一、應用場景
在開發過程中會有這樣的場景：需要在容器啓動的時候執行一些內容，如讀取配置文件信息，清除緩存信息等。在Spring框架下是通過ApplicationListener監聽器來實現的。在Spring Boot中，我們也可以根據下面要提到的兩個接口來幫助我們實現這樣的需求。這兩個接口就是CommandLineRunner和ApplicationRunner，它們的執行時機是容器啓動完成的時候。
二、共同點與區別
共同點：
1）執行時機都是在容器啓動完成的時候進行；
2）這兩個接口中都有一個run()方法
不同點：
ApllicationRunner中run方法的參數爲ApplicationArguments，而CommandLineRunner接口的run方法的參數爲String數組。這兩個接口間沒有很大的區別，如果想要更詳細地獲取命令行參數，那就使用ApplicationRunner接口。
三、如何修改執行順序
如果有多個實現類，我們需要按照一定的順序執行的話，那麼應該怎麼辦？
方案一：可以在實現類加上@Order註解指定執行的順序
方案二：可以在實現類上實現Ordered來標識。
注意：數字越小，優先級越高，也就是@Order(1)註解的類會在@Order(2)註解的類之前執行。
四、案例分析
Spring Boot啓動類：
@SpringBootApplication
public class Application {
public static void main(String[] args) {
System.out.println("Spring BOOT 啓動開始");
SpringApplication.run(Application.class,args);
System.out.println("Spring BOOT 啓動結束");
}
}
實現CommandLineRunner接口類：
@Component
public class CommandLineRunnerTest implements CommandLineRunner{
@Override
public void run(String[] args)throws Exception{
System.out.println("CommandLineRunner=====執行開始");
System.out.println("hehe");
System.out.println("CommandLineRunner=====執行完畢");
}
}
實現ApplicationRunner接口類：
@Component
public class ApplicationRunerTest implements ApplicationRunner{
@Override
public void run(ApplicationArguments args)throws Exception{
System.out.println("ApplicationRunner=====執行開始");
System.out.println(args.getNonOptionArgs());
System.out.println(args.getOptionNames());
System.out.println("ApplicationRunner=====執行完成");
}
}
系統啓動日誌輸出：
D:\Java\jdk1.8.0_152\bin\java -agentlib:jdwp=transport=dt_socket,address=127.0.0.1:2777,suspend=y,server=n -javaagent:C:\Users\chao\.IntelliJIdea2017.3\system\captureAgent\debugger-agent.jar=C:\Users\chao\AppData\Local\Temp\capture2129.props -Dfile.encoding=GBK -classpath "D:\Java\jdk1.8.0_152\jre\lib\charsets.jar;D:\Java\jdk1.8.0_152\jre\lib\deploy.jar;D:\Java\jdk1.8.0_152\jre\lib\ext\access-bridge-64.jar;D:\Java\jdk1.8.0_152\jre\lib\ext\cldrdata.jar;D:\Java\jdk1.8.0_152\jre\lib\ext\dnsns.jar;D:\Java\jdk1.8.0_152\jre\lib\ext\jaccess.jar;D:\Java\jdk1.8.0_152\jre\lib\ext\jfxrt.jar;D:\Java\jdk1.8.0_152\jre\lib\ext\localedata.jar;D:\Java\jdk1.8.0_152\jre\lib\ext\nashorn.jar;D:\Java\jdk1.8.0_152\jre\lib\ext\sunec.jar;D:\Java\jdk1.8.0_152\jre\lib\ext\sunjce_provider.jar;D:\Java\jdk1.8.0_152\jre\lib\ext\sunmscapi.jar;D:\Java\jdk1.8.0_152\jre\lib\ext\sunpkcs11.jar;D:\Java\jdk1.8.0_152\jre\lib\ext\zipfs.jar;D:\Java\jdk1.8.0_152\jre\lib\javaws.jar;D:\Java\jdk1.8.0_152\jre\lib\jce.jar;D:\Java\jdk1.8.0_152\jre\lib\jfr.jar;D:\Java\jdk1.8.0_152\jre\lib\jfxswt.jar;D:\Java\jdk1.8.0_152\jre\lib\jsse.jar;D:\Java\jdk1.8.0_152\jre\lib\management-agent.jar;D:\Java\jdk1.8.0_152\jre\lib\plugin.jar;D:\Java\jdk1.8.0_152\jre\lib\resources.jar;D:\Java\jdk1.8.0_152\jre\lib\rt.jar;G:\springboot-learning-example\springboot-helloworld\target\classes;G:\repository\org\springframework\boot\spring-boot-starter-web\1.5.1.RELEASE\spring-boot-starter-web-1.5.1.RELEASE.jar;G:\repository\org\springframework\boot\spring-boot-starter\1.5.1.RELEASE\spring-boot-starter-1.5.1.RELEASE.jar;G:\repository\org\springframework\boot\spring-boot\1.5.1.RELEASE\spring-boot-1.5.1.RELEASE.jar;G:\repository\org\springframework\boot\spring-boot-autoconfigure\1.5.1.RELEASE\spring-boot-autoconfigure-1.5.1.RELEASE.jar;G:\repository\org\springframework\boot\spring-boot-starter-logging\1.5.1.RELEASE\spring-boot-starter-logging-1.5.1.RELEASE.jar;G:\repository\ch\qos\logback\logback-classic\1.1.9\logback-classic-1.1.9.jar;G:\repository\ch