SpringBoot中Filter?bean如何添加到Servlet容器

更新時(shí)間：2023年08月04日 15:06:32 作者：yagefuma

這篇文章主要介紹了SpringBoot中Filter bean是怎么被添加到Servlet容器中的,本文分步驟結(jié)合實(shí)例代碼給大家介紹的非常詳細(xì),對(duì)大家的學(xué)習(xí)或工作具有一定的參考借鑒價(jià)值,需要的朋友可以參考下

對(duì)于Spring Boot的IOC容器——ServletWebServerApplicationContext，其中的Filter bean，每個(gè)Filter bean都會(huì)被獨(dú)立的注冊(cè)成為Servlet的Filter。大概的注冊(cè)過程分成2步：

IOC容器——ServletWebServerApplicationContext將Filter接口的實(shí)現(xiàn)類封裝成FilterRegistrationBean，放到ServletContextInitializerBeans實(shí)例的成員變量initializers變量(LinkedMultiValueMap)中
Spring 容器（ServletWebServerApplicationContext）從ServletContextInitializerBeans實(shí)例的成員變量initializers變量(LinkedMultiValueMap)，中獲取所有的ServletContextInitializer實(shí)現(xiàn)類，調(diào)用它們的onStartUp函數(shù)，F(xiàn)ilterRegistrationBean的onStartup函數(shù)就是在調(diào)用ServletContext的addFilter函數(shù)向Servlet添加Filter

1. IOC容器——ServletWebServerApplicationContext將Filter接口的實(shí)現(xiàn)類封裝成FilterRegistrationBean，放到ServletContextInitializerBeans實(shí)例的成員變量initializers變量(LinkedMultiValueMap)中

1.Spring容器——ServletWebServerApplicationContext的refresh()函數(shù)被調(diào)用。

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

2.ServletWebServerApplicationContext的createWebServer()函數(shù)，

在函數(shù)中會(huì)調(diào)用getSelfInitializer()函數(shù)獲取所有的ServletContextInitializer實(shí)例，
而獲取所有的ServletContextInitializer實(shí)例的過程中，會(huì)查找所有實(shí)現(xiàn)了Filter接口的bean，并注冊(cè)成FilterRegistrationBean（實(shí)現(xiàn)了ServletContextInitializer接口，所以也屬于ServletContextInitializer實(shí)例），
然后把FilterRegistrationBean放到initializers變量(LinkedMultiValueMap)中

private void createWebServer() {
    WebServer webServer = this.webServer;    
    ServletContext servletContext = getServletContext();    
    if (webServer == null && servletContext == null) {
       StartupStep createWebServer = this.getApplicationStartup().start("spring.boot.webserver.create");       
       ServletWebServerFactory factory = getWebServerFactory();       
       createWebServer.tag("factory", factory.getClass().toString());  
       //  getSelfInitializer()函數(shù)中獲取所有ServletContextInitializer實(shí)例，調(diào)用onStartup方法完成注冊(cè)
       this.webServer = factory.getWebServer(getSelfInitializer());
       ......
}
private org.springframework.boot.web.servlet.ServletContextInitializer getSelfInitializer() {
    return this::selfInitialize;
    }
private void selfInitialize(ServletContext servletContext) throws ServletException {
    prepareWebApplicationContext(servletContext);    
    registerApplicationScope(servletContext);    
    WebApplicationContextUtils.registerEnvironmentBeans(getBeanFactory(), servletContext);  
    //   獲取所有ServletContextInitializer實(shí)例，調(diào)用onStartup方法
    for (ServletContextInitializer beans : getServletContextInitializerBeans()) {
       beans.onStartup(servletContext);   
        }
}
// 傳入BeanFactory，new 一個(gè)ServletContextInitializerBeans對(duì)象，這個(gè)對(duì)象實(shí)現(xiàn)了Collection接口，是一個(gè)集合，
// 集合內(nèi)的元素是需要內(nèi)置在Servlet Context上的ServletContextInitializer bean
protected Collection<ServletContextInitializer> getServletContextInitializerBeans() {
    return new ServletContextInitializerBeans(getBeanFactory());
    }

