SpingBoot+Banner默认信息输出原理

àì夳堔傛蜴生んèń 2023-03-04 05:26 37阅读 0赞

# 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);
    		}
    	}