Spring Statemachine with Spring Boot Tutorial

Introduction

Spring Statemachine is a powerful framework that provides a way to model the state of an application using finite state machines. This tutorial will guide you through the process of setting up a Spring Boot application with Spring Statemachine, including configuration, state definitions, transitions, and event handling.

Prerequisites

Before we start, ensure you have the following installed:

• Java Development Kit (JDK) 11 or later
• Apache Maven
• An IDE (like IntelliJ IDEA or Eclipse)
• Basic understanding of Spring Boot

Setting Up the Spring Boot Project

We will create a new Spring Boot project using Spring Initializr. Follow the steps below:

1. Go to Spring Initializr.
2. Select the following dependencies:
   • Spring Web
   • Spring Statemachine
   • Spring Boot DevTools (optional)
3. Click on "Generate" to download the project.
4. Extract the downloaded zip file and open it in your IDE.

Adding Spring Statemachine Configuration

In this section, we will define the state machine configuration. Create a new class named StateMachineConfig in the config package.

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.statemachine.config.EnableStateMachine;
import org.springframework.statemachine.config.builders.StateMachineConfigurer;
import org.springframework.statemachine.config.builders.StateMachineConfigurerAdapter;
import org.springframework.statemachine.config.builders.StateMachineStateConfigurer;
import org.springframework.statemachine.config.builders.StateMachineTransitionConfigurer;
import org.springframework.statemachine.state.State;

@Configuration
@EnableStateMachine
public class StateMachineConfig extends StateMachineConfigurerAdapter<String, String> {

    @Override
    public void configure(StateMachineStateConfigurer<String, String> states) throws Exception {
        states
            .withStates()
            .initial("STATE1")
            .state("STATE2")
            .state("STATE3");
    }

    @Override
    public void configure(StateMachineTransitionConfigurer<String, String> transitions) throws Exception {
        transitions
            .withExternal()
            .source("STATE1").target("STATE2").event("TO_STATE2")
            .and()
            .withExternal()
            .source("STATE2").target("STATE3").event("TO_STATE3")
            .and()
            .withExternal()
            .source("STATE3").target("STATE1").event("TO_STATE1");
    }
}

In this configuration, we defined three states: STATE1, STATE2, and STATE3. We also defined transitions between these states based on the events TO_STATE2, TO_STATE3, and TO_STATE1.

Creating State Machine Service

Next, we will create a service to interact with the state machine. Create a new class called StateMachineService in the service package.

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.statemachine.StateMachine;
import org.springframework.statemachine.config.StateMachineFactory;
import org.springframework.statemachine.state.State;

public class StateMachineService {

    @Autowired
    private StateMachineFactory<String, String> stateMachineFactory;

    public StateMachine<String, String> startStateMachine() {
        StateMachine<String, String> stateMachine = stateMachineFactory.getStateMachine();
        stateMachine.start();
        return stateMachine;
    }

    public void sendEvent(StateMachine<String, String> stateMachine, String event) {
        stateMachine.sendEvent(event);
    }

    public State<String, String> getCurrentState(StateMachine<String, String> stateMachine) {
        return stateMachine.getState();
    }
}

This service provides methods to start the state machine, send events, and get the current state.

Testing the State Machine

Now, let’s test our state machine. You can create a REST controller to expose endpoints for triggering events. Create a class called StateMachineController in the controller package.

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;

@RestController
@RequestMapping("/statemachine")
public class StateMachineController {

    @Autowired
    private StateMachineService stateMachineService;

    private StateMachine<String, String> stateMachine;

    public StateMachineController() {
        this.stateMachine = stateMachineService.startStateMachine();
    }

    @GetMapping("/state")
    public String getCurrentState() {
        return stateMachineService.getCurrentState(stateMachine).getId();
    }

    @PostMapping("/event/{event}")
    public String sendEvent(@PathVariable String event) {
        stateMachineService.sendEvent(stateMachine, event);
        return "Event sent: " + event;
    }
}

This controller exposes a GET endpoint to retrieve the current state and a POST endpoint to send events. You can test the state machine using a tool like Postman or curl.

Running the Application

To run the application, execute the following command in the terminal from the root of your project:

mvn spring-boot:run

Once the application is running, you can access the current state by visiting http://localhost:8080/statemachine/state and send events using POST http://localhost:8080/statemachine/event/{event}.

Conclusion

In this tutorial, you learned how to set up a simple state machine using Spring Statemachine with Spring Boot. You defined states, transitions, and created a service and controller to interact with the state machine. This framework provides a robust way to handle state transitions in your applications.