The source code process of SpringBoot printing Banner banner and how to modify it

printBanner

The printBanner(environment) method is called in the constructor of org.springframework.context.ConfigurableApplicationContext

if (this.bannerMode == Banner.Mode.OFF) {
			return null;
		}
		ResourceLoader resourceLoader = (this.resourceLoader != null) ? this.resourceLoader
				: new DefaultResourceLoader(null);
		SpringApplicationBannerPrinter bannerPrinter = new SpringApplicationBannerPrinter(resourceLoader, this.banner);
		if (this.bannerMode == Mode.LOG) {
			return bannerPrinter.print(environment, this.mainApplicationClass, logger);
		}
		return bannerPrinter.print(environment, this.mainApplicationClass, System.out);
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Banner.Mode print mode

The Banner.Mode enumeration class sets the banner printing mode in three ways

		/**
		 * Disable printing of the banner.
		 不打印
		 */
		OFF,

		/**
		 * Print the banner to System.out.
		 打印到控制台
		 */
		CONSOLE,

		/**
		 * Print the banner to the log file.
		 打印到日志文件
		 */
		LOG
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The printing mode can be set through the configuration file

#不打印
spring.main.banner-mode=off
#打印到控制台
spring.main.banner-mode=console
#打印到日志
spring.main.banner-mode=log

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Look back at the printBanner method

Then created the SpringApplicationBannerPrinter class to print the banner

SpringApplicationBannerPrinter bannerPrinter = new SpringApplicationBannerPrinter(resourceLoader, this.banner);
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resourceLoader is now the default resource loader

while this.banner = null

Look at this SpringApplicationBannerPrinter class is accessed for the first time, initializes the property values ​​of static members and initializes DEFAULT_BANNER

The way to modify the banner one implements the Banner interface

So we can directly create a Banner class to implement the Banner interface to imitate SpringBootBanner

public class MyBanner implements Banner {
    private static final String[] BANNER = { "", " \n" +
            "                                .::::.\n" +
            "                              .::::::::.\n" +
            "                              :::::::::::\n" +
            "                              ':::::::::::..\n" +
            "                               :::::::::::::::'\n" +
            "                                ':::::::::::.\n" +
            "                                  .::::::::::::::'\n" +
            "                                .:::::::::::...\n" +
            "                               ::::::::::::::''\n" +
            "                   .:::.       '::::::::''::::\n" +
            "                 .::::::::.      ':::::'  '::::\n" +
            "                .::::':::::::.    :::::    '::::.\n" +
            "              .:::::' ':::::::::. :::::      ':::.\n" +
            "            .:::::'     ':::::::::.:::::       '::.\n" +
            "          .::::''         '::::::::::::::       '::.\n" +
            "         .::''              '::::::::::::         :::...\n" +
            "      ..::::                  ':::::::::'        .:' ''''\n" +
            "   ..''''':'                    ':::::.' " };

    private static final String SPRING_BOOT = " :: fuck :: ";

    private static final int STRAP_LINE_SIZE = 42;

    @Override
    public void printBanner(Environment environment, Class<?> sourceClass, PrintStream printStream) {
        for (String line : BANNER) {
            printStream.println(line);
        }
        String version = SpringBootVersion.getVersion();
        version = (version != null) ? " (v" + version + ")" : "";
        StringBuilder padding = new StringBuilder();
        while (padding.length() < STRAP_LINE_SIZE - (version.length() + SPRING_BOOT.length())) {
            padding.append(" ");
        }

        printStream.println(AnsiOutput.toString(AnsiColor.GREEN, SPRING_BOOT, AnsiColor.DEFAULT, padding.toString(),
                AnsiStyle.FAINT, version));
        printStream.println();
    }
}

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Modify the main method of the main startup class

 public static void main(String[] args) {
       
       SpringApplication springApplication = new SpringApplication(AppTest.class);
        springApplication.setBanner(new MyBanner());

        springApplication.run( args);

    }
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Effect:

Continue to analyze the printBanner method

org.springframework.boot.SpringApplication#printBanner

Call the bannerPrinter.print(environment, this.mainApplicationClass, System.out) method

Three parameters ConfigurableEnvironment configuration environment

​ mainApplicationClass The bytecode object of the main startup class

​ System.out output stream

跟进去 来到 org.springframework.boot.SpringApplicationBannerPrinter#print(org.springframework.core.env.Environment, java.lang.Class<?>, java.io.PrintStream)

​

getBanner

看下这个 getBanner(environment) 从配置环境中拿 Banner对象的方法

首先创建了一个 Banners 对象 org.springframework.boot.SpringApplicationBannerPrinter.Banners

然后调用 banners.addIfNotNull(getImageBanner(environment));

getImageBanner(environment)

看下怎么从图片中拿到Banner对象

也就是图片只支持这三种格式

resourceLoader.getResource("banner." + ext)
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最重要看这行代码

去类加载路径下找 banner.gif,banner.jpg,banner.png文件 如果存在 则添加到 banners 集合中然后 立马返回

如果都没找到,继续执行

getTextBanner(environment)

banners.addIfNotNull(getTextBanner(environment));
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org.springframework.boot.SpringApplicationBannerPrinter#getTextBanner

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;
	}
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static final String DEFAULT_BANNER_LOCATION = "banner.txt";
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去类加载路径下找 banner.txt 文件 找到添加到 banners 集合里 然后立马返回

修改banner的方式二 类加载路径下创建 banner.文件

banner文件分两种 一种图片 图片的加载顺序为 gif,jpg,png

​ 一种txt

每种类型只能添加一个 同时最多打印两个banner 一个为图片类型的 一个为txt类型的

如 我在resource路径下放了两个banner文件,一个图片一个txt

生成banner的网站

关于佛祖的ascii艺术字，Spring Boot 佛祖 Banner-bootschool.net

然后resource路径下先进一个banner.txt 粘贴 再启动项目