3.ServletContextInitializerBeans的構(gòu)建

public ServletContextInitializerBeans(ListableBeanFactory beanFactory,       Class<? extends ServletContextInitializer>... initializerTypes) {
    this.initializers = new LinkedMultiValueMap<>();    
    this.initializerTypes = (initializerTypes.length != 0) ? Arrays.asList(initializerTypes)
          : Collections.singletonList(ServletContextInitializer.class);    
     // 找直接定義為ServletContextInitializer的bean（比如FilterRegistrationBean），DelegatingFilterProxyRegistrationBean等，
     // 添加到initializers中
    addServletContextInitializerBeans(beanFactory);    
     // 找實(shí)現(xiàn)了Filter接口的bean，將他們封裝成ServletContextInitializer bean（對(duì)于Filter的實(shí)現(xiàn)類也就是封裝成FilterRegistrationBean），
     // 添加到initializers中
    addAdaptableBeans(beanFactory);   
    //排序  
    List<ServletContextInitializer> sortedInitializers = this.initializers.values().stream()
          .flatMap((value) -> value.stream().sorted(AnnotationAwareOrderComparator.INSTANCE))
          .collect(Collectors.toList());    
          this.sortedList = Collections.unmodifiableList(sortedInitializers);    
          logMappings(this.initializers);
}
protected void addAdaptableBeans(ListableBeanFactory beanFactory) {
    MultipartConfigElement multipartConfig = getMultipartConfig(beanFactory);    
    // 獲取實(shí)現(xiàn)了Servlet接口的bean
    addAsRegistrationBean(beanFactory, Servlet.class, new ServletRegistrationBeanAdapter(multipartConfig)); 
    // 查找所有實(shí)現(xiàn)了Filter接口的bean，并注冊(cè)成FilterRegistrationBean，
    // 然后把FilterRegistrationBean放到initializers變量(LinkedMultiValueMap)中
    addAsRegistrationBean(beanFactory, Filter.class, new FilterRegistrationBeanAdapter());    
    for (Class<?> listenerType : ServletListenerRegistrationBean.getSupportedTypes()) {
       addAsRegistrationBean(beanFactory, EventListener.class, (Class<EventListener>) listenerType,             
                 new ServletListenerRegistrationBeanAdapter());    
       }
}

所以我們可以看到ServletContextInitializerBeans構(gòu)造函數(shù)是怎么構(gòu)造一個(gè)包含
ServletContextInitializer bean集合的：

找直接定義為ServletContextInitializer的bean（比如FilterRegistrationBean），
DelegatingFilterProxyRegistrationBean等，添加到initializers中
找實(shí)現(xiàn)了Filter接口的bean，將他們封裝成ServletContextInitializer bean（對(duì)于Filter的實(shí)現(xiàn)類也就是封裝成FilterRegistrationBean），添加到initializers中
排序然后一并返回

所以ServletContextInitializerBeans實(shí)例表示的是：一個(gè)從ListableBeanFactory bean容器中獲得的ServletContextInitializer實(shí)例的集合。這個(gè)集合中的每個(gè)元素來自容器中定義的每個(gè)如下類型的bean :

實(shí)現(xiàn)了ServletContextInitializer接口的bean
具體可能以ServletRegistrationBean/FilterRegistrationBean/EventListenerRegistrationBean的形式存在。這些 bean 設(shè)計(jì)的目的是用來注冊(cè)相應(yīng)的 Servlet/Filter/EventListener bean 到 ServletContext

- **實(shí)現(xiàn)了Servlet/Filter/EventListener接口的 bean**

這些 bean直接以實(shí)現(xiàn)裸的Servlet/Filter/EventListener接口的 bean的形式存在，但是Springboot會(huì)將它們封裝成相應(yīng)的 RegistrationBean(也是ServletContextInitializer ),然后也注冊(cè)到ServletContext。

也就是說，Spring幫我們將實(shí)現(xiàn)裸的Servlet/Filter/EventListener接口的 bean，封裝成ServletRegistrationBean/FilterRegistrationBean/EventListenerRegistrationBean。

2. Spring 容器（ServletWebServerApplicationContext）從ServletContextInitializerBeans實(shí)例的成員變量initializers變量(LinkedMultiValueMap)，中獲取所有的ServletContextInitializer實(shí)現(xiàn)類，調(diào)用它們的startUp函數(shù)，F(xiàn)ilterRegistrationBean的onStartup函數(shù)就是在調(diào)用ServletContext的addFilter函數(shù)向Servlet添加Filter

1.還是要回到上面1.2中的createWebServer()函數(shù)中，這次我們不看getSelfInitializer()，而是看factory.getWebServer(...)函數(shù)。

private void createWebServer() {
    WebServer webServer = this.webServer;    
    ServletContext servletContext = getServletContext();    
    if (webServer == null && servletContext == null) {
       StartupStep createWebServer = this.getApplicationStartup().start("spring.boot.webserver.create");       
       ServletWebServerFactory factory = getWebServerFactory();       
       createWebServer.tag("factory", factory.getClass().toString());  
       //  getSelfInitializer()函數(shù)中獲取所有ServletContextInitializer實(shí)例，調(diào)用onStartup方法完成注冊(cè)
       this.webServer = factory.getWebServer(getSelfInitializer());
       ......
}

