项目启动时执行指定任务如何实现？

ApplicationRunner

/**
 * Interface used to indicate that a bean should <em>run</em> when it is contained within
 * a {@link SpringApplication}. Multiple {@link ApplicationRunner} beans can be defined
 * within the same application context and can be ordered using the {@link Ordered}
 * interface or {@link Order @Order} annotation.
 *
 * @author Phillip Webb
 * @since 1.3.0
 * @see CommandLineRunner
 */
@FunctionalInterface
public interface ApplicationRunner {

  /**
   * Callback used to run the bean.
   * @param args incoming application arguments
   * @throws Exception on error
   */
  void run(ApplicationArguments args) throws Exception;

}

CommandLineRunner

/**
 * Interface used to indicate that a bean should <em>run</em> when it is contained within
 * a {@link SpringApplication}. Multiple {@link CommandLineRunner} beans can be defined
 * within the same application context and can be ordered using the {@link Ordered}
 * interface or {@link Order @Order} annotation.
 * <p>
 * If you need access to {@link ApplicationArguments} instead of the raw String array
 * consider using {@link ApplicationRunner}.
 *
 * @author Dave Syer
 * @see ApplicationRunner
 */
@FunctionalInterface
public interface CommandLineRunner {

  /**
   * Callback used to run the bean.
   * @param args incoming main method arguments
   * @throws Exception on error
   */
  void run(String... args) throws Exception;

}

乍眼一看就名字不一样，再一看还有传入的参数不一样其他都一样，再看看他们在SpringApplication中的区别

  private void callRunners(ApplicationContext context, ApplicationArguments args) {
    List<Object> runners = new ArrayList<>();
    runners.addAll(context.getBeansOfType(ApplicationRunner.class).values());
    runners.addAll(context.getBeansOfType(CommandLineRunner.class).values());
    AnnotationAwareOrderComparator.sort(runners);
    for (Object runner : new LinkedHashSet<>(runners)) {
      if (runner instanceof ApplicationRunner) {
        callRunner((ApplicationRunner) runner, args);
      }
      if (runner instanceof CommandLineRunner) {
        callRunner((CommandLineRunner) runner, args);
      }
    }
  }

  private void callRunner(ApplicationRunner runner, ApplicationArguments args) {
    try {
      (runner).run(args);
    }
    catch (Exception ex) {
      throw new IllegalStateException("Failed to execute ApplicationRunner", ex);
    }
  }

  private void callRunner(CommandLineRunner runner, ApplicationArguments args) {
    try {
      (runner).run(args.getSourceArgs());
    }
    catch (Exception ex) {
      throw new IllegalStateException("Failed to execute CommandLineRunner", ex);
    }
  }

这不是就是复制黏贴吗？源码就这？让我来我也行，哈哈

其实看到上面的注释也大概明白，可以实现多个，执行顺序可以实现Ordered接口或根据@Order注解来排序。

CommandLineRunner的使用示例

@Component
@Order(1)
public class MyCommandLineRunner1 implements CommandLineRunner {
    @Override
    public void run(String... args) throws Exception {
        System.out.println("MyCommandLineRunner1------>" + Arrays.toString(args));
    }
}

@Component
@Order(2)
public class MyCommandLineRunner2 implements CommandLineRunner {
    @Override
    public void run(String... args) throws Exception {
        System.out.println("MyCommandLineRunner2------>" + Arrays.toString(args));
    }
}

当然你也可以这样写

@Component
//@Order(1)
public class MyCommandLineRunner1 implements CommandLineRunner, Ordered {
    @Override
    public void run(String... args) throws Exception {
        System.out.println("MyCommandLineRunner1------>" + Arrays.toString(args));
    }

    @Override
    public int getOrder() {
        return 1;
    }
}

@Component
//@Order(2)
public class MyCommandLineRunner2 implements CommandLineRunner, Ordered {
    @Override
    public void run(String... args) throws Exception {
        System.out.println("MyCommandLineRunner2------>" + Arrays.toString(args));
    }

    @Override
    public int getOrder() {
        return 2;
    }
}

我们可以配置在系统启动时需要传入的参数，这里以 intelliJ IDEA 为例，单击右上角的编辑启动配置。

参数之间使用空格隔开。

项目启动后的运行结果

ApplicationRunner的使用示例

@Component
@Order(1)
public class MyApplicationRunner1 implements ApplicationRunner {

    @Override
    public void run(ApplicationArguments args) throws Exception {
        System.out.println("MyApplicationRunner1------>" + Arrays.toString(args.getSourceArgs()));
    }
}

@Component
@Order(2)
public class MyApplicationRunner2 implements ApplicationRunner {

    @Override
    public void run(ApplicationArguments args) throws Exception {
        System.out.println("MyApplicationRunner2------>" + Arrays.toString(args.getSourceArgs()));
    }
}

项目启动后的运行结果

你会发现很多人都会用ApplicationRunner，你自己去写，然后品，你细品，你就知道原因了。