SpringBoot CommandLineRunner 初识

在 SpringBoot 官方 Guides Building an Application with Spring Boot 中看到一段如下代码：

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package hello;

import java.util.Arrays;

import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.Bean;

@SpringBootApplication
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

    @Bean
    public CommandLineRunner commandLineRunner(ApplicationContext ctx) {
        return args -> {

            System.out.println("Let's inspect the beans provided by Spring Boot:");

            String[] beanNames = ctx.getBeanDefinitionNames();
            Arrays.sort(beanNames);
            for (String beanName : beanNames) {
                System.out.println(beanName);
            }

        };
    }

}

其中实现了一个 CommandLineRunner 匿名内部类，那么 CommandLineRunner 接口有哪些作用呢？工作机制又是什么？

SpringBoot Reference 1.5.9.RELEASE 23.8 Using the ApplicationRunner or CommmandLineRunner 中有这么一段话：

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If you need to run some specific code once the SpringApplication has started, you can implement the ApplicationRunner or CommandLineRunner interfaces. Both interfaces work in the same way and offer a single run method which will be called just before SpringApplication.run(…​) completes.

创建一个普通的 SpringBoot Application，并编写一个CommandLineRunner 实现类：

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package com.example.springboot.commandlinerunner;

import org.springframework.boot.CommandLineRunner;
import org.springframework.stereotype.Component;

@Component
public class HelloCommandLineRunner implements CommandLineRunner {

	@Override
	public void run(String... strings) throws Exception {
		System.out.println("Hello CommandLineRunner");
	}

}

运行该 SpringBoot Application，控制台将出现如下输出：

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  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v1.5.9.RELEASE)

2017-11-29 19:53:28.157  INFO 10544 --- [           main] ingBootCommandLineRunnerHelloApplication : Starting SpringBootCommandLineRunnerHelloApplication on DESKTOP-49M29KH with PID 10544 (D:\lxmuse-spring-boot\spring-boot-command-line-runner\spring-boot-command-line-runner-hello\target\classes started by Richard in D:\lxmuse-spring-boot\spring-boot-command-line-runner\spring-boot-command-line-runner-hello)
2017-11-29 19:53:28.159  INFO 10544 --- [           main] ingBootCommandLineRunnerHelloApplication : No active profile set, falling back to default profiles: default
2017-11-29 19:53:28.220  INFO 10544 --- [           main] s.c.a.AnnotationConfigApplicationContext : Refreshing org.springframework.context.annotation.AnnotationConfigApplicationContext@6dde5c8c: startup date [Wed Nov 29 19:53:28 CST 2017]; root of context hierarchy
2017-11-29 19:53:28.737  INFO 10544 --- [           main] o.s.j.e.a.AnnotationMBeanExporter        : Registering beans for JMX exposure on startup
Hello CommandLineRunner
2017-11-29 19:53:28.746  INFO 10544 --- [           main] ingBootCommandLineRunnerHelloApplication : Started SpringBootCommandLineRunnerHelloApplication in 0.833 seconds (JVM running for 1.802)
2017-11-29 19:53:28.747  INFO 10544 --- [       Thread-4] s.c.a.AnnotationConfigApplicationContext : Closing org.springframework.context.annotation.AnnotationConfigApplicationContext@6dde5c8c: startup date [Wed Nov 29 19:53:28 CST 2017]; root of context hierarchy
2017-11-29 19:53:28.749  INFO 10544 --- [       Thread-4] o.s.j.e.a.AnnotationMBeanExporter        : Unregistering JMX-exposed beans on shutdown

可以发现，在完全启动前已经执行了 HelloCommandLineRunner 中的 run 方法。

Reference 中提到 ApplicationRunner 和 CommmandLineRunner 具有相同的作用。
同理编写一个 ApplicationRunner 实现类：

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package com.example.springboot.commandlinerunner;

import org.springframework.boot.ApplicationArguments;
import org.springframework.boot.ApplicationRunner;
import org.springframework.stereotype.Component;

@Component
public class HelloApplicationRunner implements ApplicationRunner {

	@Override
	public void run(ApplicationArguments applicationArguments) throws Exception {
		System.out.println("Hello ApplicationRunner");
	}
}

重新运行 SpringBoot Application，控制台将出现如下输出：

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  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v1.5.9.RELEASE)

