探索 SpringBoot （三） 啟動流程詳解(下)
阿新 • • 發佈：2018-11-19
探索 SpringBoot （三） 啟動流程詳解(下)
文章目錄
4 SpringBoot 執行階段
接上文 我們看看 SpringBoot 到底幹了啥吧。
- 我們繼續回到初始的地方 看看 run 方法
new SpringApplication(primarySources).run(args) ... public ConfigurableApplicationContext run(String... args) { // 用於計時 不是重點 這裡不深入講解 有興趣的小夥伴自己去讀原始碼 StopWatch stopWatch = new StopWatch(); stopWatch.start(); ConfigurableApplicationContext context = null; Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>(); configureHeadlessProperty(); SpringApplicationRunListeners listeners = getRunListeners(args); listeners.starting(); try { ApplicationArguments applicationArguments = new DefaultApplicationArguments( args); ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments); configureIgnoreBeanInfo(environment); Banner printedBanner = printBanner(environment); context = createApplicationContext(); exceptionReporters = getSpringFactoriesInstances( SpringBootExceptionReporter.class, new Class[] { ConfigurableApplicationContext.class }, context); prepareContext(context, environment, listeners, applicationArguments, printedBanner); refreshContext(context); afterRefresh(context, applicationArguments); stopWatch.stop(); if (this.logStartupInfo) { new StartupInfoLogger(this.mainApplicationClass) .logStarted(getApplicationLog(), stopWatch); } listeners.started(context); 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; }
4.1 Spring 應用執行監聽者的載入和執行
SpringApplicationRunListeners listeners = getRunListeners(args);
listeners.starting();
...
listeners.started(context);
...
listeners.running(context);
- 這裡就是初始化了應用監聽者。在應用的不同階段 呼叫了不同的方法。我們看看 getRunListeners 幹了啥
private SpringApplicationRunListeners getRunListeners(String[] args) { Class<?>[] types = new Class<?>[] { SpringApplication.class, String[].class }; return new SpringApplicationRunListeners(logger, getSpringFactoriesInstances( SpringApplicationRunListener.class, types, this, args)); } class SpringApplicationRunListeners { private final Log log; private final List<SpringApplicationRunListener> listeners; SpringApplicationRunListeners(Log log, Collection<? extends SpringApplicationRunListener> listeners) { this.log = log; this.listeners = new ArrayList<>(listeners); } public void starting() { for (SpringApplicationRunListener listener : this.listeners) { listener.starting(); } } public void environmentPrepared(ConfigurableEnvironment environment) { for (SpringApplicationRunListener listener : this.listeners) { listener.environmentPrepared(environment); } } ... }
getSpringFactoriesInstances(SpringApplicationRunListener.class, ...)
這個方法上面講過了 就是載入 spring.factory 下面的實現類，目前
key 為 SpringApplicationRunListener 的實現類就 一個 EventPublishingRunListener
我們 大概看下這個東西長啥樣
public class EventPublishingRunListener implements SpringApplicationRunListener, Ordered {
private final SpringApplication application;
private final String[] args;
private final SimpleApplicationEventMulticaster initialMulticaster;
public EventPublishingRunListener(SpringApplication application, String[] args) {
this.application = application;
this.args = args;
this.initialMulticaster = new SimpleApplicationEventMulticaster();
for (ApplicationListener<?> listener : application.getListeners()) {
this.initialMulticaster.addApplicationListener(listener);
}
}
@Override
public int getOrder() {
return 0;
}
@Override
public void starting() {
this.initialMulticaster.multicastEvent(
new ApplicationStartingEvent(this.application, this.args));
}
@Override
public void environmentPrepared(ConfigurableEnvironment environment) {
this.initialMulticaster.multicastEvent(new ApplicationEnvironmentPreparedEvent(
this.application, this.args, environment));
}
...
