Alian解读SpringBoot 2.6.0 源码（五）：启动流程分析之打印Banner

一、背景

上两篇我们解读了环境准备及配置文件的加载，本计划是打印banner和创建容器一起解读的，但是创建容器的内容也不少，又会超出字数，编辑特别的慢，希望官方优化下，这次就单独把打印banner分出来了，虽说我觉得这个打印这个东西意义不是很大，不管怎么样，我们还是去了解下，首先我们还是先回顾下启动的整体流程。

1.1、run方法整体流程

接下来的几个方法所在类的具体路径：org.springframework.boot.SpringApplication

 public ConfigurableApplicationContext run(String... args) {// 1、记录启动的开始时间（单位纳秒）long startTime = System.nanoTime();// 2、初始化启动上下文、初始化应用上下文DefaultBootstrapContext bootstrapContext = createBootstrapContext();ConfigurableApplicationContext context = null;// 3、设置无头属性：“java.awt.headless”，默认值为：true（没有图形化界面）configureHeadlessProperty();// 4、获取所有 Spring 运行监听器SpringApplicationRunListeners listeners = getRunListeners(args);// 发布应用启动事件listeners.starting(bootstrapContext, this.mainApplicationClass);try {// 5、初始化默认应用参数类（命令行参数）ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);// 6、根据运行监听器和应用参数 来准备 Spring 环境ConfigurableEnvironment environment = prepareEnvironment(listeners, bootstrapContext, applicationArguments);// 配置忽略bean信息configureIgnoreBeanInfo(environment);// 7、创建 Banner 并打印Banner printedBanner = printBanner(environment);// 8、创建应用上下文context = createApplicationContext();// 设置applicationStartupcontext.setApplicationStartup(this.applicationStartup);// 9、准备应用上下文prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);// 10、刷新应用上下文(核心)refreshContext(context);// 11、应用上下文刷新后置处理afterRefresh(context, applicationArguments);// 13、时间信息、输出日志记录执行主类名Duration timeTakenToStartup = Duration.ofNanos(System.nanoTime() - startTime);if (this.logStartupInfo) {new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), timeTakenToStartup);}// 14、发布应用上下文启动完成事件listeners.started(context, timeTakenToStartup);// 15、执行所有 Runner 运行器callRunners(context, applicationArguments);} catch (Throwable ex) {// 运行错误处理handleRunFailure(context, ex, listeners);throw new IllegalStateException(ex);}try {// 16、发布应用上下文就绪事件（可以使用了）Duration timeTakenToReady = Duration.ofNanos(System.nanoTime() - startTime);listeners.ready(context, timeTakenToReady);} catch (Throwable ex) {// 运行错误处理handleRunFailure(context, ex, null);throw new IllegalStateException(ex);}// 17、返回应用上下文return context;}

1.2、本文解读范围

本文主要讲解到Banner打印，也就是：

 // 7、创建 Banner 并打印Banner printedBanner = printBanner(environment);

二、打印banner

2.1、整体流程

此方法所在类的具体路径：org.springframework.boot.SpringApplication

 // banner打印模式默认是控制台private Banner.Mode bannerMode = Banner.Mode.CONSOLE;private Banner printBanner(ConfigurableEnvironment environment) {// 默认是控制台if (this.bannerMode == Banner.Mode.OFF) {return null;}// 由于此时resourceLoader 为null,所以resourceLoader 最终为DefaultResourceLoaderResourceLoader resourceLoader = (this.resourceLoader != null) ? this.resourceLoader: new DefaultResourceLoader(null);// 实例化一个SpringApplicationBannerPrinterSpringApplicationBannerPrinter bannerPrinter = new SpringApplicationBannerPrinter(resourceLoader, this.banner);// 默认是控制台if (this.bannerMode == Mode.LOG) {return bannerPrinter.print(environment, this.mainApplicationClass, logger);}// 调用SpringApplicationBannerPrinter的打印方法return bannerPrinter.print(environment, this.mainApplicationClass, System.out);}

如果Banner的打印模式是关闭的就不再执行
获取资源加载器
实例化SpringApplicationBannerPrinter
如果Banner的打印模式是输出到日志，则通过SpringApplicationBannerPrinter 进行打印
默认是输出到控制台，也是通过SpringApplicationBannerPrinter

