springboot情操陶冶-SpringApplication(一)
阿新 • • 發佈：2019-02-05
SpringApplication是所有springboot的入口類，分析此類有助於我們瞭解springboot的工作機制。本文以2.0.3.REALEASE版本作分析
SpringApplication
呼叫例項如下
package com.example.demospringbootweb; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; @SpringBootApplication public class DemoSpringbootWebApplication { public static void main(String[] args) { SpringApplication.run(DemoSpringbootWebApplication.class, args); } }
呼叫的是SpringApplication.run()方法進行應用程式的啟動。程式碼很簡單也容易讓使用者上手，筆者這就進入其具體的類以探瑰寶。
註釋描述
先看下其官方註釋，有助於我們入門。由於註釋過長，筆者此處只對其主要內容作下翻譯總結
- 可以簡單的通過main()函式來輔助啟動一個spring應用程式。預設情況下其會按照以下步驟來輔助我們建立的應用
- 建立一個關聯的ApplicationContext例項
- 註冊CommandLinePropertySource例項暴露命令列的引數作為spring的屬性
- 重新整理ApplicationContext，並載入所有的單例beans
- 觸發實現了CommandLineRunner的例項beans
- SpringApplications可以讀取來自不同源的beans。官方建議使用者使用@Configuration註解相應的啟動類，當然也支援從以下方式載入相應的beans
- AnnotatedBeanDefinitionReader載入指定的類
- XmlBeanDefinitionReader載入XML的配置資訊或者GroovyBeanDefinitionReader載入groovy指令碼資源
- ClassPathBeanDefinitionScanner掃描指定的包載入相應bean
過於抽象，筆者繼續通過原始碼來對上述的內容進行回顧
建構函式
/**
* Create a new {@link SpringApplication} instance. The application context will load
* beans from the specified primary sources (see {@link SpringApplication class-level}
* documentation for details. The instance can be customized before calling
* {@link #run(String...)}.
* @param resourceLoader the resource loader to use
* @param primarySources the primary bean sources
* @see #run(Class, String[])
* @see #setSources(Set)
*/
@SuppressWarnings({ "unchecked", "rawtypes" })
public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
this.resourceLoader = resourceLoader;
// 載入的主類，可指定多個
Assert.notNull(primarySources, "PrimarySources must not be null");
this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
// 推斷是否為web環境
this.webApplicationType = deduceWebApplicationType();
// 載入ApplicationContextInitializer介面類
setInitializers((Collection) getSpringFactoriesInstances(
ApplicationContextInitializer.class));
// 載入ApplicationListener介面類
setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
// 推斷主函式類
this.mainApplicationClass = deduceMainApplicationClass();
}對上述的註釋作下簡單的解釋
SpringApplication#deduceWebApplicationType()
推斷是否為web環境，原始碼如下
private WebApplicationType deduceWebApplicationType() {
if (ClassUtils.isPresent(REACTIVE_WEB_ENVIRONMENT_CLASS, null)
&& !ClassUtils.isPresent(MVC_WEB_ENVIRONMENT_CLASS, null)) {
return WebApplicationType.REACTIVE;
}
for (String className : WEB_ENVIRONMENT_CLASSES) {
if (!ClassUtils.isPresent(className, null)) {
return WebApplicationType.NONE;
}
}
return WebApplicationType.SERVLET;
}從程式碼層看總共有三種應用型別，也代表了三個環境型別
- WebApplicationType.REACTIVE reactive web應用(classpath環境下須有org.springframework.web.reactive.DispatcherHandler)
- WebApplicationType.SERVLET servlet web應用(classpath環境下存在javax.servlet.Servlet或者org.springframework.web.context.ConfigurableWebApplicationContext)
- WebApplicationType.NONE 簡單的JAVA應用(classpath環境不存在上述的類)
SpringApplication#deduceMainApplicationClass()
推斷主函式類，原始碼如下
private Class<?> deduceMainApplicationClass() {
try {
StackTraceElement[] stackTrace = new RuntimeException().getStackTrace();
for (StackTraceElement stackTraceElement : stackTrace) {
if ("main".equals(stackTraceElement.getMethodName())) {
