【Spring】內嵌Tomcat&去Xml&除錯Mvc

渠成發表於2020-06-28

菜瓜:今天聽到個名詞“父子容器”,百度了一下,感覺概念有點空洞,這是什麼核武器?

水稻:你說的是SpringMvc和Spring吧,其實只是一個概念而已,用來將兩個容器做隔離,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出來之後這個概念基本就被淡化掉,沒有太大意義,SpringBoot中只有一個容器了。

菜瓜:能不能給個demo?

水稻:可以。由於現在SpringBoot已經大行其道,Mvc你可能接觸的少,甚至沒接觸過。

  • 早些年啟動一個Mvc專案費老鼻子勁了,要配置各種Xml檔案(Web.xml,spring.xml,spring-dispather.xml),然後開發完的專案要打成War包發到Tomcat容器中
  • 現在可以直接引入Tomcat包,用main方法直接調起。為了除錯方便,我就演示一個Pom引入Tomcat的例子
  • ①啟動類
  • 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;
    
    /**
     * 參考: * https://docs.spring.io/spring/docs/current/spring-framework-reference/web.html#mvc-servlet
     * <p>
     * 嵌入tomcat,由Tomcat發起對Spring容器的初始化呼叫過程
     * <p>
     * - 啟動過程
     * * - Servlet規範,Servlet容器在啟動之後會SPI載入META-INF/services目錄下的實現類並呼叫其onStartup方法
     * * - Spring遵循規範實現了ServletContainerInitializer介面。該介面在執行時會收集WebApplicationInitializer介面實現類並迴圈呼叫其onStartup方法
     * * - 其中AbstractDispatcherServletInitializer
     * * * - 將spring上下文放入ContextLoaderListener監聽器,該監聽會發起對refresh方法的呼叫
     * * * - 註冊dispatcherServlet,後續會由tomcat呼叫HttpServletBean的init方法,完成子容器的refresh呼叫
     * *
     *
     * @author QuCheng on 2020/6/28.
     */
    public class SpringWebStart {
    
        public static void main(String[] args) {
            Tomcat tomcat = new Tomcat();
            try {
    // 此處需要取一個目錄 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("子容器中獲取父容器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("父容器中獲取子容器bean" + applicationContext.getBean(ControllerT.class));
            } catch (NoSuchBeanDefinitionException e) {
                System.out.println("找不到子容器的bean");
            }
        }
    }

    // 呼叫
    SpringWebStart的main方法啟動-會有如下列印
    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
    子容器中獲取父容器beancom.vip.qc.mvc.service.ServiceChild@4acfc43a
    
    
  • Demo比較簡單,不過也能反映父子容器的關係

菜瓜:嗯,效果看到了,能不能講一下啟動過程

水稻:稍等,我去下載原始碼。上面程式碼演示中已經提前說明了,父子容器的載入是Tomcat依據Servlet規範發起呼叫完成的

  • spring-web原始碼包的/META-INF中能找到SPI的實際載入類SpringServletContainerInitializer#onStartup()方法會蒐集實現WebApplicationInitializer介面的類,並呼叫其onStartup方法
  • 上面MyWebApplicationInitializer啟動類是WebApplicationInitializer的子類,未實現onStartup,實際呼叫的是其抽象父類AbstractDispatcherServletInitializer的方法。跟進去 
  • @Override
    public void onStartup(ServletContext servletContext) throws ServletException {
       //① 建立Spring父容器上下文-物件放入ContextLoadListener,後續調起完成初始化,
       super.onStartup(servletContext);
       //② 建立DispatcherServlet物件,後續會由tomcat呼叫其init方法,完成子容器的初始化工作
       registerDispatcherServlet(servletContext);
    }
    
    // ①進來
    protected void registerContextLoaderListener(ServletContext servletContext) {
        // 此處會回撥我們啟動類的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進來
    protected void registerDispatcherServlet(ServletContext servletContext) {
            。。。
        // 此處會回撥我們啟動類的getServletConfigClasses()方法 - 子容器配置
        WebApplicationContext servletAppContext = createServletApplicationContext();
            。。。
        // 初始化的dispatcherServlet,會加入Tomcat容器中-後續呼叫
        // FrameworkServlet#initServletBean()會完成上下文初始化工作
        FrameworkServlet dispatcherServlet = createDispatcherServlet(servletAppContext);
            。。。
    }

菜瓜:這樣容器就可以用了嗎?

水稻:是的,這樣就可以直接在瀏覽器上面訪問http://localhost:8081/hello,不過這是一個最簡陋的web專案

菜瓜:懂了,最簡陋是什麼意思

水稻:如果我們想加一些常見的Web功能,譬如說攔截器,過濾器啥的。可以通過@EnableWebMvc註解自定義一些功能

  • 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 我是攔截器1 pre");
            return true;
        }
    
        @Override
        public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
            System.out.println("嘻嘻 我是攔截器1 post");
        }
    
        @Override
        public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
            System.out.println("嘻嘻 我是攔截器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 我是攔截器2 pre");
            return true;
        }
    
        @Override
        public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
            System.out.println("嘻嘻 我是攔截器2 post");
        }
    
        @Override
        public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
            System.out.println("嘻嘻 我是攔截器2 after");
        }
    
    } 

菜瓜:我知道,這裡還有個Mvc請求呼叫流程和這個攔截器有關。而且這個攔截器不是MethodInterceptor(切面)

水稻:沒錯,說到這裡順便複習一下Mvc的請求過程

  • 請求最開始都是通過Tomcat容器轉發過來的,呼叫鏈:HttpServlet#service() -> FrameworkServlet#processRequest() -> DispatcherServlet#doDispather()
  •  1 protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
     2     。。。
     3   processedRequest = checkMultipart(request);
     4   multipartRequestParsed = (processedRequest != request);
     5   // 1.返回一個持有methodHandler(按照URL匹配得出的被呼叫bean物件以及目標方法)呼叫鏈(攔截器鏈)物件
     6   mappedHandler = getHandler(processedRequest);
     7   。。。
     8   // 2.按照我們現在寫程式碼的方式,只會用到HandlerMethod,其他三種基本不會用
     9   HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
    10   。。。
    11   // 3.前置過濾器 - 順序呼叫
    12   if (!mappedHandler.applyPreHandle(processedRequest, response)) {
    13       return;
    14   }
    15   // 4.Actually invoke the handler.
    16   mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
    17   。。。
    18     applyDefaultViewName(processedRequest, mv);
    19   // 5.後置過濾器 - 逆序呼叫
    20   mappedHandler.applyPostHandle(processedRequest, response, mv);
    21   。。。
    22   // 6.處理試圖 - 內部render
    23   processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
    24   }
    25   catch (Exception ex) {
    26      // 異常處理
    27      triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
    28   }
    29       // 異常處理
    30   catch (Throwable err) {
    31      triggerAfterCompletion(processedRequest, response, mappedHandler,
    32                     new NestedServletException("Handler processing failed", err));
    33   }
    34     。。。

     

 菜瓜:這個之前看過不少,百度一大堆,不過還是原始碼親切

 

總結:

  • 目前基本網際網路專案都是SpringBoot起手了,再難遇到SpringMvc的專案,不過熟悉該流程有利於我們更加深刻的理解Ioc容器
  • Mvc攔截器鏈也是日常開發中會用到的功能,順便熟悉一下請求的執行過程

 

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