可以通过配置文件修改打印的模式（log，console，off），比如：

spring:main:banner-mode: log

类的具体路径：org.springframework.boot.SpringApplicationBannerPrinter

class SpringApplicationBannerPrinter {static final String BANNER_LOCATION_PROPERTY = "spring.banner.location";static final String BANNER_IMAGE_LOCATION_PROPERTY = "spring.banner.image.location";static final String DEFAULT_BANNER_LOCATION = "banner.txt";static final String[] IMAGE_EXTENSION = { "gif", "jpg", "png" };private static final Banner DEFAULT_BANNER = new SpringBootBanner();private final ResourceLoader resourceLoader;private final Banner fallbackBanner;SpringApplicationBannerPrinter(ResourceLoader resourceLoader, Banner fallbackBanner) {this.resourceLoader = resourceLoader;this.fallbackBanner = fallbackBanner;}// 打印Banner到日志文件Banner print(Environment environment, Class<?> sourceClass, Log logger) {// 通过环境配置获取BannerBanner banner = getBanner(environment);try {// 打印Banner到日志文件logger.info(createStringFromBanner(banner, environment, sourceClass));} catch (UnsupportedEncodingException ex) {logger.warn("Failed to create String for banner", ex);}// 返回打印对象return new PrintedBanner(banner, sourceClass);}// 打印Banner到控制台Banner print(Environment environment, Class<?> sourceClass, PrintStream out) {// 通过环境配置获取BannerBanner banner = getBanner(environment);// 打印Banner到控制台banner.printBanner(environment, sourceClass, out);// 返回打印对象return new PrintedBanner(banner, sourceClass);}// 获取bannersprivate Banner getBanner(Environment environment) {// 实例化Banners,Banners是Banner的实现类Banners banners = new Banners();// 获取图片形式的Banner,如果不为空则加入列表banners.addIfNotNull(getImageBanner(environment));// 获取文本形式的Banner,如果不为空则加入列表banners.addIfNotNull(getTextBanner(environment));// 只要列表不为空则返回Bannersif (banners.hasAtLeastOneBanner()) {return banners;}// 此处为nullif (this.fallbackBanner != null) {return this.fallbackBanner;}// 默认是SpringBootBannerreturn DEFAULT_BANNER;}// 获取文本形式的bannerprivate Banner getTextBanner(Environment environment) {// 获取属性"spring.banner.location"的值，没有取到就使用默认值"banner.txt"String location = environment.getProperty(BANNER_LOCATION_PROPERTY, DEFAULT_BANNER_LOCATION);// 通过资源加载器去指定的路径加载资源Resource resource = this.resourceLoader.getResource(location);try {// 如果文本资源存在，且路径中不含有"liquibase-core"if (resource.exists() && !resource.getURL().toExternalForm().contains("liquibase-core")) {// 符合条件时构建ResourceBanner对象返回return new ResourceBanner(resource);}} catch (IOException ex) {// Ignore}// 默认返回nullreturn null;}// 获取图片形式的bannerprivate Banner getImageBanner(Environment environment) {// 获取属性"spring.banner.image.location"的值String location = environment.getProperty(BANNER_IMAGE_LOCATION_PROPERTY);// 如果配置了值if (StringUtils.hasLength(location)) {// 通过资源加载器加载资源Resource resource = this.resourceLoader.getResource(location);// 如果图片资源存在，则构建ImageBanner返回，否则返回nullreturn resource.exists() ? new ImageBanner(resource) : null;}//如果没有配置值for (String ext : IMAGE_EXTENSION) {// 则尝试加载"banner.gif", "banner.jpg", "banner.png"Resource resource = this.resourceLoader.getResource("banner." + ext);if (resource.exists()) {// 只要加载到了，则构建ImageBanner返回return new ImageBanner(resource);}}return null;}private String createStringFromBanner(Banner banner, Environment environment, Class<?> mainApplicationClass)throws UnsupportedEncodingException {// 构建字节数组输出流ByteArrayOutputStream baos = new ByteArrayOutputStream();// 构建打印流banner.printBanner(environment, mainApplicationClass, new PrintStream(baos));// 获取"spring.banner.charset"，默认编码为"UTF-8"String charset = environment.getProperty("spring.banner.charset", "UTF-8");// 转为字符串return baos.toString(charset);}// 静态内部类Bannersprivate static class Banners implements Banner {private final List<Banner> banners = new ArrayList<>();void addIfNotNull(Banner banner) {if (banner != null) {this.banners.add(banner);}}boolean hasAtLeastOneBanner() {return !this.banners.isEmpty();}@Overridepublic void printBanner(Environment environment, Class<?> sourceClass, PrintStream out) {for (Banner banner : this.banners) {banner.printBanner(environment, sourceClass, out);}}}// 静态内部类PrintedBannerprivate static class PrintedBanner implements Banner {private final Banner banner;private final Class<?> sourceClass;PrintedBanner(Banner banner, Class<?> sourceClass) {this.banner = banner;this.sourceClass = sourceClass;}@Overridepublic void printBanner(Environment environment, Class<?> sourceClass, PrintStream out) {sourceClass = (sourceClass != null) ? sourceClass : this.sourceClass;this.banner.printBanner(environment, sourceClass, out);}}}

