springboot入口类

SpringApplication类

run方法进去看到

	public static ConfigurableApplicationContext run(Class<?> primarySource, String... args) {return run(new Class<?>[] { primarySource }, args);}public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {return new SpringApplication(primarySources).run(args);}

看到new SpringApplication

return new SpringApplication(primarySources).run(args);

进构造方法看

/*** Create a new {@link SpringApplication} instance. The application context will load* beans from the specified primary sources (see {@link SpringApplication class-level}* documentation for details. The instance can be customized before calling* {@link #run(String...)}.* @param primarySources the primary bean sources* @see #run(Class, String[])* @see #SpringApplication(ResourceLoader, Class...)* @see #setSources(Set)*/public SpringApplication(Class<?>... primarySources) {this(null, primarySources);}/*** Create a new {@link SpringApplication} instance. The application context will load* beans from the specified primary sources (see {@link SpringApplication class-level}* documentation for details. The instance can be customized before calling* {@link #run(String...)}.* @param resourceLoader the resource loader to use* @param primarySources the primary bean sources* @see #run(Class, String[])* @see #setSources(Set)*/@SuppressWarnings({ "unchecked", "rawtypes" })public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {this.resourceLoader = resourceLoader;Assert.notNull(primarySources, "PrimarySources must not be null");this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));this.webApplicationType = WebApplicationType.deduceFromClasspath();setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));this.mainApplicationClass = deduceMainApplicationClass();}

简单介绍流程

1.设置加载器 (当前流程为null)
2.传入的加载类 null判断
3.设置加载类,set去重
4.判断项目类型 NONE(非web),SERVLET(servlet web),REACTIVE(响应式 web)
5.设置程序上下文初始化器
6.设置监听器
7.推断出程序主入口类

	public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {//1.设置加载器this.resourceLoader = resourceLoader;//2.传入的加载类 null判断Assert.notNull(primarySources, "PrimarySources must not be null");//3.设置加载类,set去重this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));//4.根据依赖 判断项目类型 NONE(非web),SERVLET(servlet web),REACTIVE(响应式 web)this.webApplicationType = WebApplicationType.deduceFromClasspath();//5.设置应用程序上下文 初始化器setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));//6.设置监听器setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));//7.推断程序主入口类this.mainApplicationClass = deduceMainApplicationClass();}

主要方法介绍

WebApplicationType.deduceFromClasspath();

通过反射查找下列这几个类,来判断项目的类型,NONE(非web),SERVLET(servlet web),REACTIVE(响应式 web)

/*** The application should not run as a web application and should not start an* embedded web server.*/NONE,/*** The application should run as a servlet-based web application and should start an* embedded servlet web server.*/SERVLET,/*** The application should run as a reactive web application and should start an* embedded reactive web server.*/REACTIVE;private static final String[] SERVLET_INDICATOR_CLASSES = { "javax.servlet.Servlet","org.springframework.web.context.ConfigurableWebApplicationContext" };private static final String WEBMVC_INDICATOR_CLASS = "org.springframework.web.servlet.DispatcherServlet";private static final String WEBFLUX_INDICATOR_CLASS = "org.springframework.web.reactive.DispatcherHandler";private static final String JERSEY_INDICATOR_CLASS = "org.glassfish.jersey.servlet.ServletContainer";private static final String SERVLET_APPLICATION_CONTEXT_CLASS = "org.springframework.web.context.WebApplicationContext";private static final String REACTIVE_APPLICATION_CONTEXT_CLASS = "org.springframework.boot.web.reactive.context.ReactiveWebApplicationContext";static WebApplicationType deduceFromClasspath() {//isPresent.isPresent() 判断对应类是否存在 (基于反射Class.forName).  if (ClassUtils.isPresent(WEBFLUX_INDICATOR_CLASS, null) && !ClassUtils.isPresent(WEBMVC_INDICATOR_CLASS, null)&& !ClassUtils.isPresent(JERSEY_INDICATOR_CLASS, null)) {return WebApplicationType.REACTIVE;}for (String className : SERVLET_INDICATOR_CLASSES) {if (!ClassUtils.isPresent(className, null)) {return WebApplicationType.NONE;}}return WebApplicationType.SERVLET;}

getSpringFactoriesInstances(Class type);

这个方法在后续会频繁出现,就是通type去类路径下所有的 META-INF/spring.factories中找到对应需要加载的类然后通过反射创建实例

	private <T> Collection<T> getSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, Object... args) {//1.获取类加载器ClassLoader classLoader = getClassLoader();//2.获取type对应需要加载的类(所有spring.factories中获取)// Use names and ensure unique to protect against duplicatesSet<String> names = new LinkedHashSet<>(SpringFactoriesLoader.loadFactoryNames(type, classLoader));//3.根据Set<names>创建对象,(反射获取构造器然后创对象)List<T> instances = createSpringFactoriesInstances(type, parameterTypes, classLoader, args, names);//4.根据order排序AnnotationAwareOrderComparator.sort(instances);return instances;}

