那么我们来总结下@SpringbootApplication：就是说，他已经把很多东西准备好，具体是否使用取决于我们的程序或者说配置，那我们到底用不用？那我们继续来看一行代码
public static void main(String[] args) { SpringApplication.run(StartEurekaApplication.class, args); }
那们来看下在执行run方法到底有没有用到哪些自动配置的东西，比如说内置的Tomcat，那我们来找找内置Tomcat，我们点进run
public static ConfigurableApplicationContext run(Object[] sources, String[] args) { return new SpringApplication(sources).run(args); }
然后他调用又一个run方法，我们点进来看
public ConfigurableApplicationContext run(String... args) { //计时器 StopWatch stopWatch = new StopWatch(); stopWatch.start(); ConfigurableApplicationContext context = null; FailureAnalyzers analyzers = null; configureHeadlessProperty(); //监听器 SpringApplicationRunListeners listeners = getRunListeners(args); listeners.starting(); try { ApplicationArguments applicationArguments = new DefaultApplicationArguments( args); ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments); Banner printedBanner = printBanner(environment); //准备上下文 context = createApplicationContext(); analyzers = new FailureAnalyzers(context); //预刷新context prepareContext(context, environment, listeners, applicationArguments, printedBanner); //刷新context refreshContext(context); //刷新之后的context afterRefresh(context, applicationArguments); listeners.finished(context, null); stopWatch.stop(); if (this.logStartupInfo) { new StartupInfoLogger(this.mainApplicationClass) .logStarted(getApplicationLog(), stopWatch); } return context; } catch (Throwable ex) { handleRunFailure(context, listeners, analyzers, ex); throw new IllegalStateException(ex); } }
那我们关注的就是 refreshContext(context); 刷新context，我们点进来看
private void refreshContext(ConfigurableApplicationContext context) { refresh(context); if (this.registerShutdownHook) { try { context.registerShutdownHook(); } catch (AccessControlException ex) { // Not allowed in some environments. } } }
我们继续点进refresh(context);
protected void refresh(ApplicationContext applicationContext) { Assert.isInstanceOf(AbstractApplicationContext.class, applicationContext); ((AbstractApplicationContext) applicationContext).refresh(); }
他会调用 ((AbstractApplicationContext) applicationContext).refresh();方法，我们点进来看
public void refresh() throws BeansException, IllegalStateException { synchronized (this.startupShutdownMonitor) { // Prepare this context for refreshing. prepareRefresh(); // Tell the subclass to refresh the internal bean factory. ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory(); // Prepare the bean factory for use in this context. prepareBeanFactory(beanFactory); try { // Allows post-processing of the bean factory in context subclasses. postProcessBeanFactory(beanFactory); // Invoke factory processors registered as beans in the context. invokeBeanFactoryPostProcessors(beanFactory); // Register bean processors that intercept bean creation. registerBeanPostProcessors(beanFactory); // Initialize message source for this context. initMessageSource(); // Initialize event multicaster for this context. initApplicationEventMulticaster(); // Initialize other special beans in specific context subclasses. onRefresh(); // Check for listener beans and register them. registerListeners(); // Instantiate all remaining (non-lazy-init) singletons. finishBeanFactoryInitialization(beanFactory); // Last step: publish corresponding event. finishRefresh(); } catch (BeansException ex) { if (logger.isWarnEnabled()) { logger.warn("Exception encountered during context initialization - " + "cancelling refresh attempt: " + ex); } // Destroy already created singletons to avoid dangling resources. destroyBeans(); // Reset 'active' flag. cancelRefresh(ex); // Propagate exception to caller. throw ex; } finally { // Reset common introspection caches in Spring's core, since we // might not ever need metadata for singleton beans anymore... resetCommonCaches(); } } }
