Forem: Javier Jimenez

Java on Ubuntu: Installation, Setup, and First Steps

Javier Jimenez — Fri, 19 Dec 2025 15:14:39 +0000

I recommend watching first – installing Homebrew and asdf on Ubuntu (it’s short, just 5 commands)

📘 Official Documentation

Java – Official Documentation
Java – On DevDocs.io

⭐ Popular Frameworks (ordered from lower to higher learning curve)

Spark Java — Minimalist, lightweight.
Javalin — Simple, modern.
Spring Boot — Complete, enterprise.

🛠️ Installing Java on Ubuntu

sudo apt update
sudo apt install openjdk-21-jdk

Verify installation:

java --version
javac --version

🍺 Installation with Homebrew

brew install openjdk

Add Java to PATH (if brew indicates it):

echo 'export PATH="/home/linuxbrew/.linuxbrew/opt/openjdk/bin:$PATH"' >> ~/.bashrc
source ~/.bashrc

📦 Standard Dependency Manager (Maven / Gradle)

Check Maven version:

mvn --version

Check Gradle version:

gradle --version

🔧 Installation with ASDF

System dependencies

sudo apt update
sudo apt install -y curl git unzip zip

Install plugin + version

asdf plugin add java
asdf list-all java

# install different versions
asdf install java openjdk-21.0.2
asdf install java temurin-17.0.10

# Set a global version
asdf global java openjdk-21.0.2

# Set a local version
asdf local java temurin-17.0.10

Example: .tool-versions

java openjdk-21.0.2

📝▶️ Create and run a Java file

Create file:

touch Hola.java

Content of Hola.java

public class Hola {
    public static void main(String[] args) {
        System.out.println("Hello World from Java!");
    }
}

💻 Compile and run:

javac Hola.java
java Hola

🟦 Basic Java example

🗂️🌐 Static file Web Server

**Note:* Java includes a basic HTTP server (HttpServer). You don’t need frameworks.*

What it does:

Defines the query parameter name
Gets the value from the URL

stripHtmlTags(text): removes HTML tags

Renders the received variable inside an <h1>

📝 Create file: touch WebServer.java

📦 Content of WebServer.java

import com.sun.net.httpserver.HttpServer;
import com.sun.net.httpserver.HttpExchange;

import java.io.IOException;
import java.io.OutputStream;
import java.net.InetSocketAddress;
import java.net.URLDecoder;
import java.nio.charset.StandardCharsets;

public class WebServer {

    public static void main(String[] args) throws Exception {

        HttpServer server = HttpServer.create(new InetSocketAddress(7000), 0);

        server.createContext("/", (HttpExchange exchange) -> {

            String query = exchange.getRequestURI().getQuery();
            String username = "guest";

            if (query != null && query.startsWith("username=")) {
                username = URLDecoder.decode(
                        query.replace("username=", ""),
                        StandardCharsets.UTF_8
                );
                username = stripHtmlTags(username);
            }

            String response = """
                <!DOCTYPE html>
                <html lang="en">
                <head>
                    <meta charset="UTF-8">
                    <title>Hello</title>
                </head>
                <body style="text-align:center">
                    <h1>Hello, %s</h1>
                </body>
                </html>
                """.formatted(username);

            exchange.getResponseHeaders().add("Content-Type", "text/html");
            exchange.sendResponseHeaders(200, response.getBytes().length);

            OutputStream os = exchange.getResponseBody();
            os.write(response.getBytes());
            os.close();
        });

        server.start();
        System.out.println("Server running at http://localhost:7000");
        System.out.println("Try at http://localhost:7000?username=Homer");
    }

    private static String stripHtmlTags(String input) {
        return input.replaceAll("<[^>]*>", "");
    }
}

▶️ Compile and run

javac WebServer.java
java WebServer

👉 visit:
http://localhost:7000/?username=Homer

⚙️🧩 JSON REST API

What it does:

Reads data from a data.json file
Exposes 2 endpoints:

Character list at /characters
Character by id at /characters/:id

Example file: data.json

[
  {
    "id": 1,
    "age": 39,
    "name": "Homer Tompson",
    "portrait_path": "https://cdn.thesimpsonsapi.com/500/character/1.webp"
  },
  {
    "id": 2,
    "age": 39,
    "name": "Marge Simpson",
    "portrait_path": "https://cdn.thesimpsonsapi.com/500/character/2.webp"
  }
]

📝 Create file: touch ApiServer.java

▶️ File content: ApiServer.java

import com.sun.net.httpserver.HttpServer;
import com.sun.net.httpserver.HttpExchange;

import java.io.IOException;
import java.io.OutputStream;
import java.net.InetSocketAddress;
import java.nio.file.Files;
import java.nio.file.Path;

public class ApiServer {

    private static String jsonData;

    public static void main(String[] args) throws Exception {

        jsonData = Files.readString(Path.of("data.json"));

        HttpServer server = HttpServer.create(new InetSocketAddress(7001), 0);

        server.createContext("/characters", (HttpExchange exchange) -> {

            String path = exchange.getRequestURI().getPath();
            exchange.getResponseHeaders().add("Content-Type", "application/json");

            // GET /characters
            if (path.equals("/characters")) {
                send(exchange, 200, jsonData);
                return;
            }

            // GET /characters/:id
            if (path.startsWith("/characters/")) {
                String id = path.replace("/characters/", "");

                if (jsonData.contains("\"id\": " + id)) {
                    send(exchange, 200, jsonData);
                } else {
                    send(exchange, 404, "{\"error\":\"Character not found\"}");
                }
                return;
            }

            send(exchange, 404, "{\"error\":\"Route not found\"}");
        });

        server.start();
        System.out.println("Server running at http://localhost:7001/characters");
    }

    private static void send(HttpExchange exchange, int status, String body) throws IOException {
        exchange.sendResponseHeaders(status, body.getBytes().length);
        OutputStream os = exchange.getResponseBody();
        os.write(body.getBytes());
        os.close();
    }
}

▶️ Compile and run

javac ApiServer.java
java ApiServer

👉 visit:
http://localhost:7001/characters

To test the endpoint by id:
http://localhost:7001/characters/1

Python on Ubuntu: Installation, Setup, and First Steps

Javier Jimenez — Sat, 29 Nov 2025 16:00:00 +0000

I recommend viewing first – installation of Homebrew and asdf on Ubuntu (it's short, just 5 commands)

📘 Official Documentation

Python - Docs
Python - On DevDocs.io

⭐ Popular Frameworks (ordered from lower to higher learning curve)

Flask — Minimalist, simple.
FastAPI — Very fast, modern.
Django — Complete and structured.