\qos\logback\logback-core\1.1.9\logback-core-1.1.9.jar;G:\repository\org\slf4j\slf4j-api\1.7.22\slf4j-api-1.7.22.jar;G:\repository\org\slf4j\jcl-over-slf4j\1.7.22\jcl-over-slf4j-1.7.22.jar;G:\repository\org\slf4j\jul-to-slf4j\1.7.22\jul-to-slf4j-1.7.22.jar;G:\repository\org\slf4j\log4j-over-slf4j\1.7.22\log4j-over-slf4j-1.7.22.jar;G:\repository\org\springframework\spring-core\4.3.6.RELEASE\spring-core-4.3.6.RELEASE.jar;G:\repository\org\yaml\snakeyaml\1.17\snakeyaml-1.17.jar;G:\repository\org\springframework\boot\spring-boot-starter-tomcat\1.5.1.RELEASE\spring-boot-starter-tomcat-1.5.1.RELEASE.jar;G:\repository\org\apache\tomcat\embed\tomcat-embed-core\8.5.11\tomcat-embed-core-8.5.11.jar;G:\repository\org\apache\tomcat\embed\tomcat-embed-el\8.5.11\tomcat-embed-el-8.5.11.jar;G:\repository\org\apache\tomcat\embed\tomcat-embed-websocket\8.5.11\tomcat-embed-websocket-8.5.11.jar;G:\repository\org\hibernate\hibernate-validator\5.3.4.Final\hibernate-validator-5.3.4.Final.jar;G:\repository\javax\validation\validation-api\1.1.0.Final\validation-api-1.1.0.Final.jar;G:\repository\org\jboss\logging\jboss-logging\3.3.0.Final\jboss-logging-3.3.0.Final.jar;G:\repository\com\fasterxml\classmate\1.3.3\classmate-1.3.3.jar;G:\repository\com\fasterxml\jackson\core\jackson-databind\2.8.6\jackson-databind-2.8.6.jar;G:\repository\com\fasterxml\jackson\core\jackson-annotations\2.8.0\jackson-annotations-2.8.0.jar;G:\repository\com\fasterxml\jackson\core\jackson-core\2.8.6\jackson-core-2.8.6.jar;G:\repository\org\springframework\spring-web\4.3.6.RELEASE\spring-web-4.3.6.RELEASE.jar;G:\repository\org\springframework\spring-aop\4.3.6.RELEASE\spring-aop-4.3.6.RELEASE.jar;G:\repository\org\springframework\spring-beans\4.3.6.RELEASE\spring-beans-4.3.6.RELEASE.jar;G:\repository\org\springframework\spring-context\4.3.6.RELEASE\spring-context-4.3.6.RELEASE.jar;G:\repository\org\springframework\spring-webmvc\4.3.6.RELEASE\spring-webmvc-4.3.6.RELEASE.jar;G:\repository\org\springframework\spring-expression\4.3.6.RELEASE\spring-expression-4.3.6.RELEASE.jar;G:\repository\junit\junit\4.12\junit-4.12.jar;G:\repository\org\hamcrest\hamcrest-core\1.3\hamcrest-core-1.3.jar;C:\Program Files\JetBrains\IntelliJ IDEA 2017.3\lib\idea_rt.jar" org.spring.springboot.Application
Connected to the target VM, address: '127.0.0.1:2777', transport: 'socket'
Spring BOOT 啓動開始
. ____ _ __ _ _
/\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
\\/ ___)| |_)| | | | | || (_| | ) ) ) )
' |____| .__|_| |_|_| |_\__, | / / / /
=========|_|==============|___/=/_/_/_/
:: Spring Boot :: (v1.5.1.RELEASE)
2019-08-11 12:33:13.941 INFO 416 --- [ main] org.spring.springboot.Application : Starting Application on LAPTOP-CRSICKSO with PID 416 (G:\springboot-learning-example\springboot-helloworld\target\classes started by chao in G:\springboot-learning-example\springboot-helloworld)
2019-08-11 12:33:13.947 INFO 416 --- [ main] org.spring.springboot.Application : No active profile set, falling back to default profiles: default
2019-08-11 12:33:14.072 INFO 416 --- [ main] ationConfigEmbeddedWebApplicationContext : Refreshing org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@6892b3b6: startup date [Sun Aug 11 12:33:14 GMT+08:00 2019]; root of context hierarchy
2019-08-11 12:33:16.253 INFO 416 --- [ main] trationDelegate$BeanPostProcessorChecker : Bean 'org.springframework.boot.autoconfigure.validation.ValidationAutoConfiguration' of type [class org.springframework.boot.autoconfigure.validation.ValidationAutoConfiguration] is not eligible for getting processed by all BeanPostProcessors (for example: not eligible for auto-proxying)