反正就記住 通過 getRunListeners 方法 初始化了一個監聽者 EventPublishingRunListener，當呼叫 listeners.starting(); 的時候相當於呼叫了 EventPublishingRunListener 的
@Override
public void starting() {
this.initialMulticaster.multicastEvent(
new ApplicationStartingEvent(this.application, this.args));
}
這個方法， spring 這樣做也是便於擴充套件。
-
我們接著往下看看之後發生了什麼
-
initialMulticaster 其實就是一個廣播者，負責廣播事件。 我們看看 multicastEvent 方法
@Override
public void multicastEvent(ApplicationEvent event) {
multicastEvent(event, resolveDefaultEventType(event));
}
@Override
public void multicastEvent(final ApplicationEvent event, @Nullable ResolvableType eventType) {
ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event));
for (final ApplicationListener<?> listener : getApplicationListeners(event, type)) {
Executor executor = getTaskExecutor();
if (executor != null) {
executor.execute(() -> invokeListener(listener, event));
}
else {
invokeListener(listener, event);
}
}
}
protected void invokeListener(ApplicationListener<?> listener, ApplicationEvent event) {
ErrorHandler errorHandler = getErrorHandler();
if (errorHandler != null) {
try {
doInvokeListener(listener, event);
}
catch (Throwable err) {
errorHandler.handleError(err);
}
}
else {
doInvokeListener(listener, event);
}
}
@SuppressWarnings({"unchecked", "rawtypes"})
private void doInvokeListener(ApplicationListener listener, ApplicationEvent event) {
try {
listener.onApplicationEvent(event);
}
catch (ClassCastException ex) {
String msg = ex.getMessage();
if (msg == null || matchesClassCastMessage(msg, event.getClass())) {
// Possibly a lambda-defined listener which we could not resolve the generic event type for
// -> let's suppress the exception and just log a debug message.
Log logger = LogFactory.getLog(getClass());
if (logger.isDebugEnabled()) {
logger.debug("Non-matching event type for listener: " + listener, ex);
}
}
else {
throw ex;
}
}
}
最終呼叫到這個方法上面了，
listener.onApplicationEvent(event);
你肯定好奇這個 listener 是什麼，其實就是我們上一篇載入的 ApplicationListener 的實現類，去執行 listener 的方法。
我們梳理一下：
1 SpringApplicationRunListeners listeners = getRunListeners(args); 載入監聽者 EventPublishingRunListener
2 EventPublishingRunListener 內部維護一個廣播者，在構造的時候從上下文獲取監聽者（ApplicationListener 的實現類） 並且放入廣播列表
3 當 spring 執行到對應生命週期的時候 呼叫對應方法，比如 listeners.starting(); 經過 EventPublishingRunListener 內部的廣播者 最終呼叫到 listener.onApplicationEvent(event); （ApplicationListener 的實現類）
4 最後 listener 不同的實現類 進行不同的時間處理邏輯
好了 關於 spring 的 事件/監聽器 模型就講完了。
4.2 解析輸入引數 構建執行環境
// 這裡就是講 run 方法傳入的引數 以 key-value 的形式解析 沒有太大的難度
ApplicationArguments applicationArguments = new DefaultApplicationArguments(
args);
// 這裡的作用就是根據輸入引數 解析出那些事可用的配置，監聽者對應事件的通知
ConfigurableEnvironment environment = prepareEnvironment(listeners,
applicationArguments);
...
private ConfigurableEnvironment prepareEnvironment(
SpringApplicationRunListeners listeners,
ApplicationArguments applicationArguments) {
// Create and configure the environment
ConfigurableEnvironment environment = getOrCreateEnvironment();
configureEnvironment(environment, applicationArguments.getSourceArgs());
listeners.environmentPrepared(environment);
bindToSpringApplication(environment);
if (!this.isCustomEnvironment) {
environment = new EnvironmentConverter(getClassLoader())
.convertEnvironmentIfNecessary(environment, deduceEnvironmentClass());
}
ConfigurationPropertySources.attach(environment);
return environment;
}
4.3 上下文建立
因為這一塊內容比較多 也比較難 所以樓主也就簡單介紹一下
context = createApplicationContext();
...