通过环境配置获取Banner，先获取图片Banner（ImageBanner），然后是文本Banner（ResourceBanner），都没有获取到则使用默认的SpringBootBanner
打印Banner到控制台或者日志文件，如果是图片Banner，需要先转为打印流，图片Banner和文本Banner同时存在时，都会打印，先打印图片banner
返回打印对象

2.1.1、图片Banner获取流程

通过在配置文件配置spring.banner.image.location，通过资源加载器加载资源，获取到资源则返回对象ImageBanner，未获取到则返回null
未指定spring.banner.image.location的值时，可以在classPath中添加banner.gif、banner.jpg、banner.png任意一个文件，但是如果添加了多个，则会打印一个，优先级：gif > jpg > png。

2.1.2、文本Banner获取流程

通过在配置文件配置spring.banner.location，通过环境对象Environment获取路径，如果没有获取到则默认使用classPath下"banner.txt"
通过资源加载器去加载，如果加载到了，并且满足条件，则返回对象ResourceBanner，否则返回null

2.2、具体实现

ResourceBanner的打印需要处理占位符，然后转为字符串进行输出

public class ResourceBanner implements Banner {private Resource resource;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));// 获取属性解析器for (PropertyResolver resolver : getPropertyResolvers(environment, sourceClass)) {// 解析处理占位符banner = resolver.resolvePlaceholders(banner);}// 输出out.println(banner);} catch (Exception ex) {logger.warn(LogMessage.format("Banner not printable: %s (%s: '%s')", this.resource, ex.getClass(), ex.getMessage()), ex);}}protected List<PropertyResolver> getPropertyResolvers(Environment environment, Class<?> sourceClass) {List<PropertyResolver> resolvers = new ArrayList<>();resolvers.add(environment);resolvers.add(getVersionResolver(sourceClass));resolvers.add(getAnsiResolver());resolvers.add(getTitleResolver(sourceClass));return resolvers;}
}

ImageBanner 的打印时会先将资源转为输入流，然后再转为图片输入流，然后转为对象数组Frame[ ]，Frame是 ImageBanner 静态内部类，里包含BufferedImage及delayTime，然后遍历数组进行打印。

public class ImageBanner implements Banner {private final Resource image;@Overridepublic void printBanner(Environment environment, Class<?> sourceClass, PrintStream out) {String headless = System.getProperty("java.awt.headless");try {System.setProperty("java.awt.headless", "true");// 打印printBanner(environment, out);} catch (Throwable ex) {logger.warn(LogMessage.format("Image banner not printable: %s (%s: '%s')", this.image, ex.getClass(),ex.getMessage()));logger.debug("Image banner printing failure", ex);} finally {if (headless == null) {System.clearProperty("java.awt.headless");} else {System.setProperty("java.awt.headless", headless);}}}private void printBanner(Environment environment, PrintStream out) throws IOException {int width = getProperty(environment, "width", Integer.class, 76);int height = getProperty(environment, "height", Integer.class, 0);int margin = getProperty(environment, "margin", Integer.class, 2);boolean invert = getProperty(environment, "invert", Boolean.class, false);// 获取位属性BitDepth bitDepth = getBitDepthProperty(environment);// 获取像素属性PixelMode pixelMode = getPixelModeProperty(environment);// 获取Frame[]Frame[] frames = readFrames(width, height);for (int i = 0; i < frames.length; i++) {if (i > 0) {// 充值光标resetCursor(frames[i - 1].getImage(), out);}// 打印输出printBanner(frames[i].getImage(), margin, invert, bitDepth, pixelMode, out);// 延迟后继续打印sleep(frames[i].getDelayTime());}}private Frame[] readFrames(int width, int height) throws IOException {// Java7的语法，自动关闭流// 图片资源转为输入流try (InputStream inputStream = this.image.getInputStream()) {// 输入流转为图片输入流try (ImageInputStream imageStream = ImageIO.createImageInputStream(inputStream)) {// 根据宽高和图片输入流获取Frame[]return readFrames(width, height, imageStream);}}}private Frame[] readFrames(int width, int height, ImageInputStream stream) throws IOException {// 返回包含所有当前已注册 ImageReader 的 IteratorIterator<ImageReader> readers = ImageIO.getImageReaders(stream);Assert.state(readers.hasNext(), "Unable to read image banner source");ImageReader reader = readers.next();try {// 返回一个适合此格式的默认 ImageReadParam 对象ImageReadParam readParam = reader.getDefaultReadParam();// 设置指定的 ImageInputStream 输入源reader.setInput(stream);// 返回当前输入源中可用的图像数int frameCount = reader.getNumImages(true);Frame[] frames = new Frame[frameCount];for (int i = 0; i < frameCount; i++) {// 通过ImageReader 把图片输入流转为Frameframes[i] = readFrame(width, height, reader, i, readParam);}// 返回数组对象return frames;} finally {reader.dispose();}}private Frame readFrame(int width, int height, ImageReader reader, int imageIndex, ImageReadParam readParam)throws IOException {// 使用所提供的 ImageReadParam 来读取通过索引 imageIndex 指定的对象BufferedImage image = reader.read(imageIndex, readParam);// 跳转图像大小BufferedImage resized = resizeImage(image, width, height);// 获取延迟时间int delayTime = getDelayTime(reader, imageIndex);// 返回Framereturn new Frame(resized, delayTime);}private static class Frame {private final BufferedImage image;private final int delayTime;Frame(BufferedImage image, int delayTime) {this.image = image;this.delayTime = delayTime;}BufferedImage getImage() {return this.image;}int getDelayTime() {return this.delayTime;}}}

