接下来看@ComponentScan注解，@ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class), @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })，这个注解就是扫描包，然后放入spring容器。
@ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM,classes = {TypeExcludeFilter.class}), @Filter(type = FilterType.CUSTOM,classes = {AutoConfigurationExcludeFilter.class})}) public @interface SpringBootApplication {}
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。
接下来继续看run方法：
public static void main(String[] args) { SpringApplication.run(Application.class, args); }
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，我们点进run：
public ConfigurableApplicationContext run(String... args) { //计时器 StopWatch stopWatch = new StopWatch(); stopWatch.start(); ConfigurableApplicationContext context = null; Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList(); this.configureHeadlessProperty(); //监听器 SpringApplicationRunListeners listeners = this.getRunListeners(args); listeners.starting(); Collection exceptionReporters; try { ApplicationArguments applicationArguments = new DefaultApplicationArguments(args); ConfigurableEnvironment environment = this.prepareEnvironment(listeners, applicationArguments); this.configureIgnoreBeanInfo(environment); Banner printedBanner = this.printBanner(environment); //准备上下文 context = this.createApplicationContext(); exceptionReporters = this.getSpringFactoriesInstances(SpringBootExceptionReporter.class, new Class[]{ConfigurableApplicationContext.class}, context); //预刷新context this.prepareContext(context, environment, listeners, applicationArguments, printedBanner); //刷新context this.refreshContext(context); //刷新之后的context this.afterRefresh(context, applicationArguments); stopWatch.stop(); if (this.logStartupInfo) { (new StartupInfoLogger(this.mainApplicationClass)).logStarted(this.getApplicationLog(), stopWatch); } listeners.started(context); this.callRunners(context, applicationArguments); } catch (Throwable var10) { this.handleRunFailure(context, var10, exceptionReporters, listeners); throw new IllegalStateException(var10); } try { listeners.running(context); return context; } catch (Throwable var9) { this.handleRunFailure(context, var9, exceptionReporters, (SpringApplicationRunListeners)null); throw new IllegalStateException(var9); } }
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(); } } }
由此可知，就是一个spring的bean的加载过程。继续来看一个方法叫做 onRefresh()：
protected void onRefresh() throws BeansException { // For subclasses: do nothing by default. }
他在这里并没有直接实现，但是我们找他的具体实现：
比如Tomcat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); } }
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，那是如何创建的呢，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。
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>
首先自定义一个stater。
<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-starter</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。
来自：博客园
链接：cnblogs.com/cmt/p/14553189.html
