【Spring】内嵌Tomcat&去Xml&调试Mvc

菜瓜：今天听到个名词“父子容器”，百度了一下，感觉概念有点空洞，这是什么核武器？

水稻：你说的是SpringMvc和Spring吧，其实只是一个概念而已，用来将两个容器做隔离，起到解耦的作用，其中子容器可以拿到父容器的bean，父容器拿不到子容器的。但是SpringBoot出来之后这个概念基本就被淡化掉，没有太大意义，SpringBoot中只有一个容器了。

菜瓜：能不能给个demo？

水稻：可以。由于现在SpringBoot已经大行其道，Mvc你可能接触的少，甚至没接触过。

• 早些年启动一个Mvc项目费老鼻子劲了，要配置各种Xml文件（Web.xml，spring.xml，spring-dispather.xml）,然后开发完的项目要打成War包发到Tomcat容器中
• 现在可以直接引入Tomcat包，用main方法直接调起。为了调试方便，我就演示一个Pom引入Tomcat的例子
• ①启动类

• package com.vip.qc.mvc;
  
  import org.apache.catalina.Context;
  import org.apache.catalina.LifecycleException;
  import org.apache.catalina.LifecycleListener;
  import org.apache.catalina.startup.Tomcat;
  import org.springframework.context.annotation.ComponentScan;
  import org.springframework.context.annotation.Configuration;
  import org.springframework.stereotype.Controller;
  import org.springframework.web.servlet.support.AbstractAnnotationConfigDispatcherServletInitializer;
  
  /**
   * 参考： * https://docs.spring.io/spring/docs/current/spring-framework-reference/web.html#mvc-servlet
   * <p>
   * 嵌入tomcat，由Tomcat发起对Spring容器的初始化调用过程
   * <p>
   * - 启动过程
   * * - Servlet规范，Servlet容器在启动之后会SPI加载META-INF/services目录下的实现类并调用其onStartup方法
   * * - Spring遵循规范实现了ServletContainerInitializer接口。该接口在执行时会收集WebApplicationInitializer接口实现类并循环调用其onStartup方法
   * * - 其中AbstractDispatcherServletInitializer
   * * * - 将spring上下文放入ContextLoaderListener监听器，该监听会发起对refresh方法的调用
   * * * - 注册dispatcherServlet，后续会由tomcat调用HttpServletBean的init方法，完成子容器的refresh调用
   * *
   *
   * @author QuCheng on 2020/6/28.
   */
  public class SpringWebStart {
  
      public static void main(String[] args) {
          Tomcat tomcat = new Tomcat();
          try {
              // 此处需要取一个目录
              Context context = tomcat.addContext("/", System.getProperty("java.io.tmp"));
              context.addLifecycleListener((LifecycleListener) Class.forName(tomcat.getHost().getConfigClass()).newInstance());
              tomcat.setPort(8081);
              tomcat.start();
              tomcat.getServer().await();
          } catch (LifecycleException | ClassNotFoundException | IllegalAccessException | InstantiationException e) {
              e.printStackTrace();
          }
      }
  
      static class MyWebApplicationInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {
  
          private final static String PACKAGE_PATH = "com.vip.qc.mvc.controller";
          private final static String PACKAGE_PATH_CHILD = "com.vip.qc.mvc.service";
  
          @Override
          protected String[] getServletMappings() {
              return new String[]{"/"};
          }
  
          @Override
          protected Class<?>[] getRootConfigClasses() {
              // spring 父容器
              return new Class[]{AppConfig.class};
          }
  
          @Override
          protected Class<?>[] getServletConfigClasses() {
              // servlet 子容器
              return new Class[]{ServletConfig.class};
          }
  
          @Configuration
          @ComponentScan(value = PACKAGE_PATH_CHILD, excludeFilters = @ComponentScan.Filter(classes = Controller.class))
          static class AppConfig {
          }
  
          @Configuration
          @ComponentScan(value = PACKAGE_PATH, includeFilters = @ComponentScan.Filter(classes = Controller.class))
          static class ServletConfig {
          }
      }
  
  } 

• ②Controller&Service

• package com.vip.qc.mvc.controller;
  
  import com.vip.qc.mvc.service.ServiceChild;
  import org.springframework.beans.BeansException;
  import org.springframework.context.ApplicationContext;
  import org.springframework.context.ApplicationContextAware;
  import org.springframework.stereotype.Controller;
  import org.springframework.web.bind.annotation.RequestMapping;
  import org.springframework.web.bind.annotation.ResponseBody;
  
  import javax.annotation.Resource;
  