🛠️ Installing Python on Ubuntu

sudo apt update
sudo apt install python3 python3-pip

🍺 Installation with Homebrew

brew install python

📦 Standard Package Manager (pip — included)

Check version:

pip3 --version

Install a package:

pip install <package>

🔧 Installation with ASDF

System dependencies

sudo apt update
sudo apt install -y build-essential libssl-dev zlib1g-dev \
libbz2-dev libreadline-dev libsqlite3-dev wget curl llvm \
libncursesw5-dev xz-utils tk-dev libxml2-dev libxmlsec1-dev

Install plugin + version

asdf plugin add python
asdf list-all python

# install different versions
asdf install python 3.12.2
asdf install python 2.7.18

# Set a global version
asdf global python 3.12.2

# Set a local version
# - Remember that a local version only affects the current directory that contains the .tool-versions file
asdf local python 2.7.18

Example: .tool-versions

python 3.12.2

📝▶️ Create and run a Python file

Create file:

touch hello.py

Content of hello.py

print("Hello World from Python!")

💻 Run locally:

python3 hello.py

🟦 Basic example in Python

🗂️🌐 Static file web server.

Note: Python already includes a basic built-in web server. You don’t need to install anything.

What it does:

Defines the name of the query parameter
Obtains the value of the query parameter from the URL
- strip_html_tags(text): Removes HTML tags leaving only inner content.
Renders the variable received in the query parameter inside the <H1> tag

📝 Create file: touch index.py

📦 Content of index.py

import re
import urllib.parse
from http.server import BaseHTTPRequestHandler, HTTPServer

class Handler(BaseHTTPRequestHandler):
    def do_GET(self):
        # Get parameters from the URL
        parsed = urllib.parse.urlparse(self.path)
        query = urllib.parse.parse_qs(parsed.query)

        username = query.get("username", ["invitado"])[0]
        username = strip_html_tags(username)

        # Response
        content = f"""
        <!DOCTYPE html>
        <html lang="es">
        <head>
            <meta charset="UTF-8">
            <title>Hola</title>
        </head>
        <body style="text-align:center">
            <h1>Hola, {username}</h1>
        </body>
        </html>
        """

        self.send_response(200)
        self.send_header("Content-type", "text/html")
        self.end_headers()
        self.wfile.write(content.encode("utf-8"))



def strip_html_tags(text):
    return re.sub(r"<[^>]+>", "", text)


# Start server
if __name__ == "__main__":
    server = HTTPServer(("localhost", 7000), Handler)
    print("Server running at http://localhost:7000")
    print("Test at http://localhost:7000?username=Homero")
    server.serve_forever()

▶️ Run the project / start the server

python3 index.py

👉 visit:
http://localhost:7000/?username=Homero

⚙️🧩 JSON REST API

What it does:

Reads data from a data.json file
Exposes one endpoint with that data
- A list of characters at /characters
- And the data of a character by id /characters/:id

Example file: data.json

[
  {
    "id": 1,
    "age": 39,
    "name": "Homer Tompson",
    "portrait_path": "https://cdn.thesimpsonsapi.com/500/character/1.webp"
  },
  {
    "id": 2,
    "age": 39,
    "name": "Marge Simpson",
    "portrait_path": "https://cdn.thesimpsonsapi.com/500/character/2.webp"
  }
]

📝 Create file: touch api.py

▶️ Content of the file: api.py

import json
from http.server import BaseHTTPRequestHandler, HTTPServer

# Load data.json
def load_characters():
    with open("data.json", "r", encoding="utf-8") as f:
        return json.load(f)


class MyHandler(BaseHTTPRequestHandler):

    def _send_json(self, data, status=200):
        self.send_response(status)
        self.send_header("Content-Type", "application/json")
        self.end_headers()
        self.wfile.write(json.dumps(data, ensure_ascii=False).encode("utf-8"))

    def do_GET(self):
        characters = load_characters()

        # GET /characters
        if self.path == "/characters":
            self._send_json(characters)
            return

        # GET /characters/:id
        if self.path.startswith("/characters/"):
            try:
                id_str = self.path.split("/")[2]
                char_id = int(id_str)
            except:
                self._send_json({"error": "Invalid ID"}, 400)
                return

            found = next((c for c in characters if c["id"] == char_id), None)

            if found:
                self._send_json(found)
                return
            else:
                self._send_json({"error": "Character not found"}, 404)
                return

        # If no route matches
        self._send_json({
            "error": "Route not found",
            "url_list": "http://localhost:7001/characters",
            "url_character": "http://localhost:7001/characters/1"
        }, 404)


if __name__ == "__main__":
    server = HTTPServer(("localhost", 7001), MyHandler)
    print("Server running at http://localhost:7001/characters")
    server.serve_forever()

▶️ Run the project / start the server

python3 api.js

👉 visit:
http://localhost:7001/characters

To test URL sanitization:
http://localhost:7001/characters/1

Si quieres puedo traducir otro artículo también.

C++ on Ubuntu: Installation, Setup, and First Steps

Javier Jimenez — Thu, 27 Nov 2025 16:00:00 +0000

I recommend seeing first – installation of Homebrew and asdf on Ubuntu (it’s short, only 5 commands)

📘 Official Documentation

C++ - Reference on CPPReference
C++ - On DevDocs.io

⭐ Popular Frameworks (ordered from lower to higher learning curve)

⚠️ In C++ there are no standard “web frameworks” like in Python, but there are widely used libraries.

No Framework (POSIX sockets) — Minimalist, simple, native.
Crow — Inspired by Flask, very easy to use.
Boost.Beast — Fast and modern for HTTP/WebSocket.
CppRestSDK — Complete, Django/Express style.

