前言

（其实直接在main方法里写也不是执行不了） 如果只是简单的一些语句，写在main中可能会方便一些

但如果需要调用spring容器中的对象可能会要吃瘪，因为main方法是static的，而获取ioc对象不能使用static直接获取（会报错） 当调用@AutoWired获得ioc容器中的对象时

	@Autowired
    private static TestService testService;
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Exception in thread "main" java.lang.NullPointerException

当调用@Resource获得ioc容器中的对象时

	@Resource
    private static TestService testService;
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Caused by: java.lang.IllegalStateException: @Resource annotation is not supported on static fields

两个函数接口

有两个函数接口类都可以实现

1.ApplicationRunner接口

源码

package org.springframework.boot;

@FunctionalInterface
public interface ApplicationRunner {
    void run(ApplicationArguments args) throws Exception;
}
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使用方法

使用@SpringBootApplication注释的ApplicationMain启动类实现ApplicationRunner接口，并实现run方法即可 在main方法将spring启动完成后会执行run方法中的程序

@SpringBootApplication
public class BootTestApplication implements ApplicationRunner{

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

    @Override
    public void run(ApplicationArguments args) throws Exception {
        System.out.println("ApplicationRunner.run");
    }
}
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2.CommandLineRunner接口

源码

package org.springframework.boot;

@FunctionalInterface
public interface CommandLineRunner {
    void run(String... args) throws Exception;
}
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使用方法

其实CommandLineRunner和ApplicationRunner使用方法差不多

使用@SpringBootApplication注释的ApplicationMain启动类实现接口，并实现run方法即可 在main方法将spring启动完成后会执行run方法中的程序

@SpringBootApplication
public class BootTestApplication implements CommandLineRunner {

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

    @Override
    public void run(String... args) throws Exception {
        System.out.println("CommandLineRunner.run");
    }
}
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为什么会被执行？两个接口谁先执行？为什么？

举个栗子

我们来看个例子 现在我们有一个service类

@Service
public class TestService {
    public void test(String name){
        System.out.println(name);
    }
}
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然后main启动类中同时实现ApplicationRunner和CommandLineRunner接口，并调用这个service的方法 看看是谁先被输出

@SpringBootApplication
public class BootTestApplication implements ApplicationRunner , CommandLineRunner {

    @Autowired
    private TestService service;

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

    @Override
    public void run(ApplicationArguments args) throws Exception {
        service.test("ApplicationRunner.run");
    }

    @Override
    public void run(String... args) throws Exception {
        service.test("CommandLineRunner.run");
    }
}
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结果

可以看到，无论运行几次，结果都是ApplicationRunner先执行，CommandLineRunner后执行

ApplicationRunner.run

CommandLineRunner.run

如图

简单源码分析

我们查看SpringApplication.run(BootTestApplication.class, args) 一层一层被调用到

public ConfigurableApplicationContext run(String... args) {
        StopWatch stopWatch = new StopWatch();
        stopWatch.start();
        ConfigurableApplicationContext context = null;
        Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList();
        this.configureHeadlessProperty();
        SpringApplicationRunListeners listeners = this.getRunListeners(args);
        listeners.starting();

        Collection exceptionReporters;
        try {
            ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
            ConfigurableEnvironment environment = this.prepareEnvironment(listeners, applicationArguments);
            this.configureIgnoreBeanInfo(environment);
            Banner printedBanner = this.printBanner(environment);
            context = this.createApplicationContext();
            exceptionReporters = this.getSpringFactoriesInstances(SpringBootExceptionReporter.class, new Class[]{ConfigurableApplicationContext.class}, context);
            this.prepareContext(context, environment, listeners, applicationArguments, printedBanner);
            this.refreshContext(context);
            this.afterRefresh(context, applicationArguments);
            stopWatch.stop();
            if (this.logStartupInfo) {
                (new StartupInfoLogger(this.mainApplicationClass)).logStarted(this.getApplicationLog(), stopWatch);
            }

            listeners.started(context);
            this.callRunners(context, applicationArguments);
        } catch (Throwable var10) {
            this.handleRunFailure(context, var10, exceptionReporters, listeners);
            throw new IllegalStateException(var10);
        }

        try {
            listeners.running(context);
            return context;
        } catch (Throwable var9) {
            this.handleRunFailure(context, var9, exceptionReporters, (SpringApplicationRunListeners)null);
            throw new IllegalStateException(var9);
        }
    }
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其中有一条this.callRunners(context, applicationArguments);就是回调方法了，我们点开可以看到

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);
        Iterator var4 = (new LinkedHashSet(runners)).iterator();

        while(var4.hasNext()) {
            Object runner = var4.next();
            if (runner instanceof ApplicationRunner) {
                this.callRunner((ApplicationRunner)runner, args);
            }

            if (runner instanceof CommandLineRunner) {
                this.callRunner((CommandLineRunner)runner, args);
            }
        }
    }
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如果启动类是ApplicationRunner的实现类，那么会调用runner.run(args); 也就是启动类中实现了ApplicationRunner的run方法

	if(runner instanceof ApplicationRunner) {
		this.callRunner((ApplicationRunner)runner, args);
	}

	private void callRunner(ApplicationRunner runner, ApplicationArguments args) {
        try {
            runner.run(args);
        } catch (Exception var4) {
            throw new IllegalStateException("Failed to execute ApplicationRunner", var4);
        }
    }
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如果启动类是CommandLineRunner 的实现类，那么会调用runner.run(args.getSourceArgs()); 也就是启动类中实现了CommandLineRunner的run方法

	if (runner instanceof CommandLineRunner) {
    	this.callRunner((CommandLineRunner)runner, args);
    }

	private void callRunner(CommandLineRunner runner, ApplicationArguments args) {
        try {
            runner.run(args.getSourceArgs());
        } catch (Exception var4) {
            throw new IllegalStateException("Failed to execute CommandLineRunner", var4);
        }
    }