Spring boot啟動流程原始碼解析
閱讀須知
- 版本:2.0.4
- 文章中使用/* */註釋的方法會做深入分析
正文
@SpringBootApplication
public class BootApplication {
public static void main(String[] args) {
SpringApplication.run(BootApplication.class, args);
}
}
這段程式碼相信大家都很熟悉,spring boot的啟動類,我們就以這段程式碼作為切入點,來分析spring boot的啟動流程:
SpringApplication:
public static ConfigurableApplicationContext run(Class<?> primarySource,
String... args) {
return run(new Class<?>[] { primarySource }, args);
}
public static ConfigurableApplicationContext run(Class<?>[] primarySources,
String[] args) {
/* 構建SpringApplication並執行,建立並且重新整理一個新的ApplicationContext */
return new SpringApplication(primarySources).run(args);
}
SpringApplication:
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));
// 判斷是否能夠成功載入一些關鍵的類來確認web應用型別,這個型別後面會用到
this.webApplicationType = deduceWebApplicationType();
/* 獲取並設定Spring上下文初始化器 */
setInitializers((Collection) getSpringFactoriesInstances(
ApplicationContextInitializer.class));
/* 獲取並設定Spring應用監聽器 */
setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
// 追述到應用主類,也就是main方法所在的類
this.mainApplicationClass = deduceMainApplicationClass();
}
這裡ApplicationContextInitializer和ApplicationListener我們會在後面用到的時候說明它們的作用。
SpringApplication:
private <T> Collection<T> getSpringFactoriesInstances(Class<T> type) {
return getSpringFactoriesInstances(type, new Class<?>[] {});
}
private <T> Collection<T> getSpringFactoriesInstances(Class<T> type,
Class<?>[] parameterTypes, Object... args) {
ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
/* 載入工廠名稱,Set防止重複 */
Set<String> names = new LinkedHashSet<>(
SpringFactoriesLoader.loadFactoryNames(type, classLoader));
// 建立工廠例項
List<T> instances = createSpringFactoriesInstances(type, parameterTypes,
classLoader, args, names);
// 根據@Order和@Priority進行排序
AnnotationAwareOrderComparator.sort(instances);
return instances;
}
SpringFactoriesLoader:
public static List<String> loadFactoryNames(Class<?> factoryClass, @Nullable ClassLoader classLoader) {
String factoryClassName = factoryClass.getName();
/* 載入工廠配置,根據傳入的factoryClass獲取工廠名稱集合 */
return loadSpringFactories(classLoader).getOrDefault(factoryClassName, Collections.emptyList());
}
SpringFactoriesLoader:
private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {
MultiValueMap<String, String> result = cache.get(classLoader);
if (result != null) {
return result;
}
try {
// 載入資源,路徑META-INF/spring.factories
Enumeration<URL> urls = (classLoader != null ?
classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :
ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
result = new LinkedMultiValueMap<>();
while (urls.hasMoreElements()) {
URL url = urls.nextElement();
UrlResource resource = new UrlResource(url);
Properties properties = PropertiesLoaderUtils.loadProperties(resource);
for (Map.Entry<?, ?> entry : properties.entrySet()) {
// value用逗號分隔組成集合
List<String> factoryClassNames = Arrays.asList(
StringUtils.commaDelimitedListToStringArray((String) entry.getValue()));
// 新增key和集合的對映
result.addAll((String) entry.getKey(), factoryClassNames);
}
}
// 結果快取
cache.put(classLoader, result);
return result;
}
catch (IOException ex) {
throw new IllegalArgumentException("Unable to load factories from location [" +
FACTORIES_RESOURCE_LOCATION + "]", ex);
}
}
我們來看一下META-INF/spring.factories
檔案中有什麼內容:
# 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
# Error Reporters
org.springframework.boot.SpringBootExceptionReporter=\
org.springframework.boot.diagnostics.FailureAnalyzers
# 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.web.context.ServerPortInfoApplicationContextInitializer
# Application Listeners
org.springframework.context.ApplicationListener=\
org.springframework.boot.ClearCachesApplicationListener,\
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.context.logging.ClasspathLoggingApplicationListener,\
org.springframework.boot.context.logging.LoggingApplicationListener,\
org.springframework.boot.liquibase.LiquibaseServiceLocatorApplicationListener
# Environment Post Processors
org.springframework.boot.env.EnvironmentPostProcessor=\
org.springframework.boot.cloud.CloudFoundryVcapEnvironmentPostProcessor,\
org.springframework.boot.env.SpringApplicationJsonEnvironmentPostProcessor,\
org.springframework.boot.env.SystemEnvironmentPropertySourceEnvironmentPostProcessor
# Failure Analyzers
org.springframework.boot.diagnostics.FailureAnalyzer=\
org.springframework.boot.diagnostics.analyzer.BeanCurrentlyInCreationFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.BeanNotOfRequiredTypeFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.BindFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.BindValidationFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.UnboundConfigurationPropertyFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.ConnectorStartFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.NoUniqueBeanDefinitionFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.PortInUseFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.ValidationExceptionFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.InvalidConfigurationPropertyNameFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.InvalidConfigurationPropertyValueFailureAnalyzer
