Snippets: Quick Solutions to Common Config Problems

mConfig shines for everyday config pains. Copy-paste these snippets—no setup hassles.

Each solves a general problem using mConfig's magic (OS paths, layers, reloads, schemes).

Starters for full projects • FAQ for fixes • CLI

1. Replace Hardcoded Strings/Ports (Zero Magic Strings)

Problem: Ports, hosts scattered in code—hard to change/deploy.

Config cfg = ConfigUtil.quickConfig("myco", "myapp", "network");
String peer = cfg.getString("peer");  // localhost
int port = cfg.getInteger("port");    // 8080
double prob = cfg.getDouble("probability");  // 0.5

Place: ~/.config/myco/myapp/network.properties (auto-discovered).

Why mConfig? Searches OS standards (XDG, AppData), formats (properties/YAML/JSON), reloads live.

Getting Started

2. Env Vars → Structured Config (No Manual Parsing)

Problem: process.env mess; want hierarchical config.

Add dep: mConfigSourceEnvVar

Env vars:

myapp_network_peer=localhost
myapp_network_port=8080

try (ConfigFactory f = ConfigFactoryBuilder.create("myco", "myapp").build()) {
    String peer = f.getConfig("network").getString("peer");  // SESSION override
}

Why? <app>_<config>_<key> convention; layers over files.

mConfigSourceEnvVar

3. Type-Safe Config with Defaults/Validation

Problem: Runtime NumberFormatException; scattered defaults.

src/main/resources/.config/myco/myapp/network.scheme.json:

[{"name":"port","type":"int","default":8080,"min":1,"max":65535}]

ConfigScheme scheme = ConfigScheme.fromClasspath("network.scheme.json");
Config cfg = factory.getConfig("network", scheme);
int port = cfg.getInteger("port");  // Validates!

Why? Centralized scheme—no call-site defaults.

Configuration Schemes

4. Hot-Reload on File Changes

Problem: Restart for config tweaks? No thanks.

Config cfg = factory.getConfig("network");  // Watches files
// Edit network.properties → cfg.getInteger("port") updates instantly

Why? Built-in watcher; no polling/Spring @Refresh.

Priorities

5. Discover Available Configs (No Guesswork)

Problem: "Where's my config?"

factory.listAvailableConfigurations().forEach(cdi ->
    System.out.println(cdi.getConfigName() + " @ " + cdi.getUri())
);

Why? Traces sources/scopes; CLI equiv: mconfig myco:myapp list

6. Secrets Without Log Leaks

Problem: Passwords in logs/heap.

In scheme: "type":"secret"

SecretValue pw = (SecretValue) cfg.getEntry("db.password");  // Masked: ********
String clear = pw.clearValue();  // JIT decrypt/use

mConfigSecrets

7. JPMS-Compatible (No IllegalAccessError)

module-info.java:

module com.example {
    requires metabit.mconfig.core;
    requires metabit.mconfig.util;
}

Deps: mConfigStandard (BOM) or mConfigBase.

JPMS FAQ

8. Tests: Isolated Configs

ConfigFactoryBuilder.setTestMode(true);
ConfigFactoryBuilder.setTestConfigPaths(ConfigScope.USER, List.of("src/test/resources"));
Config cfg = ConfigFactoryBuilder.create("myco", "myapp").build().getConfig("network");

src/test/resources/.config/myco/myapp/network.properties

Test Mode

Pro Tip: Enable logging (mConfigLoggingSlf4j + DEBUG) for traces.

Full Docs