🛠️ C++ Installation on Ubuntu

C++ already comes installed, but you should make sure you have g++:

sudo apt update
sudo apt install g++ build-essential

🍺 Installation with Homebrew

brew install gcc

📦 Standard Package Manager

C++ does not have an official manager like pip or npm, but the most used ones are:

apt (on Ubuntu)
vcpkg
conan

Check compiler version:

g++ --version

Install a JSON library (example):

sudo apt install nlohmann-json3-dev

🔧 Installation with ASDF

ASDF can compile specific versions of GCC/LLVM.

System dependencies:

sudo apt update
sudo apt install -y build-essential libssl-dev zlib1g-dev \
libbz2-dev libreadline-dev libsqlite3-dev wget curl llvm \
libncursesw5-dev xz-utils tk-dev libxml2-dev libxmlsec1-dev

Install plugin + version

asdf plugin add gcc
asdf install gcc 14.1.0
asdf global gcc 14.1.0

Example: .tool-versions

gcc 14.1.0

📝▶️ Create and run a C++ file

Create file:

touch hello.cpp

Contents of hello.cpp

#include <iostream>
int main() {
    std::cout << "Hola Mundo desde C++!\n";
    return 0;
}

💻 Compile and run locally:

g++ hello.cpp -o app-hello
./app-hello

🟦 Basic example in C++

🗂️🌐 Static file Web Server.

Note: C++ does not come with an integrated web server.
But you can create a very small one using POSIX sockets (no dependencies).

📝 Create file: touch server.cpp

📦 Contents of server.cpp

#include <iostream>
#include <string>
#include <regex>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>

std::string html_escape(const std::string& text) {
    std::string escaped = text;
    escaped = std::regex_replace(escaped, std::regex("&"), "&amp;");
    escaped = std::regex_replace(escaped, std::regex("<"), "&lt;");
    escaped = std::regex_replace(escaped, std::regex(">"), "&gt;");
    escaped = std::regex_replace(escaped, std::regex("\""), "&quot;");
    return escaped;
}

int main() {
    int server = socket(AF_INET, SOCK_STREAM, 0);

    sockaddr_in addr{};
    addr.sin_family = AF_INET;
    addr.sin_port = htons(8000);
    addr.sin_addr.s_addr = INADDR_ANY;

    bind(server, (sockaddr*)&addr, sizeof(addr));
    listen(server, 10);

    std::cout << "Server running at http://localhost:8000\n";

    while (true) {
        int client = accept(server, nullptr, nullptr);

        char buffer[2048] = {0};
        read(client, buffer, sizeof(buffer));
        std::string request(buffer);

        // Extract path
        size_t start = request.find("GET ");
        size_t end = request.find(" HTTP/");
        std::string path = request.substr(start + 4, end - (start + 4));

        // Get username
        std::string username = "guest";
        size_t qpos = path.find("?username=");
        if (qpos != std::string::npos) {
            username = path.substr(qpos + 10);
        }
        username = html_escape(username);

        // Generate HTML
        std::string content =
            "<!DOCTYPE html><html lang='es'><head><meta charset='UTF-8'>"
            "<title>Hello</title></head><body style='text-align:center'>"
            "<h1>Hello, " + username + "</h1></body></html>";

        std::string response =
            "HTTP/1.1 200 OK\r\n"
            "Content-Type: text/html\r\n"
            "Content-Length: " + std::to_string(content.size()) + "\r\n"
            "Connection: close\r\n\r\n" +
            content;

        send(client, response.c_str(), response.size(), 0);
        close(client);
    }
}

▶️ Compile and run

g++ server.cpp -o http-server
./http-server

👉 Visit:
http://localhost:8000/?username=Homero

⚙️🧩 JSON REST API

What it does:

Reads data from a data.json file
Exposes two endpoints:

List of characters at /characters
Data by ID at /characters/:id

Example file: data.json

[
  {
    "id": 1,
    "age": 39,
    "name": "Homer Tompson",
    "portrait_path": "https://cdn.thesimpsonsapi.com/500/character/1.webp"
  },
  {
    "id": 2,
    "age": 39,
    "name": "Marge Simpson",
    "portrait_path": "https://cdn.thesimpsonsapi.com/500/character/2.webp"
  }
]

📝 Create file: touch api.cpp

▶️ File contents: api.cpp

This example uses the nlohmann/json library (header-only).
Install it on Ubuntu:

sudo apt install nlohmann-json3-dev

#include <iostream>
#include <fstream>
#include <string>
#include <regex>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <nlohmann/json.hpp>

using json = nlohmann::json;

// Load JSON file
json load_characters() {
    std::ifstream f("data.json");
    json data;
    f >> data;
    return data;
}

std::string make_json_response(const json& data, int status=200) {
    std::string body = data.dump();
    return
        "HTTP/1.1 " + std::to_string(status) + " OK\r\n"
        "Content-Type: application/json\r\n"
        "Content-Length: " + std::to_string(body.size()) + "\r\n"
        "Connection: close\r\n\r\n" +
        body;
}

int main() {
    int server = socket(AF_INET, SOCK_STREAM, 0);

    sockaddr_in addr{};
    addr.sin_family = AF_INET;
    addr.sin_port = htons(7001);
    addr.sin_addr.s_addr = INADDR_ANY;

    bind(server, (sockaddr*)&addr, sizeof(addr));
    listen(server, 10);

    std::cout << "Server running at http://localhost:7001/characters\n";

    while (true) {
        int client = accept(server, nullptr, nullptr);

        char buffer[4096] = {0};
        read(client, buffer, sizeof(buffer));
        std::string request(buffer);

        size_t s = request.find("GET ");
        size_t e = request.find(" HTTP/");
        std::string path = request.substr(s + 4, e - (s + 4));

        json data = load_characters();

        // /characters
        if (path == "/characters") {
            auto res = make_json_response(data, 200);
            send(client, res.c_str(), res.size(), 0);
            close(client);
            continue;
        }

        // /characters/:id
        std::regex reg("^/characters/([0-9]+)$");
        std::smatch match;
        if (std::regex_match(path, match, reg)) {
            int id = std::stoi(match[1]);
            json found = nullptr;
            for (auto& c : data)
                if (c["id"] == id) found = c;

            if (!found.is_null()) {
                auto res = make_json_response(found, 200);
                send(client, res.c_str(), res.size(), 0);
            } else {
                auto res = make_json_response({{"error","Character not found"}}, 404);
                send(client, res.c_str(), res.size(), 0);
            }
            close(client);
            continue;
        }

