Java Keep Configuration and Diagnostics Deliberate

Understand the idea

Use environment variables, system properties or a suitable configuration layer according to the deployment environment. Validate values at startup rather than passing malformed text deeper into the application. A default is appropriate only when it is safe and documented. Logging should describe an operation and relevant non-sensitive context, not dump passwords, tokens or complete private records.

Run it locally

Use a local JDK 21 or newer. Save the complete example as Main.java in a separate lab folder, then compile and run it with the commands below. Java examples do not run in Bhylu’s browser playground. The -ea option enables assertion checks used by some lessons.

JDK and terminal setup

javac --release 21 -encoding UTF-8 -d out Main.java
java -ea -cp out Main

A worked example

public class Main {
    public static void main(String[] args) {
        String configured = System.getProperty("workshop.capacity", "12");
        int capacity = Integer.parseInt(configured);
        if (capacity <= 0) throw new IllegalArgumentException("capacity must be positive");
        System.out.println("Capacity configured: " + capacity);
    }
}

Expected output

Capacity configured: 12

The property has a documented local default. A launcher can supply -Dworkshop.capacity=18 before the class name to choose another value. Parse and validate once at the boundary. A database password should use a suitable secret-delivery mechanism and should never be printed just because a connection failed.