springBoot啓動源碼解析（一）
前言：近期打算重擼幾行spring代碼，順手記記流水帳，基於
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.1.5.RELEASE</version>
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啓動一個springBoot程序（Servlet環境）:java
@Slf4j
@EnableDiscoveryClient
@SpringBootApplication
public class KeplerPostLoanApplication {
/** * 項目啓動類 * * @param args 啓動參數 */
public static void main(String[] args) {
SpringApplication.run(KeplerPostLoanApplication.class, args)
}
}
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調用SpringApplication.run方法web
public static ConfigurableApplicationContext run(Class<?>[] primarySources,
String[] args) {
return new SpringApplication(primarySources).run(args);
}
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先執行SpringApplication的構造方法，進行初始化動做，包括：spring
- 一、識別webApplicationType類型 = Servlet
- 二、識別mainApplicationClass類=KeplerPostLoanApplication.class
- 三、加載META-INF/spring.factories文件中定義的定義的ApplicationContextInitializer、ApplicationListener
public SpringApplication(Class<?>... primarySources) {
this(null, primarySources);
}
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();
// 加載META-INF/spring.factories文件中，定義的ApplicationContextInitializer
setInitializers((Collection)getSpringFactoriesInstances(
ApplicationContextInitializer.class));
// 加載META-INF/spring.factories文件中，定義的ApplicationListener
setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
this.mainApplicationClass = deduceMainApplicationClass();
}
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接下來看一下run作了什麼bootstrap
/** * 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) {
StopWatch stopWatch = new StopWatch();
stopWatch.start();
ConfigurableApplicationContext context = null;
Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
configureHeadlessProperty();
// 獲取SpringApplicationRunListener
// 默認只有EventPublishingRunListener，用來結合spring啓動流程，發佈SpringApplicationEvent
SpringApplicationRunListeners listeners = getRunListeners(args);
// 發佈ApplicationStartingEvent,例如
// ApplicationPidFileWriter(saves application PID into file)
listeners.starting();
try {
ApplicationArguments applicationArguments = new DefaultApplicationArguments(
args);
//建立容器環境
ConfigurableEnvironment environment = prepareEnvironment(listeners,
applicationArguments);
configureIgnoreBeanInfo(environment);
Banner printedBanner = printBanner(environment);
// 建立容器上下文
context = createApplicationContext();
exceptionReporters = getSpringFactoriesInstances(
SpringBootExceptionReporter.class,
new Class[] { ConfigurableApplicationContext.class }, context);
// 準備上下文
prepareContext(context, environment, listeners, applicationArguments,
printedBanner);
// 刷新上下文
refreshContext(context);
// 子類擴展
afterRefresh(context, applicationArguments);
stopWatch.stop();
if (this.logStartupInfo) {
new StartupInfoLogger(this.mainApplicationClass)
.logStarted(getApplicationLog(), stopWatch);
}
// 發佈ApplicationStartedEvent
listeners.started(context);
// 回調ApplicationRunner、CommandLineRunner
callRunners(context, applicationArguments);
}
catch (Throwable ex) {
handleRunFailure(context, ex, exceptionReporters, listeners);
throw new IllegalStateException(ex);
}
try {
listeners.running(context);
}
catch (Throwable ex) {
handleRunFailure(context, ex, exceptionReporters, null);
throw new IllegalStateException(ex);
}
return context;
}
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概括下SpringApplication.run方法的關鍵動做設計模式
- 第一步：構造容器環境（prepareEnvironment）
- 第二步：建立容器（createApplicationContext）
- 第三步：準備容器（prepareContext）
- 第四步：刷新容器（refreshContext）
- 第五步：刷新容器後的擴展接口（afterRefresh）
- 第六步：回調Runner類（callRunners）
其中：執行過程當中，經過SpringApplicationRunListener的實現類EventPublishingRunListener在對應動做的時間點，Spring啓動事件。tomcat
附上，springApplicationEvent事件列表bash
主要以上6步，下面具體分析。
第一步：構造容器環境
/** SpringApplication.java **/
private ConfigurableEnvironment prepareEnvironment( SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments) {
// 一、初始化environment
ConfigurableEnvironment environment = getOrCreateEnvironment();
// 二、加載默認配置,defaultProperties、springApplicationCommandLineArgs
configureEnvironment(environment, applicationArguments.getSourceArgs());
// 3.發佈ApplicationEnvironmentPreparedEvent,例如
// (若是是spring Cloud環境的話)BootstrapApplicationListener,建立bootstrapContext上下文，加載bootstrap.properties，
// 補充下，BootstrapApplicationListener會初始化Spring Cloud上下文,初始化過程當中，同樣會調用SpringApplication.run方法（即當前方法）
// ConfigFileApplicationListener，加載application的YamlProperty文件與PropertiesProperty文件,添加PropertySourceOrderingPostProcessor
// 補充下，有須要擴展，須要注意優先級，保證是否定期望的在bootstrap.properties、application.properties加載前或者加載後
listeners.environmentPrepared(environment);
bindToSpringApplication(environment);
if (!this.isCustomEnvironment) {
environment = new EnvironmentConverter(getClassLoader())
.convertEnvironmentIfNecessary(environment, deduceEnvironmentClass());
}
ConfigurationPropertySources.attach(environment);
return environment;
}
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首先getOrCreateEnvironment方法實現以下: new 一個StandardXXXEnvironment()，其中，構造函數中會執行customizePropertySources方法，加載基礎的的PropertySource（系統變量、環境變量、web變量）app
