SpringBoot应用启动过程分析

SpringBoot应用启动过程分析

SpringBoot项目通过SpringApplication.run(App.class, args)来启动：

@Configuration

public class App {

public static void main(String[] args) {

SpringApplication.run(App.class, args);

}

}

接下来，通过源码来看看SpringApplication.run()方法的执行过程。如果对源码不感兴趣，直接下拉到文章末尾，看启动框图。

1、调用SpringApplication类的静态方法

public static ConfigurableApplicationContext run(Object source, String... args) {

return run(new Object[] { source }, args);

}

public static ConfigurableApplicationContext run(Object[] sources, String[] args) {

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

}

2、SpringApplication对象初始化

public SpringApplication(Object... sources) {

initialize(sources);

}

@SuppressWarnings({ "unchecked", "rawtypes" })

private void initialize(Object[] sources) {

if (sources != null && sources.length > 0) {

this.sources.addAll(Arrays.asList(sources));

}

// 判断是否为WEB环境

this.webEnvironment = deduceWebEnvironment();

// 找到META-INF/spring.factories中ApplicationContextInitializer所有实现类，并将其实例化

setInitializers((Collection) getSpringFactoriesInstances(

ApplicationContextInitializer.class));

// 找到META-INF/spring.factories中ApplicationListener所有实现类，并将其实例化

setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));

// 获取当前main方法类对象，即测试类中的App实例

this.mainApplicationClass = deduceMainApplicationClass();

}

对象初始化过程中，使用到了getSpringFactoriesInstances方法：

private Collection extends T> getSpringFactoriesInstances(Class type) {

return getSpringFactoriesInstances(type, new Class>[] {});

}

private Collection extends T> getSpringFactoriesInstances(Class type,

Class>[] parameterTypes, Object... args) {

ClassLoader classLoader = Thread.currentThread().getContextClassLoader();

// Use names and ensure unique to protect against duplicates

// 读取META-INF/spring.factories指定接口的实现类

Set names = new LinkedHashSet(

SpringFactoriesLoader.loadFactoryNames(type, classLoader));

List instances = createSpringFactoriesInstances(type, parameterTypes,

classLoader, args, names);

AnnotationAwareOrderComparator.sort(instances);

return instances;

}

@SuppressWarnings("unchecked")

private List createSpringFactoriesInstances(Class type,

Class>[] parameterTypes, ClassLoader classLoader, Object[] args,

Set names) {

List instances = new ArrayList(names.size());

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);

}

}

return instances;

}

// 读取META-INF/spring.factories文件

public static List loadFactoryNames(Class> factoryClass, ClassLoader classLoader) {

String factoryClassName = factoryClass.getName();

try {

Enumeration urls = (classLoader != null ? classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :

ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));

List result = new ArrayList();

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文件内容，spring boot版本1.3.6.RELEASE

# 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

# 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.context.web.ServerPortInfoApplicationContextInitializer

# 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

# Environment Post Processors

org.springframework.boot.env.EnvironmentPostProcessor=\

org.springframework.boot.cloud.CloudFoundryVcapEnvironmentPostProcessor,\

org.springframework.boot.env.SpringApplicationjsonEnvironmentPostProcessor

ApplicationListener接口是Spring框架的事件监听器，其作用可理解为SpringApplicationRunListener发布通知事件时，由ApplicationListener负责接收。SpringApplicationRunListener接口的实现类就是EventPublishingRunListener，其在SpringBoot启动过程中，负责注册ApplicationListener监听器，在不同时间节点发布不同事件类型，如果有ApplicationListener实现类监听了该事件，则接收处理。

public interface SpringApplicationRunListener {

/**

* 通知监听器，SpringBoot开始启动

*/

void started();

/**

* 通知监听器，环境配置完成

*/

void environmentPrepared(ConfigurableEnvironment environment);

/**

* 通知监听器，ApplicationContext已创建并初始化完成

*/

void contextPrepared(ConfigurableApplicationContext context);

/**

* 通知监听器，ApplicationContext已完成IOC配置

*/

void contextLoaded(ConfigurableApplicationContext context);

/**

* 通知监听器，SpringBoot开始完毕

*/

void finished(ConfigurableApplicationContext context, Throwable exception);

}

附图为ApplicationListener监听接口实现类，每个类对应了一种事件。

3、SpringApplication核心run方法

/**

* Run the Spring application, creating and refreshing a new

* {@link ApplicationContext}.