# FailureAnalysisReporters
org.springframework.boot.diagnostics.FailureAnalysisReporter=\
org.springframework.boot.diagnostics.LoggingFailureAnalysisReporter
檔案中我們看到了ApplicationContextInitializer和ApplicationListener的key value配置,還有一些其他的介面,遇到後我們在進行分析。構建好SpringApplication後,接下來就是執行它的run方法:
SpringApplication:
public ConfigurableApplicationContext run(String... args) {
// StopWatch是一個簡單的秒錶,允許多個任務的計時,暴露每個命名任務的總執行時間和執行時間
StopWatch stopWatch = new StopWatch();
stopWatch.start();
ConfigurableApplicationContext context = null;
Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
configureHeadlessProperty();
// 獲取SpringApplicationRunListener集合,同樣是從上面載入的配置中獲取
SpringApplicationRunListeners listeners = getRunListeners(args);
listeners.starting();
try {
ApplicationArguments applicationArguments = new DefaultApplicationArguments(
args);
/* 準備環境 */
ConfigurableEnvironment environment = prepareEnvironment(listeners,
applicationArguments);
configureIgnoreBeanInfo(environment);
// 列印banner,就是我們在控制檯看到的那個Spring的logo
Banner printedBanner = printBanner(environment);
// 根據不同的webApplicationType返回不同的應用上下文例項
context = createApplicationContext();
// 同樣從上面載入的配置中獲取SpringBootExceptionReporter
exceptionReporters = getSpringFactoriesInstances(
SpringBootExceptionReporter.class,
new Class[] { ConfigurableApplicationContext.class }, context);
/* 準備上下文 */
prepareContext(context, environment, listeners, applicationArguments,
printedBanner);
/* 重新整理上下文 */
refreshContext(context);
// 重新整理後操作,預設空實現,子類覆蓋
afterRefresh(context, applicationArguments);
stopWatch.stop();
if (this.logStartupInfo) {
new StartupInfoLogger(this.mainApplicationClass)
.logStarted(getApplicationLog(), stopWatch);
}
listeners.started(context);
// 呼叫所有ApplicationRunner和CommandLineRunner的run方法
callRunners(context, applicationArguments);
}
catch (Throwable ex) {
// 執行失敗的異常處理、日誌列印和通知
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;
}
在這裡我們看到很多處SpringApplicationRunListener的相關方法呼叫,我們來說明一下它的作用,就像它的命名一樣,主要是監聽SpringApplication的run方法的各個關鍵步驟,在上面載入的配置中,我們看到了一個實現為EventPublishingRunListener,主要作用是釋出應用的啟動執行、啟動完成等一些關鍵事件,具體程式碼有興趣的同學可以自行查閱。
SpringApplication:
private ConfigurableEnvironment prepareEnvironment(
SpringApplicationRunListeners listeners,
ApplicationArguments applicationArguments) {
// 建立Environment
ConfigurableEnvironment environment = getOrCreateEnvironment();
/* 配置environment */
configureEnvironment(environment, applicationArguments.getSourceArgs());
listeners.environmentPrepared(environment);
// 將environment繫結到SpringApplication
bindToSpringApplication(environment);
if (this.webApplicationType == WebApplicationType.NONE) {
environment = new EnvironmentConverter(getClassLoader())
.convertToStandardEnvironmentIfNecessary(environment);
}
// 附加一個ConfigurationPropertySource到environment
ConfigurationPropertySources.attach(environment);
return environment;
}
SpringApplication:
protected void configureEnvironment(ConfigurableEnvironment environment,
String[] args) {
// 在此應用程式的環境中新增、刪除或重新排序PropertySource
configurePropertySources(environment, args);
// 配置此應用程式環境的啟用(或預設為啟用)配置檔案
// 可以通過spring.profiles.active屬性在配置檔案處理期間啟用其他配置檔案
configureProfiles(environment, args);
}
SpringApplication:
private void prepareContext(ConfigurableApplicationContext context,
ConfigurableEnvironment environment, SpringApplicationRunListeners listeners,
ApplicationArguments applicationArguments, Banner printedBanner) {
context.setEnvironment(environment);
// 應用相應的ApplicationContext後置處理,子類可以覆蓋,
// 預設實現為context設定beanNameGenerator和resourceLoader
postProcessApplicationContext(context);
// 在context重新整理之前應用之前載入的ApplicationContextInitializer
// 在META-INF/spring.factories中預設配置了4個ApplicationContextInitializer,具體作用可以自行了解一下
applyInitializers(context);
listeners.contextPrepared(context);
// 日誌列印
if (this.logStartupInfo) {
logStartupInfo(context.getParent() == null);
logStartupProfileInfo(context);
}
// 新增特定的boot單例bean
context.getBeanFactory().registerSingleton("springApplicationArguments",
applicationArguments);
if (printedBanner != null) {
context.getBeanFactory().registerSingleton("springBootBanner", printedBanner);
}
// 獲取所有資源,示例中就是獲取到我們的啟動類
Set<Object> sources = getAllSources();
Assert.notEmpty(sources, "Sources must not be empty");
// 載入資源註冊成為Spring的bean
load(context, sources.toArray(new Object[0]));
listeners.contextLoaded(context);
}
SpringApplication:
private void refreshContext(ConfigurableApplicationContext context) {
refresh(context);
if (this.registerShutdownHook) {
try {
context.registerShutdownHook();
}
catch (AccessControlException ex) {
}
}
}
這裡上下文的重新整理和註冊關閉鉤子我們都在之前的Spring原始碼分析文章中分析過,不再贅述。讀者可能會有疑惑,Spring boot不是有非常厲害的自動配置麼,文章中並沒有看到啊,Spring boot的自動配置我們會用單獨的文章來分析,本篇文章我們主要分析整個啟動流程的步驟和一些擴充套件,到這裡,整個Spring boot的啟動流程就分析完了。