OhDear HealthChecks

This library provides bases classes for exposing health check results to OhDear application monitoring service. It follows their documentation to give you compatible Java classes you can directly format to JSON data and expose through one HTTP endpoint.

It is very similar to Dropwizard Health Checks, but it has a little bit more precise information. At least for statuses, as with Dropwizard you'll only get choice for OK or Not OK, while 5 different status are defined when using OhDear application monitoring.

Dependency

Copy this dependency into your pom.xml file.

<dependency>
    <groupId>net.zileo</groupId>
    <artifactId>ohdear-healthchecks</artifactId>
    <version>1.1.2</version>
</dependency>

Version 1.0.3 requires Java 11, version 1.1.2 requires Java 21. No major differences between both (only one more NullPointerException pre-check).

How to use it

First, write one or more checks by extending the HealthCheck class and overriding the perform() method. The best practice is to create one check for each part of your app or service you want to monitor, like for example a database connection, a file system, the availability of an external service, etc...

    public class MyOwnHealthCheck extends HealthCheck {

        public MyOwnHealthCheck() {
            super("my_own_health_check", "My own health check");
        }

        @Override
        public HealthCheckResult perform() {
            return HealthCheckResult.ok("OK!", "System is fine");
        }

    }

The check needs a technical name and a label, that will be displayed in your OhDear dashboard. In the perform() method you'll implement how you want to execute your check. You'll return a HealthCheckResult object, defining a status, a short summary of that result, and a longer message if needed. Available status are ok, warning, failed, crashed and skipped. Those are available as static builders methods on the HealthCheckResult class, or you can use the class constructor.

To execute your checks and get their result, create a HealthCheckRegistry object in your application. Register a new instance for each one of your different health checks. Then you'll be able to call the performAll().

    HealthCheckRegistry registry = new HealthCheckRegistry();
    registry.register(new MyOwnHealthCheck());
    CheckResultsHolder results = registry.performAll();
    return results; // Format it to JSON

That registry should of course be referenced as a singleton object, with the health checks registration being executed at startup time, depending on which Java framework your application is based on.

Using with DropWizard Health Checks

You already implemented health checks with Dropwizard library and want to reuse them with OhDear? Feel free to reuse and adapt below code, acting as a bridge between Dropwizard results and this library.

    @Inject
    private HealthCheckRegistry registry;

    public CheckResultsHolder getCheckResults() {
        CheckResultsHolder results = new CheckResults();

        for (Entry<String, Result> entry : registry.runHealthChecks().entrySet()) {
            CheckResult result = new CheckResult(entry.getKey());
            result.setStatus(entry.getValue().isHealthy() ? CheckResultStatus.OK : CheckResultStatus.FAILED);
           
            if (!entry.getValue().isHealthy()) {
                result.setShortSummary(entry.getValue().getMessage());
                result.setNotificationMessage(entry.getValue().getMessage());
            }
           
            results.checkResults.add(result);
        }

        results.setFinishedDate(new Date());
        return data;
    }

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