2.TomcatServletWebServerFactory的getWebServer(...)函數(shù)

public WebServer getWebServer(ServletContextInitializer... initializers) {
    if (this.disableMBeanRegistry) {
       Registry.disableRegistry();    
    }
    ......
    // 將前面獲取到的所有ServletContextInitializer實(shí)例作為參數(shù)，傳下去
    prepareContext(tomcat.getHost(), initializers);    
    return getTomcatWebServer(tomcat);
 }

3.TomcatServletWebServerFactory的prepareContext(...)

protected void prepareContext(Host host, ServletContextInitializer[] initializers) {
    ......
    // 合并一下
    ServletContextInitializer[] initializersToUse = mergeInitializers(initializers);    
    host.addChild(context);   
    // 將前面獲取到的所有ServletContextInitializer實(shí)例作為參數(shù)，傳下去 
    configureContext(context, initializersToUse);    
    postProcessContext(context);}

4.tomcatServletWebServerFactory的configureContext（...），創(chuàng)建了TomcatStarter，并將TomcatStarter綁定到Tomcat上，這樣Tomcat啟動(dòng)時(shí)就會(huì)回調(diào)TomcatStarter的onStartup函數(shù)。

protected void configureContext(Context context, ServletContextInitializer[] initializers) {
    // 將前面獲取到的所有ServletContextInitializer實(shí)例作為參數(shù)，傳下去 
    TomcatStarter starter = new TomcatStarter(initializers);
    // 下面這一系列操作是將TomcatStarter綁定到Tomcat上，這樣TomcatStarter就會(huì)在Tomcat啟動(dòng)時(shí)被回調(diào)
    if (context instanceof TomcatEmbeddedContext) {
    TomcatEmbeddedContext embeddedContext = (TomcatEmbeddedContext) context;    
    embeddedContext.setStarter(starter);    
    embeddedContext.setFailCtxIfServletStartFails(true);
    }
    context.addServletContainerInitializer(starter, NO_CLASSES);
    ......
}

5.TomcatStarter的startUp函數(shù)被調(diào)用的時(shí)候，就會(huì)變量所有的ServletContextInitializer實(shí)例的onStartup函數(shù)，

public void onStartup(Set<Class<?>> classes, ServletContext servletContext) throws ServletException {
    try {
       for (ServletContextInitializer initializer : this.initializers) {
          initializer.onStartup(servletContext);       
          }
    }
    catch (Exception ex) {
       this.startUpException = ex;       
       // Prevent Tomcat from logging and re-throwing when we know we can       
       // deal with it in the main thread, but log for information here.      
       if (logger.isErrorEnabled()) {
          logger.error("Error starting Tomcat context. Exception: " + ex.getClass().getName() + ". Message: "                + ex.getMessage());       
          }
    }
}

6.回顧第一章：“Filter接口的實(shí)現(xiàn)類封裝成FilterRegistrationBean”，而FilterRegistrationBean又是ServletContextInitializer接口的實(shí)現(xiàn)類，所以上面第5步，也會(huì)回調(diào)FilterRegistrationBean的onStartup函數(shù)，

//FilterRegistrationBean
public final void onStartup(ServletContext servletContext) throws ServletException {
    String description = getDescription();    
    if (!isEnabled()) {
       logger.info(StringUtils.capitalize(description) + " was not registered (disabled)");       return;    
       }
    // 這里
    register(description, servletContext);
}

7.DynamicRegistrationBean.class

protected final void register(String description, ServletContext servletContext) {
    //這里
    D registration = addRegistration(description, servletContext);    
    if (registration == null) {
       logger.info(StringUtils.capitalize(description) + " was not registered (possibly already registered?)");       
       return;    
       }
    configure(registration);
    }

8.AbstractFilterRegistrationBean.class，看到?jīng)]，最終還是用ServletContext的addFilter函數(shù)，向Servlet容器中添加Filter。

protected Dynamic addRegistration(String description, ServletContext servletContext) {
    // getFilter()在FilterRegistrationBean中被實(shí)現(xiàn)，返回的就是那個(gè)Filter接口的實(shí)現(xiàn)類。
    Filter filter = getFilter();   
    // 將Filter接口的實(shí)現(xiàn)類添加到Servlet容器中 
    return servletContext.addFilter(getOrDeduceName(filter), filter);
  }

參考資料

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