简析Spring Boot启动时控制台打印logo的实现原理

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简析Spring Boot启动时控制台打印logo的实现原理

2023-02-10

Banner

Spring Boot应用程序启动之后都会在输出的日志中打印具有独特表示的logo和版本信息。示例如下：

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  .   ____          _            __ _ _
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 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
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( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
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 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
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  '  |____| .__|_| |_|_| |_\__, | / / / /
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 =========|_|==============|___/=/_/_/_/
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 :: Spring Boot ::               (v2.5.14)

那么它究竟是如何实现的呢？带着这种好奇和疑问，开始正文。

Spring Boot实现方案#

打印输出的核心关键工具类是SpringBootBanner。源码如下：

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class SpringBootBanner implements Banner {
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  private static final String[] BANNER = { "", "  .   ____          _            __ _ _",
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      " /\\\\ / ___'_ __ _ _(_)_ __  __ _ \\ \\ \\ \\", "( ( )\\___ | '_ | '_| | '_ \\/ _` | \\ \\ \\ \\",
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      " \\\\/  ___)| |_)| | | | | || (_| |  ) ) ) )", "  '  |____| .__|_| |_|_| |_\\__, | / / / /",
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      " =========|_|==============|___/=/_/_/_/" };
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  private static final String SPRING_BOOT = " :: Spring Boot :: ";
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  private static final int STRAP_LINE_SIZE = 42;
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  @Override
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  public void printBanner(Environment environment, Class<?> sourceClass, PrintStream printStream) {
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    for (String line : BANNER) {
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      printStream.println(line);
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    }
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    String version = SpringBootVersion.getVersion();
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    version = (version != null) ? " (v" + version + ")" : "";
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    StringBuilder padding = new StringBuilder();
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    while (padding.length() < STRAP_LINE_SIZE - (version.length() + SPRING_BOOT.length())) {
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      padding.append(" ");
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    }
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    printStream.println(AnsiOutput.toString(AnsiColor.GREEN, SPRING_BOOT, AnsiColor.DEFAULT, padding.toString(),
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        AnsiStyle.FAINT, version));
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    printStream.println();
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  }
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}

Spring Boot提供了 spring.banner.location 支持玩家自定义banner，支持图片格式（banner.gif, banner.jpg, banner.png），也支持文本格式(banner.txt)。

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spring:
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    banner:
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        charset: utf-8
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        location: classpath:banner.txt    # banner文本文件路径
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        image:    # banner图片文件路径
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            location: classpath:banner.png
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            width: 80
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            margin: 1
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            invert: false
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  main:
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    banner-mode: "off"

可以通过Banner生成器在线生成想要的字符文字效果。

Banner中提供了几个变量占位符，用来丰富打印的数据内容。列表如下：

变量	描述
${application.version}	应用程序的版本号
${application.formatted-version}
${spring-boot.version}	Spring Boot版本号
${spring-boot.formatted-version}
${Ansi.NAME} (or$ {AnsiColor.NAME}, ${AnsiBackground.NAME},$ {AnsiStyle.NAME})	ANSI设置
${application.title}	应用程序标题

Banner有一个输出模式的控制开关，内置三种模式 OFF(关闭)， CONSOLE(仅控制台), LOG(追加日志)

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public interface Banner {
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  /**
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   * Print the banner to the specified print stream.
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   * @param environment the spring environment
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   * @param sourceClass the source class for the application
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   * @param out the output print stream
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   */
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  void printBanner(Environment environment, Class<?> sourceClass, PrintStream out);
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  /**
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   * An enumeration of possible values for configuring the Banner.
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   */
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  enum Mode {
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    /**
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     * Disable printing of the banner.
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     */
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    OFF,
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    /**
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     * Print the banner to System.out.
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     */
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    CONSOLE,
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    /**
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     * Print the banner to the log file.
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     */
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    LOG
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  }
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}
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//    通过SpringApplication设置定制的Banner实例
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//    SpringApplication.setBanner(…)

控制Banner输出的核心业务方法如下：

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

了解Spring Boot的实现方案后，我就可以在项目中实现自定义的Banner。

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public enum StructBanner {
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    INSTANCE;
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    private static final Logger LOGGER = LoggerFactory.getLogger(StructBanner.class);
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    /**
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     * font: doom
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     * content: "*Struct>>>"
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     */
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    private static final String[] BANNER = {
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            "    _    _____ _                   _  ______   ",
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            " /\\| |/\\/  ___| |                 | | \\ \\ \\ \\  ",
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            " \\ ` ' /\\ `--.| |_ _ __ _   _  ___| |_ \\ \\ \\ \\ ",
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            "|_     _|`--. \\ __| '__| | | |/ __| __| > > > >",
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            " / , . \\/\\__/ / |_| |  | |_| | (__| |_ / / / / ",
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            " \\/|_|\\/\\____/ \\__|_|   \\__,_|\\___|\\__/_/_/_/  "
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    };
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    private static final String STRUCT_STORE_SERVICE = " :: Struct Store Service :: ";
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    private static final String VERSION = loadVersionProperties();
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    /**
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     * Print struct store service banner.
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     */
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    public void print() {
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        PrintStream ps = System.out;
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        for (String line : BANNER) {
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            ps.println(line);
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        }
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        ps.println(STRUCT_STORE_SERVICE + "    (" + getVersion() + ")");
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    }
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    /**
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     * Get struct library version.
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     *
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     * @return Struct library version.
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     */
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    public String getVersion() {
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        return VERSION;
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    }
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    static String loadVersionProperties() {
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        Properties prop = new Properties();
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        try (InputStream in = StructBanner.class.getResourceAsStream("/META-INF/maven/org.structutil/struct-spring/pom.properties")) {
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            prop.load(in);
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            return prop.getProperty("version", "Unknown");
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        } catch (Throwable e) {
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            LOGGER.error("");
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        }
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        return "Unknown";
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    }
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}

打印输出结果：

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    _    _____ _                   _  ______
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 /\| |/\/  ___| |                 | | \ \ \ \
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 \ ` ' /\ `--.| |_ _ __ _   _  ___| |_ \ \ \ \
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|_     _|`--. \ __| '__| | | |/ __| __| > > > >
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 / , . \/\__/ / |_| |  | |_| | (__| |_ / / / /
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 \/|_|\/\____/ \__|_|   \__,_|\___|\__/_/_/_/
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 :: Struct Store Service ::     (Unknown)

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赞助

简析Spring Boot启动时控制台打印logo的实现原理

https://tinyzzh.github.io/posts/2023-02-10-spring_boot_banner/

作者

TinyZ Zzh

发布于

2023-02-10

许可协议

CC BY-NC-SA 4.0

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Spring Boot实现方案#

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