ServletContextInitializer添加 servlet filter listener
https://www.cnblogs.com/pomer-huang/p/9639322.html
關於springboot中添加Filter的方法
https://www.jianshu.com/p/3d421fbce734
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Spring Boot Servlet : ServletContextInitializer
概述
功能介紹
Spring Boot提供的在Servlet 3.0+環境中用於程序化配置ServletContext的接口。該接口ServletContextInitializer主要被RegistrationBean實現用於往ServletContext容器中注冊Servlet,Filter或者EventListener。這些ServletContextInitializer的設計目的主要是用於這些實例被Spring IoC容器管理。這些ServletContextInitializer實例不會被SpringServletContainerInitializer檢測，因此不會被Servlet容器自動啟動。
該接口
ServletContextInitializer和Spring Web的另外一個接口WebApplicationInitializer看起來幾乎一模一樣。但二者使用目的不同。Spring Web中,WebApplicationInitializer也是針對Servlet 3.0+環境，設計用於程序化配置ServletContext，跟傳統的web.xml相對或者配合使用。WebApplicationInitializer實現類會被SpringServletContainerInitializer自動檢測和啟動。
繼承關系
使用
關於ServletContextInitializer的應用可以參考下面的例子。TomcatStarter是Spring Boot Web Servlet應用結合Tomcat使用時的一個ServletContainerInitializer實現。從下面代碼不難看出，一組ServletContextInitializer會被設置到ServletContainerInitializer TomcatStarter上，而TomcatStarter在Servlet容器啟動過程中調用自己的方法#onStartup,會逐一調用這些ServletContextInitializer的方法#onStartup初始化ServletContext。
package org.springframework.boot.web.embedded.tomcat; import java.util.Set; import javax.servlet.ServletContainerInitializer; import javax.servlet.ServletContext; import javax.servlet.ServletException; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.springframework.boot.web.servlet.ServletContextInitializer; class TomcatStarter implements ServletContainerInitializer { private static final Log logger = LogFactory.getLog(TomcatStarter.class); // 使用者會指定一組 ServletContextInitializer 給 TomcatStarter private final ServletContextInitializer[] initializers; private volatile Exception startUpException; TomcatStarter(ServletContextInitializer[] initializers) { this.initializers = initializers; } // Servlet 容器啟動時回會用該方法，該方法會逐一調用每個 ServletContextInitializer 的方法 // #onStartup 會指定 ServletContext 進行初始化。這些 ServletContextInitializer 的目的 // 通常會是 注冊 Servlet, Filter 或者 EventListener 。 @Override 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()); } } } public Exception getStartUpException() { return this.startUpException; } }
源代碼
源代碼版本 : 2.1.3.RELEASE
package org.springframework.boot.web.servlet; import javax.servlet.ServletContext; import javax.servlet.ServletException; import org.springframework.web.SpringServletContainerInitializer; import org.springframework.web.WebApplicationInitializer; @FunctionalInterface public interface ServletContextInitializer { /** * Configure the given ServletContext with any servlets, filters, listeners * context-params and attributes necessary for initialization. * @param servletContext the ServletContext to initialize * @throws ServletException if any call against the given ServletContext * throws a ServletException */ void onStartup(ServletContext servletContext) throws ServletException; }
參考文章
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springboot 2.1.3.RELEASE添加filter,servlet源碼學習
Servlet規范中，通過ServeltContext來注冊Filter、Servlet，這里分析Filter，Servlet是相同邏輯
springboot2.0中，我們通過
FilterRegistrationBean將指定得filter來實現ServeltContext注冊filter
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FilterRegistrationBean的實例化過程
public
FilterRegistrationBean(T filter, ServletRegistrationBean... servletRegistrationBeans) {
super
(servletRegistrationBeans);
Assert.notNull(filter,
"Filter must not be null"
);
this
.filter = filter;
}
super
的實例化
AbstractFilterRegistrationBean(ServletRegistrationBean... servletRegistrationBeans) {
Assert.notNull(servletRegistrationBeans,
"ServletRegistrationBeans must not be null"
);
Collections.addAll(
this
.servletRegistrationBeans, servletRegistrationBeans);
}
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可知FilterRegistrationBean得實例化過程就是將Filter保存到servletRegistrationBeans（一個set）中
再分析FilterRegistrationBean類
FilterRegistrationBean的父類是一個ServletContextInitializer，他有一個方法onStartup(ServletContext servletContext)
其結果最終會調用
servletContext.addFilter(this.getOrDeduceName(filter), filter)
現在看看ServletContextInitializer.onStartup的調用地方
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springboot啟動
new
SpringApplication(XXApplication.
class
).run(XXApplication.
class
,args)
調用
refreshContext(context); -> refresh(context); -> ((AbstractApplicationContext) applicationContext).refresh();
-> ServletWebServerApplicationContext.onRefresh(); -> createWebServer();
WebServer webServer =
this
.webServer;
ServletContext servletContext = getServletContext();
if
(webServer ==
null
&& servletContext ==
null
) {
ServletWebServerFactory factory = getWebServerFactory();
this
.webServer = factory.getWebServer(getSelfInitializer());
}
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再分析getSelfInitializer方法
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prepareWebApplicationContext(servletContext);
registerApplicationScope(servletContext);
WebApplicationContextUtils.registerEnvironmentBeans(getBeanFactory(),servletContext);
for
(ServletContextInitializer beans :getServletContextInitializerBeans()) {
//調用ServletContextInitializer的onStartup方法
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beans.onStartup(servletContext);
}
-> getServletContextInitializerBeans()
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->
new
ServletContextInitializerBeans(getBeanFactory())
-> addAdaptableBeans(beanFactory)
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addAdaptableBeans(ListableBeanFactory beanFactory) 代碼如下：
MultipartConfigElement multipartConfig = getMultipartConfig(beanFactory);
//將servlet類的bean包裝為ServletRegistrationBean
addAsRegistrationBean(beanFactory, Servlet.
class
,
new
ServletRegistrationBeanAdapter(multipartConfig));
//將Filter的bean包裝為FilterRegistrationBean
addAsRegistrationBean(beanFactory, Filter.
class
,
new
FilterRegistrationBeanAdapter());
for
(Class<?> listenerType : ServletListenerRegistrationBean.getSupportedTypes())
{
addAsRegistrationBean(beanFactory, EventListener.
class
,(Class<EventListener>) listenerType,
new
ServletListenerRegistrationBeanAdapter());
}
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這里提一下，如果Servlet的bean實例名為dispatcherServlet，且該實例在seen集合中（seen集合為自定義配置的實例，通過ServletContextInitializerBeans.addServletContextInitializerBean入口可以查看源碼），則設置默認值為 /
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String url = (totalNumberOfSourceBeans !=
1
) ?
"/"
+ name +
"/"
:
"/"
;
if
(name.equals(DISPATCHER_SERVLET_NAME)) {
url =
"/"
;
// always map the main dispatcherServlet to "/"
}
ServletRegistrationBean<Servlet> bean =
new
ServletRegistrationBean<>(source,url);
bean.setName(name);
bean.setMultipartConfig(
this
.multipartConfig);
return
bean;
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總結：springboot啟動時，會將所有的 FilterRegistrationBean、ServletRegistrationBean以及被spring管理的Servlet和Filter的實例，通過 ServletContext注冊Servlet以及Filter