* @param args the application arguments (usually passed from a java main method)

* @return a running {@link ApplicationContext}

*/

public ConfigurableApplicationContext run(String... args) {

// 任务执行时间监听，记录起止时间差

StopWatch stopWatch = new StopWatch();

stopWatch.start();

ConfigurableApplicationContext context = null;

configureHeadlessProperty();

// 启动SpringApplicationRunListener监听器

SpringApplicationRunListeners listeners = getRunListeners(args);

listeners.started();

try {

ApplicationArguments applicationArguments = new DefaultApplicationArguments(

args);

// 创建并刷新ApplicationContext

context = createAndRefreshContext(listeners, applicationArguments);

afterRefresh(context, applicationArguments);

// 通知监听器，应用启动完毕

listeners.finished(context, null);

stopWatch.stop();

if (this.logStartupInfo) {

new StartupInfoLogger(this.mainApplicationClass)

.logStarted(getApplicationLog(), stopWatch);

}

return context;

}

catch (Throwable ex) {

handleRunFailure(context, listeners, ex);

throw new IllegalStateException(ex);

}

}

这里，需要看看createAndRefreshContext()方法是如何创建并刷新ApplicationContext。

private ConfigurableApplicationContext createAndRefreshContext(

SpringApplicationRunListeners listeners,

ApplicationArguments applicationArguments) {

ConfigurableApplicationContext context;

// Create and configure the environment

// 创建并配置运行环境，WebEnvironment与StandardEnvironment选其一

ConfigurableEnvironment environment = getOrCreateEnvironment();

configureEnvironment(environment, applicationArguments.getSourceArgs());

listeners.environmentPrepared(environment);

if (isWebEnvironment(environment) && !this.webEnvironment) {

environment = convertToStandardEnvironment(environment);

}

// 是否打印Banner，就是启动程序时出现的图形

if (this.bannerMode != Banner.Mode.OFF) {

printBanner(environment);

}

// Create, load, refresh and run the ApplicationContext

// 创建、装置、刷新、运行ApplicationContext

context = createApplicationContext();

context.setEnvironment(environment);

postProcessApplicationContext(context);

applyInitializers(context);

// 通知监听器，ApplicationContext创建完毕

listeners.contextPrepared(context);

if (this.logStartupInfo) {

logStartupInfo(context.getParent() == null);

logStartupProfileInfo(context);

}

// Add boot specific singleton beans

context.getBeanFactory().registerSingleton("springApplicationArguments",

applicationArguments);

// Load the sources

// 将beans载入到ApplicationContext容器中

Set

Assert.notEmpty(sources, "Sources must not be empty");

load(context, sources.toArray(new Object[sources.size()]));

// 通知监听器，beans载入ApplicationContext完毕

listeners.contextLoaded(context);

// Refresh the context

refresh(context);

if (this.registerShutdownHook) {

try {

context.registerShutdownHook();

}

catch (AccessControlException ex) {

// Not allowed in some environments.

}

}

return context;

}

其中利用createApplicationContext()来实例化ApplicationContext对象，即DEFAULT_WEB_CONTEXT_CLASS 、DEFAULT_CONTEXT_CLASS两个对象其中一个。

protected ConfigurableApplicationContext createApplicationContext() {

Class> contextClass = this.applicationContextClass;

if (contextClass == null) {

try {

contextClass = Class.forName(this.webEnvironment

? DEFAULT_WEB_CONTEXT_CLASS : DEFAULT_CONTEXT_CLASS);

}

catch (ClassNotFoundException ex) {

throw new IllegalStateException(

"Unable create a default ApplicationContext, "

+ "please specify an ApplicationContextClass",

ex);

}

}

return (ConfigurableApplicationContext) BeanUtils.instantiate(contextClass);

}

postProcessApplicationContext(context)、applyInitializers(context)均为初始化ApplicationContext工作。

SpringBoot启动过程分析就先到这里，过程中关注几个对象：

Aphttp://plicationContext：Spring高级容器，与BeanFactory类似。

SpringApplicationRunListener：SprintBoot启动监听器，负责向ApplicationListener注册各类事件。

Environment：运行环境。

4、启动过程框图

5、接口文档

http://docs.spring.io/spring-framework/docs/current/javadoc-api/

总结

以上所述是给大家介绍的SpringBoot应用启动过程分析，希望对大家有所帮助，如果大家有任何疑问请给我留言，会及时回复大家的。在此也非常感谢大家对我们网站的支持！

版权声明：本文内容由网络用户投稿，版权归原作者所有，本站不拥有其著作权，亦不承担相应法律责任。如果您发现本站中有涉嫌抄袭或描述失实的内容，请联系我们jiasou666@gmail.com 处理，核实后本网站将在24小时内删除侵权内容。