private ConfigurableEnvironment getOrCreateEnvironment() {
if (this.environment != null) {
return this.environment;
}
switch (this.webApplicationType) {
case SERVLET:
return new StandardServletEnvironment();
case REACTIVE:
return new StandardReactiveWebEnvironment();
default:
return new StandardEnvironment();
}
}
public AbstractEnvironment() {
customizePropertySources(this.propertySources);
}
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附上StandardEnvironment的customizePropertySources實現less
@Override
protected void customizePropertySources(MutablePropertySources propertySources) {
// 屬性獲取時，for each propertySources,先匹配到就返回，
// 因此systemProperties(如：java -Dsource=xxx -jar xxx.jar)優先級高於systemEnvironment(環境變量)
propertySources.addLast(new MapPropertySource("systemProperties", getSystemProperties()));
propertySources.addLast(new SystemEnvironmentPropertySource("systemEnvironment", getSystemEnvironment()));
}
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第二步：建立容器
實際上，就是new AnnotationConfigServletWebServerApplicationContext()dom
// SpringApplication.java
protected ConfigurableApplicationContext createApplicationContext() {
Class<?> contextClass = this.applicationContextClass;
if (contextClass == null) {
try {
switch (this.webApplicationType) {
case SERVLET:
contextClass = Class.forName(DEFAULT_SERVLET_WEB_CONTEXT_CLASS);
break;
case REACTIVE:
contextClass = Class.forName(DEFAULT_REACTIVE_WEB_CONTEXT_CLASS);
break;
default:
contextClass = Class.forName(DEFAULT_CONTEXT_CLASS);
}
}
catch (ClassNotFoundException ex) {
throw new IllegalStateException(
"Unable create a default ApplicationContext, "
+ "please specify an ApplicationContextClass",
ex);
}
}
return (ConfigurableApplicationContext) BeanUtils.instantiateClass(contextClass);
}
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重點關注：構造方法中， 建立了AnnotatedBeanDefinitionReader、ClassPathBeanDefinitionScanner兩個對象
// AnnotationConfigServletWebServerApplicationContext.java
public AnnotationConfigServletWebServerApplicationContext() {
this.reader = new AnnotatedBeanDefinitionReader(this);
this.scanner = new ClassPathBeanDefinitionScanner(this);
}
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其中，AnnotatedBeanDefinitionReader 建立過程當中，註冊了多個十分重要的BeanPostProcessor，包括處理@Configuration註解的ConfigurationClassPostProcessor等。
public AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry) {
this(registry, getOrCreateEnvironment(registry));
}
public AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry, Environment environment) {
Assert.notNull(registry, "BeanDefinitionRegistry must not be null");
Assert.notNull(environment, "Environment must not be null");
this.registry = registry;
this.conditionEvaluator = new ConditionEvaluator(registry, environment, null);
// Register all relevant annotation post processors in the given registry，包括：
// ConfigurationClassPostProcessor
// AutowiredAnnotationBeanPostProcessor
// RequiredAnnotationBeanPostProcessor
// CommonAnnotationBeanPostProcessor
// PersistenceAnnotationBeanPostProcessor
// EventListenerMethodProcessor
// DefaultEventListenerFactory
AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);
}
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第三步：準備容器
/** SpringApplication.java **/
private void prepareContext(ConfigurableApplicationContext context, ConfigurableEnvironment environment, SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments, Banner printedBanner) {
context.setEnvironment(environment);
postProcessApplicationContext(context);
// 調用ApplicationContextInitializer.initialize()，例如：
// EnvironmentDecryptApplicationInitializer
// PropertySourceBootstrapConfiguration
applyInitializers(context);
// ApplicationContextInitializedEvent,暫無例子
listeners.contextPrepared(context);
if (this.logStartupInfo) {
logStartupInfo(context.getParent() == null);
logStartupProfileInfo(context);
}
// Add boot specific singleton beans
ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
beanFactory.registerSingleton("springApplicationArguments", applicationArguments);
if (printedBanner != null) {
beanFactory.registerSingleton("springBootBanner", printedBanner);
}
if (beanFactory instanceof DefaultListableBeanFactory) {
((DefaultListableBeanFactory) beanFactory)
.setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
}
// Load the sources
Set<Object> sources = getAllSources();
Assert.notEmpty(sources, "Sources must not be empty");
// 加載springBoot啓動類注入到spring容器中bean map中
// AnnotatedBeanDefinitionReader.doRegisterBean()
load(context, sources.toArray(new Object[0]));
// 發佈ApplicationPreparedEvent
// ConfigFileApplicationListener,注入PropertySourceOrderingPostProcessor，調整defaultProperties到尾部
listeners.contextLoaded(context);
}
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第四步：刷新容器
refresh方法在spring整個源碼體系中舉足輕重，後續單獨講解。
private void refreshContext(ConfigurableApplicationContext context) {
refresh(context);
if (this.registerShutdownHook) {
try {
context.registerShutdownHook();
}
catch (AccessControlException ex) {
// Not allowed in some environments.
