Custom actuator endpoints in Spring Boot - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this custom actuator endpoint?

Given the following Spring Boot custom actuator endpoint code, what will be the JSON output when accessing /actuator/customStatus?

Spring Boot

import org.springframework.boot.actuate.endpoint.annotation.Endpoint;
import org.springframework.boot.actuate.endpoint.annotation.ReadOperation;
import org.springframework.stereotype.Component;

@Component
@Endpoint(id = "customStatus")
public class CustomStatusEndpoint {

    @ReadOperation
    public Status status() {
        return new Status("UP", "All systems operational");
    }

    public record Status(String state, String message) {}
}

A {"status":"UP","info":"All systems operational"}

B {"state":"UP","message":"All systems operational"}

C {"state":"DOWN","message":"All systems operational"}

D {"state":"UP"}

💡 Hint

Look at the record fields and the returned object structure.

The endpoint returns a Status record with fields 'state' and 'message'. The JSON output matches these field names and values exactly.

📝 Syntax

intermediate

Which option correctly defines a write operation in a custom actuator endpoint?

You want to create a custom actuator endpoint with a write operation that accepts a String parameter. Which code snippet correctly defines the write operation method?

Spring Boot

import org.springframework.boot.actuate.endpoint.annotation.WriteOperation;
import org.springframework.boot.actuate.endpoint.annotation.Selector;

// Method to define:

A

@WriteOperation
public String updateStatus(@Selector String newStatus) { return "Updated to " + newStatus; }

B

@WriteOperation
public String updateStatus(String newStatus) { return "Updated to " + newStatus; }

C

@WriteOperation
public String updateStatus() { return "Updated"; }

D

@WriteOperation
public void updateStatus(String newStatus) { System.out.println(newStatus); }

💡 Hint

Write operations with parameters require @Selector annotation for each parameter.

In Spring Boot actuator custom endpoints, parameters for write operations must be annotated with @Selector to be bound from the request.

🔧 Debug

advanced

Why does this custom actuator endpoint fail to register?

Consider this custom endpoint class: @Component @Endpoint(id = "failEndpoint") public class FailEndpoint { public String status() { return "OK"; } } Why does Spring Boot fail to register this endpoint?

A The class must extend AbstractEndpoint to be recognized.

B The endpoint id 'failEndpoint' is invalid because it contains uppercase letters.

C The method 'status' lacks a @ReadOperation annotation.

D The class is missing @RestController annotation.

💡 Hint

Check if the method is properly annotated to expose it as an endpoint operation.

Spring Boot actuator requires methods to be annotated with @ReadOperation, @WriteOperation, or @DeleteOperation to expose them as endpoint operations.

❓ state_output

advanced

What is the state of the custom endpoint after calling the write operation twice?

Given this custom endpoint: @Component @Endpoint(id = "counter") public class CounterEndpoint { private int count = 0; @ReadOperation public int getCount() { return count; } @WriteOperation public void increment() { count++; } } If you call the write operation /actuator/counter twice, then call the read operation, what is the returned count?

A 2

B 1

C 0

D Cannot determine because endpoints are stateless

💡 Hint

Consider the instance variable and how many times increment is called.

The count starts at 0 and increments by 1 each time the write operation is called. After two calls, count is 2.

🧠 Conceptual

expert

Which statement about custom actuator endpoints is true?

Select the correct statement about custom actuator endpoints in Spring Boot.

A Custom actuator endpoints require extending AbstractEndpoint class to function.

B Custom actuator endpoints must be registered manually in application.properties to be exposed.

C Custom actuator endpoints cannot accept parameters in their operations.

D Custom actuator endpoints can expose multiple operations annotated with @ReadOperation, @WriteOperation, and @DeleteOperation within the same class.

💡 Hint

Think about the flexibility of operation types in one endpoint class.

A single custom actuator endpoint class can have multiple methods annotated with different operation annotations to expose various HTTP methods.