Custom actuator endpoints in Spring Boot - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a custom actuator endpoint class.

Spring Boot

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

@[1](id = "custom")
public class CustomEndpoint {

    @ReadOperation
    public String custom() {
        return "Hello from custom endpoint!";
    }
}

Drag options to blanks, or click blank then click option'

AService

BComponent

CEndpoint

DController

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Component instead of @Endpoint

Forgetting to specify the id in the annotation

The @Endpoint annotation marks the class as a custom actuator endpoint with the given id.

2fill in blank

medium

Complete the code to register the custom endpoint as a Spring bean.

Spring Boot

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class EndpointConfig {

    @Bean
    public CustomEndpoint [1]() {
        return new CustomEndpoint();
    }
}

Drag options to blanks, or click blank then click option'

AcustomEndpoint

Bendpoint

Ccustom

DcustomActuator

Attempts:

3 left

💡 Hint

Common Mistakes

Using the same name as the endpoint id

Using uppercase letters at the start

The bean method name is usually the camelCase version of the class name, here customEndpoint.

3fill in blank

hard

Fix the error in the method that exposes the endpoint data.

Spring Boot

import org.springframework.boot.actuate.endpoint.annotation.ReadOperation;

public class CustomEndpoint {

    @ReadOperation
    public String [1]() {
        return "Custom data";
    }
}

Drag options to blanks, or click blank then click option'

Afetch

Bcustom

Cread

DgetData

Attempts:

3 left

💡 Hint

Common Mistakes

Using method names that conflict with Spring reserved names

Using verbs that are not descriptive

The method name can be any valid name, but to match the example and avoid confusion, use custom.

4fill in blank

hard

Fill both blanks to create a custom actuator endpoint that returns a map with status and message.

Spring Boot

import org.springframework.boot.actuate.endpoint.annotation.Endpoint;
import org.springframework.boot.actuate.endpoint.annotation.ReadOperation;
import java.util.Map;

@[1](id = "status")
public class StatusEndpoint {

    @[2]
    public Map<String, String> status() {
        return Map.of("status", "UP", "message", "All systems go");
    }
}

Drag options to blanks, or click blank then click option'

AEndpoint

BReadOperation

CComponent

DService

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up @Component with @Endpoint

Forgetting to annotate the method

The class must be annotated with @Endpoint and the method with @ReadOperation to expose the data.

5fill in blank

hard

Fill all three blanks to create a custom actuator endpoint that accepts a path variable and returns a greeting message.

Spring Boot

import org.springframework.boot.actuate.endpoint.annotation.Endpoint;
import org.springframework.boot.actuate.endpoint.annotation.ReadOperation;
import org.springframework.boot.actuate.endpoint.annotation.Selector;

@[1](id = "greet")
public class GreetEndpoint {

    @[2]
    public String greet(@[3] String name) {
        return "Hello, " + name + "!";
    }
}

Drag options to blanks, or click blank then click option'

AEndpoint

BReadOperation

CSelector

DComponent

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to use @Selector for the method parameter

Using @Component instead of @Endpoint

The class uses @Endpoint, the method uses @ReadOperation, and the parameter uses @Selector to accept a path variable.

Practice

1. What annotation is used to define a custom actuator endpoint in Spring Boot?

easy

A. @Endpoint

B. @Controller

C. @Service

D. @RestController

Solution

1. Step 1: Understand the purpose of custom actuator endpoints

   Custom actuator endpoints allow you to add your own monitoring or info checks in Spring Boot.

2. Step 2: Identify the correct annotation for defining custom endpoints

   The @Endpoint annotation is specifically designed to mark a class as a custom actuator endpoint.

3. Final Answer:

   @Endpoint -> Option A

4. Quick Check:

   Custom actuator endpoint = @Endpoint [OK]

Hint: Custom actuator endpoints always use @Endpoint annotation [OK]

Common Mistakes:

• Confusing @Endpoint with @Controller
• Using @Service instead of @Endpoint
• Using @RestController which is for REST APIs

2. Which annotation should you use on a method inside a custom actuator endpoint to expose a read-only operation?

easy

A. @WriteOperation

B. @ReadOperation

C. @GetMapping

D. @PostMapping

Solution

1. Step 1: Recall method annotations for custom actuator endpoints

   Custom actuator endpoints use specific annotations to define operations: read or write.

