如果需要在容器启动的时候就开始执行一些内容。比如配置初始化等,SpringBoot提供的这个接口就是干这个的。同时,通过其源码发现,它还提供了另外一个有同样功能的接口叫ApplicationRunner。两者的区别在于所接受的参数类型不一样。
CommandLineRunner的run方法定义如下:
/**
* Callback used to run the bean.
* @param args incoming main method arguments
* @throws Exception on error
*/
void run(String... args) throws Exception;
而ApplicationRunner的定义如下:
/**
* Callback used to run the bean.
* @param args incoming application arguments
* @throws Exception on error
*/
void run(ApplicationArguments args) throws Exception;
其他方面没什么区别。都是在容器启动时做指定动作。
简单使用示例:
@SpringBootApplication(exclude = {DataSourceAutoConfiguration.class})
public class Application implements CommandLineRunner {
@Autowired
CollectorExecRateService collectorExecRateService;
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
@Override
public void run(String... strings) throws Exception {
DefaultExports.initialize();
//do something you need
}
}
最后,对于CommandLineRunner中run方法的执行时机,是在Spring容器完全启动完成的时候被执行。
看下源码中的说明:( 源码位置:SpringApplication.run(String... args),springboot版本:2.0.2 )
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);
//这里是去调用CommandLineRunner or ApplicationRunner的run方法
callRunners(context, applicationArguments);
}
callRunners的方法很简单,就是排序后执行run方法:
private void callRunners(ApplicationContext context, ApplicationArguments args) {
List<Object> runners = new ArrayList<>();
//注册所有实现两个接口的class
runners.addAll(context.getBeansOfType(ApplicationRunner.class).values());
runners.addAll(context.getBeansOfType(CommandLineRunner.class).values());
//根据order排序
AnnotationAwareOrderComparator.sort(runners);
//遍历所有注册的方法,执行其内容
for (Object runner : new LinkedHashSet<>(runners)) {
if (runner instanceof ApplicationRunner) {
//执行ApplicationRunner中的run
callRunner((ApplicationRunner) runner, args);
}
if (runner instanceof CommandLineRunner) {
//执行CommandLineRunner中的run
callRunner((CommandLineRunner) runner, args);
}
}
}
//执行ApplicationRunner
private void callRunner(ApplicationRunner runner, ApplicationArguments args) {
try {
(runner).run(args);
}
catch (Exception ex) {
throw new IllegalStateException("Failed to execute ApplicationRunner", ex);
}
}
//执行CommandLineRunner
private void callRunner(CommandLineRunner runner, ApplicationArguments args) {
try {
(runner).run(args.getSourceArgs());
}
catch (Exception ex) {
throw new IllegalStateException("Failed to execute CommandLineRunner", ex);
}
}