springboot知识点整合

朱雀 2022-10-19 12:53 173阅读 0赞

#### springboot是什么 ####

> Spring Boot是由Pivotal团队提供的全新框架，其设计目的是用来简化新Spring应用的初始搭建以及开发过程。该框架使用了特定的方式来进行配置，从而使开发人员不再需要定义样板化的配置。

在我看来springboot最大好处就是简化配置，以前一个SpringMvc项目需要在xml配置各种东西，现在简化了很多配置，提高了开发效率

#### springboot是如何自动配置的 ####

一般我的启动类会有\*\*@SpringBootApplication\*\*注解，这是一个组合注解

@Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    @Inherited
    @SpringBootConfiguration
    @EnableAutoConfiguration
    @ComponentScan(excludeFilters = {
    		@Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
    		@Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })

这里比较重要的是\*\*@EnableAutoConfiguration\*\*

@Import(AutoConfigurationImportSelector.class)
    public @interface EnableAutoConfiguration {
    }

@Import是Spring提供的，会注入后面这个类**AutoConfigurationImportSelector**

其中方法调用为selectImports->getAutoConfigurationEntry->getCandidateConfigurations

往里面看会将**META-INF/spring.factories**文件里需要的类型获取

获取类的方法会在springboot启动的时候AbstractApplicationContext.refresh()调用。

#### springboot的启动流程 ####

以tomcat为例来看看springboot的启动加载流程

我们一般会运行main方法SpringApplication.run

先看看SpringApplication的构造方法

public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
       this.resourceLoader = resourceLoader;
       Assert.notNull(primarySources, "PrimarySources must not be null");
       this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
      // 获取类型
       this.webApplicationType = WebApplicationType.deduceFromClasspath();
      // 获取初始化的类并set进去
       setInitializers((Collection) getSpringFactoriesInstances(
             ApplicationContextInitializer.class));
      // 获取监听器
       setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
       this.mainApplicationClass = deduceMainApplicationClass();
    }

接下来我们主要看springboot的run方法

public ConfigurableApplicationContext run(String... args) {
      // 计时器
       StopWatch stopWatch = new StopWatch();
       stopWatch.start();
       ConfigurableApplicationContext context = null;
       Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
       configureHeadlessProperty();
       SpringApplicationRunListeners listeners = getRunListeners(args);
       listeners.starting();
       try {
          ApplicationArguments applicationArguments = new DefaultApplicationArguments(
                args);
          ConfigurableEnvironment environment = prepareEnvironment(listeners,
                applicationArguments);
          configureIgnoreBeanInfo(environment);
         // 打印banner
          Banner printedBanner = printBanner(environment);
         // 创建context容器
         // AnnotationConfigServletWebServerApplicationContext
          context = createApplicationContext();
          exceptionReporters = getSpringFactoriesInstances(
                SpringBootExceptionReporter.class,
                new Class[] { ConfigurableApplicationContext.class }, context);
          prepareContext(context, environment, listeners, applicationArguments,
                printedBanner);
         // 刷新上下文
          refreshContext(context);
          afterRefresh(context, applicationArguments);
          stopWatch.stop();
          if (this.logStartupInfo) {
             new StartupInfoLogger(this.mainApplicationClass)
                   .logStarted(getApplicationLog(), stopWatch);
          }
          listeners.started(context);
          callRunners(context, applicationArguments);
       }
       catch (Throwable ex) {
          handleRunFailure(context, ex, exceptionReporters, listeners);
          throw new IllegalStateException(ex);
       }
    
       try {
          listeners.running(context);
       }
       catch (Throwable ex) {
          handleRunFailure(context, ex, exceptionReporters, null);
          throw new IllegalStateException(ex);
       }
       return context;
    }

我们主要看refreshContext方法，他会调用父类**AbstractApplicationContext**的**refresh**方法，里面会调用子类的**onRefresh**方法，这是一个模板方法模式。接下来看

protected void onRefresh() {
       super.onRefresh();
       try {
       		// 创建web容器
          createWebServer();
       }
       catch (Throwable ex) {
          throw new ApplicationContextException("Unable to start web server", ex);
       }
    }

**createWebServer**方法会创建web容器接下来就能看见创建tomcat的代码了

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);
    }

#### 参考 ####

https://mp.weixin.qq.com/s/axRia4KH1YUSVI3WcOfWPg

https://mp.weixin.qq.com/s/TnVL1chwTqlXmlOdcuJCSg

https://mp.weixin.qq.com/s/y6pUTKRCucoeCGmgqwRDow