2019-08-11 12:33:16.412 INFO 416 --- [ main] trationDelegate$BeanPostProcessorChecker : Bean 'validator' of type [class org.springframework.validation.beanvalidation.LocalValidatorFactoryBean] is not eligible for getting processed by all BeanPostProcessors (for example: not eligible for auto-proxying)
2019-08-11 12:33:17.472 INFO 416 --- [ main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat initialized with port(s): 8080 (http)
2019-08-11 12:33:17.501 INFO 416 --- [ main] o.apache.catalina.core.StandardService : Starting service Tomcat
2019-08-11 12:33:17.503 INFO 416 --- [ main] org.apache.catalina.core.StandardEngine : Starting Servlet Engine: Apache Tomcat/8.5.11
2019-08-11 12:33:17.718 INFO 416 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext
2019-08-11 12:33:17.718 INFO 416 --- [ost-startStop-1] o.s.web.context.ContextLoader : Root WebApplicationContext: initialization completed in 3656 ms
2019-08-11 12:33:17.936 INFO 416 --- [ost-startStop-1] o.s.b.w.servlet.ServletRegistrationBean : Mapping servlet: 'dispatcherServlet' to [/]
2019-08-11 12:33:17.947 INFO 416 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: 'characterEncodingFilter' to: [/*]
2019-08-11 12:33:17.948 INFO 416 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: 'hiddenHttpMethodFilter' to: [/*]
2019-08-11 12:33:17.948 INFO 416 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: 'httpPutFormContentFilter' to: [/*]
2019-08-11 12:33:17.948 INFO 416 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: 'requestContextFilter' to: [/*]
2019-08-11 12:33:18.478 INFO 416 --- [ main] s.w.s.m.m.a.RequestMappingHandlerAdapter : Looking for @ControllerAdvice: org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@6892b3b6: startup date [Sun Aug 11 12:33:14 GMT+08:00 2019]; root of context hierarchy
2019-08-11 12:33:18.626 INFO 416 --- [ main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/]}" onto public java.lang.String org.spring.springboot.web.HelloWorldController.sayHello()
2019-08-11 12:33:18.633 INFO 416 --- [ 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)
2019-08-11 12:33:18.634 INFO 416 --- [ 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)
2019-08-11 12:33:18.698 INFO 416 --- [ main] o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped URL path [/webjars/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2019-08-11 12:33:18.698 INFO 416 --- [ main] o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped URL path [/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2019-08-11 12:33:18.792 INFO 416 --- [ main] o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped URL path [/**/favicon.ico] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2019-08-11 12:33:19.366 INFO 416 --- [ main] o.s.j.e.a.AnnotationMBeanExporter : Registering beans for JMX exposure on startup
2019-08-11 12:33:19.619 INFO 416 --- [ main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat started on port(s): 8080 (http)
ApplicationRunner=====執行開始
[]
[]
ApplicationRunner=====執行完成
CommandLineRunner=====執行開始
hehe
CommandLineRunner=====執行完畢
2019-08-11 12:33:19.629 INFO 416 --- [ main] org.spring.springboot.Application : Started Application in 6.381 seconds (JVM running for 7.409)
Spring BOOT 啓動結束
由上述執行結果看：ApplicationRunner接口實現方法默認先於CommandLineRunner接口實現方法執行