在日常開發中難免會經常遇到這樣的應用場景，在專案初始化時執行指定的程式碼實現一些功能，或者在專案啟動後執行一些程式碼實現功能。這個時候就需要用到Spring提供的一些介面、註解了。本文都是以SpringBoot為基礎。

1.Spring容器啟動前執行

   1.1介面類InitializingBean

         直接在程式碼中實現該介面afterPropertiesSet方法，並在該方法中執行程式碼。

         值得注意的是  在該介面執行時Spring 容器是還沒有初始化完成的。在這裡取spring容器中的物件可能會被丟擲空指標異常。

@Component
public class TestConfigInitializingBean implements InitializingBean {
	private static final Logger LOGGER = LoggerFactory.getLogger(TestConfigInitializingBean.class);

	@Override
	public void afterPropertiesSet() throws Exception {
		LOGGER.info("--------------------------------------------");
		LOGGER.info("-----正在執行InitializingBean實現類程式碼-----");
		LOGGER.info("--------------------------------------------");
	}

}
 

     1.2 註解實現@PostConstruct

        這種方式相對於InitializingBean介面實現要方便一些。直接在需要的方法上新增該註解即可。

        這種方式與上面InitializingBean介面一樣都是在spring容器初始化前執行，所有在該註解方法中獲取容器內物件可能存在空指標異常

@Component
public class TestPostConstruct {

	private static final Logger LOGGER = LoggerFactory.getLogger(TestPostConstruct.class);

	@PostConstruct
	public void initPostConstruct() {
		LOGGER.info("--------------------------------------------");
		LOGGER.info("-----正在執行@PostConstruct實現類程式碼-----");
		LOGGER.info("--------------------------------------------");
	}

}
 

2 Spring容器初始化完成後執行

  2.1 實現監聽器 ApplicationListener<ApplicationEvent>

      關於這個介面，很多人可能會遇到多次執行該方法。其實這是正常現象，我在執行這段程式碼時，被重複呼叫了3次

     通過debug除錯觀察發現，3次執行引數ApplicationEvent event都是不同的。

     第一次引數內source是AnnotationConfigEmbeddedWebApplicationContext

     第二次引數內source是TomcatEmbeddedServletContainer

     第三次引數內source是SpringApplication

    我個人的理解為springboot web容器載入時觸發該方法一次，springboot自帶tomcat容器初始化時觸發容器一次

     第三次是springApplication  建立並初始化Spring上下文時再次觸發該監聽

      直接上程式碼

@Component
public class TestConfigApplicationListener implements ApplicationListener<ApplicationEvent> {
	private static final Logger LOGGER = LoggerFactory.getLogger(TestConfigApplicationListener.class);

	@Override
	public void onApplicationEvent(ApplicationEvent event) {
		LOGGER.info("--------------------------------------------");
		LOGGER.info("-----正在執行ApplicationListener實現類程式碼-----");
		LOGGER.info("--------------------------------------------");
	}

}

    補充： ApplicationEvent該類是一個監聽事件抽象類，它下面有很多子類。分別實現不同的事件監聽。該監聽器的具體執行時間可根據不同的監聽型別物件（ApplicationEvent子類）在不同的時間執行 專案啟動前、啟動後等，具體每個類的監聽後面的文章在分析。

    原理：ApplicationContextAware介面提供了publishEvent方法，實現了Observe（觀察者）設計模式的傳播機制，實現了對bean的傳播。通過ApplicationContextAware把系統中所有ApplicationEvent傳播給所有的ApplicationListener。

      2.2 實現介面ApplicationRunner

        在程式碼中實現介面的run方法，並在run方法中編寫邏輯程式碼

       該方法可以通過@order(value= 數字) 來控制執行順序，順序是依次從小到大執行

@Component
@Order(value = 3)
public class TestConfigApplicationRunner implements ApplicationRunner {
	private static final Logger LOGGER = LoggerFactory.getLogger(TestConfigApplicationRunner.class);

