Spring Boot之 CommandLineRunner、ApplicationRunner和@PostConstruct

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在使用Spring Boot开发的工作中，我们经常会需要遇到一种功能需求，比如在服务启动时候，去加载一些配置，去请求一下其他服务的接口。Spring Boot给我们提供了三种常用的实现方法：
第一种是实现CommandLineRunner接口，
第二种是实现ApplicationRunner接口
第三种是使用注解：@PostConstruct

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1、CommandLineRunner执行的时间节点是在Application完成初始化工作之后。
2、CommandLineRunner在有多个实现的时候，可以使用@order注解指定执行先后顺序。
3、源码在：org.springframework.boot.SpringApplication#run()，可以看看

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package org.springframework.boot;

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

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public ConfigurableApplicationContext run(String... args) {
        StopWatch stopWatch = new StopWatch();
        stopWatch.start();
        DefaultBootstrapContext bootstrapContext = this.createBootstrapContext();
        ConfigurableApplicationContext context = null;
        this.configureHeadlessProperty();
        SpringApplicationRunListeners listeners = this.getRunListeners(args);
        listeners.starting(bootstrapContext, this.mainApplicationClass);

        try {
            ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
            ConfigurableEnvironment environment = this.prepareEnvironment(listeners, bootstrapContext, applicationArguments);
            this.configureIgnoreBeanInfo(environment);
            Banner printedBanner = this.printBanner(environment);
            context = this.createApplicationContext();
            context.setApplicationStartup(this.applicationStartup);
            this.prepareContext(bootstrapContext, 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, listeners);
            throw new IllegalStateException(var10);
        }

        try {
            listeners.running(context);
            return context;
        } catch (Throwable var9) {
            this.handleRunFailure(context, var9, (SpringApplicationRunListeners)null);
            throw new IllegalStateException(var9);
        }
    }

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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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import org.springframework.boot.CommandLineRunner;
import org.springframework.core.annotation.Order;
import org.springframework.stereotype.Component;

import java.util.Arrays;

@Component
@Order(1)
public class CommandLineRunnerTest implements CommandLineRunner {
    @Override
    public void run(String... args) throws Exception {
        System.out.println("----CommandLineRunnerTest1 start---"+ Arrays.toString(args));
    }
}

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ApplicationRunner跟CommandLineRunner是区别是在run方法里接收的参数不同，CommandLineRuner接收的参数是String... args，而ApplicationRunner的run方法的参数是ApplicationArguments 

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package org.springframework.boot;

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

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import org.springframework.boot.ApplicationArguments;
import org.springframework.boot.ApplicationRunner;
import org.springframework.core.annotation.Order;
import org.springframework.stereotype.Component;

import java.util.List;
import java.util.Set;

@Component
@Order(1)
public class ApplicationRunnerTest implements ApplicationRunner {
    @Override
    public void run(ApplicationArguments args) throws Exception {
        System.out.println("---ApplicationRunnerTest start----");

        List<String> nonOptionArgs = args.getNonOptionArgs();
        System.out.println("[非选项参数]>>> " + nonOptionArgs);
        Set<String> optionNames = args.getOptionNames();
        for(String optionName: optionNames) {
            System.out.println("[选项参数]>>> name:" + optionName
                    + ";value:" + args.getOptionValues(optionName));
        }
    }
}

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@PostConstruct是在javaEE5的时候引入的,它并不是Spring提供的，但是Spring有对@PostConstruct的实现。并且是在对象加载完之后执行。

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@Documented
@Retention (RUNTIME)
@Target(METHOD)
public @interface PostConstruct {
}

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import org.springframework.stereotype.Component;

import javax.annotation.PostConstruct;

@Component
public class PostConstructTest {

    @PostConstruct
    public void start(){
        System.out.println("---PostConstruct start---");
    }


}

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