When working across multiple Java applications, one problem appears again and again:
you keep rewriting the same “basic but essential” components.
common_java is a lightweight utility-style library that groups these repeated concerns into reusable modules — from validation and caching to HTTP, database helpers, and email utilities.
Let’s walk through what this library provides.
📦 1. Project Overview
The library is organized into clear functional packages:
-
validator→ input validation logic -
string→ string utilities -
cache→ in-memory caching (including LRU cache) -
network→ HTTP and IP utilities -
http→ URL fetch example app -
alert→ email composition and sending -
database→ JDBC helpers and result handling -
properties→ config loading utilities
This is a classic “common utilities” architecture: each package solves a real-world repetitive backend problem.
✅ 2. Validation Layer
Key classes:
-
Validator -
EmailValidator
This layer focuses on ensuring data correctness before processing.
Typical responsibilities:
- checking input format
- validating email structure
- centralizing reusable validation rules
💡 Design idea:
Instead of scattering validation logic across services, it is centralized.
Example concept:
Validator.isNotNull(value);
EmailValidator.isValid(email);
🧵 3. String Utilities
Hex.java
This likely provides:
- hex encoding / decoding
- conversion between byte arrays and hex strings
💡 Why it matters:
Hex utilities are commonly needed in:
- encryption
- networking
- debugging binary data
⚡ 4. Cache System (Most Interesting Part)
Core classes:
-
Cache -
LRUCache -
CacheElement -
Node -
LinkedListNode -
DoublyLinkedList -
DummyNode -
CacheApp
🧠 What this module shows
This is a classic LRU Cache implementation using:
-
Hash-based lookup (likely via
Cache) - Doubly linked list for ordering
- Node abstraction for entries
🔁 LRU Cache concept
Least Recently Used (LRU) cache works like this:
- Recently used items stay in memory
- Old unused items are removed first
🧱 Data structure design
This design typically combines:
- HashMap → O(1) access
- Doubly Linked List → O(1) insert/remove
💡 Why multiple node classes?
-
Node→ base structure -
LinkedListNode→ real element -
DummyNode→ sentinel node (simplifies edge cases)
This shows clean separation of concerns in data structure design.
🚀 Why this module stands out
This is not just a utility — it’s a fully custom cache engine, useful for:
- performance optimization
- memory control
- backend caching strategies
🌐 5. Network Utilities
Classes:
-
HttpUtil -
HttpClientApp -
HttpResponse -
HttpResponseCode -
IP
What this module does
It likely provides:
- HTTP GET/POST helpers
- response wrapper object
- HTTP status code abstraction
- IP-related utilities
💡 Design strength
Instead of directly using low-level HTTP calls everywhere, the library:
✔ wraps HTTP logic
✔ standardizes response handling
✔ centralizes error handling
This improves consistency across projects.
📧 6. Email / Alert System
Classes:
-
Email -
EmailAddress -
EmailBody -
EmailAttachment -
SMTP -
EmailApp
What this represents
A structured email system with:
- strongly typed email components
-
separation of:
-
recipient (
EmailAddress) -
content (
EmailBody) -
attachments (
EmailAttachment)
-
recipient (
- SMTP abstraction
💡 Why this design is good
Instead of passing raw strings:
sendEmail(to, subject, body)
You model email as an object:
Email email = new Email(...)
This improves:
- readability
- validation
- maintainability
🗄️ 7. Database Utilities
Classes:
-
DatabaseManager -
DatabaseStatementManager -
StatementUtil -
Jdbc -
Result -
RStoListMap
What this module solves
JDBC in Java is powerful but verbose.
This module likely simplifies:
- connection handling
- statement execution
- result set mapping
💡 Key idea: abstraction over JDBC
Instead of repeating boilerplate:
Connection conn = ...
PreparedStatement stmt = ...
ResultSet rs = ...
You centralize it into utilities.
🔁 RStoListMap
This likely converts:
ResultSet → List<Map<String, Object>>
This is extremely useful for:
- APIs
- JSON conversion
- dynamic queries
⚙️ 8. Configuration Utilities
ConfigApp
This likely handles:
-
loading
.propertiesfiles - environment configuration
- app-level settings
💡 Why it matters:
🌍 9. HTTP Example App
UrlFetchApp
This is likely a demo or utility showing:
- fetching URL content
-
using
HttpUtil
This acts as:
🧠 Overall Design Observations
✔ Strengths
1. Clear modular separation
Each package has a single responsibility.
2. Real-world utility coverage
It covers:
- validation
- caching
- HTTP
- database
This is basically a mini backend toolkit.
3. Strong focus on reusability
🚀 Final Summary
common_java is essentially a personal backend utility framework that helps reduce repetitive Java boilerplate across projects.
It demonstrates:
- practical backend engineering patterns
- data structure implementation (LRU cache)
- abstraction over JDBC and HTTP
- structured email handling
- reusable validation logic
