菜瓜:我自己去调Mvc的源码差点没给Spring的逻辑秀死。。。难受

水稻:那今天咱们看一个简单易用的SpringBoot吧

菜瓜:可以,这个我熟悉

水稻:熟悉?

菜瓜:当我没说,请开始你的表演

水稻:我没有别的意思,就是单纯的反问(手动狗头)。平时工作中用多了SpringBoot。咱们今天带着几个问题来看看它的操作吧

  1. 如何启动Spring容器
  2. 如何内嵌Tomcat容器
  3. 如何完成自动装配,就是0配置

菜瓜:你确定这是我熟悉的SpringBoot???

水稻:。。。看过来

  • 启动类点进去
  • public ConfigurableApplicationContext run(String... args) {
    StopWatch stopWatch = new StopWatch();
    stopWatch.start();
    ...
    listeners.starting();
    try {
    ...
    // ①创建Spring上下文容器对象 - 默认Servlet容器
    context = createApplicationContext();
    ...
    // ②调用refresh方法 - 回到熟悉的容器启动流程
    refreshContext(context);
    afterRefresh(context, applicationArguments);
    ...
    ...
    return context;
    }
  • ① 创建上下文对象
    • protected ConfigurableApplicationContext createApplicationContext() {
      Class<?> contextClass = this.applicationContextClass;
      if (contextClass == null) {
      try {
      switch (this.webApplicationType) {
      case SERVLET:
      contextClass = Class.forName(DEFAULT_SERVLET_WEB_CONTEXT_CLASS);
      break;
      case REACTIVE:
      contextClass = Class.forName(DEFAULT_REACTIVE_WEB_CONTEXT_CLASS);
      break;
      default:
      contextClass = Class.forName(DEFAULT_CONTEXT_CLASS);
      }
      }
      catch (ClassNotFoundException ex) {
      ...
      }
      }
      return (ConfigurableApplicationContext) BeanUtils.instantiateClass(contextClass);
      }
  • ②启动容器
    •     @Override
      public void refresh() throws BeansException, IllegalStateException {
      synchronized (this.startupShutdownMonitor) {
      prepareRefresh();
      ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory(); // Prepare the bean factory for use in this context.
      prepareBeanFactory(beanFactory); try {
      ...
      // ①springboot 内嵌tomcat容器
      onRefresh();
      ... } @Override
      protected void onRefresh() {
      super.onRefresh();
      try {
      // ②创建Servlet容器 默认tomcat
      createWebServer();
      }
      ...
      } private void createWebServer() {
      WebServer webServer = this.webServer;
      ServletContext servletContext = getServletContext();
      if (webServer == null && servletContext == null) {
      ServletWebServerFactory factory = getWebServerFactory();
      // ③看进去 回到mvc集成tomcat的场景
      this.webServer = factory.getWebServer(getSelfInitializer());
      }
      ...
      initPropertySources();
      } @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);
      }

水稻:好了,第一步和第二步完成了

菜瓜:就这???

水稻:是不是极其简单,令人发指。重头戏是后面的自动装配

  • 回到咱们启动类的注解上
  • ...
    // 标记自身被扫描
    @SpringBootConfiguration
    // 下一步 - 自动装配入口
    @EnableAutoConfiguration
    // 扫描bean路径 - 约定是启动类所在的包:所以没事别把启动类挪走(都是泪)
    @ComponentScan(excludeFilters = {
    @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
    @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
    public @interface SpringBootApplication ->
    @Import(AutoConfigurationImportSelector.class)
    public @interface EnableAutoConfiguration -> 重要
    public class AutoConfigurationImportSelector ... {
    @Override
    public void process(AnnotationMetadata annotationMetadata,
    DeferredImportSelector deferredImportSelector) {
    ...
    // 获取以EnableAutoConfiguration命名的/META-INF/Spring.factories文件中的value去重
    AutoConfigurationEntry autoConfigurationEntry = ((AutoConfigurationImportSelector) deferredImportSelector).getAutoConfigurationEntry(getAutoConfigurationMetadata(), annotationMetadata);
    // 启动的时候断点可以看到
    this.autoConfigurationEntries.add(autoConfigurationEntry);
    for (String importClassName : autoConfigurationEntry.getConfigurations()) {
    this.entries.putIfAbsent(importClassName, annotationMetadata);
    }
    }
    }
  • AutoConfigurationImportSelector 中的process是被ConfigurationClassPostProcessor通过processConfigBeanDefinitions方法调用(调用链如下)
    1. this.processConfigBeanDefinitions(registry);
    2. parser.parse(candidates);
    3. this.parse(((AnnotatedBeanDefinition)bd).getMetadata(), holder.getBeanName());
    4. sourceClass = this.doProcessConfigurationClass(configClass, sourceClass);
    5. this.processImports(configClass, sourceClass, this.getImports(sourceClass), true);
    6. this.deferredImportSelectorHandler.handle(configClass, (DeferredImportSelector)selector);
    7. handler.processGroupImports();
    8. grouping.getImports().forEach...
    9. this.group.process(...);
    --
    搜集到需要自动装配的类,封装成BeanDefinition后续实例化,实现自动装配功能
    譬如引入WebMvcAutoConfiguration类 - webmvc功能自动集成
    org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration 

菜瓜:原来如此。你把调用链拎出来就简单了很多。自动装配就是通过SPI加载org.springframework.boot.autoconfigure包下的class,封装成BeanDefinition后交给容器加载

总结:SpringBoot只需要一行代码便能启动一个Java应用。完全解放开发者复杂的配置

  • 内嵌Servlet容器,默认tomcat
  • 启动SpringWeb容器
  • 自动装配了简单web应用需要的工具和组建