  /**
   * @author QuCheng on 2020/6/28.
   */
  @Controller
  public class ControllerT implements ApplicationContextAware {
  
      @Resource
      private ServiceChild child;
  
      @RequestMapping("/hello")
      @ResponseBody
      public String containter() {
          child.getParent();
          System.out.println("parentContainer");
          return "containter";
      }
  
      @Override
      public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
          System.out.println("子容器" + applicationContext);
          System.out.println("子容器中获取父容器bean" + applicationContext.getBean(ServiceChild.class));
      }
  }
  
  package com.vip.qc.mvc.service;
  
  import com.vip.qc.mvc.controller.ControllerT;
  import org.springframework.beans.BeansException;
  import org.springframework.beans.factory.NoSuchBeanDefinitionException;
  import org.springframework.context.ApplicationContext;
  import org.springframework.context.ApplicationContextAware;
  import org.springframework.stereotype.Service;
  
  /**
   * @author QuCheng on 2020/6/28.
   */
  @Service
  public class ServiceChild implements ApplicationContextAware {
  
      //    @Resource
      private ControllerT controllerT;
  
      public void getParent() {
  
          System.out.println(controllerT);
      }
  
      @Override
      public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
          System.out.println("父容器" + applicationContext);
          try {
              System.out.println("父容器中获取子容器bean" + applicationContext.getBean(ControllerT.class));
          } catch (NoSuchBeanDefinitionException e) {
              System.out.println("找不到子容器的bean");
          }
      }
  }
  
  // 调用SpringWebStart的main方法启动-会有如下打印
  父容器Root WebApplicationContext, started on Sun Jun 28 22:03:52 CST 2020
  找不到子容器的bean
  子容器WebApplicationContext for namespace 'dispatcher-servlet', started on Sun Jun 28 22:03:58 CST 2020, parent: Root WebApplicationContext
  子容器中获取父容器beancom.vip.qc.mvc.service.ServiceChild@4acfc43a

• Demo比较简单，不过也能反映父子容器的关系

菜瓜：嗯，效果看到了，能不能讲一下启动过程

水稻：稍等，我去下载源码。上面代码演示中已经提前说明了，父子容器的加载是Tomcat依据Servlet规范发起调用完成的

• spring-web源码包的/META-INF中能找到SPI的实际加载类SpringServletContainerInitializer#onStartup()方法会搜集实现WebApplicationInitializer接口的类，并调用其onStartup方法
• 上面MyWebApplicationInitializer启动类是WebApplicationInitializer的子类，未实现onStartup，实际调用的是其抽象父类AbstractDispatcherServletInitializer的方法。跟进去

• @Override
  public void onStartup(ServletContext servletContext) throws ServletException {
     //① 创建Spring父容器上下文-对象放入ContextLoadListener，后续调起完成初始化，
     super.onStartup(servletContext);
     //② 创建DispatcherServlet对象，后续会由tomcat调用其init方法，完成子容器的初始化工作
     registerDispatcherServlet(servletContext);
  }
  
  // ①进来
  protected void registerContextLoaderListener(ServletContext servletContext) {
      // 此处会回调我们启动类的getRootConfigClasses()方法 - 父容器配置
      WebApplicationContext rootAppContext = createRootApplicationContext();
      if (rootAppContext != null) {
          ContextLoaderListener listener = new ContextLoaderListener(rootAppContext);
          istener.setContextInitializers(getRootApplicationContextInitializers());
          servletContext.addListener(listener);
      }
      else {
          logger.debug("No ContextLoaderListener registered, as " +
                "createRootApplicationContext() did not return an application context");
      }
  }
  
  // ②进来
  protected void registerDispatcherServlet(ServletContext servletContext) {
          。。。
      // 此处会回调我们启动类的getServletConfigClasses()方法 - 子容器配置
      WebApplicationContext servletAppContext = createServletApplicationContext();
          。。。
      // 初始化的dispatcherServlet，会加入Tomcat容器中-后续调用
      // FrameworkServlet#initServletBean()会完成上下文初始化工作
      FrameworkServlet dispatcherServlet = createDispatcherServlet(servletAppContext);
          。。。
  }

