Balance of responsibility between the client and the server in a client-server architecture.

  • Client Responsibilities:
    • Initiates communication with the server.
    • Sends requests for data or services.
    • Processes responses from the server.
    • Displays data to the user. Deployment models for cloud computing.
  • Public Cloud:
    • Services are provided over the public internet and available to anyone who wants to purchase them.
    • Examples: AWS, Azure, Google Cloud.
    • Advantages: Scalability, cost-effectiveness, no maintenance overhead.
  • Private Cloud:
    • Services are maintained on a private network and are accessible only to a limited number of users.
    • Azure in a box
    • Advantages: Enhanced security, control over resources, customization.
    • Running on-premises or in a data center and utilized by different business divisions.
    • Usually managed by governmental agencies or large enterprises that secure any data.
  • Hybrid Cloud:
    • A combination of public and private clouds, allowing data and applications to be shared between them.
    • describes IT which spans data centers owned by corp and also utilizing cloud services.
    • Advantages: Flexibility, cost-efficiency, scalability.
  • Community Cloud:
    • Infrastructure is shared by several organizations with similar requirements and concerns.
    • Advantages: Cost-sharing, collaboration, industry-specific compliance.
    • run by third party or shared ownership of orgs

What is the internet

  • The internet is a global network of interconnected computers communicating or documents linked together using a common protocol.

    URL –> Unified Resource Locator

  • A URL is a reference to a web resource that specifies its location on a computer network and a mechanism for retrieving it.

HTTP –> HyperText Transfer Protocol

  • HTTP is the foundation of data communication on the World Wide Web. It is used to load web pages using hypertext links.
  • stateless

URI –> Uniform Resource Identifier

  • A URI is a string of characters that identifies a particular resource. It can be a URL or a URN.
  • A URI is a superset of a URL and a URN.

Http Client

  • initiates a TCP connection to the server on port 80
  • sends an HTTP request to the server over this TCP connection
  • Request Methods
    • GET: Retrieve data from the server.
    • POST: Send data to the server to create a resource.
    • PUT: Send data to the server to update a resource.
    • DELETE: Delete a resource on the server.
    • HEAD: Retrieve only the headers of a response.
    • OPTIONS: Retrieve the communication options for the target resource.

Http Server

  • listens for incoming connections on port 80
  • receives the HTTP request from the client
  • Returns an HTTP response to the client and closes the connection
  • Response Status Codes
    • 1xx: Informational
    • 2xx: Success
    • 3xx: Redirection
    • 4xx: Client Error
    • 5xx: Server Error
  • MIME Types
    • Multipurpose Internet Mail Extensions
    • Describes the type of data in a file
    • Examples: text/html, image/jpeg, application/json

HTTP Internet Helpers

Web Caching

  • Web caching is the process of storing copies of web resources to reduce bandwidth usage, server load, and latency.
  • Caches can be located on the client side, server side, or between the client and server.
  • Advantages: Faster load times, reduced server load, improved user experience.
  • Disadvantages: Stale content, privacy concerns, cache consistency issues. HTTP Internet Optimizations
  • Intermediary servers
  • forward proxy

Use the Postman tool to send HTTP requests and view responses.

Create an Http client in Java

import java.net.HttpURLConnection;
import java.net.URL;
import java.io.BufferedReader;
    
public class HttpClient {
    public static void main(String[] args) {
        try {
            URL url = new URL("https://jsonplaceholder.typicode.com/posts/1");
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            connection.setRequestMethod("GET");
            connection.connect();
    
            BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
            String line;
            StringBuilder response = new StringBuilder();
    
            while ((line = reader.readLine()) != null) {
                response.append(line);
            }
    
            reader.close();
            connection.disconnect();
    
            System.out.println(response.toString());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Two arguments

  • URL: The URL of the resource to be accessed.
  • Number of Hops: The maximum number of hops allowed in the network.
import java.util.*;

// Web Crawl
// Given a URL and the number of hops, return the list of URLs that can be visited within the specified number of hops.


public class WebCrawl {
    public static List<String> webCrawl(String url, int hops) {
        List<String> result = new ArrayList<>();
        Set<String> visited = new HashSet<>();
        Queue<String> queue = new LinkedList<>();
        queue.offer(url);
        visited.add(url);
        int level = 0;
        while (!queue.isEmpty() && level <= hops) {
            int size = queue.size();
            for (int i = 0; i < size; i++) {
                String current = queue.poll();
                result.add(current);
                List<String> neighbors = getNeighbors(current);
                for (String neighbor : neighbors) {
                    if (!visited.contains(neighbor)) {
                        queue.offer(neighbor);
                        visited.add(neighbor);
                    }
                }
            }
            level++;
        }
        return result;
    }

    private static List<String> getNeighbors(String url) {
        // Dummy method to get neighbors of a URL
        return new ArrayList<>();
    }

    public static void main(String[] args) {
        String url = "https://example.com";
        int hops = 2;
        List<String> result = webCrawl(url, hops);
        for (String link : result) {
            System.out.println(link);
        }
    }
}

import java.util.*;

// Web Crawl
// Given a URL and the number of hops, return the list of URLs that can be visited within the specified number of hops.

public class WebCrawl {
    public static List<String> webCrawl(String url, int hops) {
        List<String> result = new ArrayList<>();
        Set<String> visited = new HashSet<>();
        Queue<String> queue = new LinkedList<>();
        queue.offer(url);
        visited.add(url);
        int level = 0;
        while (!queue.isEmpty() && level <= hops) {
            int size = queue.size();
            for (int i = 0; i < size; i++) {
                String current = queue.poll();
                result.add(current);
                List<String> neighbors = getNeighbors(current);
                for (String neighbor : neighbors) {
                    if (!visited.contains(neighbor)) {
                        queue.offer(neighbor);
                        visited.add(neighbor);
                    }
                }
            }
            level++;
        }
        return result;
    }

    private static List<String> getNeighbors(String url) {
        // Dummy method to get neighbors of a URL
        return new ArrayList<>();
    }

    public static void main(String[] args) {
        String url = "https://example.com";
        int hops = 2;
        List<String> result = webCrawl(url, hops);
        for (String link : result) {
            System.out.println(link);
        }
    }
}