有兴趣的小伙伴可以看看具体的实现，详情见代码注释

2.3、打印效果

我们再配置文件中加入如下配置：

server:port: 8080servlet:context-path: /springbootspring:main:sources: com.alian.springbootbanner-mode: consolebanner:location: classpath:banner.txtimage:location: classpath:csdn.jpg

也就是我们指定了图片Banner和文本Banner资源的路径，然后分别把 banner.txt 和 csdn.png 放到 classpath 下，当然这里不配置文本Banner的地址也可以，只要放了那个文本文件，因为默认会读取 classpath 下的 banner.txt 。

             &#########     *@@@@@@@@@@  &@@@@@#@@*        :@@@@@@@#@.        &##@##########  @@@@#@@@@@@@@#  @@@@@@@@@@@#@@   @##@@@@@@@@@@#      ####@#           @@@@@           #@@@      @@@@@  @@@@*     @@@@@     #@###             @@@@#@@@@       @@@@       @@@@  #@@@      @@@@@     ####@                 @##@@@@#@   #@@@       @@@#  #@@#      @@@#8     #@####                    @@@@@8  #@#*     o@@@@   #@@@      @@@#      ##@##########@  @#@@@@@#@@@@@@  :@@@@@@@@#@@@@    #@@#      @@@@      8#########:  @#@@@@@@@#@     @@@@@@@#@@o      @@@@       @@@@      ___                                     ___           ___     /  /\                      ___          /  /\         /__/\    /  /::\                    /  /\        /  /::\        \  \:\   /  /:/\:\    ___     ___   /  /:/       /  /:/\:\        \  \:\  /  /:/~/::\  /__/\   /  /\ /__/::\      /  /:/~/::\   _____\__\:\ /__/:/ /:/\:\ \  \:\ /  /:/ \__\/\:\__  /__/:/ /:/\:\ /__/::::::::\\  \:\/:/__\/  \  \:\  /:/     \  \:\/\ \  \:\/:/__\/ \  \:\~~\~~\/\  \::/        \  \:\/:/       \__\::/  \  \::/       \  \:\  ~~~ \  \:\         \  \::/        /__/:/    \  \:\        \  \:\     \  \:\         \__\/         \__\/      \  \:\        \  \:\    \__\/                                   \__\/         \__\/    2021-12-07 11:45:32 895 [main] INFO initialize 108:Tomcat initialized with port(s): 8080 (http)
2021-12-07 11:45:32 900 [main] INFO log 173:Initializing ProtocolHandler ["http-nio-8080"]
2021-12-07 11:45:32 900 [main] INFO log 173:Starting service [Tomcat]
2021-12-07 11:45:32 900 [main] INFO log 173:Starting Servlet engine: [Apache Tomcat/9.0.55]
2021-12-07 11:45:32 941 [main] INFO log 173:Initializing Spring embedded WebApplicationContext
2021-12-07 11:45:32 942 [main] INFO prepareWebApplicationContext 290:Root WebApplicationContext: initialization completed in 474 ms
2021-12-07 11:45:33 132 [main] INFO log 173:Starting ProtocolHandler ["http-nio-8080"]
2021-12-07 11:45:33 142 [main] INFO start 220:Tomcat started on port(s): 8080 (http) with context path '/springboot'
2021-12-07 11:45:33 157 [main] INFO logStarted 61:Started SpringbootApplication in 1.116 seconds (JVM running for 1.621)

2.4、Banner生成网址

比较常用的Banner制作网站如下：

http://patorjk.com/software/taag/
https://www.bootschool.net/ascii
http://www.network-science.de/ascii/
http://www.degraeve.com/img2txt.php