「SpringBoot」CommandLineRunner & ApplicationRunner

启动成功后，我们可以使用如下几种方式进行初始化操作：

@PostConstruct 注解
ApplicationReadyEvent 事件
CommandLineRunner/ApplicationRunner接口

这三个方法执行有一定的顺序，依次是：

@PostConstruct -> CommandLineRunner/ApplicationRunner -> ApplicationReadyEvent

@SpringBootApplication
public class DemoApplication implements CommandLineRunner, ApplicationRunner, ApplicationListener<ApplicationReadyEvent> {

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

    @Override
    public void run(String... args) throws Exception {
        System.out.println("command line runner");
    }

    @Override
    public void run(ApplicationArguments args) throws Exception {
        System.out.println("application runner");
    }

    @PostConstruct
    public void init(){
        System.out.println("post contruct");
    }

    @Override
    public void onApplicationEvent(ApplicationReadyEvent applicationReadyEvent) {
        System.out.println("ready envent");
    }

}

上面程序执行之后的输出结果：

post contruct
application runner
command line runner
ready envent

CommandLineRunner/ApplicationRunner 方法可以接收来自命令行的参数，这是和其他两种方式最大的差别！

CommandLineRunner接收的所有参数作为一个字符串数组，直接传入到对应的run方法里：

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

ApplicationRunner会对接收的命令行参数进行解析，所有以--开头的参数都会作为Option参数：

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

public interface ApplicationArguments {
    String[] getSourceArgs();
    Set<String> getOptionNames();
    boolean containsOption(String name);
    List<String> getOptionValues(String name);
    List<String> getNonOptionArgs();
}

getSourceArgs()返回所有的参数为一个数组，和 CommandLineRunner 中的参数是一致的
getOptionNames()返回以--开头的参数名称
getOptionValues(String name)返回对应参数选项的值
getNonOptionArgs()返回非--开头的参数

@SpringBootApplication
public class DemoApplication implements ApplicationRunner {

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

    @Override
    public void run(ApplicationArguments args) throws Exception {
        for(String s : args.getSourceArgs()){
            System.out.println("source arg: " + s);
        }
        for(String s : args.getOptionNames()){
            System.out.println("option arg: " + s);
        }
        for(String s : args.getNonOptionArgs()){
            System.out.println("non-option arg: " + s);
        }
    }

}

这段代码执行结果：

$ java -jar demo.jar --time=2001 avatar.jpg -t
source arg: --time=2001
source arg: avatar.jpg
source arg: -t
option arg: time
non-option arg: avatar.jpg
non-option arg: -t

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