SpingBoot+Banner默认信息输出原理

SpingBoot 服务启动加载Banner信息

SpingBoot 加载Banner没有多少难度，只是研究SpringBoot启动源码的一个开始。

Banner信息

public Banner print(Environment environment, Class<?> sourceClass, PrintStream out) {
     
		//获取Banner 对象属性
		Banner banner = getBanner(environment);
		//输出Banner信息
		banner.printBanner(environment, sourceClass, out);
		return new PrintedBanner(banner, sourceClass);
	}

获取Banner信息

private Banner getBanner(Environment environment) {
     
		Banners banners = new Banners();
		banners.addIfNotNull(getImageBanner(environment));
//获取Resource下的 banner 信息
		banners.addIfNotNull(getTextBanner(environment));
		if (banners.hasAtLeastOneBanner()) {
     
			return banners;
		}
		if (this.fallbackBanner != null) {
     
			return this.fallbackBanner;
		}
 //如果没有找到配置的 Banner 那么返回一个空的Banner，系统会打印默认的Banner信息和springboot的版本信息。
		return DEFAULT_BANNER;
	}

获取Resource下的 Banner信息

private Banner getTextBanner(Environment environment) {
     
		String location = environment.getProperty(BANNER_LOCATION_PROPERTY,
				DEFAULT_BANNER_LOCATION);
//BANNER_LOCATION_PROPERTY=” spring.banner.location”;
//DEFAULT_BANNER_LOCATION)=” banner.txt”;
//location= banner.txt
// resourceLoader 类加载器加载
		Resource resource = this.resourceLoader.getResource(location);
		if (resource.exists()) {
     
//如果Resource 下面有banner.txt那么返回自定义的 banner，没有返回空的对象，//控制台就会输出默认的banner信息
			return new ResourceBanner(resource);
		}
		return null;
	}

输出Banner

这里就不做研究了
@Override
	public void printBanner(Environment environment, Class<?> sourceClass,
			PrintStream out) {
     
		try {
     
			String banner = StreamUtils.copyToString(this.resource.getInputStream(),
					environment.getProperty("spring.banner.charset", Charset.class,
							StandardCharsets.UTF_8));

			for (PropertyResolver resolver : getPropertyResolvers(environment,
					sourceClass)) {
     
				banner = resolver.resolvePlaceholders(banner);
			}
			out.println(banner);
		}
		catch (Exception ex) {
     
			logger.warn("Banner not printable: " + this.resource + " (" + ex.getClass()
					+ ": '" + ex.getMessage() + "')", ex);
		}
	}