itstack-demo-design

This repository is the companion code for a Chinese-language book called "Relearning Java Design Patterns," written by a developer who goes by the handle Xiao Fu Ge. The book and code together teach software design patterns through 22 real business scenarios drawn from actual internet industry work, covering areas like payment systems, marketing campaigns, flash sales, middleware components, and source code analysis.

Design patterns are well-established solutions to common coding problems that experienced programmers have refined over decades. The classic set comes from a 1994 book by four authors known as the Gang of Four, who organized them into three families: creational patterns (how objects are created), structural patterns (how objects are composed together), and behavioral patterns (how objects communicate). This repo walks through all three families using Java code.

The approach is practical rather than theoretical. Each chapter pairs a pattern with a working Java project built around a realistic scenario, so you can read the book section alongside runnable code. The author spent 50 days pulling examples from real transaction, marketing, and middleware systems to illustrate where each pattern actually fits, rather than using toy examples that do not resemble production code.

The full source is available on both GitHub and Gitee. A print edition of the book was published on JD.com with updated diagrams and color printing. An older free electronic version can be accessed by following the author's WeChat public account. The README links to several related standalone projects by the same author, including a distributed lottery system, a ChatGPT microservice application, and a desktop-style instant messaging clone built with Netty and JavaFX.

This repo is most useful for Java developers who have heard of design patterns but have not applied them in real work, and who learn better from seeing code in a business context than from abstract explanations.