	@Override
	public void run(ApplicationArguments args) throws Exception {
		LOGGER.info("--------------------------------------------");
		LOGGER.info("-----正在執行ApplicationRunner實現類程式碼-----");
		LOGGER.info("--------------------------------------------");
	}

}

       2.2 實現介面CommandLineRunner

        CommandLineRunner介面的使用方式與ApplicationRunner介面基本相似，不同的只是方法的引數型別，CommandLineRunner的引數是基本型別，而ApplicationRunner是的引數是ApplicationArguments物件，經過封裝，使用者可對引數進行更多操作

@Component
@Order(value = 2)
public class TestConfigCommandLineRunner implements CommandLineRunner {

	private static final Logger LOGGER = LoggerFactory.getLogger(TestConfigCommandLineRunner.class);

	@Override
	public void run(String... args) throws Exception {
		LOGGER.info("--------------------------------------------");
		LOGGER.info("-----正在執行CommandLineRunner實現類程式碼-----");
		LOGGER.info("--------------------------------------------");
	}

}

程式碼最終執行結果日誌：

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::       (v1.5.10.RELEASE)

2018-09-05 12:20:08.212  INFO 7140 --- [           main] com.port.test.PortTestApp                : Starting PortTestApp on DESKTOP-R7GPPNQ with PID 7140 (E:\workSpace\learn-project\port-test\target\classes started by zane in E:\workSpace\learn-project\port-test)
2018-09-05 12:20:08.214  INFO 7140 --- [           main] com.port.test.PortTestApp                : No active profile set, falling back to default profiles: default
2018-09-05 12:20:08.255  INFO 7140 --- [           main] ationConfigEmbeddedWebApplicationContext : Refreshing org.springframework.boot[email protected]140e5a13: startup date [Wed Sep 05 12:20:08 CST 2018]; root of context hierarchy
2018-09-05 12:20:09.431  INFO 7140 --- [           main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat initialized with port(s): 8080 (http)
2018-09-05 12:20:09.443  INFO 7140 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2018-09-05 12:20:09.445  INFO 7140 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet Engine: Apache Tomcat/8.5.27
2018-09-05 12:20:09.554  INFO 7140 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2018-09-05 12:20:09.554  INFO 7140 --- [ost-startStop-1] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 1301 ms
2018-09-05 12:20:09.681  INFO 7140 --- [ost-startStop-1] o.s.b.w.servlet.ServletRegistrationBean  : Mapping servlet: 'dispatcherServlet' to [/]
2018-09-05 12:20:09.684  INFO 7140 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'characterEncodingFilter' to: [/*]
2018-09-05 12:20:09.685  INFO 7140 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'hiddenHttpMethodFilter' to: [/*]
2018-09-05 12:20:09.685  INFO 7140 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'httpPutFormContentFilter' to: [/*]
2018-09-05 12:20:09.685  INFO 7140 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'requestContextFilter' to: [/*]
2018-09-05 12:20:09.733  INFO 7140 --- [           main] c.p.t.config.TestConfigInitializingBean  : --------------------------------------------
2018-09-05 12:20:09.733  INFO 7140 --- [           main] c.p.t.config.TestConfigInitializingBean  : -----正在執行InitializingBean實現類程式碼-----
2018-09-05 12:20:09.733  INFO 7140 --- [           main] c.p.t.config.TestConfigInitializingBean  : --------------------------------------------
2018-09-05 12:20:09.736  INFO 7140 --- [           main] com.port.test.config.TestPostConstruct   : --------------------------------------------
2018-09-05 12:20:09.736  INFO 7140 --- [           main] com.port.test.config.TestPostConstruct   : -----正在執行@PostConstruct實現類程式碼-----
2018-09-05 12:20:09.736  INFO 7140 --- [           main] com.port.test.config.TestPostConstruct   : --------------------------------------------
2018-09-05 12:20:09.969  INFO 7140 --- [           main] s.w.s.m.m.a.RequestMappingHandlerAdapter : Looking for @ControllerAdvice: org.springframework.boot[email protected]140e5a13: startup date [Wed Sep 05 12:20:08 CST 2018]; root of context hierarchy
