springboot 啓動時是如何打印banner的, 以及如何配置一個自己的banner
入口方法
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);
}
printBanner是banner打印的入口方法, 該方法根據不同的Banner.Mode爲枚舉類型, 值有OFF, CONSOLE, LOG, 分別對應不打印, 控制檯輸出, 輸出到日誌文件.
對於CONSOLE和LOG類型需要通過ResourceLoader resourceLoader加載banner資源. banner打印需要通過SpringApplicationBannerPrinter類中的print方法(重載)進行處理, 對於CONSOLE類型, 第三個參數爲PrintStream類型, 傳入System.out進行處理, LOG類型則通過日誌對象logger(其定義爲private static final Log logger = LogFactory.getLog(SpringApplication.class);)進行處理. 不過兩個重載方法邏輯是一致的.
以CONSOLE類型爲例, 其代碼爲:
Banner print(Environment environment, Class<?> sourceClass, PrintStream out) {
Banner banner = getBanner(environment);
banner.printBanner(environment, sourceClass, out);
return new PrintedBanner(banner, sourceClass);
}
首先要獲取一個Banner對象(函數式), 調用打印方法printBanner輸出banner, 打印完畢, 構造一個PrintedBanner繼承於Banner返回.
下面具體看一下getBanner方法:
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;
}
Banners類是Banner接口的實現, 內部維護一個private final List<Banner> banners = new ArrayList<>();用來存放所有的Banner, 該類也重寫printBanner爲:
@Override
public void printBanner(Environment environment, Class<?> sourceClass, PrintStream out) {
for (Banner banner : this.banners) {
banner.printBanner(environment, sourceClass, out);
}
}
即: 將banners中的banner對象全部打印. 而banners中的banner來自於getImageBanner和getTextBanner加載的資源. 下面分別來看一下這兩個方法.
getImageBanner
static final String BANNER_IMAGE_LOCATION_PROPERTY = "spring.banner.image.location";
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;
}
BANNER_IMAGE_LOCATION_PROPERTY配置用來表示圖片類型banner資源的加載位置, 之後resourceLoader會生成一個對應位置資源的操作對象Resource resource.
如果該位置下存在資源則返回ImageBanner類型的對象, 該類也是Banner的一個實現.
如果沒有定義BANNER_IMAGE_LOCATION_PROPERTY則resourceLoader加載以banner爲前綴, "gif", "jpg", "png"等格式的文件. 如果存在則直接返回一個ImageBanner類型的對象.
注意如果不存在由於addIfNotNull會判斷Banner是否爲null, 是則不會將其放入banners中.
getTextBanner
static final String BANNER_LOCATION_PROPERTY = "spring.banner.location";
static final String DEFAULT_BANNER_LOCATION = "banner.txt";
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;
}
此時會從BANNER_LOCATION_PROPERTY出加載banner.txt文件, 並返回ResourceBanner對象.
對於一個默認的系統配置, 無法加載圖片和文本banner此時直接返回一個默認的DEFAULT_BANNER, 其爲SpringBootBanner類型. 該類定義如下, 可以看到BANNER爲系統的默認
輸出.
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();
}
}
自定義banner
從上面的分析我們可知, banner有三種形式:
- 圖片
ImageBanner, banner是在spring.banner.image.location位置下的, 或者是默認路徑下的banner.png|gif|jpg文件 - 文本
ResourceBanner, banner是在spring.banner.location位置下的, 或者是默認路徑下的banner.txt文件. - 系統默認
SpringBootBanner, banner樣式是寫在一個String數組中的
對於圖片, 在資源目錄下添加一個banner.png文件, 運行:
另外springboot還提供了圖片打印的一些參數控制, 比如長度,寬度,bitdepth(值爲4, 8, 分別只16色和256色), pixelmode(值爲block, 默認text, 分別對應方塊輸出和字符畫)
一通配置之後的打印banner.
那麼, 這些參數又是在什麼時候生效的呢? 這就要看ImageBanner中重寫的printBanner
下面的方法是核心方法, 就不分析了.
private void printBanner(Environment environment, PrintStream out) throws IOException {
int width = getProperty(environment, "width", Integer.class, 76);
int height = getProperty(environment, "height", Integer.class, 0);
int margin = getProperty(environment, "margin", Integer.class, 2);
boolean invert = getProperty(environment, "invert", Boolean.class, false);
BitDepth bitDepth = getBitDepthProperty(environment);
PixelMode pixelMode = getPixelModeProperty(environment);
Frame[] frames = readFrames(width, height);
for (int i = 0; i < frames.length; i++) {
if (i > 0) {
resetCursor(frames[i - 1].getImage(), out);
}
printBanner(frames[i].getImage(), margin, invert, bitDepth, pixelMode, out);
sleep(frames[i].getDelayTime());
}
}
對於文本, 在資源目錄下添加banner.txt文件. 運行:
