1 package com.microservice.framework; 2 3 import org.springframework.boot.SpringApplication; 4 import org.springframework.boot.autoconfigure.SpringBootApplication; 5 6 @SpringBootApplication 7 public class MySpringAplication { 8 9 public void run(String[] args) {10 SpringApplication sa = new SpringApplication(MySpringAplication.class);11 sa.run(args);12 }13 14 }SpringBoot启动过程：
1、构建SpringApplication对象
2、执行run()
一、构建SpringApplication对象
1 /**2 * The application context will load beans from the specified sources 3 */4 public SpringApplication(Object... sources) {5 initialize(sources);6 }说明：
- 实例化该类的时候会加载bean到applicationContext中去
- 这里的入参是MySpringApplication.class这样一个Class<com.microservice.framework.MySpringApplication>对象
private final Set<Object> sources = new LinkedHashSet<Object>(); private boolean webEnvironment; private Class<?> mainApplicationClass; private void initialize(Object[] sources) { if (sources != null && sources.length > 0) { this.sources.addAll(Arrays.asList(sources)); } this.webEnvironment = deduceWebEnvironment(); setInitializers((Collection) getSpringFactoriesInstances( ApplicationContextInitializer.class)); setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class)); this.mainApplicationClass = deduceMainApplicationClass(); }步骤：
- 将传入的MySpringApplication.class对象放入Set集合
- 判断是否是web环境
- 创建ApplicationInitializer列表
- 初始化ApplicationListener列表
- 初始化主类mainApplicationClass
1.1、将传入的MySpringApplication.class对象放入Set集合
1.2、判断是否是web环境：
private static final String[] WEB_ENVIRONMENT_CLASSES = { "javax.servlet.Servlet", "org.springframework.web.context.ConfigurableWebApplicationContext" }; private boolean deduceWebEnvironment() { for (String className : WEB_ENVIRONMENT_CLASSES) { if (!ClassUtils.isPresent(className, null)) { return false; } } return true; }说明：通过在classpath中查看是否存在WEB_ENVIRONMENT_CLASSES这个数组中所包含的所有类（实际上就是2个类），如果存在那么当前程序即是一个Web应用程序，反之则不然。
1.3、创建ApplicationContextInitializer列表
1 private List<ApplicationContextInitializer<?>> initializers; 2 3 public void setInitializers( 4 Collection<? extends ApplicationContextInitializer<?>> initializers) { 5 this.initializers = new ArrayList<ApplicationContextInitializer<?>>(); 6 this.initializers.addAll(initializers); 7 } 8 9 private <T> Collection<? extends T> getSpringFactoriesInstances(Class<T> type) {10 return getSpringFactoriesInstances(type, new Class<?>[] {});11 }12 13 private <T> Collection<? extends T> getSpringFactoriesInstances(Class<T> type,14 Class<?>[] parameterTypes, Object... args) {15 ClassLoader classLoader = Thread.currentThread().getContextClassLoader();16 17 // Use names and ensure unique to protect against duplicates18 Set<String> names = new LinkedHashSet<String>(19 SpringFactoriesLoader.loadFactoryNames(type, classLoader));20 List<T> instances = new ArrayList<T>(names.size());21 22 // Create instances from the names23 for (String name : names) {24 try {25 Class<?> instanceClass = ClassUtils.forName(name, classLoader);26 Assert.isAssignable(type, instanceClass);27 Constructor<?> constructor = instanceClass.getConstructor(parameterTypes);28 T instance = (T) constructor.newInstance(args);29 instances.add(instance);30 }31 catch (Throwable ex) {32 throw new IllegalArgumentException(33 "Cannot instantiate " + type + " : " + name, ex);34 }35 }36 37 AnnotationAwareOrderComparator.sort(instances);38 return instances;39 }步骤：
- 调用SpringFactoriesLoader.loadFactoryNames(type, classLoader)来获取所有Spring Factories的名字，（这里是获取了四个ApplicationContextInitializer实现类的全类名，见下边）
- 为每一个Spring Factories根据读取到的名字创建其对象。（这里创建了4个对象）
- 将创建好的对象列表排序并返回。
其中，SpringFactoriesLoader.loadFactoryNames(type, classLoader)如下：
