Spring Boot在启动的时候会打印一个默认的SpringBoot的图案

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.0.1.RELEASE)

打印图案的行为由SpringApplicationBannerPrinter控制，要打印的图案通过getBanner()获取Banner并打印。

1. 首先通过文件控制图案，检查是否存在banner文件，存在则构建ImageBanner和ResourceBanner去打印
2. 其次通过自定义的Banner 实现类控制图案，注入fallbackBanner进行打印。
3. 最后使用默认的SpringBootBanner打印默认图案

private Banner getBanner(Environment environment, Banner definedBanner) {
    //1、文件控制图案
	Banners banners = new Banners();
	banners.addIfNotNull(getImageBanner(environment));
	banners.addIfNotNull(getTextBanner(environment));
	if (banners.hasAtLeastOneBanner()) {
		return banners;
	}
    //2.自定义的Banner 实现类控制图案
	if (this.fallbackBanner != null) {
		return this.fallbackBanner;
	}
    //默认的SpringBootBanner
	return DEFAULT_BANNER;
}

private static class Banners implements Banner {

	private final List<Banner> banners = new ArrayList<Banner>();

	public void addIfNotNull(Banner banner) {
		if (banner != null) {
			this.banners.add(banner);
		}
	}

	public boolean hasAtLeastOneBanner() {
		return !this.banners.isEmpty();
	}

	@Override
	public void printBanner(Environment environment, Class<?> sourceClass,
							PrintStream out) {
		for (Banner banner : this.banners) {
			banner.printBanner(environment, sourceClass, out);
		}
	}

}

文件控制图案

通过文件控制图案的方式里，会到配置文件 application.proeprties 里根据spring.banner.location和spring.banner.image.location找到文件和图片文档地址，如果没有就到classpath目录下找默认的banner.txt和banner.gif/banner.jpg/banner.png，默认文件也没有就返回null不采用文件内容控制，图片会根据颜色深度转成字符图案。

/* SpringApplicationBannerPrinter.java
 */
static final String BANNER_LOCATION_PROPERTY = "banner.location";
static final String DEFAULT_BANNER_LOCATION = "banner.txt";
private Banner getTextBanner(Environment environment) {
	String location = environment.getProperty(BANNER_LOCATION_PROPERTY,
											  DEFAULT_BANNER_LOCATION);
	Resource resource = this.resourceLoader.getResource(location);
	if (resource.exists()) {
		return new ResourceBanner(resource);
	}
	return null;
}

static final String BANNER_IMAGE_LOCATION_PROPERTY = "banner.image.location";
static final String[] IMAGE_EXTENSION = { "gif", "jpg", "png" };
private Banner getImageBanner(Environment environment) {
	String location = environment.getProperty(BANNER_IMAGE_LOCATION_PROPERTY);
	if (StringUtils.hasLength(location)) {
		Resource resource = this.resourceLoader.getResource(location);
		return (resource.exists() ? new ImageBanner(resource) : null);
	}
	for (String ext : IMAGE_EXTENSION) {
		Resource resource = this.resourceLoader.getResource("banner." + ext);
		if (resource.exists()) {
			return new ImageBanner(resource);
		}
	}
	return null;
}

自定义Banner

定制化 ASCII 字符：http://network-science.de/ascii/
定制化 ASCII 图片：https://www.degraeve.com/img2txt.php

新建类实现Banner并实现printBanner方法

import java.io.PrintStream;

import org.springframework.boot.Banner;
import org.springframework.core.env.Environment;

public class HelloBanner implements Banner
{

    @Override
    public void printBanner(Environment environment, Class<?> sourceClass, PrintStream out) {

        String banner = "##     ## ######## ##       ##        #######  \r\n"
                + "##     ## ##       ##       ##       ##     ## \r\n"
                + "##     ## ##       ##       ##       ##     ## \r\n"
                + "######### ######   ##       ##       ##     ## \r\n"
                + "##     ## ##       ##       ##       ##     ## \r\n"
                + "##     ## ##       ##       ##       ##     ## \r\n"
                + "##     ## ######## ######## ########  #######  ";

        out.println(banner);
    }
}

SpringApplication设置banner

@SpringBootApplication
public class Application
{
    public static void main(String[] args) {
        SpringApplication springApplication = new SpringApplication(Application.class);
        springApplication.setBanner(new MyBanner());
        springApplication.run(args);
    }
}

关闭Banner

Banner有三种打印模式,默认是CONSOLE打印到控制台。

public interface Banner {
	enum Mode {
		OFF,
		CONSOLE,
		LOG
	}
}

如果要关闭打印图案，在SpringBootApplication中后缀.bannerMode(Banner.Mode.OFF)

@SpringBootApplication
public class Application {

    public static void main(String[] args) {
        new SpringApplicationBuilder(Application.class).bannerMode(Banner.Mode.OFF)
                .run(args);
    }

}

也可以在配置文件中配置spring.main.banner-mode=off关闭