菜瓜：这样容器就可以用了吗？

水稻：是的，这样就可以直接在浏览器上面访问http://localhost:8081/hello，不过这是一个最简陋的web项目

菜瓜：懂了，最简陋是什么意思

水稻：如果我们想加一些常见的Web功能，譬如说拦截器，过滤器啥的。可以通过@EnableWebMvc注解自定义一些功能

• package com.vip.qc.mvc;
  
  import com.vip.qc.mvc.interceptor.MyInterceptor1;
  import com.vip.qc.mvc.interceptor.MyInterceptor2;
  import org.springframework.context.annotation.Configuration;
  import org.springframework.web.servlet.config.annotation.EnableWebMvc;
  import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
  import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
  
  import javax.annotation.Resource;
  
  /**
   * @author QuCheng on 2020/6/28.
   */
  @Configuration
  @EnableWebMvc
  public class WebMvcConfig implements WebMvcConfigurer {
  
      @Resource
      private MyInterceptor1 interceptor1;
      @Resource
      private MyInterceptor2 interceptor2;
  
      @Override
      public void addInterceptors(InterceptorRegistry registry) {
          registry.addInterceptor(interceptor1).addPathPatterns("/interceptor/**");
          registry.addInterceptor(interceptor2).addPathPatterns("/interceptor/**");
      }
  }
  
  package com.vip.qc.mvc.interceptor;
  
  import org.springframework.context.annotation.Configuration;
  import org.springframework.web.servlet.HandlerInterceptor;
  import org.springframework.web.servlet.ModelAndView;
  
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  
  /**
   * @author QuCheng on 2020/6/28.
   */
  @Configuration
  public class MyInterceptor1 implements HandlerInterceptor {
  
      @Override
      public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
          System.out.println("嘻嘻 我是拦截器1 pre");
          return true;
      }
  
      @Override
      public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
          System.out.println("嘻嘻 我是拦截器1 post");
      }
  
      @Override
      public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
          System.out.println("嘻嘻 我是拦截器1 after");
      }
  }
  
  package com.vip.qc.mvc.interceptor;
  
  import org.springframework.context.annotation.Configuration;
  import org.springframework.web.servlet.HandlerInterceptor;
  import org.springframework.web.servlet.ModelAndView;
  
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  
  /**
   * @author QuCheng on 2020/6/28.
   */
  @Configuration
  public class MyInterceptor2 implements HandlerInterceptor {
  
      @Override
      public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
          System.out.println("嘻嘻 我是拦截器2 pre");
          return true;
      }
  
      @Override
      public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
          System.out.println("嘻嘻 我是拦截器2 post");
      }
  
      @Override
      public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
          System.out.println("嘻嘻 我是拦截器2 after");
      }
  
  } 

菜瓜：我知道，这里还有个Mvc请求调用流程和这个拦截器有关。而且这个拦截器不是MethodInterceptor（切面）

水稻：没错，说到这里顺便复习一下Mvc的请求过程

• 请求最开始都是通过Tomcat容器转发过来的，调用链：HttpServlet#service() -> FrameworkServlet#processRequest() -> DispatcherServlet#doDispather()

•  protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
       。。。
     processedRequest = checkMultipart(request);
     multipartRequestParsed = (processedRequest != request);
     // 1.返回一个持有methodHandler（按照URL匹配得出的被调用bean对象以及目标方法）调用链(拦截器链)对象
     mappedHandler = getHandler(processedRequest);
     。。。
     // 2.按照我们现在写代码的方式，只会用到HandlerMethod，其他三种基本不会用
     HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
     。。。
     // 3.前置过滤器 - 顺序调用
     if (!mappedHandler.applyPreHandle(processedRequest, response)) {
         return;
     }
     // 4.Actually invoke the handler.
     mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
     。。。
       applyDefaultViewName(processedRequest, mv);
     // 5.后置过滤器 - 逆序调用
     mappedHandler.applyPostHandle(processedRequest, response, mv);
     。。。
     // 6.处理试图 - 内部render
     processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
     }
     catch (Exception ex) {
        // 异常处理
        triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
     }
         // 异常处理
     catch (Throwable err) {
        triggerAfterCompletion(processedRequest, response, mappedHandler,
                       new NestedServletException("Handler processing failed", err));
     }
       。。。

菜瓜：这个之前看过不少，百度一大堆，不过还是源码亲切

总结：

• 目前基本互联网项目都是SpringBoot起手了，再难遇到SpringMvc的项目，不过熟悉该流程有利于我们更加深刻的理解Ioc容器
• Mvc拦截器链也是日常开发中会用到的功能，顺便熟悉一下请求的执行过程