【Spring】內嵌Tomcat&去Xml&除錯Mvc

渠成發表於2020-06-28
SpringTomcatXML除錯MVC

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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