to:

• Explain the role of a web server in a web application

• Describe how back-end frameworks process and respond to requests

• Understand how routing maps URLs to specific logic

• Identify the parts of a server-side response cycle

• Recognise how requests are handled differently on the back end compared to the front end

Syllabus references

Programming for the web

Designing web applications

• Observe and describe the back-end process used to manage a web request – role of webserver software – web framework – objects – libraries – databases

What is a web server?

A web server is a program that listens for incoming HTTP requests from a browser (client) and returns the correct response.

Examples of web servers:

• Apache

• Nginx

• Gunicorn (Python)

• Node.js (JavaScript)

When a user visits a webpage:

1. The browser sends a request to the web server

2. The server forwards the request to the appropriate handler or framework

3. The server sends back the HTML, JSON, or other data as a response

The role of a web framework

A web framework is a back-end development tool that simplifies handling requests, managing routes, and connecting to databases.

Popular frameworks include:

• Flask and Django (Python)

• Express (JavaScript/Node.js)

• Laravel (PHP)

• Ruby on Rails (Ruby)

Frameworks allow developers to define how the server should respond to different types of requests using routes and controllers.

Example (Python with Flask)

from flask import Flask

app = Flask(__name__)

@app.route("/")
def home():
    return "Welcome to the homepage!"

This example responds with a welcome message when a user visits the root URL (/).

A web server receives requests and passes them to a framework. The framework processes the request and generates a response, which is sent back to the browser.

How routing works

Routing is how a web framework maps a specific URL (e.g. /login) to a function that handles the request. Developers define routes for:

• Pages (/home, /about)

• Actions (/submit, /logout)

• API endpoints (/api/users, /api/data)

Routing logic determines which code is run and what response is sent.

Summary

The back end of a web application is responsible for receiving requests, running server-side logic, and returning the appropriate response. Web servers and frameworks work together to route requests, connect to resources like databases, and generate dynamic content for users.