}
}
}
@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
initMessageSource();
// Initialize event multicaster for this context.
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
onRefresh();
// Check for listener beans and register them.
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
finishRefresh();
}
catch (BeansException ex) {
if (logger.isWarnEnabled()) {
logger.warn("Exception encountered during context initialization - " +
"cancelling refresh attempt: " + ex);
}
// Destroy already created singletons to avoid dangling resources.
destroyBeans();
// Reset 'active' flag.
cancelRefresh(ex);
// Propagate exception to caller.
throw ex;
}
finally {
// Reset common introspection caches in Spring's core, since we
// might not ever need metadata for singleton beans anymore...
resetCommonCaches();
}
}
}
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第五步：刷新容器後的擴展接口（afterRefresh）
protected void afterRefresh(ConfigurableApplicationContext context, ApplicationArguments args) {
}
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擴展接口，設計模式中的模板方法，默認爲空實現,子類擴展。
第六步：回調Runner類（callRunners）
容器就緒後，觸發回調動做，目前見到的實現有 JobLauncherCommandLineRunner,啓動jobLauncher
private void callRunners(ApplicationContext context, ApplicationArguments args) {
List<Object> runners = new ArrayList<>();
runners.addAll(context.getBeansOfType(ApplicationRunner.class).values());
runners.addAll(context.getBeansOfType(CommandLineRunner.class).values());
AnnotationAwareOrderComparator.sort(runners);
for (Object runner : new LinkedHashSet<>(runners)) {
if (runner instanceof ApplicationRunner) {
callRunner((ApplicationRunner) runner, args);
}
if (runner instanceof CommandLineRunner) {
callRunner((CommandLineRunner) runner, args);
}
}
}
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本章節經常使用擴展接口以及使用案例
執行順序（重點關注）：
- ApplicationStartingEvent
- ApplicationEnvironmentPreparedEvent
- ApplicationContextInitializer
- ApplicationContextInitializedEvent
- ApplicationPreparedEvent
- ApplicationStartedEvent
- ApplicationRunner、CommandLineRunner
- ApplicationReadyEvent
使用案例：
1. ApplicationStartingEvent
- 簡單描述：程序啓動時，最先觸發的動做
- 應用場景：
- ApplicationPidFileWriter(saves application PID into file)
- LoggingApplicationListener(configures the {@link LoggingSystem})
2. ApplicationEnvironmentPreparedEvent
- 簡單描述： 建立環境Environment完成，而且已經載默認的配置，例如systemEnvironment、systemProperties
- 應用場景：比較多的是加載自定義的配置、spring Cloud也經過這個事件，去初始化Cloud上下文。
- BootstrapApplicationListener：初始化BootstrapApplicationContext上下文，包括加載bootstrap.properties、載入spring.factories 定義的BootstrapConfiguration
- ConfigFileApplicationListener：加載application.properties、application.yml、RandomValuePropertySource
3. ApplicationContextInitializer
- 描述：
- 應用場景：例如對properties進行進一步的處理，好比解密
- EnvironmentDecryptApplicationInitializer
4. ApplicationContextInitializedEvent
5. ApplicationPreparedEvent
6. ApplicationStartedEvent
- 簡述：applicationStarted
- 應用場景：好比能夠增長監控
- TomcatMetricsBinder：暴露tomcat線程信息
7. ApplicationRunner、CommandLineRunner
- 簡述：觸發回調動做。
- 應用場景：
- JobLauncherCommandLineRunner：springBatch,啓動JobLauncher
8. ApplicationReadyEvent
- 簡述：標誌着容器啓動完成
- 應用場景：
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