一. 测试代码
@SpringBootApplication public class SbmvcApplication { public static void main(String[] args) { SpringApplication.run(SbmvcApplication.class, args); } }
此处我的springboot 版本是 2.0.3.RELEASE
<?xml version="1.0" encoding="UTF-8"?> <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>2.0.3.RELEASE</version> <relativePath/> <!-- lookup parent from repository --> </parent> <groupId>com.study.demo</groupId> <artifactId>sbmvc</artifactId> <version>0.0.1-SNAPSHOT</version> <name>sbmvc</name> <description>Demo project for Spring Boot</description> <properties> <java.version>1.8</java.version> </properties> <dependencies> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency> </dependencies> <build> <plugins> <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> </plugin> </plugins> </build> </project>
二. 调试
public static ConfigurableApplicationContext run(Class<?> primarySource, String... args) { return run(new Class<?>[] { primarySource }, args); } public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) { return new SpringApplication(primarySources).run(args); }
1. 创建 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));
//判断运行环境类型 this.webApplicationType = deduceWebApplicationType();
//加载 spring.factories 配置文件, 并设置 ApplicationContextInitializer 配置到 this.initializers 属性中 setInitializers((Collection) getSpringFactoriesInstances( ApplicationContextInitializer.class));
//同样是加载配置文件, 设置 ApplicationListener配置 到 this.listeners 属性中 setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
//这里是拿入口类, 如本例中的 Sbmvcapplication this.mainApplicationClass = deduceMainApplicationClass(); }
deduceWebApplicationType()
private static final String REACTIVE_WEB_ENVIRONMENT_CLASS = "org.springframework." + "web.reactive.DispatcherHandler"; private static final String MVC_WEB_ENVIRONMENT_CLASS = "org.springframework." + "web.servlet.DispatcherServlet"; private static final String[] WEB_ENVIRONMENT_CLASSES = { "javax.servlet.Servlet", "org.springframework.web.context.ConfigurableWebApplicationContext" }; 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; }
从这里看, 程序分为3中运行环境,
NONE : 非 web 的运行环境
SERVLET : 普通 web 的运行环境
REACTIVE : 响应式 web 的运行环境
这里主要看的是 SERVLET 启动.
getSpringFactoriesInstances()
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(); // Use names and ensure unique to protect against duplicates Set<String> names = new LinkedHashSet<>( SpringFactoriesLoader.loadFactoryNames(type, classLoader)); List<T> instances = createSpringFactoriesInstances(type, parameterTypes, classLoader, args, names); AnnotationAwareOrderComparator.sort(instances); return instances; }
这里主要看一下 SpringFactoriesLoader.loadFactoryNames() 方法
public static List<String> loadFactoryNames(Class<?> factoryClass, @Nullable ClassLoader classLoader) { String factoryClassName = factoryClass.getName(); return loadSpringFactories(classLoader).getOrDefault(factoryClassName, Collections.emptyList()); } public static final String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories"; private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) { MultiValueMap<String, String> result = cache.get(classLoader); if (result != null) { return result; } try { 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()) { 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); } }
看到这, 能明白, 是在加载 META-INF/spring.factories 文件中的配置.
key 就是传入类的引用, value 是配置的值, 多个值之间用英文逗号隔开, 如:
# 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
deduceMainApplicationClass()
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; }
这里调用了非java代码, 跟踪不了具体执行过程, 但是从结果看, 拿到的是 SbmvcApplication 类
总结
在创建 SpringApplication 的时候, 干了以下几件事情:
1. 判断了运行环境类型为 SERVLET
2. 加载了 spring.factories 文件中的 ApplicationContextInitializer 配置到 this.initializers 属性中 - 6个初始化器
# spring-boot 包里面 # 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 # spring-boot-autoconfigure 包里面 # Initializers org.springframework.context.ApplicationContextInitializer= org.springframework.boot.autoconfigure.SharedMetadataReaderFactoryContextInitializer, org.springframework.boot.autoconfigure.logging.ConditionEvaluationReportLoggingListener
3. 加载了 spring.factories 文件中的 ApplicationListener 配置 到 this.listeners 属性中 - 10个监听器
# spring-boot 包里面
# 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
# spring-boot-autoconfigure 包里面 # Application Listeners org.springframework.context.ApplicationListener= org.springframework.boot.autoconfigure.BackgroundPreinitializer
4. 拿到入口类SbmvcApplication , 放入 this.mainApplicationClass 属性中.