这点代码似曾相识啊 没错，就是一个spring的bean的加载过程我在，解析springIOC加载过程的时候介绍过这里面的方法，如果你看过Spring源码的话 ，应该知道这些方法都是做什么的。现在我们不关心其他的，我们来看一个方法叫做 onRefresh();方法
protected void onRefresh() throws BeansException { // For subclasses: do nothing by default. }
他在这里并没有实现，但是我们找他的其他实现，我们来找
我们既然要找Tomcat那就肯定跟web有关，我们可以看到有个
ServletWebServerApplicationContext
@Override protected void onRefresh() { super.onRefresh(); try { createWebServer(); } catch (Throwable ex) { throw new ApplicationContextException("Unable to start web server", ex); } }
我们可以看到有一个createWebServer();方法他是创建web容器的，而Tomcat不就是web容器，那他是怎么创建的呢，我们继续看
private void createWebServer() { WebServer webServer = this.webServer; ServletContext servletContext = getServletContext(); if (webServer == null && servletContext == null) { ServletWebServerFactory factory = getWebServerFactory(); this.webServer = factory.getWebServer(getSelfInitializer()); } else if (servletContext != null) { try { getSelfInitializer().onStartup(servletContext); } catch (ServletException ex) { throw new ApplicationContextException("Cannot initialize servlet context", ex); } } initPropertySources(); }
factory.getWebServer(getSelfInitializer());他是通过工厂的方式创建的
public interface ServletWebServerFactory { WebServer getWebServer(ServletContextInitializer... initializers); }
可以看到 它是一个接口，为什么会是接口。因为我们不止是Tomcat一种web容器。
我们看到还有Jetty，那我们来看TomcatServletWebServerFactory
@Override public WebServer getWebServer(ServletContextInitializer... initializers) { Tomcat tomcat = new Tomcat(); File baseDir = (this.baseDirectory != null) ? this.baseDirectory : createTempDir("tomcat"); tomcat.setBaseDir(baseDir.getAbsolutePath()); Connector connector = new Connector(this.protocol); tomcat.getService().addConnector(connector); customizeConnector(connector); tomcat.setConnector(connector); tomcat.getHost().setAutoDeploy(false); configureEngine(tomcat.getEngine()); for (Connector additionalConnector : this.additionalTomcatConnectors) { tomcat.getService().addConnector(additionalConnector); } prepareContext(tomcat.getHost(), initializers); return getTomcatWebServer(tomcat); }
那这块代码，就是我们要寻找的内置Tomcat，在这个过程当中，我们可以看到创建Tomcat的一个流程。因为run方法里面加载的东西很多，所以今天就浅谈到这里。如果不明白的话， 我们在用另一种方式来理解下，
大家要应该都知道stater举点例子
<dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-data-redis</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-freemarker</artifactId> </dependency>
所以我们不防不定义一个stater来理解下，我们做一个需求，就是定制化不同的人跟大家说你们好，我们来看
<parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>2.1.4.RELEASE</version> <relativePath/> </parent> <groupId>com.zgw</groupId> <artifactId>gw-spring-boot-srater</artifactId> <version>1.0-SNAPSHOT</version> <dependencies> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-autoconfigure</artifactId> </dependency> </dependencies>
我们先来看maven配置写入版本号，如果自定义一个stater的话必须依赖spring-boot-autoconfigure这个包,我们先看下项目目录
public class GwServiceImpl implements GwService{ @Autowired GwProperties properties; @Override public void Hello() { String name=properties.getName(); System.out.println(name+"说:你们好啊"); } }
我们做的就是通过配置文件来定制name这个是具体实现
@Component @ConfigurationProperties(prefix = "spring.gwname") public class GwProperties { String name="zgw"; public String getName() { return name; } public void setName(String name) { this.name = name; } }
这个类可以通过@ConfigurationProperties读取配置文件
@Configuration @ConditionalOnClass(GwService.class) //扫描类 @EnableConfigurationProperties(GwProperties.class) //让配置类生效 public class GwAutoConfiguration { /** * 功能描述 托管给spring * @author zgw * @return */ @Bean @ConditionalOnMissingBean public GwService gwService() { return new GwServiceImpl(); } }
这个为配置类，为什么这么写因为，spring-boot的stater都是这么写的，我们可以参照他仿写stater，以达到自动配置的目的，然后我们在通过spring.factories也来进行配置
org.springframework.boot.autoconfigure.EnableAutoConfiguration=com.gw.GwAutoConfiguration
然后这样一个简单的stater就完成了，然后可以进行maven的打包，在其他项目引入就可以使用，在这里列出代码地址