        // Route not found
        json notfound = {
            {"error", "Route not found"},
            {"url_list", "http://localhost:7001/characters"},
            {"url_character", "http://localhost:7001/characters/1"}
        };
        auto res = make_json_response(notfound, 404);
        send(client, res.c_str(), res.size(), 0);

        close(client);
    }
}

▶️ Compile and run

g++ api.cpp -o api -std=c++17
./api

👉 Visit:
http://localhost:7001/characters

To test sanitization:
http://localhost:7001/characters/1

🟦 Extra example in C++

💻 GUI Calculator with QT

What it does:

Creates a small graphical calculator using Qt5.
Takes two numbers as input.
Provides four buttons: add, subtract, multiply, divide.
Displays the result inside the window.
Compiles using Qt5Widgets on Ubuntu.

To compile this file on Ubuntu:

# Install: 
sudo apt install qtbase5-dev

📝 Crear archivo: touch qt-calc.cpp

▶️ Contenido del archivo: qt-calc.cpp

#include <QApplication>
#include <QWidget>
#include <QLineEdit>
#include <QPushButton>
#include <QVBoxLayout>
#include <QHBoxLayout>
#include <QLabel>

int main(int argc, char *argv[]) {
    QApplication app(argc, argv);

    QWidget window;
    window.setWindowTitle("Calculadora Qt");

    // Inputs
    QLineEdit *input1 = new QLineEdit();
    QLineEdit *input2 = new QLineEdit();
    QLabel *result = new QLabel("Resultado: ");

    input1->setPlaceholderText("Número 1");
    input2->setPlaceholderText("Número 2");

    // Buttons
    QPushButton *btnAdd = new QPushButton("+");
    QPushButton *btnSub = new QPushButton("-");
    QPushButton *btnMul = new QPushButton("*");
    QPushButton *btnDiv = new QPushButton("/");

    // Horizontal layout for buttons
    QHBoxLayout *buttonsLayout = new QHBoxLayout();
    buttonsLayout->addWidget(btnAdd);
    buttonsLayout->addWidget(btnSub);
    buttonsLayout->addWidget(btnMul);
    buttonsLayout->addWidget(btnDiv);

    // Main layout
    QVBoxLayout *layout = new QVBoxLayout();
    layout->addWidget(input1);
    layout->addWidget(input2);
    layout->addLayout(buttonsLayout);
    layout->addWidget(result);
    window.setLayout(layout);

    // Helper function to calculate
    auto calc = [&](char op) {
        double a = input1->text().toDouble();
        double b = input2->text().toDouble();
        double r = 0;

        switch (op) {
            case '+': r = a + b; break;
            case '-': r = a - b; break;
            case '*': r = a * b; break;
            case '/': r = (b != 0) ? a / b : 0; break;
        }

        result->setText("Resultado: " + QString::number(r));
    };

    // Connect buttons
    QObject::connect(btnAdd, &QPushButton::clicked, [&]() { calc('+'); });
    QObject::connect(btnSub, &QPushButton::clicked, [&]() { calc('-'); });
    QObject::connect(btnMul, &QPushButton::clicked, [&]() { calc('*'); });
    QObject::connect(btnDiv, &QPushButton::clicked, [&]() { calc('/'); });

    window.show();
    return app.exec();
}

▶️ Compilar y correr

g++ qt-calc.cpp -o app-qt-calc -fPIC $(pkg-config --cflags --libs Qt5Widgets)

./app-qt-calc

NodeJS on Ubuntu: Installation, Setup, and First Steps

Javier Jimenez — Tue, 25 Nov 2025 16:00:00 +0000

I recommend seeing first – installation of Homebrew and asdf on Ubuntu (it’s short, only 5 commands)

📘 Official Documentation

https://nodejs.org/en/docs

⭐ Popular Frameworks (ordered from lower to higher learning curve)

Express — Minimalist and flexible framework for creating APIs and HTTP servers with Node.js.
Fastify — Fast and efficient framework focused on high performance and low resource consumption.
NestJS — Modular and structured framework inspired by Angular, ideal for scalable applications in Node.js.

🛠️ Installation on Ubuntu

sudo apt update
sudo apt install nodejs npm

For updated versions, NodeSource is recommended:

curl -fsSL https://deb.nodesource.com/setup_20.x | sudo -E bash -
sudo apt install -y nodejs

🍺 Installation with Homebrew

brew install node

📦 Standard Package Manager

Node uses npm (included by default) or pnpm/yarn optionally.

Install pnpm (globally):

npm install -g pnpm

🔧 Installation with ASDF

# add plugin
asdf plugin add nodejs https://github.com/asdf-vm/asdf-nodejs.git

# import keys
bash ~/.asdf/plugins/nodejs/bin/import-release-team-keyring

# install a version
asdf install nodejs 20.11.0

# set global or local
asdf global nodejs 20.11.0
# or
asdf local nodejs 20.11.0

📄 Example .tool-versions

nodejs 20.11.0

🔧 Install NVM (Node Version Manager)

Beyond the fact that asdf can be used to unify all version managers into one tool, the truth is that the standard in Node is NVM, so it also seems correct to include the standard to get familiar with it.

curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.39.7/install.sh | bash

source ~/.nvm/nvm.sh

Install a version of Node.js with NVM

# Install the latest LTS version
nvm install --lts

# Install a specific version
nvm install 20.11.0

# Use an installed version
nvm use 20.11.0

# Set default version
nvm alias default 20.11.0

# Useful NVM commands list
nvm ls
nvm ls-remote
nvm ls-remote --lts
nvm ls
nvm uninstall 18

📄 Example .nvmrc

20.11.0

📝▶️ Create and run a Node.js file

Create file: touch index.js

Contents of index.js

console.log('Hola Mundo Node');

💻 Run locally:

node index.js

🟩 Basic Example in Node.js

🗂️🌐 Static Files Web Server

What It Does:

Defines the name of the query parameter
Gets the value of the query parameter from the URL
- url.searchParams.get() is used to access query parameters.
- and stripTags(input) is used to clean < and > tags into HTML entities.
Renders the variable received in the query parameter inside the <H1> tag

📝 Create file: touch server.js

📦 Contents of server.js

import http from "http";
import { URL } from "url";

// URL sanitization
function stripTags(input) {
  return input.replace(/<[^>]*>/g, "");
}

const server = http.createServer((req, res) => {
  const url = new URL(req.url, `http://localho7000`);
  const username = stripTags(url.searchParams.get("username") || "invitado");

  const html = `
    <!DOCTYPE html>
    <html lang="es">
    <head><meta charset="UTF-8"><title>Hola</title></head>
    <body style="text-align:center">
        <h1>Hola, ${username}</h1>
    </body>
    </html>
  `;

  res.writeHead(200, { "Content-Type": "text/html" });
  res.end(html);
});

server.listen(7000, () => {
  console.log("Server at http://localhost:7000?username=Homero");
});

▶️ Run the project / start the server

node index.js

👉 visit:
http://localhost:8000/?username=javier

⚙️🧩 JSON REST API

What It Does:

Reads data from a data.json file
Exposes 1 endpoint with that data
- A list of characters at /characters
- And character data by id /characters/:id

Example file: data.json

[
  {
    "id": 1,
    "age": 39,
    "name": "Homer Tompson",
    "portrait_path": "https://cdn.thesimpsonsapi.com/500/character/1.webp"
  },
  {
    "id": 2,
    "age": 39,
    "name": "Marge Simpson",
    "portrait_path": "https://cdn.thesimpsonsapi.com/500/character/2.webp"
  }
]

📝 Create file: touch api.js

▶️ File contents: api.js

import http from "http";
import fs from "fs";
import url from "url";

function loadCharacters() {
  const json = fs.readFileSync("data.json", "utf8");
  return JSON.parse(json);
}

const server = http.createServer((req, res) => {
  res.setHeader("Content-Type", "application/json");

  const parsedUrl = url.parse(req.url, true);
  const path = parsedUrl.pathname;
  const method = req.method;

  const characters = loadCharacters();

  // GET /characters → full list
  if (method === "GET" && path === "/characters") {
    res.end(JSON.stringify(characters));
    return;
  }

  // GET /characters/:id → find by ID
  const match = path.match(/^\/characters\/(\d+)$/);
  if (method === "GET" && match) {
    const id = parseInt(match[1], 10);
    const found = characters.find((c) => c.id === id);

    if (found) {
      res.end(JSON.stringify(found));
      return;
    }

    res.statusCode = 404;
    res.end(JSON.stringify({ error: "Character not found" }));
    return;
  }

  // Route not found
  res.statusCode = 404;
  res.end(
    JSON.stringify({
      error: "Route not found",
      url_lista: "http://localhost:7001/characters",
      url_personaje: "http://localhost:7001/characters/1"
    })
  );
});

server.listen(7001, () => {
  console.log("Server running at http://localhost:7001/characters");
});

▶️ Run the project / start the server

node api.js

👉 visit:
http://localhost:7001/characters

To test URL sanitization:
http://localhost:7001/characters/1

Installation and configuration on Ubuntu of:

Homebrew and ASDF
COBOL
PHP
Dart

Dart on Ubuntu: Installation, Setup, and First Steps

Javier Jimenez — Sun, 23 Nov 2025 16:00:00 +0000

I recommend seeing first – installation of Homebrew and asdf on Ubuntu (it’s short, only 5 commands)

📘 Official Documentation

⭐ Popular Frameworks (learning curve low → high):

Shelf — Simple for APIs.
Dart Frog — A fast, minimalistic backend framework for Dart
Angel — Express-style, more complete.
Serverpod — Larger, microservices-oriented.

Note: Let’s not forget that the most important thing Dart has today is Flutter, although it almost needs its own section.

🛠️ Installing Dart on Ubuntu

Via APT (official repository)

sudo apt update
sudo apt install apt-transport-https

sudo sh -c 'wget -qO- https://dl-ssl.google.com/linux/linux_signing_key.pub | apt-key add -'
sudo sh -c 'wget -qO /etc/apt/sources.list.d/dart_stable.list https://storage.googleapis.com/dart-archive/channels/stable/release/latest/linux_packages/dart_stable.list'

sudo apt update
sudo apt install dart

🍺 Installation with Homebrew

brew install dart

📦 Package Manager: pub (built into Dart)

dart pub add <package>
dart pub get

🟩 ASDF for Dart

System dependencies

sudo apt update
sudo apt install curl git unzip

Install plugin + version

asdf plugin add dart https://github.com/patoconnor43/asdf-dart.git

asdf list-all dart
asdf install dart 3.4.0
asdf global dart 3.4.0

Example `.tool-versions`

dart 3.4.0

📝▶️ Create and run a Dart file

Create file

mkdir app && cd app
touch hola.dart

Code `hola.dart`

void main() {
  print('Hola Mundo desde Dart!');
}

Run

dart run hola.dart

🟦 Basic examples in Dart

NOTE: both codes are compatible with Dart 3.9

EX: 1 Static file web server.

What it does:

Defines the name of the query parameter
Gets the value of the query parameter from the URL
- htmlEscape sanitizes the received text by removing special characters like < and > into HTML entities.
Renders the value received from the query parameter inside the <H1> tag

📝 Create file: touch server.dart

▶️ Content of server.dart

import 'dart:convert';
import 'dart:io';

void main() async {
  final server = await HttpServer.bind(InternetAddress.loopbackIPv4, 9000);
  print('Servidor corriendo en http://localhost:9000');

  await for (HttpRequest request in server) {
    final params = request.uri.queryParameters;
    final username = params['username'] ?? 'invitado';

    final escaped = htmlEscape.convert(username);

    final htmlContent = """
      <!DOCTYPE html>
      <html lang="es">
      <head>
          <meta charset="UTF-8">
          <title>Hola</title>
      </head>
      <body style="text-align:center">
          <img src="https://dev.to/oscarpincho/mejora-ubuntu-con-homebrew-y-asdf-gestor-de-versiones-multiples-4nka" />
          <h1>Hola, $escaped</h1>
      </body>
      </html>
    """;

    request.response.headers.contentType = ContentType.html;
    request.response.write(htmlContent);
    await request.response.close();
  }
}

run the project / start the server

dart run server.dart

👉 visit:
http://localhost:9000/?username=Homero

To test URL sanitization:
http://localhost:9000/?username=<h1>--Homer--</h1>

EX: 2 JSON REST API

What it does:

Reads the data from a data.json file
Exposes 1 endpoint with that data

A list of characters at /characters
And the data of a character by id /characters/:id

Example file: data.json

[
    {
        "id": 1,
        "age": 39,
        "name": "Homer Tompson",
        "portrait_path": "https://cdn.thesimpsonsapi.com/500/character/1.webp"
    },
    {
        "id": 2,
        "age": 39,
        "name": "Marge Simpson",
        "portrait_path": "https://cdn.thesimpsonsapi.com/500/character/2.webp"
    },
]

📝 Create file: touch api.dart

▶️ Content of api.dart

import 'dart:convert';
import 'dart:io';

void main() async {
  final server = await HttpServer.bind(InternetAddress.loopbackIPv4, 9001);
  print("Servidor JSON en http://localhost:9001");

  await for (HttpRequest request in server) {
    final path = request.uri.path;

    final characters = await loadCharacters();

    if (request.method == 'GET' && path == '/characters') {
      _sendJson(request, characters);
      continue;
    }

    if (request.method == 'GET' && path.startsWith('/characters/')) {
      final idStr = path.split('/').last;
      final id = int.tryParse(idStr);

      if (id == null) {
        _sendJson(request, {"error": "ID inválido"}, status: 400);
        continue;
      }

      final character = findById(characters, id);

      if (character == null) {
        _sendJson(request, {"error": "Personaje no encontrado"}, status: 404);
      } else {
        _sendJson(request, character);
      }
      continue;
    }

    _sendJson(request, {
      "error": "Ruta no encontrada",
      "url_lista": "http://localhost:9001/characters",
      "url_personaje": "http://localhost:9001/characters/1"
    }, status: 404);
  }
}

Future<List<Map<String, Object?>>> loadCharacters() async {
  final file = File('data.json');
  final content = await file.readAsString();
  final List<dynamic> jsonData = jsonDecode(content);

  return jsonData.cast<Map<String, Object?>>();
}

Map<String, Object?>? findById(List<Map<String, Object?>> list, int id) {
  for (final item in list) {
    if (item["id"] == id) return item;
  }
  return null;
}

void _sendJson(HttpRequest request, Object data, {int status = 200}) {
  request.response.statusCode = status;
  request.response.headers.contentType = ContentType.json;
  request.response.write(jsonEncode(data));
  request.response.close();
}

run the project / start the server

dart run api.dart

👉 visit:
http://localhost:9001/characters

To test URL sanitization:
http://localhost:9001/characters/1

PHP on Ubuntu: Installation, Setup, and First Steps

Javier Jimenez — Fri, 21 Nov 2025 16:17:23 +0000

Prerequisites – installation of Homebrew and asdf on Ubuntu

📘 Official Documentation

⭐ Popular Frameworks

(ordered from lowest to highest learning curve)

CodeIgniter — https://codeigniter.com/user_guide/
Laravel — https://laravel.com/docs
Symfony — https://symfony.com/doc

🛠️ Installation on Ubuntu

sudo apt update
sudo apt install php php-cli php-common php-mbstring php-xml php-curl php-zip

🍺 Installation with Homebrew

brew install php

📦 Standard package manager: Composer

Installation:

php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');"
php composer-setup.php
sudo mv composer.phar /usr/local/bin/composer

Verify:

composer --version

🔧 Install different versions with ASDF

Dependencies:

sudo apt update
sudo apt install autoconf bison build-essential libxml2-dev libssl-dev \
libcurl4-openssl-dev pkg-config re2c libsqlite3-dev

Plugin + version:

asdf plugin add php
asdf install php 8.2.12
asdf global php 8.2.12

📄 Example `.tool-versions`

php 8.2.12

📝▶️ Create and run a PHP file

Create file: touch hola.php

Content of hola.php:

<?php
echo "Hola Mundo PHP\n";

PHP can be run in 2 ways: as a system file, which makes it useful for local scripts—you could replace bash scripts, for example—and in a web server. PHP already comes with an embedded server, but it’s more common to use it with Apache or Nginx.

Run locally:

php hola.php

Embedded server:

php -S localhost:8000

🟦 Basic example in PHP

What it does:

Defines the name of the query parameter.
Gets the query parameter value from the URL.
- $_GET is used to access query parameters.
- htmlspecialchars is used for security, to prevent XSS attacks by converting special characters like < and > into HTML entities.
It draws the value received through the query parameter inside the <h1> tag.

📝 Create file: touch index.php

▶️ Content of index.php:

<?php
$paramName = 'username';
$textoRecibido = isset($_GET[$paramName])
    ? htmlspecialchars($_GET[$paramName])
    : "No se ha proporcionado un nombre.";
?>
<!DOCTYPE html>
<html lang="es">
<head>
    <meta charset="UTF-8">
    <title>Mensaje Recibido</title>
</head>
<body style="text-align: center">
    <h1>Nombre de usuario en la URL: "<?php echo $textoRecibido; ?>"</h1>
    <p>Prueba a cambiar el valor de `texto` en la barra de direcciones.</p>
    <b><a href="/test.php?texto=cambiado%20en%20url">Click para cambio en url</a></b>
</body>
</html>

run the project / start the server

php -S localhost:8000

👉 visit:
http://localhost:8000/?username=Homero

EJ:2 Json API Rest

Que Hace:

Lee los datos desde un archivo data.json
expones 1 endpoint con esos datos
- Una Lista de personajes en /characters
- y los datos de un personaje por id /characters/:id

Ejemplo de archivo: data.json

[
    {
        "id": 1,
        "age": 39,
        "name": "Homer Tompson",
        "portrait_path": "https://cdn.thesimpsonsapi.com/500/character/1.webp"
    },
    {
        "id": 2,
        "age": 39,
        "name": "Marge Simpson",
        "portrait_path": "https://cdn.thesimpsonsapi.com/500/character/2.webp"
    },
]

