Custom actuator endpoints in Spring Boot - Step-by-Step Execution

Concept Flow - Custom actuator endpoints

Start Spring Boot App

↓

Define Custom Endpoint Class

↓

Annotate with @Endpoint

↓

Add @ReadOperation or @WriteOperation

↓

App Runs and Registers Endpoint

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Call /actuator/custom

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Execute Method and Return Data

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Client Receives Response

The app starts, registers a custom actuator endpoint class with annotated methods, then serves data when the endpoint URL is called.

Execution Sample

Spring Boot

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

@Endpoint(id = "custom")
public class CustomEndpoint {
  @ReadOperation
  public String info() { return "Hello from custom endpoint"; }
}

Defines a custom actuator endpoint named 'custom' that returns a simple string when accessed.

Execution Table

Step	Action	Annotation Used	Result	Endpoint URL
1	Spring Boot starts	N/A	App context initialized	N/A
2	CustomEndpoint class loaded	@Endpoint(id="custom")	Endpoint registered	N/A
3	info() method detected	@ReadOperation	Method ready to serve GET requests	N/A
4	HTTP GET /actuator/custom called	N/A	info() method invoked	/actuator/custom
5	info() returns string	N/A	"Hello from custom endpoint"	/actuator/custom
6	Response sent to client	N/A	Client receives "Hello from custom endpoint"	/actuator/custom

💡 Execution stops after response is sent to client for the custom actuator endpoint.

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 5	Final
App Context	Empty	Initialized with CustomEndpoint bean	CustomEndpoint methods registered	N/A	Running with endpoint ready
CustomEndpoint.info()	Not called	Registered	Ready	"Hello from custom endpoint"	Returned response

Key Moments - 3 Insights

Why do we need @Endpoint and @ReadOperation annotations?

The @Endpoint annotation marks the class as a custom actuator endpoint (see Step 2). The @ReadOperation marks the method to handle GET requests (see Step 3). Without these, Spring Boot won't register or expose the endpoint.

What URL do I use to call my custom endpoint?

The URL is /actuator/{id} where id is from @Endpoint(id). Here, it is /actuator/custom as shown in Steps 4-6.

Can the method return other data types?

Yes, methods can return any serializable data like String, Map, or POJOs. Spring Boot converts it to JSON automatically (Step 5).

Visual Quiz - 3 Questions

Look at the execution table, what annotation registers the class as an actuator endpoint?

A @ReadOperation

B @Endpoint

C @WriteOperation

D @Component

💡 Hint

Check Step 2 in the execution table where the class is registered.

At which step does the custom endpoint method get called?

A Step 4

B Step 2

C Step 3

D Step 6

💡 Hint

Look for the HTTP GET request triggering the method invocation.

If you change @Endpoint(id = "custom") to @Endpoint(id = "info"), what changes?

A The app will not start

B The method name must change to info()

C The endpoint URL changes to /actuator/info

D The response string changes automatically

💡 Hint

Refer to the URL column in the execution table and how id affects it.

Concept Snapshot

Custom actuator endpoints let you add your own monitoring URLs.
Use @Endpoint(id = "name") on a class.
Use @ReadOperation for GET methods.
Spring Boot exposes it at /actuator/name.
Return any data; it converts to JSON.
Useful for custom health or info checks.

Full Transcript

This visual trace shows how to create a custom actuator endpoint in Spring Boot. First, the app starts and loads the CustomEndpoint class annotated with @Endpoint. This registers the endpoint with Spring Boot. Then, the method annotated with @ReadOperation is detected and prepared to handle GET requests. When a client calls /actuator/custom, the info() method runs and returns a string. The response is sent back to the client. Variables like the app context and method state change from uninitialized to ready and then to returned response. Key points include the importance of annotations to register and expose the endpoint, the URL pattern based on the id, and the flexibility of return types. The quiz tests understanding of annotations, method invocation step, and URL naming.