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Spring Boot — Complete Beginner's Guide & Notes

Based on: Merchandise Store hands-on tutorial by Anerud

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Table of Contents

1. What is Spring Boot?
2. Problem Statement & System Design
3. Database Design (ER Diagram)

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Spring Boot for Beginners — Building a "Creator Store" Backend

A complete, hands-on study guide built from a beginner-friendly Spring Boot tutorial. By the end you'll understand why, how, and what Spring Boot is — and you'll have built a real REST API backend that powers an influencer's merchandise store, the same way companies like Walmart, Netflix, Amazon, and Google use Spring Boot in production.

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Table of Contents

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Reset Linux user password (bypass PAM pwquality)

When passwd or chpasswd rejects a weak password due to PAM policy, hash it directly with SHA-512:

echo "USERNAME:NEWPASSWORD" | sudo chpasswd -c SHA512

This skips the PAM password stack and writes the hash straight to /etc/shadow.

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API Documentation Generator — Claude Code Instructions

Your Job

Whenever I add, update, or delete an API in this collection, your job is to automatically sync API_DOC.md (or a specified markdown file) to reflect the latest state of all APIs.

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How to Detect Changes

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source venv/bin/activate

pip uninstall

pip list

pip install -e .

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Just paste it into the browser console, and it will count contributions for you.

const currentYear = String(new Date().getFullYear());
const targetElement = document.querySelector(".col-12.calendar-block.gl-my-3");

if (targetElement) {
  const userContribElements = Array.from(document.querySelectorAll(".user-contrib-cell"));

  const totalContribution = userContribElements.reduce((acc, el) => {

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def rgba_to_hex(rgba_color):
    # Convert the RGBA color value to a 32-bit integer
    hex_value = (int(rgba_color[3] * 255) << 24) | (rgba_color[0] << 16) | (rgba_color[1] << 8) | rgba_color[2]

    # Convert the 32-bit integer to a hexadecimal string
    hex_string = hex(hex_value)

    # Return the result
    return hex_string
    

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data = [
  {
    id: 1,
    name: null,
    price: 1,
  },
  {
    id: "2",
    name: "Nike",
    price: "",

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minimumQuantity = [0, 11, 21, 31, 41, 51, 61, 71, 81, 91]
maximumQuantity = [4, 20, 30, 40, 50, 60, 70, 80, 90, 100];

// check number in minimumQuantity and maximumQuantity in range
const checkNumber = (number) => {
    for (let i = 0; i < minimumQuantity.length; i++) {
        if(number >= minimumQuantity[i] && number <= maximumQuantity[i]){
            return false;
        }

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<input type=date step=7 min=2014-09-08> - Monday only
<input type=time min=9:00 max=17:00 step=900> - 15m increments
<input type=week step=2 min=2014-W30>