SpringBoot 启动方法run()源码赏析

ゝ一纸荒年。 2022-12-26 00:51 195阅读 0赞

入口  
通常一个简单的SpringBoot基础项目我们会有如下代码

@SpringBootApplication
    @RestController
    @RequestMapping("/")
    public class Application { 
    
    	public static void main(String[] args) { 
    		SpringApplication.run(Application.class, args);
    	}
    
    }

值得关注的有SpringApplication.run以及注解@SpringBootApplication

## run方法 ##

public ConfigurableApplicationContext run(String... args) { 
    	    // 秒表
    		StopWatch stopWatch = new StopWatch();
    		stopWatch.start();
    		ConfigurableApplicationContext context = null;
    		Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
    		configureHeadlessProperty();
    		// 获取监听器
    		SpringApplicationRunListeners listeners = getRunListeners(args);
    		// 监听器启动
    		listeners.starting();
    		try { 
    		    // application 启动参数列表
    			ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
    			ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
    			// 配置忽略的bean信息
    			configureIgnoreBeanInfo(environment);
    			Banner printedBanner = printBanner(environment);
    			// 创建应用上下文
    			context = createApplicationContext();
    			exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,
    					new Class[] {  ConfigurableApplicationContext.class }, context);
    		    // 准备上下文，装配bean
    			prepareContext(context, environment, listeners, applicationArguments, printedBanner);
    			// 上下文刷新
    			refreshContext(context);
    			// 刷新后做什么
    			afterRefresh(context, applicationArguments);
    			stopWatch.stop();
    			if (this.logStartupInfo) { 
    				new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
    			}
    			// 监听器开始了
    			listeners.started(context);
    			// 唤醒
    			callRunners(context, applicationArguments);
    		}
    		catch (Throwable ex) { 
    			handleRunFailure(context, ex, exceptionReporters, listeners);
    			throw new IllegalStateException(ex);
    		}
    
    		try { 
    		    // 监听器正式运行
    			listeners.running(context);
    		}
    		catch (Throwable ex) { 
    			handleRunFailure(context, ex, exceptionReporters, null);
    			throw new IllegalStateException(ex);
    		}
    		return context;
    	}

## getRunListeners ##

获取监听器

private SpringApplicationRunListeners getRunListeners(String[] args) { 
    		Class<?>[] types = new Class<?>[] {  SpringApplication.class, String[].class };
    		// 获取 Spring Factory 实例对象
    		return new SpringApplicationRunListeners(logger,
    				getSpringFactoriesInstances(SpringApplicationRunListener.class, types, this, args));
    	}
    
    
    	private <T> Collection<T> getSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, Object... args) { 
    		ClassLoader classLoader = getClassLoader();
    		// Use names and ensure unique to protect against duplicates
    		// 读取 spring.factories
    		Set<String> names = new LinkedHashSet<>(SpringFactoriesLoader.loadFactoryNames(type, classLoader));
    		// 创建SpringFactory实例
    		List<T> instances = createSpringFactoriesInstances(type, parameterTypes, classLoader, args, names);
    		/** * 排序 {@link Ordered} */
    		AnnotationAwareOrderComparator.sort(instances);
    		return instances;
    	}

createSpringFactoriesInstances

@SuppressWarnings("unchecked")
       private <T> List<T> createSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes,
       		ClassLoader classLoader, Object[] args, Set<String> names) { 
           // 初始化
       	List<T> instances = new ArrayList<>(names.size());
       	for (String name : names) { 
       		try { 
       		    // 通过名字创建类的class对象
       			Class<?> instanceClass = ClassUtils.forName(name, classLoader);
       			Assert.isAssignable(type, instanceClass);
       			// 构造器获取
       			Constructor<?> constructor = instanceClass.getDeclaredConstructor(parameterTypes);
       			// 创建具体实例
       			T instance = (T) BeanUtils.instantiateClass(constructor, args);
       			// 加入实例表中
       			instances.add(instance);
       		}
       		catch (Throwable ex) { 
       			throw new IllegalArgumentException("Cannot instantiate " + type + " : " + name, ex);
       		}
       	}
       	return instances;
       }

## printBanner ##

private Banner printBanner(ConfigurableEnvironment environment) { 
    		if (this.bannerMode == Banner.Mode.OFF) { 
    			return null;
    		}
    		ResourceLoader resourceLoader = (this.resourceLoader != null) ? this.resourceLoader
    				: new DefaultResourceLoader(getClassLoader());
    		// 创建打印器
    		SpringApplicationBannerPrinter bannerPrinter = new SpringApplicationBannerPrinter(resourceLoader, this.banner);
    		if (this.bannerMode == Mode.LOG) { 
    		    // 输出
    			return bannerPrinter.print(environment, this.mainApplicationClass, logger);
    		}
            // 输出
    		return bannerPrinter.print(environment, this.mainApplicationClass, System.out);
    	}
    	Banner print(Environment environment, Class<?> sourceClass, PrintStream out) { 
    		Banner banner = getBanner(environment);
    		banner.printBanner(environment, sourceClass, out);
    		return new PrintedBanner(banner, sourceClass);
    	}

最终输出内容类：org.springframework.boot.SpringBootBanner

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();
    	}
    
    }

希望通过本篇对于springboot启动方法的解读，让大家对springboot底层有了一个大致了解，只分析了主要方法，希望对大家有帮助  
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