Spring Banner 定义了应用启动时的界面。
Spring提供了Banner的默认实现，效果如下：
可以在SpringApplication的run()方法之前，通过setBannerMode(Mode)指定Banner的模式：OFF、CONSOLE、LOG，其中OFF用于关闭Banner，如下：
SpringApplication.setBannerMode(Mode.OFF);
在resources目录下添加banner.txt1文件，内容如下：
_______ __ .__ __. ___ __
| ____|| | | \ | | / \ | |
| |__ | | | \| | / ^ \ | |
| __| | | | . ` | / /_\ \ | |
| | | | | |\ | / _____ \ | `----.
|__| |__| |__| \__| /__/ \__\ |_______|
运行可在控制台看到如下内容：
可以通过
spring.banner.location属性来指定TextBanner资源的位置，默认为banner.txt。
还可以使用图片来指定Banner，支持的类型为：git、jpg、png，与banner.txt类似，在resources目录下添加banner.gif文件，如下图：
运行后可多个该图片的多个帧像：
.:::::. .*::::*
::: ::*
*:: ::.*::
.:* ::::.
o: ::::::::
::::: .:::::::::::
:::. *:::::::::::::o::o::::::::
:: .:::::::::::::::::::::::::::::::.
:: *::::::::::::::::::::::::: ::::: ::.
:: ::::::::::::::::::::::::: **:::::: ::
: ::::::::::::::::::::::::. .:::::: *:
:: ::::::::::::::::::::::.*: :::::::* ::
:: *::::::::::::::::::. : *: :::::::: .:
*: :::::::::::::. :: : ::::::::: .:
:. :*.. :.: : :::::::::: ::
.: :.*: : .* : .::::::::::: *:
:: .: : : .::::::::::* ::
*::. ::: .::
:::* ......****::::*
.*::*****.....
*:::::::* ..****..
*:. .*::* .*:*
:: .:* :: :*
.: .:* :: *:
: .:::::::::::::::::*:* :.
:. *::* .: :*::*. :
*:* : :: .:*:
:*** :: : ::*
:: *. :. :::::::* : : *:.
:: :* *: .:::::::::::: : : **
*: **:: .:::::::::::::: .: :* **
: .:: :::::::::::::::. :*: :.
.: .:. *:::::::::::::: : :.
: :.: :::::::::::::: ::. :
** .: :. :::::::::: ::** ::
*:. : :. :* .: ::
.** : :* : .* ::
.:: :* *: ***:
:*:*. :: : *::
: .*::*: :. *::* .:
.: *:*:::::::::::::::::. :
:* :: .:* :.
.:. ::: *:. *:
.::. *::* .::
..**... *::::::::
ImageBanner是将图像中的每一帧转换为
TextBanner，因此git的Banner会出现多个。可以通过
spring.banner.image.location属性来指定ImageBanner资源的位置，默认为banner.{ext}。
spring:
banner:
location: classpath:banner.txt # TextBanner 资源位置，默认为 classpath:banner.txt
image:
location: classpath:banner.gif # ImageBanner 资源位置，默认为 classpath:banner.gif(jpg|png)
在SpringApplication的run()方法中，通过调用printBanner(environment)方法来打印Banner。
package org.springframework.boot;
public class SpringApplication {
private Banner printBanner(ConfigurableEnvironment environment) {
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);
}
}
在该方法中，通过创建SpringApplicationBannerPrinter的实例调用print()方法来打印Banner:
在SpringApplication的printBanner(environment)方法中
SpringApplicationBannerPrinter实现了Banner的加载和打印，核心流程如下：
getImageBanner()：获取spring.banner.image.location属性指定的资源，如果未指定，则顺序加载resources目录下的banner.git、banner.jpg、banner.png。getTextBanner()：获取spring.banner.location属性指定的资源，默认为banner.txt。DEFAULT_BANNER：由SpringBootBanner创建的默认资源。package org.springframework.boot;
class SpringApplicationBannerPrinter {
// TEXT BANNER LOCATION 属性 KEY，用于指定 textBanner 资源的位置
static final String BANNER_LOCATION_PROPERTY = "spring.banner.location";
// IMAGE BANNER LOCATION 属性 KEY，用于指定 imageBanner 资源的位置
static final String BANNER_IMAGE_LOCATION_PROPERTY = "spring.banner.image.location";
// 默认的 TextBanner 的资源 banner.txt
static final String DEFAULT_BANNER_LOCATION = "banner.txt";
// 支持的 ImageBanner 的类型
static final String[] IMAGE_EXTENSION = { "gif", "jpg", "png" };
// 默认的 Banner
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;
}
Banner print(Environment environment, Class<?> sourceClass, Log logger) {
// 加载Banner
Banner banner = getBanner(environment);
try {
logger.info(createStringFromBanner(banner, environment, sourceClass));
}
catch (UnsupportedEncodingException ex) {
logger.warn("Failed to create String for banner", ex);
}
return new PrintedBanner(banner, sourceClass);
}
Banner print(Environment environment, Class<?> sourceClass, PrintStream out) {
Banner banner = getBanner(environment);
banner.printBanner(environment, sourceClass, out);
return new PrintedBanner(banner, sourceClass);
}
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;
}
// 加载 TextBanner
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;
}
// 加载 ImageBanner
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;
}
}
package org.springframework.boot;
class SpringBootBanner implements Banner {
private static final String[] BANNER = {"",
" . ____ _ __ _ _",
" /\\\\ / ___'_ __ _ _(_)_ __ __ _ \\ \\ \\ \\",
"( ( )\\___ | '_ | '_| | '_ \\/ _` | \\ \\ \\ \\",
" \\\\/ ___)| |_)| | | | | || (_| | ) ) ) )",
" ' |____| .__|_| |_|_| |_\\__, | / / / /",
" =========|_|==============|___/=/_/_/_/"};
private static final String SPRING_BOOT = " :: Spring Boot :: ";
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();
}
}
本文叙述了Spring应用Banner的用法及原理，Banner可应用于描述应用的组织、功能或版本信息等。