2. Step 2: Match read-only operation annotation

   The @ReadOperation annotation marks a method as a read-only operation accessible via HTTP GET.

3. Final Answer:

   @ReadOperation -> Option B

4. Quick Check:

   Read-only method = @ReadOperation [OK]

Hint: Use @ReadOperation for read-only endpoint methods [OK]

Common Mistakes:

• Using @WriteOperation for read methods
• Confusing @GetMapping with actuator annotations
• Using @PostMapping which is for REST controllers

3. Given this custom endpoint class, what will be the HTTP response body when accessing the endpoint?

@Endpoint(id = "status")
public class StatusEndpoint {
  @ReadOperation
  public String getStatus() {
    return "UP";
  }
}

medium

A. "DOWN"

B. 404 Not Found

C. "UP"

D. 500 Internal Server Error

Solution

1. Step 1: Analyze the custom endpoint class

   The class is annotated with @Endpoint(id = "status") and has a method with @ReadOperation returning "UP".

2. Step 2: Understand the HTTP response from the read operation

   Accessing the actuator endpoint with id "status" triggers the getStatus() method, returning the string "UP" as the response body.

3. Final Answer:

   "UP" -> Option C

4. Quick Check:

   Read operation returns "UP" [OK]

Hint: ReadOperation returns method result as HTTP response body [OK]

Common Mistakes:

• Expecting 404 if endpoint is defined correctly
• Confusing return value with HTTP status code
• Assuming method returns JSON object instead of string

4. Identify the error in this custom actuator endpoint code:

@Endpoint(id = "metrics")
public class MetricsEndpoint {
  @ReadOperation
  public String metrics() {
    return 12345;
  }
}

medium

A. The @ReadOperation annotation is missing

B. The method name must be getMetrics

C. The @Endpoint annotation must be on a method, not class

D. The method declares String return type but returns an int

Solution

1. Step 1: Check method return type consistency

   The method metrics() returns an integer literal 12345 but declares return type String, causing a type mismatch.

2. Step 2: Verify annotations and method naming

   The @ReadOperation annotation is present, and @Endpoint is correctly on the class. Method name can be arbitrary.

3. Final Answer:

   The method declares String return type but returns an int -> Option D

4. Quick Check:

   Return type mismatch causes error [OK]

Hint: Method return type must match declared type [OK]

Common Mistakes:

• Thinking @Endpoint goes on methods
• Assuming method name must follow getter pattern
• Ignoring type mismatch errors

5. You want to create a custom actuator endpoint that accepts a POST request to update a configuration value. Which combination of annotations and method signature is correct? A)

@Endpoint(id = "config")
public class ConfigEndpoint {
  @WriteOperation
  public String updateConfig(String key, String value) {
    // update logic
    return "Updated";
  }
}

B)

@Endpoint(id = "config")
public class ConfigEndpoint {
  @ReadOperation
  public void updateConfig(String key, String value) {
    // update logic
  }
}

C)

@Endpoint(id = "config")
public class ConfigEndpoint {
  @WriteOperation
  public void updateConfig() {
    // update logic
  }
}

D)

@Endpoint(id = "config")
public class ConfigEndpoint {
  @WriteOperation
  public String updateConfig() {
    // update logic
    return "Updated";
  }
}

hard

A. Option A is correct because @WriteOperation supports parameters and returns a response

B. Option B is correct because @ReadOperation can update values

C. Option C is correct because @WriteOperation methods cannot have parameters

D. Option D is correct because @WriteOperation methods should not have parameters

Solution

1. Step 1: Understand @WriteOperation usage

   @WriteOperation marks methods that handle write operations, typically POST, and can accept parameters for input.

2. Step 2: Analyze method signatures and annotations

   The correct combination uses @WriteOperation with String key and String value parameters and returns a String response, which is valid for POST updates. Using @ReadOperation is wrong for update operations. The other snippets lack parameters needed to receive key and value.

3. Final Answer:

   Option A is correct because @WriteOperation supports parameters and returns a response -> Option A

4. Quick Check:

   @WriteOperation with parameters for POST updates [OK]

Hint: Use @WriteOperation with parameters for POST updates [OK]

Common Mistakes:

• Using @ReadOperation for write/update methods
• Omitting parameters needed for update
• Assuming @WriteOperation methods cannot return values