spring boot 源码之banner

Banner

　　使用Spring Boot启动的jar包总是会显示一个Spring的图标。实际我们是可以自定义这个图标。Banner接口定义了打印banner的方法。

void printBanner(Environment environment, Class<?> sourceClass, PrintStream out);

SpringApplicationBannerPrinter

　　springboot用来创建banner对象的类，核心方法为getBanner即获取Banner对象。

private Banner getBanner(Environment environment) {
        Banners banners = new Banners();
        banners.addIfNotNull(getImageBanner(environment));
        banners.addIfNotNull(getTextBanner(environment));
        if (banners.hasAtLeastOneBanner()) {
            return banners;
        }
        if (this.fallbackBanner != null) {
            return this.fallbackBanner;
        }
        return DEFAULT_BANNER;
    }

　　getImageBanner和getTextBanner方法从相应的位置获取资源，然后使用响应的Banner打印相应资源。

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;
    }

    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;
    }

SpringBootBanner

　　SpringBootBanner是Banner的实现类，打印一个spring的图样。

ResourceBanner

　　读取资源，替换占位符，然后打印到相应io。

public void printBanner(Environment environment, Class<?> sourceClass,
            PrintStream out) {
        try {
            String banner = StreamUtils.copyToString(this.resource.getInputStream(),
                    environment.getProperty("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);
        }
    }

ImageBanner

　　读取图片资源，然后打印到相应io。