spring-statemachine-core<\/code> to be added in your pom.xml<\/code> file.<\/p>\n<dependency>\r\n <groupId>org.springframework.statemachine<\/groupId>\r\n <artifactId>spring-statemachine-core<\/artifactId>\r\n <version>2.1.3.RELEASE<\/version>\r\n<\/dependency>\r\n<\/pre>\nSpring State Machine Example<\/h2>\n
SSM or Spring State Machine has 2 ways of implementing states and events.<\/p>\n
\n- String<\/strong><\/li>\n
- Enumeration<\/strong><\/li>\n<\/ul>\n
Defining the Events and States<\/h2>\n
In Enumeration<\/code>, states and events are hardcoded to for type safety.<\/p>\nThis is the code for events of the BlogEvents<\/code> Enumeration.<\/p>\nBlogEvents<\/strong><\/p>\npackage guru.springframework.domain;\r\n\r\npublic enum BlogEvents {\r\n EDIT_BLOG,\r\n PUBLISH_BLOG\r\n<\/pre>\nThis is the code for states of the BlogStates<\/code> Enumeration.<\/p>\nBlogStates<\/strong><\/p>\npackage guru.springframework.domain;\r\n\r\npublic enum BlogStates {\r\n UNEDITED_BLOG,\r\n EDITING_IN_PROGRESS,\r\n BLOG_EDITED,\r\n BLOG_PUBLISHED\r\n}\r\n<\/pre>\nConfiguring the State Machine<\/h2>\n
The next step is to configure the Spring State Machine.<\/p>\n
The code for the StateMachineConfig<\/code> class is this.<\/p>\nStateMachineConfig.java<\/strong><\/p>\n@Configuration\r\n@EnableStateMachine\r\npublic class StateMachineConfig extends EnumStateMachineConfigurerAdapter<BlogStates, BlogEvents> {\r\n\r\n @Override\r\n public void configure(StateMachineStateConfigurer<BlogStates, BlogEvents> states) throws Exception {\r\n states.withStates()\r\n .initial(BlogStates.UNEDITED_BLOG)\r\n .states(EnumSet.allOf(BlogStates.class));\r\n }\r\n\r\n @Override\r\n public void configure(StateMachineTransitionConfigurer<BlogStates, BlogEvents> transitions) throws Exception {\r\n transitions\r\n .withExternal()\r\n .source(BlogStates.UNEDITED_BLOG)\r\n .target(BlogStates.EDITING_IN_PROGRESS)\r\n .event(BlogEvents.EDIT_BLOG)\r\n .and()\r\n .withExternal()\r\n .source(BlogStates.EDITING_IN_PROGRESS)\r\n .target(BlogStates.BLOG_EDITED)\r\n .event(BlogEvents.EDIT_BLOG)\r\n .and()\r\n .withExternal()\r\n .source(BlogStates.BLOG_EDITED)\r\n .target(BlogStates.BLOG_PUBLISHED)\r\n .event(BlogEvents.PUBLISH_BLOG)\r\n .and()\r\n .withExternal()\r\n .source(BlogStates.BLOG_PUBLISHED)\r\n .target(BlogStates.BLOG_EDITED)\r\n .event(BlogEvents.EDIT_BLOG) ;\r\n }\r\n\r\n@Override\r\npublic void configure(StateMachineConfigurationConfigurer<BlogStates, BlogEvents> config) throws Exception {\r\n config.withConfiguration()\r\n .autoStartup(true)\r\n .listener(new Listener());\r\n}\r\n<\/pre>\nLine 1 uses @Configuration<\/code> annotation to specify that it is a Configuration class.<\/p>\nLine 2 has @EnableStateMachine<\/code> annotation which will automatically create a default state machine when the application starts.<\/p>\nIn some scenarios it is useful to start an instance of State Machine depending on a business logic. In that case the configuration must be annotated as a factory with @EnableStateMachineFactory<\/code> annotation.<\/p>\nThe @Configuration<\/code>class extends adapters (EnumStateMachineConfigurerAdapter or StateMachineConfigurerAdapter)<\/code>, which lets you override configuration callback methods.<\/p>\nHere, in Line 6 – I have extended EnumStateMachineConfigurerAdapter<\/code> and overridden 3 methods.<\/p>\nIn Line 8 – 9 the State-configurer method()<\/code> adds the states using a configuration method while initial- and end- states are optional and can be omitted. The initial state is assigned immediately after the State Machine is created.<\/p>\nLine 13 – 33 Using StateMachineTransitionConfigurer<\/code> interface you mention transitions from one state(source) to another state(target) based on events triggered (event) . withExternal()<\/code> is transition from one state to another state where as withInternal()<\/code> is transition from state to same state.<\/p>\nIn Line 38-39 I specified properties for autostartup and added a listener for listening events using StateMachineConfigurationConfigurer<\/code> interface as argument. It is used to track state changes and here it is only used to print out the current state.<\/p>\nSetting up the Listener class<\/h2>\n
The code for the Listener Class<\/code> is this.<\/p>\nListener.java<\/strong><\/p>\npublic class Listener extends StateMachineListenerAdapter<BlogStates,BlogEvents> {\r\n @Override\r\n public void stateChanged(State<BlogStates, BlogEvents> from, State<BlogStates, BlogEvents> to) {\r\n System.out.println(\"state changed from \" + to.getId());\r\n }\r\n}<\/pre>\nHere, the listener is built on a separate adapter StateMachineListenerAdapter<\/code>.<\/p>\nSetup and Run the Application<\/h2>\n