return Class.forName(stackTraceElement.getClassName());
}
}
}
catch (ClassNotFoundException ex) {
// Swallow and continue
}
return null;
}很簡單，就是尋找哪個類下含有main方法，此處和我們常用的啟動類不謀而合
SpringApplication#getSpringFactoriesInstances()
找尋相應的介面實現類，原始碼如下
private <T> Collection<T> getSpringFactoriesInstances(Class<T> type,
Class<?>[] parameterTypes, Object... args) {
// 上下文classLoader
ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
// 通過SpringFactoriesLoader來載入相應的類
Set<String> names = new LinkedHashSet<>(
SpringFactoriesLoader.loadFactoryNames(type, classLoader));
List<T> instances = createSpringFactoriesInstances(type, parameterTypes,
classLoader, args, names);
AnnotationAwareOrderComparator.sort(instances);
return instances;
}進而檢視相應的靜態方法SpringFactoriesLoader.loadFactoryNames()，原始碼如下
public static List<String> loadFactoryNames(Class<?> factoryClass, @Nullable ClassLoader classLoader) {
String factoryClassName = factoryClass.getName();
// 關鍵處理類
return loadSpringFactories(classLoader).getOrDefault(factoryClassName, Collections.emptyList());
}關鍵處理類出來了，原始碼跟上
private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {
// 快取處理
MultiValueMap<String, String> result = cache.get(classLoader);
if (result != null) {
return result;
}
try {
// 找尋所有classpath下的"META-INF/spring.factories"檔案
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()) {
// 對含有,的進行分隔並轉為list集合
List<String> factoryClassNames = Arrays.asList(
StringUtils.commaDelimitedListToStringArray((String) entry.getValue()));
result.addAll((String) entry.getKey(), factoryClassNames);
}
}
cache.put(classLoader, result);
return result;
}
catch (IOException ex) {
throw new IllegalArgumentException("Unable to load factories from location [" +
FACTORIES_RESOURCE_LOCATION + "]", ex);
}
}由此我們得出結論，classpath環境下所有含META-INF/spring.factories的檔案，裡面約定了預設的實現。筆者以spring-boot-2.0.3.REALEASE.jar為例
# 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
因此SpringApplication建構函式中載入的ApplicationContextInitializer類有如下
- ConfigurationWarningsApplicationContextInitializer (對ComponentScan指定的值為"org"等進行報警輸出)
- ContextIdApplicationContextInitializer (建立預設名為application的ContextId物件，也可通過spring.application.name指定)
- DelegatingApplicationContextInitializer (對context.initializer.classes指定的class集合進行載入)
- ServerPortInfoApplicationContextInitializer (將local.server.port設定為指定的web埠，預設為8080)
而載入的ApplicationListener類有如下
- ClearCachesApplicationListener (反射工具快取清空事件)
- ParentContextCloserApplicationListener (父ApplicationContext關閉事件)
- FileEncodingApplicationListener (系統變數配置的file.encoding值是否與環境變數spring.mandatory-file-encoding一致事件)
- AnsiOutputApplicationListener (控制檯彩色輸出事件，可通過spring.output.ansi.enabled來指定)
- ConfigFileApplicationListener (讀取spring.profile.active/spring.profile.include配置)
- DelegatingApplicationListener (委託事件處理類)
- ClasspathLoggingApplicationListener (列印classpath資訊，級別為debug)
- LoggingApplicationListener (日誌處理事件)
- LiquibaseServiceLocatorApplicationListener (classpath是否存在liquibase的CustomResolverServiceLocator類判斷事件)
小結
由此SpringApplication建構函式完成了一些必要的初始化，重點在於ApplicationContextInitializer和ApplicationListener介面類。並且通過建構函式反射來進行例項化
限於篇幅過長，筆者將對SpringApplication#run()方法的具體解析放於下一章節來分析
作者：南柯問天 出處：http://www.cnblogs.com/question-sky/