SpringBoot原始碼學習系列之啟動原理簡介
本部落格通過debug方式簡單跟一下Springboot application啟動的原始碼,Springboot的啟動原始碼是比較複雜的,本部落格只是簡單梳理一下原始碼,淺析其原理
為了方便跟原始碼,先找個Application類,打個斷點,進行除錯,如圖所示:
step into,run方法呼叫了SpringApplication的run方法
通過debug,Springboot啟動過程,會先執行如下關鍵的建構函式
分析建構函式原始碼:
public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) { this.resourceLoader = resourceLoader; Assert.notNull(primarySources, "PrimarySources must not be null"); this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources)); // 判斷當前的web型別 this.webApplicationType = WebApplicationType.deduceFromClasspath(); //設定初始化的ApplicationInitializer類,從類路徑下面的META-INF/spring.factories配置檔案獲取所有的ApplicationInitializer儲存起來 setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class)); //同理,從類路徑下面的META-INF/spring.factories配置檔案獲取所有的ApplicationListener儲存起來 setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class)); //從多個配置類中找到有main方法的主配置類 this.mainApplicationClass = deduceMainApplicationClass(); }
注意:上面過程其實就是建立Springboot的Application啟動類的過程
deduceFromClasspath方法是判斷web型別的
繼續debug ApplicationContextInitializer這些Initializer類,可以說是初始化類的設定過程
SpringFactoriesLoader.loadFactoryNames(type, classLoader)獲取所有的Initializer類的類名
Evaluate可以看出掃描到如下的類
繼續debug,這個是Spring框架的底層類
找到主要的原始碼,loadSpringFactories方法也是從如下的位置獲取配置資訊的
從META-INF/spring.factories獲取對應的配置資訊
框架的檔案位置在autoconfiguration工程裡,顯然如果要自定義Initializer類的話,自己新建一些Initializer類,然後自己寫個META-INF/spring.factories類,也是可以被掃描到的
private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) { //用一個ConcurrentReferenceHashMap來快取資訊 MultiValueMap<String, String> result = cache.get(classLoader); if (result != null) { //快取讀取到配置資訊,返回快取資料 return result; } // 快取讀取不到的情況,重新從META-INF/spring.factories配置檔案讀取 try { Enumeration<URL> urls = (classLoader != null ? classLoader.getResources(FACTORIES_RESOURCE_LOCATION) : ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION)); result = new LinkedMultiValueMap<>(); // 遍歷迴圈讀取配置資訊 while (urls.hasMoreElements()) { URL url = urls.nextElement(); UrlResource resource = new UrlResource(url); // 用PropertiesLoaderUtils工具類讀取資原始檔 Properties properties = PropertiesLoaderUtils.loadProperties(resource); for (Map.Entry<?, ?> entry : properties.entrySet()) { //獲取到Initializer對應的全類名 String factoryTypeName = ((String) entry.getKey()).trim(); for (String factoryImplementationName : StringUtils.commaDelimitedListToStringArray((String) entry.getValue())) { result.add(factoryTypeName, factoryImplementationName.trim()); } } } // 重新放在快取裡 cache.put(classLoader, result); return result; } catch (IOException ex) { throw new IllegalArgumentException("Unable to load factories from location [" + FACTORIES_RESOURCE_LOCATION + "]", ex); } }
ApplicationInitializer類的全類名都被掃描到之後,返回剛才的原始碼,繼續看看,如圖,從命名看應該是進行類的例項化過程
step into,果然是的,還是呼叫了Spring框架的底層工具類,BeanUtils進行類的例項化過程
setListeners方法的過程同理,本文就不詳細分析:
繼續往下debug,deduceMainApplicationClass方法
private Class<?> deduceMainApplicationClass() {
try {
//獲取執行時的堆疊屬性陣列
StackTraceElement[] stackTrace = new RuntimeException().getStackTrace();
for (StackTraceElement stackTraceElement : stackTrace) {
//有main方法的Application類返回
if ("main".equals(stackTraceElement.getMethodName())) {
return Class.forName(stackTraceElement.getClassName());
}
}
}
catch (ClassNotFoundException ex) {
// Swallow and continue
}
return null;
}
獲取到的就是建立Springboot工程時的Application類
Springboot的Application類建立成功之後,才真正開始執行run方法
public ConfigurableApplicationContext run(String... args) {
StopWatch stopWatch = new StopWatch();
stopWatch.start();
ConfigurableApplicationContext context = null;
Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
//校驗java.awt.headless的
configureHeadlessProperty();
//從META-INF/spring.factories獲取SpringApplicationRunListeners,和前面的分析同理,本文就不詳細介紹
SpringApplicationRunListeners listeners = getRunListeners(args);
//回撥SpringApplicationRunListeners 的starting方法
listeners.starting();
try {
//封裝命令列引數
ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
//準備環境,環境建立完成之後,再回調SpringApplicationRunListeners 的environmentPrepared方法,表示環境準備好
ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