public static List<String> loadFactoryNames(Class<?> factoryType, @Nullable ClassLoader classLoader) {//获取限定名String factoryTypeName = factoryType.getName();return loadSpringFactories(classLoader).getOrDefault(factoryTypeName, Collections.emptyList());}//加载类路径下所有的 META-INF/spring.factories的内容 , 缓存起来private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {//缓存MultiValueMap<String, String> result = cache.get(classLoader);if (result != null) {return result;}try {//加载类路径下所有的 META-INF/spring.factoriesEnumeration<URL> urls = (classLoader != null ?classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));result = new LinkedMultiValueMap<>();while (urls.hasMoreElements()) {URL url = urls.nextElement();UrlResource resource = new UrlResource(url);Properties properties = PropertiesLoaderUtils.loadProperties(resource);for (Map.Entry<?, ?> entry : properties.entrySet()) {String factoryTypeName = ((String) entry.getKey()).trim();for (String factoryImplementationName : StringUtils.commaDelimitedListToStringArray((String) entry.getValue())) {result.add(factoryTypeName, factoryImplementationName.trim());}}}//缓存起来cache.put(classLoader, result);return result;}catch (IOException ex) {throw new IllegalArgumentException("Unable to load factories from location [" +FACTORIES_RESOURCE_LOCATION + "]", ex);}}

举例其中一个spring.factories, org.springframework.boot下的 其他的自己去对应包下看

# PropertySource Loaders
org.springframework.boot.env.PropertySourceLoader=\
org.springframework.boot.env.PropertiesPropertySourceLoader,\
org.springframework.boot.env.YamlPropertySourceLoader# Run Listeners
org.springframework.boot.SpringApplicationRunListener=\
org.springframework.boot.context.event.EventPublishingRunListener# Error Reporters
org.springframework.boot.SpringBootExceptionReporter=\
org.springframework.boot.diagnostics.FailureAnalyzers# Application Context Initializers
org.springframework.context.ApplicationContextInitializer=\
org.springframework.boot.context.ConfigurationWarningsApplicationContextInitializer,\
org.springframework.boot.context.ContextIdApplicationContextInitializer,\
org.springframework.boot.context.config.DelegatingApplicationContextInitializer,\
org.springframework.boot.rsocket.context.RSocketPortInfoApplicationContextInitializer,\
org.springframework.boot.web.context.ServerPortInfoApplicationContextInitializer# Application Listeners
org.springframework.context.ApplicationListener=\
org.springframework.boot.ClearCachesApplicationListener,\
org.springframework.boot.builder.ParentContextCloserApplicationListener,\
org.springframework.boot.cloud.CloudFoundryVcapEnvironmentPostProcessor,\
org.springframework.boot.context.FileEncodingApplicationListener,\
org.springframework.boot.context.config.AnsiOutputApplicationListener,\
org.springframework.boot.context.config.ConfigFileApplicationListener,\
org.springframework.boot.context.config.DelegatingApplicationListener,\
org.springframework.boot.context.logging.ClasspathLoggingApplicationListener,\
org.springframework.boot.context.logging.LoggingApplicationListener,\
org.springframework.boot.liquibase.LiquibaseServiceLocatorApplicationListener# Environment Post Processors
org.springframework.boot.env.EnvironmentPostProcessor=\
org.springframework.boot.cloud.CloudFoundryVcapEnvironmentPostProcessor,\
org.springframework.boot.env.SpringApplicationJsonEnvironmentPostProcessor,\
org.springframework.boot.env.SystemEnvironmentPropertySourceEnvironmentPostProcessor,\
org.springframework.boot.reactor.DebugAgentEnvironmentPostProcessor# Failure Analyzers
org.springframework.boot.diagnostics.FailureAnalyzer=\
org.springframework.boot.diagnostics.analyzer.BeanCurrentlyInCreationFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.BeanDefinitionOverrideFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.BeanNotOfRequiredTypeFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.BindFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.BindValidationFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.UnboundConfigurationPropertyFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.ConnectorStartFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.NoSuchMethodFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.NoUniqueBeanDefinitionFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.PortInUseFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.ValidationExceptionFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.InvalidConfigurationPropertyNameFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.InvalidConfigurationPropertyValueFailureAnalyzer# FailureAnalysisReporters
org.springframework.boot.diagnostics.FailureAnalysisReporter=\
org.springframework.boot.diagnostics.LoggingFailureAnalysisReporter

createSpringFactoriesInstances()通过类限定名反射创建实例

private <T> List<T> createSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes,ClassLoader classLoader, Object[] args, Set<String> names) {List<T> instances = new ArrayList<>(names.size());for (String name : names) {try {//根据名称获取对应Class对象Class<?> instanceClass = ClassUtils.forName(name, classLoader);//匹配类型 instanceClasss 是 type的子类Assert.isAssignable(type, instanceClass);//获取构造器Constructor<?> constructor = instanceClass.getDeclaredConstructor(parameterTypes);//根据构造器创建实例对象T instance = (T) BeanUtils.instantiateClass(constructor, args);instances.add(instance);}catch (Throwable ex) {throw new IllegalArgumentException("Cannot instantiate " + type + " : " + name, ex);}}return instances;}

deduceMainApplicationClass();

推断入口类,  通过当前方法的调用栈的数组 获取方法名为main的类的Class对象

	private Class<?> deduceMainApplicationClass() {try {//当前调用栈StackTraceElement[] stackTrace = new RuntimeException().getStackTrace();for (StackTraceElement stackTraceElement : stackTrace) {if ("main".equals(stackTraceElement.getMethodName())) {return Class.forName(stackTraceElement.getClassName());}}}catch (ClassNotFoundException ex) {// Swallow and continue}return null;}