參考資料
對于Spring Boot的IOC容器——ServletWebServerApplicationContext，其中的Filter bean，每個Filter bean都會被獨(dú)立的注冊成為Servlet的Filter。大概的注冊過程分成2步：
- IOC容器——ServletWebServerApplicationContext將Filter接口的實現(xiàn)類封裝成FilterRegistrationBean，放到ServletContextInitializerBeans實例的成員變量initializers變量(LinkedMultiValueMap)中
- Spring 容器（ServletWebServerApplicationContext）從ServletContextInitializerBeans實例的成員變量initializers變量(LinkedMultiValueMap)，中獲取所有的ServletContextInitializer實現(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接口的實現(xiàn)類封裝成FilterRegistrationBean，放到ServletContextInitializerBeans實例的成員變量initializers變量(LinkedMultiValueMap)中
- 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);
}
}
- ServletWebServerApplicationContext的createWebServer()函數(shù)，
- 在函數(shù)中會調(diào)用getSelfInitializer()函數(shù)獲取所有的ServletContextInitializer實例，
- 而獲取所有的ServletContextInitializer實例的過程中，會查找所有實現(xiàn)了Filter接口的bean，并注冊成FilterRegistrationBean（實現(xiàn)了ServletContextInitializer接口，所以也屬于ServletContextInitializer實例），
- 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實例，調(diào)用onStartup方法完成注冊
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實例，調(diào)用onStartup方法
for (ServletContextInitializer beans : getServletContextInitializerBeans()) {
beans.onStartup(servletContext);
}
}
// 傳入BeanFactory，new 一個ServletContextInitializerBeans對象，這個對象實現(xiàn)了Collection接口，是一個集合，
// 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());
}
- 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);
// 找實現(xiàn)了Filter接口的bean，將他們封裝成ServletContextInitializer bean（對于Filter的實現(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);
// 獲取實現(xiàn)了Servlet接口的bean
addAsRegistrationBean(beanFactory, Servlet.class, new ServletRegistrationBeanAdapter(multipartConfig));
// 查找所有實現(xiàn)了Filter接口的bean，并注冊成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
找實現(xiàn)了Filter接口的bean，將他們封裝成ServletContextInitializer bean（對于Filter的實現(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實例表示的是：一個從ListableBeanFactory bean容器中獲得的ServletContextInitializer實例的集合。這個集合中的每個元素來自容器中定義的每個如下類型的bean :
-
實現(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)計的目的是用來注冊相應(yīng)的 Servlet/Filter/EventListener bean 到 ServletContext
- **實現(xiàn)了Servlet/Filter/EventListener接口的 bean**
這些 bean直接以實現(xiàn)裸的Servlet/Filter/EventListener接口的 bean的形式存在，但是Springboot會將它們封裝成相應(yīng)的 RegistrationBean(也是ServletContextInitializer ),然后也注冊到ServletContext。文章來源：http://www.zghlxwxcb.cn/news/detail-623629.html
也就是說，Spring幫我們將實現(xiàn)裸的Servlet/Filter/EventListener接口的 bean，封裝成ServletRegistrationBean/FilterRegistrationBean/EventListenerRegistrationBean。文章來源地址http://www.zghlxwxcb.cn/news/detail-623629.html
2. Spring 容器（ServletWebServerApplicationContext）從ServletContextInitializerBeans實例的成員變量initializers變量(LinkedMultiValueMap)，中獲取所有的ServletContextInitializer實現(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
- 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實例，調(diào)用onStartup方法完成注冊
this.webServer = factory.getWebServer(getSelfInitializer());
......
}
- 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實例作為參數(shù)，傳下去
prepareContext(tomcat.getHost(), initializers);
return getTomcatWebServer(tomcat);
}
- 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實例作為參數(shù)，傳下去
configureContext(context, initializersToUse);
postProcessContext(context);}
- tomcatServletWebServerFactory的configureContext（...），創(chuàng)建了TomcatStarter，并將TomcatStarter綁定到Tomcat上，這樣Tomcat啟動時就會回調(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就會在Tomcat啟動時被回調(diào)
if (context instanceof TomcatEmbeddedContext) {
TomcatEmbeddedContext embeddedContext = (TomcatEmbeddedContext) context;
embeddedContext.setStarter(starter);
embeddedContext.setFailCtxIfServletStartFails(true);
}
context.addServletContainerInitializer(starter, NO_CLASSES);
......
}
- TomcatStarter的startUp函數(shù)被調(diào)用的時候，就會變量所有的ServletContextInitializer實例的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());
}
}
}
- 回顧第一章：“Filter接口的實現(xiàn)類封裝成FilterRegistrationBean”，而FilterRegistrationBean又是ServletContextInitializer接口的實現(xiàn)類，所以上面第5步，也會回調(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);
}
- 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);
}
- 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中被實現(xiàn)，返回的就是那個Filter接口的實現(xiàn)類。
Filter filter = getFilter();
// 將Filter接口的實現(xiàn)類添加到Servlet容器中
return servletContext.addFilter(getOrDeduceName(filter), filter);
}
到了這里，關(guān)于SpringBoot中Filter bean是怎么被添加到Servlet容器中的的文章就介紹完了。如果您還想了解更多內(nèi)容，請在右上角搜索TOY模板網(wǎng)以前的文章或繼續(xù)瀏覽下面的相關(guān)文章，希望大家以后多多支持TOY模板網(wǎng)！
