Metrics with Micrometer in Spring Boot - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this Micrometer counter increment?

Consider this Spring Boot code snippet using Micrometer:

Counter counter = meterRegistry.counter("my.counter");
counter.increment();
counter.increment(2);

What is the value of counter.count() after these calls?

Spring Boot

Counter counter = meterRegistry.counter("my.counter");
counter.increment();
counter.increment(2);
double value = counter.count();

A 0.0

B 2.0

C 1.0

D 3.0

💡 Hint

Remember that each increment adds to the counter's total count.

The counter starts at 0. The first increment adds 1, the second adds 2, so total is 3.0.

📝 Syntax

intermediate

Which option correctly registers a Gauge metric in Micrometer?

You want to register a Gauge metric named "queue.size" that tracks the size of a queue. Which code snippet is correct?

A Gauge gauge = Gauge.builder("queue.size", queue, q -> q.size()).register(meterRegistry);

B Gauge gauge = meterRegistry.gauge("queue.size", queue.size());

C Gauge gauge = Gauge.builder("queue.size", () -> queue.size()).register(meterRegistry);

D Gauge gauge = Gauge.builder("queue.size", queue).register(meterRegistry);

💡 Hint

The builder requires the object and a function to get the value.

Option A correctly uses Gauge.builder with the object and a lambda to get the size, then registers it.

🔧 Debug

advanced

Why does this Timer metric not record durations correctly?

Given this code:

Timer timer = meterRegistry.timer("process.time");
timer.record(() -> {
  // some process
  Thread.sleep(100);
});
System.out.println(timer.count());

The printed count is always 0. What is the cause?

Spring Boot

Timer timer = meterRegistry.timer("process.time");
timer.record(() -> {
  Thread.sleep(100);
});
System.out.println(timer.count());

A Thread.sleep throws InterruptedException which is not handled, so the lambda never completes.

B The timer is not registered properly with meterRegistry.

C The record method requires a Callable, not a Runnable.

D The timer.count() returns the number of recorded events, so 0 means no record was made.

💡 Hint

Check if the lambda handles checked exceptions properly.

Thread.sleep throws InterruptedException, which must be caught or declared. Without handling, the lambda fails silently and no timing occurs.

❓ state_output

advanced

What is the value of the Gauge after updating the tracked object?

Consider this code:

AtomicInteger value = new AtomicInteger(5);
Gauge gauge = Gauge.builder("current.value", value, AtomicInteger::get).register(meterRegistry);
value.set(10);
double gaugeValue = gauge.value();

What is the value of gaugeValue?

Spring Boot

AtomicInteger value = new AtomicInteger(5);
Gauge gauge = Gauge.builder("current.value", value, AtomicInteger::get).register(meterRegistry);
value.set(10);
double gaugeValue = gauge.value();

A 5.0

B 0.0

C 10.0

D Throws NullPointerException

💡 Hint

Gauge reads the current value from the object each time it is queried.

Gauge calls AtomicInteger::get on the current object, so after setting to 10, gauge.value() returns 10.0.

🧠 Conceptual

expert

Which Micrometer meter type is best to measure the rate of events per second?

You want to monitor how many requests your service receives per second. Which Micrometer meter type should you use?

A DistributionSummary

B Counter

C Gauge

D Timer

💡 Hint

Think about a metric that only increases and can be used to calculate rates.

Counter is a meter that only increases and is used to count events, which can be used to calculate rates like requests per second.