上篇回顧
上一篇prepareEnvironment()準備環境主要分析了StandardServletEnvironment的創建, 以及系統屬性, 環境變量, 配置文件等屬性文件的加載順序
目錄
1. 打印Banner printBanner()
2. SpringApplicationBannerPrinter
3. 總結
1. 打印Banner printBanner()
- 實例化ResourceLoader, 默認為null, 所以實例化一個DefaultResourceLoader
- 實例化一個SpringApplicationBannerPrinter對象
- 調用SpringApplicationBannerPrinter的print方法
public class SpringApplication {
public ConfigurableApplicationContext run(String... args) {
StopWatch stopWatch = new StopWatch();
stopWatch.start();
ConfigurableApplicationContext context = null;
Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
configureHeadlessProperty();
SpringApplicationRunListeners listeners = getRunListeners(args);
listeners.starting();
try {
ApplicationArguments applicationArguments = new DefaultApplicationArguments(
args);
ConfigurableEnvironment environment = prepareEnvironment(listeners,
applicationArguments);
configureIgnoreBeanInfo(environment);
//本文的重點
//打印Banner
Banner printedBanner = printBanner(environment);
//....
}
//打印Banner
private Banner printBanner(ConfigurableEnvironment environment) {
//如果Mode為OFF
//那么不打印Banner
if (this.bannerMode == Banner.Mode.OFF) {
return null;
}
//ResourceLoader資源加載類
//默認為DefaultResourceLoader
ResourceLoader resourceLoader = (this.resourceLoader != null)
? this.resourceLoader : new DefaultResourceLoader(getClassLoader());
//實例化一個SpringApplicationBannerPrinter
SpringApplicationBannerPrinter bannerPrinter = new SpringApplicationBannerPrinter(
resourceLoader, this.banner);
//調用SpringApplicationBannerPrinter#print方法打印Banner
if (this.bannerMode == Mode.LOG) {
//日志打印Banner
return bannerPrinter.print(environment, this.mainApplicationClass, logger);
}
//控制臺打印Banner
return bannerPrinter.print(environment, this.mainApplicationClass, System.out);
}
}
2. SpringApplicationBannerPrinter
SpringApplicationBannerPrinter打印banner過程分為5步
- 加載圖片Banner
- 先加載spring.banner.image.location指定的圖片Banner
- 不存在的話, 分別取加載classpath下banner.gif, banner.jpg和banner.png
- 實例化為ImageBanner, 維護到Banners對象中
- 加載文本Banner
- 先加載spring.banner.location指定的文本banner
- 不存在的話, 加載classpath下的banner.txt文本
- 實例化一個ResourceBanner, 維護到Banners對象中
- 圖片和文本Banner都不存在的話, 如果通過構造函數, 傳入了fallbackBanner, 那么返回fallbackBanner
- 圖片, 文本和fallbackBanner都不存在, 那么返回默認的SpringBootBanner
- 打印Banner, 返回一個PrintedBanner
- 如果Banners列表中同時存在圖片和文本Banner,那么都會打印出來
class SpringApplicationBannerPrinter {
//文本banner位置
static final String BANNER_LOCATION_PROPERTY = "spring.banner.location";
//圖片banner位置
static final String BANNER_IMAGE_LOCATION_PROPERTY = "spring.banner.image.location";
//默認banner名稱
static final String DEFAULT_BANNER_LOCATION = "banner.txt";
//支持的圖片擴展名
static final String[] IMAGE_EXTENSION = { "gif", "jpg", "png" };
//默認banner類
private static final Banner DEFAULT_BANNER = new SpringBootBanner();
//日志打印Banner
public Banner print(Environment environment, Class<?> sourceClass, Log logger) {
//獲取banner
Banner banner = getBanner(environment);
try {
//打印Banner
logger.info(createStringFromBanner(banner, environment, sourceClass));
}
catch (UnsupportedEncodingException ex) {
logger.warn("Failed to create String for banner", ex);
}
return new PrintedBanner(banner, sourceClass);
}
//控制臺打印Banner
public Banner print(Environment environment, Class<?> sourceClass, PrintStream out) {
//獲取到Banners對象, 其中維護了Banner列表
//如果Banners中沒有對象, 那么判斷fallbackBanner
//如果都沒有的話,返回默認的SpringBootBanner
Banner banner = getBanner(environment);
//一次打印Banner
banner.printBanner(environment, sourceClass, out);
return new PrintedBanner(banner, sourceClass);
}
//獲取Banner
//Banners類保存多個banner列表
private Banner getBanner(Environment environment) {
//獲取Banners列表
Banners banners = new Banners();
//添加ImageBanner
banners.addIfNotNull(getImageBanner(environment));
//添加TextBanner
banners.addIfNotNull(getTextBanner(environment));
if (banners.hasAtLeastOneBanner()) {
//如果有自定義Banner,則立即返回
return banners;
}
if (this.fallbackBanner != null) {
//如果構造函數傳參過來
//也就是通過java自定義了fallbackBanner
//那么返回fallbackBanner
return this.fallbackBanner;
}
//如果沒有的話, 返回默認Banner, SpringBootBanner
return DEFAULT_BANNER;
}
//獲取文本banner
private Banner getTextBanner(Environment environment) {
//優先獲取spring.banner.location指定的banner位置
//然后查找classpath下的banner.txt
String location = environment.getProperty(BANNER_LOCATION_PROPERTY,
DEFAULT_BANNER_LOCATION);
Resource resource = this.resourceLoader.getResource(location);
if (resource.exists()) {
//存在的話,立即返回ResourceBanner
return new ResourceBanner(resource);
}
//都沒有的話,返回null
return null;
}
//獲取圖片banner
private Banner getImageBanner(Environment environment) {
//優先獲取spring.banner.image.location指定的圖片banner
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) {
//如果沒有指定spring.banner.image.location
//那么查找classpath下的banner.jpg, banner.png, banner.gif
Resource resource = this.resourceLoader.getResource("banner." + ext);
if (resource.exists()) {
//有一個存在的話,立即返回該Banner
return new ImageBanner(resource);
}
}
//都不存在的話返回null
return null;
}
}
3. 總結
打印Banner執行步驟如下:
- 首先加載圖片Banner
- 然后加載文本Banner
- 再判斷fallbackBanner
- 最后返回默認的SpringBootBanner
- 打印Banner, 返回一個PrintedBanner對象
下一篇
我們將會在下一篇createApplicationContext()創建應用上下文, 繼續閱讀springboot源碼
