Banner 特性是通过自定义的 banner.txt 文件,替换启动时打印的横幅。除了文字之外,还可以使用 banner.gif,banner.jpg、banner.png 图像文件,将图像转换为 ASCII 艺术作品进行打印。
举个例子
application.properties
# Banner
application.version=0.0.1
application.formatted-version=v0.0.1
spring-boot.version=2.2.6.RELEASE
spring-boot.formatted-version=v2.2.6.RELEASE
application.title=\u8fd9\u662f\u4e2a\u0020\u0044\u0065\u006d\u006f\u0020\u5de5\u7a0b
banner.txt
. ____ _ __ _ _
/\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
\\/ ___)| |_)| | | | | || (_| | ) ) ) )
' |____| .__|_| |_|_| |_\__, | / / / /
=========|_|==============|___/=/_/_/_/
Application Title: ${application.title}
Application Version: ${application.version} [${application.formatted-version}]
Spring Boot Version: ${spring-boot.version} [${spring-boot.formatted-version}]
日志输出
. ____ _ __ _ _
/\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
\\/ ___)| |_)| | | | | || (_| | ) ) ) )
' |____| .__|_| |_|_| |_\__, | / / / /
=========|_|==============|___/=/_/_/_/
Application Title: 这是个 Demo 工程
Application Version: 0.0.1 [v0.0.1]
Spring Boot Version: 2.2.6.RELEASE [v2.2.6.RELEASE]
...
Application context initialized!!!
启动顺序剖析
Application.java
public ConfigurableApplicationContext run(String... args) {
...
Banner printedBanner = printBanner(environment);
...
private Banner printBanner(ConfigurableEnvironment environment) {
if (this.bannerMode == Banner.Mode.OFF) {
return null;
}
ResourceLoader resourceLoader = (this.resourceLoader != null) ? this.resourceLoader
: new DefaultResourceLoader(getClassLoader());
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);
}
源代码剖析
Banner.java
@FunctionalInterface
public interface Banner {
void printBanner(Environment environment, Class<?> sourceClass, PrintStream out);
enum Mode {
OFF,
CONSOLE,
LOG
}
}
Banner 接口都有哪些实现类
其中,SpringBootBanner、ResourceBanner、ImageBanner 三个类内容比较简单,本文就不再展开叙述。
有兴趣的小伙伴,可以自行阅读 ResourceBanner(如何读取文本资源)、以及 ImageBanner(如何读取并处理图像资源)的代码。
SpringApplicationBannerPrinter.java
SpringApplicationBannerPrinter 是 Spring 应用程序用来打印 Banner 信息的类。
整个文件不到 100 多行的代码量。为了方便剖析,我把代码拆解成以下多份内容。
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;
}
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;
}
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;
}
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;
}
private 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();
}
@Override
public void printBanner(Environment environment, Class<?> sourceClass, PrintStream out) {
for (Banner banner : this.banners) {
banner.printBanner(environment, sourceClass, out);
}
}
}
Banner print(Environment environment, Class<?> sourceClass, Log logger) {
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 String createStringFromBanner(Banner banner, Environment environment, Class<?> mainApplicationClass)
throws UnsupportedEncodingException {
ByteArrayOutputStream baos = new ByteArrayOutputStream();
banner.printBanner(environment, mainApplicationClass, new PrintStream(baos));
String charset = environment.getProperty("spring.banner.charset", "UTF-8");
return baos.toString(charset);
}
private static class PrintedBanner implements Banner {
private final Banner banner;
private final Class<?> sourceClass;
PrintedBanner(Banner banner, Class<?> sourceClass) {
this.banner = banner;
this.sourceClass = sourceClass;
}
@Override
public void printBanner(Environment environment, Class<?> sourceClass, PrintStream out) {
sourceClass = (sourceClass != null) ? sourceClass : this.sourceClass;
this.banner.printBanner(environment, sourceClass, out);
}
}
总结
用一句话来概括,当 Spring 应用程序启动时,读取资源文件信息并打印在命令行或日志文件中。
每天阅读一点点源代码,加油。