prepareContext(context, environment, listeners, applicationArguments,
printedBanner);
refreshContext(context);
afterRefresh(context, applicationArguments);
4.3.1 上下文的建立 createApplicationContext
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);
}
- 這裡就是根據上一篇中推斷出來的 webApplicationType ，載入對應的類，並且例項化上下文物件，如果是我們場景的 servlet 容器的話 實現類是這個
org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext
4.3.2 上下文環境預處理 prepareContext
prepareContext(context, environment, listeners, applicationArguments,
printedBanner);
private void prepareContext(ConfigurableApplicationContext context,
ConfigurableEnvironment environment, SpringApplicationRunListeners listeners,
ApplicationArguments applicationArguments, Banner printedBanner) {
context.setEnvironment(environment);
postProcessApplicationContext(context);
applyInitializers(context);
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");
load(context, sources.toArray(new Object[0]));
listeners.contextLoaded(context);
}
主要看看這個方法, 這個方法載入了上下文
load(context, sources.toArray(new Object[0]));
protected void load(ApplicationContext context, Object[] sources) {
if (logger.isDebugEnabled()) {
logger.debug(
"Loading source " + StringUtils.arrayToCommaDelimitedString(sources));
}
BeanDefinitionLoader loader = createBeanDefinitionLoader(
getBeanDefinitionRegistry(context), sources);
if (this.beanNameGenerator != null) {
loader.setBeanNameGenerator(this.beanNameGenerator);
}
if (this.resourceLoader != null) {
loader.setResourceLoader(this.resourceLoader);
}
if (this.environment != null) {
loader.setEnvironment(this.environment);
}
loader.load();
}
...
private BeanDefinitionRegistry getBeanDefinitionRegistry(ApplicationContext context) {
if (context instanceof BeanDefinitionRegistry) {
return (BeanDefinitionRegistry) context;
}
if (context instanceof AbstractApplicationContext) {
return (BeanDefinitionRegistry) ((AbstractApplicationContext) context)
.getBeanFactory();
}
throw new IllegalStateException("Could not locate BeanDefinitionRegistry");
}
...
BeanDefinitionLoader(BeanDefinitionRegistry registry, Object... sources) {
Assert.notNull(registry, "Registry must not be null");
Assert.notEmpty(sources, "Sources must not be empty");
this.sources = sources;
this.annotatedReader = new AnnotatedBeanDefinitionReader(registry);
this.xmlReader = new XmlBeanDefinitionReader(registry);
if (isGroovyPresent()) {
this.groovyReader = new GroovyBeanDefinitionReader(registry);
}
this.scanner = new ClassPathBeanDefinitionScanner(registry);
this.scanner.addExcludeFilter(new ClassExcludeFilter(sources));
}
這裡根據傳入的註冊資訊用多種方式去載入
4.3.3 重新整理上下文
refreshContext(context);
...
private void refreshContext(ConfigurableApplicationContext context) {
refresh(context);
if (this.registerShutdownHook) {
try {
context.registerShutdownHook();
}
catch (AccessControlException ex) {
// Not allowed in some environments.
}
}
}
...
protected void refresh(ApplicationContext applicationContext) {
Assert.isInstanceOf(AbstractApplicationContext.class, applicationContext);
((AbstractApplicationContext) applicationContext).refresh();
}
...
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();
}
}
}
這裡就是容器 和 容器裡面的 bean 的各種操作和處理了，樓主水平有限，各位看官自己慢慢研究吧。。。
4.3.4 重新整理上下文之後
afterRefresh(context, applicationArguments);
...
protected void afterRefresh(ConfigurableApplicationContext context,
ApplicationArguments args) {
}
- 你沒有看錯 就是一片空白，這個估計就是 spring 留給我們自己去實現的。
5 總結
好不容易寫完了，但是感覺意猶未盡，很多東西都沒有說清楚，像 內建容器的啟動， ioc 過程， aop 過程。也是樓主水平有限，這裡就相當於拋磚引玉吧。如果發現文章中的錯誤歡迎指正哈。