springboot情操陶冶-SpringApplication(一)

当前位置:首页高博亚洲国际 >

高博亚洲国际

springboot情操陶冶-SpringApplication(一)

时间:2019-06-13本站浏览次数:71

       

SpringApplication是所有springboot的入口类,分析此类有助于我们了解springboot的工作机制。本文以2.0.3.REALEASE版本作分析

SpringApplication

调用实例如下

package com.example.demospringbootweb;import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;@SpringBootApplicationpublic class DemoSpringbootWebApplication { public static void main(String[] args) { SpringApplication.run(DemoSpringbootWebApplication.class, args); }}

调用的是SpringApplication.run()方法进行应用程序的启动。代码很简单也容易让用户上手,笔者这就进入其具体的类以探瑰宝。

注释描述

先看下其官方注释,有助于我们入门。由于注释过长,笔者此处只对其主要内容作下翻译总结

    可以简单的通过main()函数来辅助启动一个spring应用程序。默认情况下其会按照以下步骤来辅助我们创建的应用创建一个关联的ApplicationContext实例注册CommandLinePropertySource实例暴露命令行的参数作为spring的属性刷新ApplicationContext,并加载所有的单例beans触发实现了CommandLineRunner的实例beansSpringApplications可以读取来自不同源的beans。官方建议用户使用@Configuration注解相应的启动类,当然也支持从以下方式加载相应的beansAnnotatedBeanDefinitionReader加载指定的类XmlBeanDefinitionReader加载XML的配置信息或者GroovyBeanDefinitionReader加载groovy脚本资源ClassPathBeanDefinitionScanner扫描指定的包加载相应bean

过于抽象,笔者继续通过源码来对上述的内容进行回顾

构造函数

/** * 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; // 加载的主类,可指定多个 Assert.notNull(primarySources, "PrimarySources must not be null"); this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources)); // 推断是否为web环境 this.webApplicationType = deduceWebApplicationType(); // 加载ApplicationContextInitializer接口类 setInitializers((Collection) getSpringFactoriesInstances( ApplicationContextInitializer.class)); // 加载ApplicationListener接口类 setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class)); // 推断主函数类 this.mainApplicationClass = deduceMainApplicationClass(); }

对上述的注释作下简单的解释

SpringApplication#deduceWebApplicationType()

推断是否为web环境,源码如下

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; }

从代码层看总共有三种应用类型,也代表了三个环境类型

WebApplicationType.REACTIVE reactive web应用(classpath环境下须有org.springframework.web.reactive.DispatcherHandler)WebApplicationType.SERVLET servlet web应用(classpath环境下存在javax.servlet.Servlet或者org.springframework.web.context.ConfigurableWebApplicationContext)WebApplicationType.NONE 简单的JAVA应用(classpath环境不存在上述的类)

SpringApplication#deduceMainApplicationClass()

推断主函数类,源码如下

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; }

很简单,就是寻找哪个类下含有main方法,此处和我们常用的启动类不谋而合

SpringApplication#getSpringFactoriesInstances()

找寻相应的接口实现类,源码如下

private <T> Collection<T> getSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, Object... args) { // 上下文classLoader ClassLoader classLoader = Thread.currentThread().getContextClassLoader(); // 通过SpringFactoriesLoader来加载相应的类 Set<String> names = new LinkedHashSet<>( SpringFactoriesLoader.loadFactoryNames(type, classLoader)); List<T> instances = createSpringFactoriesInstances(type, parameterTypes, classLoader, args, names); AnnotationAwareOrderComparator.sort(instances); return instances; }

进而查看相应的静态方法SpringFactoriesLoader.loadFactoryNames(),源码如下

public static List<String> loadFactoryNames(Class<?> factoryClass, @Nullable ClassLoader classLoader) { String factoryClassName = factoryClass.getName(); // 关键处理类 return loadSpringFactories(classLoader).getOrDefault(factoryClassName, Collections.emptyList()); }

关键处理类出来了,源码跟上

private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) { // 缓存处理 MultiValueMap<String, String> result = cache.get(classLoader); if (result != null) { return result; } try { // 找寻所有classpath下的"META-INF/spring.factories"文件 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()) { // 对含有,的进行分隔并转为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); } }


由此我们得出结论,classpath环境下所有含META-INF/spring.factories的文件,里面约定了默认的实现。笔者以spring-boot-2.0.3.REALEASE.jar为例

# PropertySource Loadersorg.springframework.boot.env.PropertySourceLoader=org.springframework.boot.env.PropertiesPropertySourceLoader,org.springframework.boot.env.YamlPropertySourceLoader# Run Listenersorg.springframework.boot.SpringApplicationRunListener=org.springframework.boot.context.event.EventPublishingRunListener# Error Reportersorg.springframework.boot.SpringBootExceptionReporter=org.springframework.boot.diagnostics.FailureAnalyzers# Application Context Initializersorg.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 Listenersorg.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 Processorsorg.springframework.boot.env.EnvironmentPostProcessor=org.springframework.boot.cloud.CloudFoundryVcapEnvironmentPostProcessor,org.springframework.boot.env.SpringApplicationJsonEnvironmentPostProcessor,org.springframework.boot.env.SystemEnvironmentPropertySourceEnvironmentPostProcessor# Failure Analyzersorg.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# FailureAnalysisReportersorg.springframework.boot.diagnostics.FailureAnalysisReporter=org.springframework.boot.diagnostics.LoggingFailureAnalysisReporter

因此SpringApplication构造函数中加载的ApplicationContextInitializer类有如下

ConfigurationWarningsApplicationContextInitializer (对ComponentScan指定的值为"org"等进行报警输出)ContextIdApplicationContextInitializer (创建默认名为application的ContextId对象,也可通过spring.application.name指定)DelegatingApplicationContextInitializer (对context.initializer.classes指定的class集合进行加载)ServerPortInfoApplicationContextInitializer (将local.server.port设置为指定的web端口,默认为8080)

而加载的ApplicationListener类有如下

ClearCachesApplicationListener (反射工具缓存清空事件)ParentContextCloserApplicationListener (父ApplicationContext关闭事件)FileEncodingApplicationListener (系统变量配置的file.encoding值是否与环境变量spring.mandatory-file-encoding一致事件)AnsiOutputApplicationListener (控制台彩色输出事件,可通过spring.output.ansi.enabled来指定)ConfigFileApplicationListener (读取spring.profile.active/spring.profile.include配置)DelegatingApplicationListener (委托事件处理类)ClasspathLoggingApplicationListener (打印classpath信息,级别为debug)LoggingApplicationListener (日志处理事件)LiquibaseServiceLocatorApplicationListener (classpath是否存在liquibase的CustomResolverServiceLocator类判断事件)

小结

由此SpringApplication构造函数完成了一些必要的初始化,重点在于ApplicationContextInitializerApplicationListener接口类。并且通过构造函数反射来进行实例化

限于篇幅过长,笔者将对SpringApplication#run()方法的具体解析放于下一章节来分析

, 1, 0, 9);




公司地址:(章贡区)赣州贸易广场(南康区)东山工业四路1号
联系人:魏香赞 13623816725
田继前 15336887075
电话:13937760969 传真:nlvukb@162.com
邮箱:j6txlc@hotmail.com

粤公网安备 44030702001579号

高博亚洲打不开@