After the configuration is done, a typed instance of StateMachine<States, Event><\/code> can immediately be accessed and autowired to the business logic. An initial state States.UNEDITED<\/code> is already triggered.<\/p>\nDriving a State Machine is realized via transitions that are triggered by the appropriate events.<\/p>\n
The code for the SpringStateApplication<\/code> class is this.<\/p>\nSpringStateApplication.java<\/strong><\/p>\n @SpringBootApplication\r\n@EnableStateMachine\r\npublic class SpringStateMachineApplication implements CommandLineRunner {\r\n \r\n private final StateMachine<BlogStates, BlogEvents> stateMachine;\r\n \r\n @Autowired\r\n public SpringStateMachineApplication(StateMachine<BlogStates, BlogEvents> stateMachine) {\r\n this.stateMachine = stateMachine;\r\n }\r\n \r\n public static void main(String[] args) {\r\n SpringApplication.run(SpringStateMachineApplication.class, args);\r\n }\r\n \r\n @Override\r\n public void run(String... args) {\r\n stateMachine.start();\r\n stateMachine.sendEvent(BlogEvents.EDIT_BLOG);\r\n stateMachine.sendEvent(BlogEvents.PUBLISH_BLOG);\r\n stateMachine.stop();\r\n } \r\n}<\/pre>\nIn the run method, you can send events using State Machine in 2 ways.<\/p>\n
Here, in Line 19-20 I have used the first method of sending a type safe event using the state machine api method.<\/p>\n
The other way is to send event wrapped in a Message using api method with custom event headers.<\/p>\n
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<\/a><\/p>\nThe state gets changed on running the application successfully.\u00a0 The target EDITING_IN_PROGRESS<\/code>is achieved here.<\/p>\nSummary<\/h2>\n
States<\/code> and events<\/code> within a single Spring State Machine are really simple to understand. Spring State Machine finds its uses in IOT, Bots and many more areas of application. To check if the transition is allowed or not, you can nest the states and configure the guards and the events can be triggered by the actions, or on a timer.<\/p>\nThe topic is just scratched here, there are ample amount of things to explore further.<\/p>\n
You can find the source code of this post on Github<\/a><\/p>\nTo have a deeper insight on the Spring State Machine, you can check my Udemy Best Seller Course on Spring Boot Microservices with Spring Cloud Beginner to Guru<\/a><\/p>\n![\"\"](\"http:\/\/springframework.guru\/wp-content\/uploads\/2021\/03\/microservices.jpg\")
<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"The Spring framework has a library called Spring State Machine which is a model of computation that depends on the finite states. It can only be in one state at a given time, hence it is also called a finite state machine. The transitions of this State Machine are the changes in the status of […]Continue reading<\/a><\/p>\n","protected":false},"author":111,"featured_media":4653,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_lmt_disableupdate":"","_lmt_disable":"","_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"_uf_show_specific_survey":0,"_uf_disable_surveys":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","enabled":false},"version":2}},"categories":[21],"tags":[377,375,376],"class_list":["post-7019","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-spring","tag-events","tag-spring-state-machine","tag-states"],"jetpack_publicize_connections":[],"aioseo_notices":[],"modified_by":"jt","jetpack_sharing_enabled":true,"jetpack_featured_media_url":"https:\/\/springframework.guru\/wp-content\/uploads\/2017\/07\/Banner560x292_08Web.jpg","jetpack_shortlink":"https:\/\/wp.me\/p5BZrZ-1Pd","_links":{"self":[{"href":"https:\/\/springframework.guru\/wp-json\/wp\/v2\/posts\/7019"}],"collection":[{"href":"https:\/\/springframework.guru\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/springframework.guru\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/springframework.guru\/wp-json\/wp\/v2\/users\/111"}],"replies":[{"embeddable":true,"href":"https:\/\/springframework.guru\/wp-json\/wp\/v2\/comments?post=7019"}],"version-history":[{"count":17,"href":"https:\/\/springframework.guru\/wp-json\/wp\/v2\/posts\/7019\/revisions"}],"predecessor-version":[{"id":7603,"href":"https:\/\/springframework.guru\/wp-json\/wp\/v2\/posts\/7019\/revisions\/7603"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/springframework.guru\/wp-json\/wp\/v2\/media\/4653"}],"wp:attachment":[{"href":"https:\/\/springframework.guru\/wp-json\/wp\/v2\/media?parent=7019"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/springframework.guru\/wp-json\/wp\/v2\/categories?post=7019"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/springframework.guru\/wp-json\/wp\/v2\/tags?post=7019"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
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