1 /** 2 * The location to look for factories. 3 * <p>Can be present in multiple JAR files. 4 */ 5 public static final String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories"; 6 7 /** 8 * Load the fully qualified class names of factory implementations of the 9 * given type from {@value #FACTORIES_RESOURCE_LOCATION}, using the given10 * class loader.11 */12 public static List<String> loadFactoryNames(Class<?> factoryClass, ClassLoader classLoader) {13 String factoryClassName = factoryClass.getName();14 try {15 Enumeration<URL> urls = (classLoader != null ? classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :16 ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));17 List<String> result = new ArrayList<String>();18 while (urls.hasMoreElements()) {19 URL url = urls.nextElement();20 Properties properties = PropertiesLoaderUtils.loadProperties(new UrlResource(url));21 String factoryClassNames = properties.getProperty(factoryClassName);22 result.addAll(Arrays.asList(StringUtils.commaDelimitedListToStringArray(factoryClassNames)));23 }24 return result;25 }26 catch (IOException ex) {27 throw new IllegalArgumentException("Unable to load [" + factoryClass.getName() +28 "] factories from location [" + FACTORIES_RESOURCE_LOCATION + "]", ex);29 }30 }META-INF/spring-factories
1 # Application Context Initializers2 org.springframework.context.ApplicationContextInitializer=\3 org.springframework.boot.context.ConfigurationWarningsApplicationContextInitializer,\4 org.springframework.boot.context.ContextIdApplicationContextInitializer,\5 org.springframework.boot.context.config.DelegatingApplicationContextInitializer,\6 org.springframework.boot.context.web.ServerPortInfoApplicationContextInitializer
说明：
以上四个类的作用：
至此，设置ApplicationContextInitialize就完成了。
总结：整个setInitializers实际上就是初始化了SpringApplication的属性List<ApplicationContextInitializer<?>> initializers为一个ArrayList列表，该列表中有四个实例：
- ConfigurationWarningsApplicationContextInitializer的实例
- ContextIdApplicationContextInitializer的实例
- DelegatingApplicationContextInitializer实例
- ServerPortInfoApplicationContextInitializer实例
1.4、初始化ApplicationListener列表
1 private List<ApplicationListener<?>> listeners; 2 3 /** 4 * Sets the {@link ApplicationListener}s that will be applied to the SpringApplication 5 * and registered with the {@link ApplicationContext}. 6 * @param listeners the listeners to set 7 */ 8 public void setListeners(Collection<? extends ApplicationListener<?>> listeners) { 9 this.listeners = new ArrayList<ApplicationListener<?>>();10 this.listeners.addAll(listeners);11 } META-INF/spring-factories
1 # Application Listeners 2 org.springframework.context.ApplicationListener=\ 3 org.springframework.boot.builder.ParentContextCloserApplicationListener,\ 4 org.springframework.boot.context.FileEncodingApplicationListener,\ 5 org.springframework.boot.context.config.AnsiOutputApplicationListener,\ 6 org.springframework.boot.context.config.ConfigFileApplicationListener,\ 7 org.springframework.boot.context.config.DelegatingApplicationListener,\ 8 org.springframework.boot.liquibase.LiquibaseServiceLocatorApplicationListener,\ 9 org.springframework.boot.logging.ClasspathLoggingApplicationListener,\10 org.springframework.boot.logging.LoggingApplicationListener
以上八个listener的作用如下：
至此，整个setListeners方法结束，初始化了一个包含以上8个ApplicationListener实例的List集合。
1.5、初始化主类mainApplicationClass
1 private Class<?> mainApplicationClass; 2 3 private Class<?> deduceMainApplicationClass() { 4 try { 5 StackTraceElement[] stackTrace = new RuntimeException().getStackTrace(); 6 for (StackTraceElement stackTraceElement : stackTrace) { 7 if ("main".equals(stackTraceElement.getMethodName())) { 8 return Class.forName(stackTraceElement.getClassName()); 9 }10 }11 }12 catch (ClassNotFoundException ex) {13 // Swallow and continue14 }15 return null;16 }说明：获取main()方法所在的主类Class对象，并赋值给SpringApplication的mainApplicationClass属性。
至此，SpringApplication对象初始化完成了。
总结：整个SpringApplication初始化的过程，就是初始化了
- 一个包含入参MySpringApplication.class的sources的Set<Object>
- 一个当前环境是否是web环境的boolean webEnvironment
- 一个包含4个ApplicationContextInitializer实例的List
- 一个包含8个ApplicationListener实例的List
- 一个main方法所在的主类的Class对象。
注意：
本文基本参照http://zhaox.github.io/java/2016/03/22/spring-boot-start-flow 完成，该文的作者已经解析的很好了，我这里再抄一遍，只是为了加深记忆！！！
原标题：附3 springboot源码解析
关键词：Spring
我知道了 