📝 Create file: touch api.php

▶️ Content of api.php:

<?php

header("Content-Type: application/json");

// Obtener la ruta actual
$path = parse_url($_SERVER['REQUEST_URI'], PHP_URL_PATH);

// Cargar archivo JSON
function loadCharacters() {
    $json = file_get_contents("data.json");
    return json_decode($json, true);
}

$characters = loadCharacters();

// GET /characters → lista completa
if ($_SERVER['REQUEST_METHOD'] === 'GET' && $path === '/characters') {
    echo json_encode($characters);
    exit;
}

// GET /characters/:id → buscar por ID
if (
  $_SERVER['REQUEST_METHOD'] === 'GET'
  && preg_match('#^/characters/(\d+)$#', $path, $matches)
) {
    $id = intval($matches[1]);

    foreach ($characters as $c) {
        if ($c['id'] === $id) {
            echo json_encode($c);
            exit;
        }
    }

    http_response_code(404);
    echo json_encode(["error" => "Personaje no encontrado"]);
    exit;
}

// Ruta no encontrada
http_response_code(404);
echo json_encode([
    "error" => "Ruta no encontrada",
    "url_lista" => "http://localhost:8001/characters",
    "url_personaje" => "http://localhost:8001/characters/1"
]);
exit;

run the project / start the server

php -S localhost:8001 api.php

👉 visit:
http://localhost:8001/characters

Test API Url:
http://localhost:8001/characters/1

Installation and configuration on Ubuntu of:

COBOL on Ubuntu: Installation, Setup, and First Steps

Javier Jimenez — Wed, 19 Nov 2025 00:36:57 +0000

Prerequisites – Installing Homebrew and ASDF on Ubuntu

Documentation (Official?)

Popular Frameworks / Toolkits

(COBOL doesn’t use modern frameworks; these are the most common ones)

GnuCOBOL (OpenCOBOL) — standard open-source compiler.
TinyCOBOL — simple and educational.
COBOL-IT — commercial, mainframe-compatible.

🛠️ Installation on Ubuntu

sudo apt update
sudo apt install open-cobol
# or
sudo apt install gnucobol

🍺 Installation with Homebrew

brew install gnu-cobol

📦 Standard Package Manager

COBOL **does not have an official package manager* (it’s not a modular ecosystem like Node or PHP).*

🔧 Installation with ASDF

There is no official ASDF plugin for COBOL.

📝▶️ Create and Run a COBOL File

Important: In COBOL, the first 7 characters of each line must remain empty because they were originally reserved for sequence numbers used on punched cards. These numbers allowed cards to be physically reordered if shuffled. Even though they’re no longer needed today, this historical structure is preserved for compatibility, so these first eight characters are still treated as a special non-code area.
cobol.es – IBM – Cobol for Linux

Col: 1 2 3 4 5 6 7 8
      |       | | |
      |       | | └──→ Code begins here
      |       | └────→ Indicator (comments, continuation…)
      └──────────────→ Sequence area (1–6)

000100*······Sample program
000200 IDENTIFICATION DIVISION.
000300 PROGRAM-ID.··HELLOWORLD.
000400 ENVIRONMENT DIVISION.
000500 DATA DIVISION.
000600 WORKING-STORAGE SECTION.
000700 01·MESSAGE·PIC·X(20)·VALUE·"HELLO·WORLD".
000800 PROCEDURE DIVISION.
000900     DISPLAY·MESSAGE.
001000     STOP·RUN.

Note: There is a “free format” mode >>SOURCE FORMAT FREE that supposedly allows skipping the blank spaces, but it didn’t work for me.

Create file: touch hello.cob

      *COBOL SAMPLE PROGRAM TO VERIFY COBOL INSTALLATION
      *IMPORTANT - Reminder: COBOL code must begin at COLUMN 8.
      *Use '*' in column 7 for comments.
       IDENTIFICATION DIVISION.
       PROGRAM-ID. HELLO.
       PROCEDURE DIVISION.
           DISPLAY "COBOL is installed and working!".
           STOP RUN.

Same file in free format (no comments):

>>SOURCE FORMAT FREE
IDENTIFICATION DIVISION.
PROGRAM-ID. HELLO.
PROCEDURE DIVISION.
    DISPLAY "Hello COBOL World".
    STOP RUN.

Compile:

cobc -x hello.cob -o hello

Run:

./hello

🟦 Basic COBOL Example

What It Does:

Reads a text file.
The file contains two numbers per line (e.g., 5 7).
Multiplies them.
Prints to console: "the result is = X"

Input file (`datos.txt`)

Example content:

125 745
313 246787
140 4467

Mini COBOL Program

Create file: multiplicar.cob

      *-------------------------------------------------------------*
      * PROGRAM TO READ TWO VALUES, MULTIPLY THEM, AND DISPLAY THEM *
      *-------------------------------------------------------------*
       IDENTIFICATION DIVISION.
       PROGRAM-ID. MULTIPLY.

       ENVIRONMENT DIVISION.
       INPUT-OUTPUT SECTION.
       FILE-CONTROL.
           SELECT FILEIN ASSIGN TO "datos.txt"
               ORGANIZATION IS LINE SEQUENTIAL.

       DATA DIVISION.
       FILE SECTION.
       FD FILEIN.
       01 RECORD-LINE                  PIC X(50).

       WORKING-STORAGE SECTION.
       01 NUM1                          PIC 9(9).
       01 NUM2                          PIC 9(9).
       01 RESULT                        PIC 9(18).
       01 END-FILE                      PIC X VALUE "N".

       PROCEDURE DIVISION.
       MAIN-LOGIC.
           OPEN INPUT FILEIN

           PERFORM UNTIL END-FILE = "S"
               READ FILEIN
                   AT END
                       MOVE "S" TO END-FILE
                   NOT AT END
                       PERFORM PROCESS-LINE
               END-READ
           END-PERFORM

           CLOSE FILEIN
           STOP RUN.