configureIgnoreBeanInfo(environment);
//控制檯列印Banner資訊的,後面再簡單分析
Banner printedBanner = printBanner(environment);
// 建立Spring的IOC容器,建立過程比較複雜,會分析是web型別的ioc容器,還是普通的ioc容器等等
context = createApplicationContext();
exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,
new Class[] { ConfigurableApplicationContext.class }, context);
//將environment儲存到ioc,執行applyInitializers方法,applyInitializers方法執行完成之後,再回調SpringApplicationRunListeners的contextPrepared方法
//applyInitializers方法作用:回撥之前儲存的所有的ApplicationContextInitializer的initialize方法
prepareContext(context, environment, listeners, applicationArguments, printedBanner);
//重新整理ioc容器,其實就是ioc容器的初始化過程,還沒進行屬性設定,後置處理器,僅僅是掃描、建立、載入所有元件等等過程
refreshContext(context);
afterRefresh(context, applicationArguments);
stopWatch.stop();
if (this.logStartupInfo) {
new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
}
//回撥所有SpringApplicationRunListener的started方法
listeners.started(context);
//從ioc容器中獲取所有的ApplicationRunner和CommandLineRunner進行回撥,ApplicationRunner先回調,CommandLineRunner再回調
callRunners(context, applicationArguments);
}
catch (Throwable ex) {
handleRunFailure(context, ex, exceptionReporters, listeners);
throw new IllegalStateException(ex);
}
try {
//回撥所有SpringApplicationRunListener的running方法
listeners.running(context);
}
catch (Throwable ex) {
handleRunFailure(context, ex, exceptionReporters, null);
throw new IllegalStateException(ex);
}
//Springboot應用啟動成功後,才返回啟動的ioc容器
return context;
}
回顧一下前面原始碼的環境準備方法,找重點程式碼,如圖,可以看出環境準備完成後會回撥SpringApplicationRunListener的environmentPrepared方法,表示環境準備完成
banner列印的方法,如圖,執行完成,控制檯的banner資訊就打印出來了:
ioc初始化之前,會執行applyInitializers方法,執行完成後,再回調SpringApplicationRunListener的contextPrepared方法
applyInitializers():回撥之前儲存的所有的ApplicationContextInitializer的initialize方法
從ioc容器中獲取所有的ApplicationRunner和CommandLineRunner進行回撥
ok,從原始碼的簡單分析,可以看出有幾個重要的事件監聽機制,下面引用尚矽谷視訊的例子:
只需要放在ioc容器中的有:
- ApplicationRunner
@Component
public class HelloApplicationRunner implements ApplicationRunner {
@Override
public void run(ApplicationArguments args) throws Exception {
System.out.println("ApplicationRunner...run....");
}
}
- CommandLineRunner
@Component
public class HelloCommandLineRunner implements CommandLineRunner {
@Override
public void run(String... args) throws Exception {
System.out.println("CommandLineRunner...run..."+ Arrays.asList(args));
}
}
配置在META-INF/spring.factories的有:
- ApplicationContextInitializer
public class HelloApplicationContextInitializer implements
ApplicationContextInitializer<ConfigurableApplicationContext> {
@Override
public void initialize(ConfigurableApplicationContext applicationContext) {
System.out.println("ApplicationContextInitializer...initialize..."+applicationContext);
}
}
- SpringApplicationRunListener
package com.example.springboot.web.listener;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.SpringApplicationRunListener;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.core.env.ConfigurableEnvironment;
public class HelloSpringApplicationRunListener implements SpringApplicationRunListener {
//必須有的構造器
public HelloSpringApplicationRunListener(SpringApplication application, String[] args){
}
@Override
public void starting() {
System.out.println("SpringApplicationRunListener...starting...");
}
@Override
public void environmentPrepared(ConfigurableEnvironment environment) {
Object o = environment.getSystemProperties().get("os.name");
System.out.println("SpringApplicationRunListener...environmentPrepared.."+o);
}
@Override
public void contextPrepared(ConfigurableApplicationContext context) {
System.out.println("SpringApplicationRunListener...contextPrepared...");
}
@Override
public void contextLoaded(ConfigurableApplicationContext context) {
System.out.println("SpringApplicationRunListener...contextLoaded...");
}
}
配置(META-INF/spring.factories)
org.springframework.context.ApplicationContextInitializer=\
com.example.springboot.web.listener.HelloApplicationContextInitializer
org.springframework.boot.SpringApplicationRunListener=\
com.example.springboot.web.listener.HelloSpringApplicationRunListener
例子下載:github下載鏈