2018-09-05 12:20:10.038  INFO 7140 --- [           main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/error]}" onto public org.springframework.http.ResponseEntity<java.util.Map<java.lang.String, java.lang.Object>> org.springframework.boot.autoconfigure.web.BasicErrorController.error(javax.servlet.http.HttpServletRequest)
2018-09-05 12:20:10.039  INFO 7140 --- [           main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/error],produces=[text/html]}" onto public org.springframework.web.servlet.ModelAndView org.springframework.boot.autoconfigure.web.BasicErrorController.errorHtml(javax.servlet.http.HttpServletRequest,javax.servlet.http.HttpServletResponse)
2018-09-05 12:20:10.066  INFO 7140 --- [           main] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/webjars/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2018-09-05 12:20:10.066  INFO 7140 --- [           main] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2018-09-05 12:20:10.098  INFO 7140 --- [           main] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/**/favicon.ico] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2018-09-05 12:20:10.220  INFO 7140 --- [           main] o.s.j.e.a.AnnotationMBeanExporter        : Registering beans for JMX exposure on startup
2018-09-05 12:20:10.229  INFO 7140 --- [           main] c.p.t.c.TestConfigApplicationListener    : --------------------------------------------
2018-09-05 12:20:10.230  INFO 7140 --- [           main] c.p.t.c.TestConfigApplicationListener    : -----正在執行ApplicationListener實現類程式碼-----
2018-09-05 12:20:10.230  INFO 7140 --- [           main] c.p.t.c.TestConfigApplicationListener    : --------------------------------------------
2018-09-05 12:20:10.290  INFO 7140 --- [           main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat started on port(s): 8080 (http)
2018-09-05 12:20:10.291  INFO 7140 --- [           main] c.p.t.c.TestConfigApplicationListener    : --------------------------------------------
2018-09-05 12:20:10.291  INFO 7140 --- [           main] c.p.t.c.TestConfigApplicationListener    : -----正在執行ApplicationListener實現類程式碼-----
2018-09-05 12:20:10.291  INFO 7140 --- [           main] c.p.t.c.TestConfigApplicationListener    : --------------------------------------------
2018-09-05 12:20:10.293  INFO 7140 --- [           main] c.p.t.c.TestConfigCommandLineRunner      : --------------------------------------------
2018-09-05 12:20:10.293  INFO 7140 --- [           main] c.p.t.c.TestConfigCommandLineRunner      : -----正在執行CommandLineRunner實現類程式碼-----
2018-09-05 12:20:10.293  INFO 7140 --- [           main] c.p.t.c.TestConfigCommandLineRunner      : --------------------------------------------
2018-09-05 12:20:10.293  INFO 7140 --- [           main] c.p.t.c.TestConfigApplicationRunner      : --------------------------------------------
2018-09-05 12:20:10.293  INFO 7140 --- [           main] c.p.t.c.TestConfigApplicationRunner      : -----正在執行ApplicationRunner實現類程式碼-----
2018-09-05 12:20:10.293  INFO 7140 --- [           main] c.p.t.c.TestConfigApplicationRunner      : --------------------------------------------
2018-09-05 12:20:10.294  INFO 7140 --- [           main] c.p.t.c.TestConfigApplicationListener    : --------------------------------------------
2018-09-05 12:20:10.294  INFO 7140 --- [           main] c.p.t.c.TestConfigApplicationListener    : -----正在執行ApplicationListener實現類程式碼-----
2018-09-05 12:20:10.294  INFO 7140 --- [           main] c.p.t.c.TestConfigApplicationListener    : --------------------------------------------
2018-09-05 12:20:10.295  INFO 7140 --- [           main] com.port.test.PortTestApp                : Started PortTestApp in 2.328 seconds (JVM running for 2.652)