应用启动数据初始化接口CommandLineRunner和Application详解

在SpringBoot项目中创建组件类实现CommandLineRunner或ApplicationRunner接口可实现在应用启动之后及时进行一些初始化操作，如缓存预热、索引重建等等类似一些数据初始化操作。

两个接口功能相同，都有个run方法需要重写，只是实现方法的参数不同。

CommandLineRunner接收原始的命令行启动参数，ApplicationRunner则将启动参数对象化。

1 运行时机

两个接口都是在SpringBoot应用初始化好上下文之后运行，所以在运行过程中，可以使用上下文中的所有信息，例如一些Bean等等。在框架SpringApplication类源码的run方法中，可查看Runner的调用时机callRunners，如下：

/**
 * Run the Spring application, creating and refreshing a new
 * {@link ApplicationContext}.
 * @param args the application arguments (usually passed from a Java main method)
 * @return a running {@link ApplicationContext}
 */
public ConfigurableApplicationContext run(String... args) {
	StopWatch stopWatch = new StopWatch();
	stopWatch.start();
	ConfigurableApplicationContext context = null;
	Collection exceptionReporters = new ArrayList<>();
	configureHeadlessProperty();
	SpringApplicationRunListeners listeners = getRunListeners(args);
	listeners.starting();
	try {
		ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
		ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
		configureIgnoreBeanInfo(environment);
		Banner printedBanner = printBanner(environment);
		context = createApplicationContext();
		exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,
				new Class[] { ConfigurableApplicationContext.class }, context);
		prepareContext(context, environment, listeners, applicationArguments, printedBanner);
		refreshContext(context);
		afterRefresh(context, applicationArguments);
		stopWatch.stop();
		if (this.logStartupInfo) {
			new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
		}
		listeners.started(context);
		//调用Runner，执行初始化操作
		callRunners(context, applicationArguments);
	}
	catch (Throwable ex) {
		handleRunFailure(context, ex, exceptionReporters, listeners);
		throw new IllegalStateException(ex);
	}
	try {
		listeners.running(context);
	}
	catch (Throwable ex) {
		handleRunFailure(context, ex, exceptionReporters, null);
		throw new IllegalStateException(ex);
	}
	return context;
}

2 实现接口

2.1 CommandLineRunner

简单实现如下，打印启动参数信息：

@Order(1)
@Component
public class CommandLineRunnerInit implements CommandLineRunner {
    private Logger logger = LoggerFactory.getLogger(this.getClass());
    private final String LOG_PREFIX = ">>>>>>>>>>CommandLineRunner >>>>>>>>>> ";
    @Override
    public void run(String... args) throws Exception {
        try {
            this.logger.error("{} args:{}", LOG_PREFIX, StringUtils.join(args, ","));
        } catch (Exception e) {
            logger.error("CommandLineRunnerInit run failed", e);
        }
    }
}

2.2 ApplicationRunner

简单实现如下，打印启动参数信息，并调用Bean的方法（查询用户数量）：

@Order(2)
@Component
public class ApplicationRunnerInit implements ApplicationRunner {
    private Logger logger = LoggerFactory.getLogger(this.getClass());
    private final String LOG_PREFIX = ">>>>>>>>>>ApplicationRunner >>>>>>>>>> ";
    private final UserRepository userRepository;
    public ApplicationRunnerInit(UserRepository userRepository) {
        this.userRepository = userRepository;
    }
    @Override
    public void run(ApplicationArguments args) throws Exception {
        try {
            this.logger.error("{} args:{}", LOG_PREFIX, JSONObject.toJSONString(args));
            for (String optionName : args.getOptionNames()) {
                this.logger.error("{} argName:{} argValue:{}", LOG_PREFIX, optionName, args.getOptionValues(optionName));
            }
            this.logger.error("{} user count:{}", LOG_PREFIX, this.userRepository.count());
        } catch (Exception e) {
            logger.error("CommandLineRunnerInit run failed", e);
        }
    }
}

3 执行顺序

如果实现了多个Runner，默认会按照添加顺序先执行ApplicationRunner的实现再执行CommandLineRunner的实现，如果多个Runner之间的初始化逻辑有先后顺序，可在实现类添加@Order注解设置执行顺序，可在源码SpringApplication类的callRunners方法中查看，如下：

private void callRunners(ApplicationContext context, ApplicationArguments args) {
 List

应用启动数据初始化接口CommandLineRunner和Application详解

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