2017-11-29 20:02:17.920  INFO 6548 --- [           main] ingBootCommandLineRunnerHelloApplication : Starting SpringBootCommandLineRunnerHelloApplication on DESKTOP-49M29KH with PID 6548 (D:\lxmuse-spring-boot\spring-boot-command-line-runner\spring-boot-command-line-runner-hello\target\classes started by Richard in D:\lxmuse-spring-boot\spring-boot-command-line-runner\spring-boot-command-line-runner-hello)
2017-11-29 20:02:17.922  INFO 6548 --- [           main] ingBootCommandLineRunnerHelloApplication : No active profile set, falling back to default profiles: default
2017-11-29 20:02:17.969  INFO 6548 --- [           main] s.c.a.AnnotationConfigApplicationContext : Refreshing org.springframework.context.annotation.AnnotationConfigApplicationContext@5123a213: startup date [Wed Nov 29 20:02:17 CST 2017]; root of context hierarchy
2017-11-29 20:02:18.534  INFO 6548 --- [           main] o.s.j.e.a.AnnotationMBeanExporter        : Registering beans for JMX exposure on startup
Hello ApplicationRunner
Hello CommandLineRunner
2017-11-29 20:02:18.546  INFO 6548 --- [           main] ingBootCommandLineRunnerHelloApplication : Started SpringBootCommandLineRunnerHelloApplication in 0.829 seconds (JVM running for 1.294)
2017-11-29 20:02:18.547  INFO 6548 --- [       Thread-4] s.c.a.AnnotationConfigApplicationContext : Closing org.springframework.context.annotation.AnnotationConfigApplicationContext@5123a213: startup date [Wed Nov 29 20:02:17 CST 2017]; root of context hierarchy
2017-11-29 20:02:18.548  INFO 6548 --- [       Thread-4] o.s.j.e.a.AnnotationMBeanExporter        : Unregistering JMX-exposed beans on shutdown

可以发现，在完全启动前已经执行了 HelloApplicationRunner 和 HelloCommandLineRunner 中的 run 方法。
并且 HelloApplicationRunner 中的 run 方法优先执行。

那么 @Order 对其有没有影响呢？
在 HelloApplicationRunner 上添加 @Order 注解，并且指定值为 2；
在 HelloCommandLineRunner 上添加 @Order 注解，并且指定值为 1；

重新运行 SpringBoot Application，控制台将出现如下输出：

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  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v1.5.9.RELEASE)

2017-11-29 20:09:21.078  INFO 772 --- [           main] ingBootCommandLineRunnerHelloApplication : Starting SpringBootCommandLineRunnerHelloApplication on DESKTOP-49M29KH with PID 772 (D:\lxmuse-spring-boot\spring-boot-command-line-runner\spring-boot-command-line-runner-hello\target\classes started by Richard in D:\lxmuse-spring-boot\spring-boot-command-line-runner\spring-boot-command-line-runner-hello)
2017-11-29 20:09:21.080  INFO 772 --- [           main] ingBootCommandLineRunnerHelloApplication : No active profile set, falling back to default profiles: default
2017-11-29 20:09:21.139  INFO 772 --- [           main] s.c.a.AnnotationConfigApplicationContext : Refreshing org.springframework.context.annotation.AnnotationConfigApplicationContext@5123a213: startup date [Wed Nov 29 20:09:21 CST 2017]; root of context hierarchy
2017-11-29 20:09:21.604  INFO 772 --- [           main] o.s.j.e.a.AnnotationMBeanExporter        : Registering beans for JMX exposure on startup
Hello CommandLineRunner
Hello ApplicationRunner
2017-11-29 20:09:21.622  INFO 772 --- [           main] ingBootCommandLineRunnerHelloApplication : Started SpringBootCommandLineRunnerHelloApplication in 0.755 seconds (JVM running for 1.256)
2017-11-29 20:09:21.623  INFO 772 --- [       Thread-4] s.c.a.AnnotationConfigApplicationContext : Closing org.springframework.context.annotation.AnnotationConfigApplicationContext@5123a213: startup date [Wed Nov 29 20:09:21 CST 2017]; root of context hierarchy
2017-11-29 20:09:21.625  INFO 772 --- [       Thread-4] o.s.j.e.a.AnnotationMBeanExporter        : Unregistering JMX-exposed beans on shutdown

HelloCommandLineRunner 将根据指定的顺序优先执行。

那么相同类型的实现类执行顺序又是如何呢？
其真正的执行原理又是什么呢？
留待再探时再解密吧！（需要深入源码）

具体代码已上传GitHub-lxmuse

赏

谢谢你请我吃糖果

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    缺失模块。
    1、请确保node版本大于6.2
    2、在博客根目录（注意不是yilia根目录）执行以下命令：
    npm i hexo-generator-json-content --save

    3、在根目录_config.yml里添加配置： 

      jsonContent:
    meta: false
    pages: false
    posts:
      title: true
      date: true
      path: true
      text: false
      raw: false
      content: false
      slug: false
      updated: false
      comments: false
      link: false
      permalink: false
      excerpt: false
      categories: false
      tags: true

很惭愧<br><br>只做了一点微小的工作<br>谢谢大家