Metrics with Micrometer in Spring Boot - Mini Project: Build & Apply

Metrics with Micrometer in Spring Boot

📖 Scenario: You are building a simple Spring Boot application that tracks how many times a greeting endpoint is called. This helps you understand how often users access your service.

🎯 Goal: Create a Spring Boot application that uses Micrometer to count the number of times the /greet endpoint is accessed.

📋 What You'll Learn

Create a Spring Boot application with a REST controller

Add a Micrometer counter metric to track endpoint calls

Configure a counter variable to hold the metric

Increment the counter each time the endpoint is called

💡 Why This Matters

🌍 Real World

Tracking how often endpoints are called helps monitor application usage and detect issues early.

💼 Career

Understanding Micrometer metrics is essential for backend developers working on Spring Boot applications to build observable and maintainable services.

1

Create a REST controller with a greeting endpoint

Create a Spring Boot REST controller class named GreetingController with a method greet mapped to /greet that returns the string "Hello, World!".

Spring Boot

@RestController
public class GreetingController {
    // Your code here
}

Hint

Use @RestController on the class and @GetMapping("/greet") on the method.

2

Add a Micrometer Counter variable

Add a private final Counter variable named greetCounter to the GreetingController class. Inject a MeterRegistry in the constructor and initialize greetCounter with Counter.builder("greet.calls").description("Number of greet calls").register(meterRegistry).

Spring Boot

@RestController
public class GreetingController {
    private final Counter greetCounter;

    public GreetingController(MeterRegistry meterRegistry) {
        // Your code here
    }

    @GetMapping("/greet")
    public String greet() {
        return "Hello, World!";
    }
}

Hint

Use constructor injection to get MeterRegistry and build the counter.

3

Increment the counter in the greet method

Inside the greet method, add a line to increment the greetCounter by calling greetCounter.increment() before returning the greeting string.

Spring Boot

@RestController
public class GreetingController {
    private final Counter greetCounter;

    public GreetingController(MeterRegistry meterRegistry) {
        this.greetCounter = Counter.builder("greet.calls")
            .description("Number of greet calls")
            .register(meterRegistry);
    }

    @GetMapping("/greet")
    public String greet() {
        // Your code here
        return "Hello, World!";
    }
}

Hint

Call greetCounter.increment() at the start of the greet method.

4

Add Micrometer dependency and enable metrics endpoint

Add the spring-boot-starter-actuator and micrometer-core dependencies to your pom.xml or build.gradle. Then, in application.properties, enable the metrics endpoint by adding management.endpoints.web.exposure.include=metrics.

Spring Boot

# Add dependencies and configuration in your project files
# Your code here

Hint

Make sure to add both dependencies and enable metrics endpoint in properties.

Practice

1. What is the primary purpose of Micrometer in a Spring Boot application?

easy

A. To manage database connections efficiently

B. To collect and expose application metrics like counters and timers

C. To handle user authentication and authorization

D. To serve static web content like images and CSS

Solution

1. Step 1: Understand Micrometer's role

   Micrometer is designed to collect metrics such as counters, timers, and gauges to monitor app performance.

2. Step 2: Compare with other options

   Options B, C, and D relate to database, security, and web content, which are not Micrometer's focus.

3. Final Answer:

   To collect and expose application metrics like counters and timers -> Option B

4. Quick Check:

   Micrometer = Metrics collection [OK]

Hint: Micrometer is for metrics, not security or database [OK]

Common Mistakes:

• Confusing Micrometer with security or database tools
• Thinking Micrometer serves static files
• Assuming Micrometer manages app logic

2. Which of the following is the correct way to create a counter metric using Micrometer in Spring Boot?

easy

A. Counter counter = Counter.builder("my.counter").register(meterRegistry);

B. Counter counter = new Counter("my.counter");

C. Counter counter = meterRegistry.createCounter("my.counter");

D. Counter counter = Counter.create("my.counter");

Solution

1. Step 1: Recall Micrometer counter creation syntax

   Micrometer uses builder pattern: Counter.builder(name).register(meterRegistry) to create counters.

2. Step 2: Check other options for correctness

   Options B, C, and D use incorrect constructors or methods not available in Micrometer.

3. Final Answer:

   Counter counter = Counter.builder("my.counter").register(meterRegistry); -> Option A

4. Quick Check:

   Use builder().register() to create counters [OK]

Hint: Use builder() and register() to create metrics [OK]

Common Mistakes:

• Trying to instantiate Counter with new keyword
• Using non-existent createCounter method
• Missing register() call after builder()

3. Given the following code snippet in a Spring Boot app using Micrometer:

Counter counter = Counter.builder("requests.count").register(meterRegistry);
counter.increment();
counter.increment(2);

What will be the value of the counter after these calls?

medium

A. 3

B. 2

C. 0

D. 1

Solution

1. Step 1: Analyze the increment calls

   The first call increments the counter by 1, the second increments by 2.

2. Step 2: Calculate total increments

   Total increments = 1 + 2 = 3.

3. Final Answer:

   3 -> Option A

4. Quick Check:

   1 + 2 = 3 increments [OK]

Hint: Add all increment values to get total count [OK]

Common Mistakes:

• Ignoring the second increment call
• Assuming increment() resets counter
• Confusing increment() with set()

4. Consider this Spring Boot code snippet using Micrometer:

Counter counter = Counter.builder("api.calls").register(meterRegistry);
counter.increment(-1);

What is the issue with this code?

medium

A. meterRegistry is not initialized properly

B. Counter names cannot contain dots

C. Counters cannot be incremented by negative values; this will throw an exception

D. increment() method does not exist on Counter

Solution

1. Step 1: Understand Counter increment rules

   Counters only allow positive increments; negative values cause errors.

2. Step 2: Validate other options

   Counter names with dots are allowed, meterRegistry is assumed valid, and increment() exists.

3. Final Answer:

   Counters cannot be incremented by negative values; this will throw an exception -> Option C

4. Quick Check:

   Counter increments must be positive [OK]

Hint: Counters only accept positive increments [OK]

Common Mistakes:

• Trying to decrement counters with negative increments
• Thinking dots in metric names are invalid
• Assuming increment() method is missing

5. You want to measure the duration of a method execution in a Spring Boot app using Micrometer. Which approach correctly uses a Timer to record the time taken by a method processData()?

hard

A. Timer timer = new Timer("process.time");
timer.start();
processData();
timer.stop();

B. Timer timer = Timer.create("process.time");
timer.record(processData());

C. meterRegistry.timer("process.time").start();
processData();
meterRegistry.timer("process.time").stop();

D. Timer timer = Timer.builder("process.time").register(meterRegistry);
timer.record(() -> processData());

Solution

1. Step 1: Identify correct Timer usage in Micrometer

   Micrometer uses Timer.builder(name).register() and timer.record(Runnable) to measure durations.

2. Step 2: Check other options for errors

   Options A, C, and D use invalid constructors or methods not supported by Micrometer.

3. Final Answer:

   Timer timer = Timer.builder("process.time").register(meterRegistry); timer.record(() -> processData()); -> Option D

4. Quick Check:

   Use Timer.builder().register() and record() for timing [OK]

Hint: Use timer.record(() -> method()) to measure duration [OK]

Common Mistakes:

• Trying to instantiate Timer with new or create()
• Calling start() and stop() manually on Timer
• Passing method call directly instead of lambda to record()