>>>>> 附3 springboot源码解析 - 构建SpringApplication _application

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package com.microservice.framework; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; @SpringBootApplication public class MySpringAplication {public void run(String[] args) { SpringApplication sa = new SpringApplication(MySpringAplication.class); sa.run(args); }}

SpringBoot启动过程：
1、构建SpringApplication对象
2、执行run()
一、构建SpringApplication对象

/** * The application context will load beans from the specified sources */ public SpringApplication(Object... sources) { initialize(sources); }

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

private List< ApplicationContextInitializer< ?> > initializers; public void setInitializers( Collection< ? extends ApplicationContextInitializer< ?> > initializers) { this.initializers = new ArrayList< ApplicationContextInitializer< ?> > (); this.initializers.addAll(initializers); }private < T> Collection< ? extends T> getSpringFactoriesInstances(Class< T> type) { return getSpringFactoriesInstances(type, new Class< ?> [] {}); }private < T> Collection< ? extends T> getSpringFactoriesInstances(Class< T> type, Class< ?> [] parameterTypes, Object... args) { ClassLoader classLoader = Thread.currentThread().getContextClassLoader(); // Use names and ensure unique to protect against duplicates Set< String> names = new LinkedHashSet< String> ( SpringFactoriesLoader.loadFactoryNames(type, classLoader)); List< T> instances = new ArrayList< T> (names.size()); // Create instances from the names for (String name : names) { try { Class< ?> instanceClass = ClassUtils.forName(name, classLoader); Assert.isAssignable(type, instanceClass); Constructor< ?> constructor = instanceClass.getConstructor(parameterTypes); T instance = (T) constructor.newInstance(args); instances.add(instance); } catch (Throwable ex) { throw new IllegalArgumentException( "Cannot instantiate " + type + " : " + name, ex); } }AnnotationAwareOrderComparator.sort(instances); return instances; }

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：

/** * The location to look for factories. * < p> Can be present in multiple JAR files. */ public static final String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories"; /** * Load the fully qualified class names of factory implementations of the * given type from {@value #FACTORIES_RESOURCE_LOCATION}, using the given * class loader. */ public static List< String> loadFactoryNames(Class< ?> factoryClass, ClassLoader classLoader) { String factoryClassName = factoryClass.getName(); try { Enumeration< URL> urls = (classLoader != null ? classLoader.getResources(FACTORIES_RESOURCE_LOCATION) : ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION)); List< String> result = new ArrayList< String> (); while (urls.hasMoreElements()) { URL url = urls.nextElement(); Properties properties = PropertiesLoaderUtils.loadProperties(new UrlResource(url)); String factoryClassNames = properties.getProperty(factoryClassName); result.addAll(Arrays.asList(StringUtils.commaDelimitedListToStringArray(factoryClassNames))); } return result; } catch (IOException ex) { throw new IllegalArgumentException("Unable to load [" + factoryClass.getName() + "] factories from location [" + FACTORIES_RESOURCE_LOCATION + "]", ex); } }

META-INF/spring-factories

1 # Application Context Initializers 2 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：

从所有jar获取所有的META-INF/spring-factories文件。（这里只有spring-boot-1.3.0.RELEASE.jar下有一个）
遍历每一个spring-factories文件，并获取其下key为factoryClass.getName()（这里是入参org.springframework.context.ApplicationContextInitializer）的value（这里有以上四个ApplicationContextInitializer实现类）

以上四个类的作用：

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【> > > > > 附3 springboot源码解析 - 构建SpringApplication】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

private List< ApplicationListener< ?> > listeners; /** * Sets the {@link ApplicationListener}s that will be applied to the SpringApplication * and registered with the {@link ApplicationContext}. * @param listeners the listeners to set */ public void setListeners(Collection< ? extends ApplicationListener< ?> > listeners) { this.listeners = new ArrayList< ApplicationListener< ?> > (); this.listeners.addAll(listeners); }

META-INF/spring-factories

# Application Listeners org.springframework.context.ApplicationListener=org.springframework.boot.builder.ParentContextCloserApplicationListener,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.liquibase.LiquibaseServiceLocatorApplicationListener,org.springframework.boot.logging.ClasspathLoggingApplicationListener,org.springframework.boot.logging.LoggingApplicationListener

以上八个listener的作用如下：

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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

private Class< ?> mainApplicationClass; private Class< ?> deduceMainApplicationClass() { try { 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; }

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