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。