Understanding Application Architecture: From Chaos to Order

Many developers face challenges when joining a new team: understanding existing code style, unfamiliar project structures, and defining a clear module/package hierarchy.

This article explains why understanding the application architecture is the first step to solving these problems.

Chaotic Application Architecture

Typical symptoms include unclear layering, lack of guidelines, inconsistent module naming, and tangled dependencies between modules and packages.

Such complexity leads to high maintenance cost and long onboarding time.

Ordered Application Architecture

A well‑structured system separates business logic from technical details. Common architectural styles such as Hexagonal, Onion, and Clean Architecture all advocate a core domain surrounded by adapters.

Module vs Package

In Maven, a <module> corresponds to a JAR artifact, while a package is a folder of classes. A module usually contains several packages.

<modules>
    <module>{appCode}-api</module>
    <module>{appCode}-service</module>
    <module>{appCode}-start</module>
</modules>

Modules should be larger than packages; packages group related classes.

Typical Layered Structure

Adapter Layer – entry points (controllers, UI adapters).

Application Layer – orchestrates use cases, validates input, calls domain services.

Domain Layer – core business logic, aggregates, domain services.

Infrastructure Layer – technical concerns (DB, RPC, external services) and anti‑corruption adapters.

Applying the Dependency Inversion Principle (DIP) makes the Domain layer depend only on abstractions, improving testability and parallel development.

Design Patterns

CQRS – separate command (state‑changing) and query (read‑only) operations.

Anti‑Corruption Layer – isolate the domain from external models.

Code Example

Before refactoring, business logic is mixed with technical checks:

boolean isCombineProduct = supplierItem.getSign().isCombProductQuote();
// ... many if‑else branches ...
if (sellableAmount < 1) {
    throw ExceptionFactory.makeFault(ServiceExceptionCode.SYSTEM_ERROR, "库存必须大于0");
}

After introducing domain models, the code becomes expressive and concise:

if (backOffer.isCloudWarehouse()) {
    return;
}
if (backOffer.isNonInWarehouse()) {
    throw new BizException("请联系仓配运营人员，建立品仓关系！");
}
if (backOffer.getStockAmount() < 1) {
    throw new BizException("实仓库存必须大于0，请确认已补货.");
}

Using proper layering and domain modeling reduces conditional branches and improves readability.

Practical Guidance

When starting a new project, discuss and document the architecture, agree on module distribution, package naming, and class conventions. Follow the “high cohesion, low coupling” principle and use package‑private visibility for internal methods.

References: ThoughtWorks DDD article, “Implementing Domain‑Driven Design”, Alibaba COLA open‑source framework.