Using ChatGPT and PlantUML to Generate UML Diagrams from Java Pseudocode

Although ChatGPT cannot directly output images, it can generate structured textual outputs like tables, code, and mathematical formulas, including text‑based graphic description languages that allow the creation of visual diagrams without a graphical editor.

The article introduces PlantUML, an open‑source tool that uses plain text to describe UML diagrams (class, sequence, use‑case, etc.), highlighting its advantages: human‑readable syntax, free usage, automatic layout, rapid updates, and high customizability.

For each diagram type, the article provides a Java‑style pseudocode example, the corresponding PlantUML code generated by ChatGPT, and the rendered diagram image. The examples cover:

Sequence diagram of a simple e‑commerce order flow.

Class diagram of a personnel system with Person, Teacher, and Student classes.

Flowchart of a shopping process with conditional branches for stock, discounts, and payment.

State diagram illustrating order state transitions (New, Shipped, Delivered, Closed).

Use‑case diagram for a library management system showing Librarian and Reader interactions.

Each PlantUML snippet is shown inside tags to preserve the exact code, for example:

public class User {
    private String name;
    private String email;
    // ...
    public void placeOrder(Order order) {
        // order logic
    }
}

public class Order {
    private User user;
    private String orderId;
    public void process() {
        OrderProcessor orderProcessor = new OrderProcessor();
        orderProcessor.processOrder(this);
    }
}

// ... other classes ...

The corresponding PlantUML for the sequence diagram is:

@startuml

actor User
participant Order
participant OrderProcessor
participant NotificationService

User -> Order: placeOrder(order)
activate Order
Order -> OrderProcessor: process()
activate OrderProcessor
OrderProcessor -> NotificationService: processOrder()
activate NotificationService
NotificationService --> User: sendNotification()
deactivate NotificationService
deactivate OrderProcessor
deactivate Order

@enduml

After generating the PlantUML code, the user copies it into the PlantUML online editor (https://www.plantuml.com) to preview and export the diagram image.

The article concludes with a concise workflow: provide Java code to ChatGPT, specify the desired UML diagram type, let ChatGPT produce PlantUML code, and finally render the diagram using the PlantUML web service. It also supplies a reusable prompt template for generating any UML diagram from code.