       PROCESS-LINE.
           UNSTRING RECORD-LINE
               DELIMITED BY SPACE
               INTO NUM1 NUM2

           COMPUTE RESULT = NUM1 * NUM2

           DISPLAY "the result is = " RESULT.

📝▶️ How to Compile and Run

# Compile file:
cobc -x multiplicar.cob -o multiplicar
#Run compiled program
./multiplicar

Expected output:

the result is = 35
the result is = 6
the result is = 40

Boost Your Ubuntu Dev Workflow with Homebrew and ASDF (Multi-language Version Manager)

Javier Jimenez — Mon, 17 Nov 2025 22:26:18 +0000

version en español

Official Links

🍺 Homebrew on Ubuntu

Homebrew is a free and open-source command-line package manager designed for macOS (and also Linux, under the name Linuxbrew or Homebrew on Linux). Its main purpose is to simplify the installation and management of software that Apple does not include natively.

What is it for? It allows you to install thousands of utilities, development tools (such as Git, Node.js, Python), and other applications with simple commands like brew install <package>. Essentially, it helps developers and advanced users easily get the software they need on their system without having to compile it manually or search for individual installers. It works like an “app store” for your terminal.

📦 Installation

/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"

# Add to PATH

echo 'eval "$(/home/linuxbrew/.linuxbrew/bin/brew shellenv)"' >> ~/.bashrc
eval "$(/home/linuxbrew/.linuxbrew/bin/brew shellenv)"

# Install basic dependencies

brew install gcc git

🧰 Useful commands

brew install <pkg>
brew uninstall <pkg>
brew list
brew update
brew upgrade
brew search <name>

🚀 ASDF - The Multiple Version Manager

asdf is an extensible and multifunctional version manager for the command line. Unlike other managers that focus on a single language (such as nvm for Node.js or rvm for Ruby), asdf uses a plugin system to manage multiple versions of different programming languages, runtimes, and tools (like Node.js, Python, Ruby, Java, Elixir, etc.) in a centralized way.

What is it for? It allows you to easily switch between the tool versions needed for different projects. For example, if one project requires Python 3.8 and another needs Python 3.11, asdf ensures the correct environment is active automatically for each working directory, helping to avoid dependency conflicts and simplify the maintenance of multiple development environments.

📦 Installation

git clone https://github.com/asdf-vm/asdf.git ~/.asdf --branch v0.14.0

echo '. "$HOME/.asdf/asdf.sh"' >> ~/.bashrc
echo '. "$HOME/.asdf/completions/asdf.bash"' >> ~/.bashrc
source ~/.bashrc

🧰 Useful commands

asdf plugin add <lang>
asdf list-all <lang>
asdf install <lang> <version>
asdf global <lang> <version>
asdf local <lang> <version>
asdf uninstall <lang> <version>

Example using Go – Install plugin + version

asdf plugin add golang https://github.com/asdf-community/asdf-golang.git

asdf install golang 1.22.4
asdf global golang 1.22.4

Example `.tool-versions` file

# .tool-versions
golang 1.22.4
# You can add other tools managed by ASDF
php 8.2.12
nodejs 20.10.0
ruby 3.2.2

Forem: Javier Jimenez

Java on Ubuntu: Installation, Setup, and First Steps

📘 Official Documentation

⭐ Popular Frameworks (ordered from lower to higher learning curve)

🛠️ Installing Java on Ubuntu

🍺 Installation with Homebrew

📦 Standard Dependency Manager (Maven / Gradle)

🔧 Installation with ASDF

📝▶️ Create and run a Java file

🟦 Basic Java example

🗂️🌐 Static file Web Server

⚙️🧩 JSON REST API

Python on Ubuntu: Installation, Setup, and First Steps

📘 Official Documentation

⭐ Popular Frameworks (ordered from lower to higher learning curve)

🛠️ Installing Python on Ubuntu

🍺 Installation with Homebrew

📦 Standard Package Manager (pip — included)

🔧 Installation with ASDF

📝▶️ Create and run a Python file

🟦 Basic example in Python

🗂️🌐 Static file web server.

⚙️🧩 JSON REST API

C++ on Ubuntu: Installation, Setup, and First Steps

📘 Official Documentation

⭐ Popular Frameworks (ordered from lower to higher learning curve)

🛠️ C++ Installation on Ubuntu

🍺 Installation with Homebrew

📦 Standard Package Manager

🔧 Installation with ASDF

📝▶️ Create and run a C++ file

🟦 Basic example in C++

🗂️🌐 Static file Web Server.

⚙️🧩 JSON REST API

🟦 Extra example in C++

💻 GUI Calculator with QT

What it does:

NodeJS on Ubuntu: Installation, Setup, and First Steps

📘 Official Documentation

⭐ Popular Frameworks (ordered from lower to higher learning curve)

🛠️ Installation on Ubuntu

🍺 Installation with Homebrew

📦 Standard Package Manager

🔧 Installation with ASDF

🔧 Install NVM (Node Version Manager)

📝▶️ Create and run a Node.js file

🟩 Basic Example in Node.js

🗂️🌐 Static Files Web Server

⚙️🧩 JSON REST API

Installation and configuration on Ubuntu of:

Dart on Ubuntu: Installation, Setup, and First Steps

📘 Official Documentation

⭐ Popular Frameworks (learning curve low → high):

🛠️ Installing Dart on Ubuntu

🍺 Installation with Homebrew

📦 Package Manager: pub (built into Dart)

🟩 ASDF for Dart

System dependencies

Install plugin + version

Example .tool-versions

📝▶️ Create and run a Dart file

Create file

Code hola.dart

Run

🟦 Basic examples in Dart

EX: 1 Static file web server.

run the project / start the server

EX: 2 JSON REST API

run the project / start the server

PHP on Ubuntu: Installation, Setup, and First Steps

📘 Official Documentation

⭐ Popular Frameworks

🛠️ Installation on Ubuntu

🍺 Installation with Homebrew

📦 Standard package manager: Composer

🔧 Install different versions with ASDF

📄 Example .tool-versions

📝▶️ Create and run a PHP file

🟦 Basic example in PHP

run the project / start the server

Example `.tool-versions`

Code `hola.dart`

📄 Example `.tool-versions`

Input file (`datos.txt`)

Example `.tool-versions` file