ServletContextInitializer添加 servlet filter listener

ServletContextInitializer添加 servlet filter listener 

https://www.cnblogs.com/pomer-huang/p/9639322.html

关于springboot中添加Filter的方法

https://www.jianshu.com/p/3d421fbce734

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Spring Boot Servlet : ServletContextInitializer

本文链接：https://blog.csdn.net/andy_zhang2007/article/details/90438116

概述

功能介绍

Spring Boot提供的在Servlet 3.0+环境中用于程序化配置ServletContext的接口。该接口ServletContextInitializer主要被RegistrationBean实现用于往ServletContext容器中注册Servlet,Filter或者EventListener。这些ServletContextInitializer的设计目的主要是用于这些实例被Spring IoC容器管理。这些ServletContextInitializer实例不会被SpringServletContainerInitializer检测，因此不会被Servlet容器自动启动。

该接口ServletContextInitializer和Spring Web的另外一个接口WebApplicationInitializer看起来几乎一模一样。但二者使用目的不同。Spring Web中,WebApplicationInitializer也是针对Servlet 3.0+环境，设计用于程序化配置ServletContext，跟传统的web.xml相对或者配合使用。WebApplicationInitializer实现类会被SpringServletContainerInitializer自动检测和启动。

继承关系

RegistrationBean的继承关系

使用

关于ServletContextInitializer的应用可以参考下面的例子。TomcatStarter是Spring Boot Web Servlet应用结合Tomcat使用时的一个ServletContainerInitializer实现。从下面代码不难看出，一组ServletContextInitializer会被设置到ServletContainerInitializer TomcatStarter上，而TomcatStarter在Servlet容器启动过程中调用自己的方法#onStartup,会逐一调用这些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);

	// 使用者会指定一组 ServletContextInitializer 给 TomcatStarter
	private final ServletContextInitializer[] initializers;

	private volatile Exception startUpException;

	TomcatStarter(ServletContextInitializer[] initializers) {
		this.initializers = initializers;
	}

	// Servlet 容器启动时回会用该方法，该方法会逐一调用每个 ServletContextInitializer 的方法
	// #onStartup 会指定 ServletContext 进行初始化。这些 ServletContextInitializer 的目的
	// 通常会是 注册 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;
	}

}

源代码

源代码版本 : 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;

}

参考文章

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springboot 2.1.3.RELEASE添加filter,servlet源码学习

 

Servlet规范中，通过ServeltContext来注册Filter、Servlet，这里分析Filter，Servlet是相同逻辑

springboot2.0中，我们通过

FilterRegistrationBean将指定得filter来实现ServeltContext注册filter

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FilterRegistrationBean的实例化过程
 
public FilterRegistrationBean(T filter, ServletRegistrationBean... servletRegistrationBeans) {
        super(servletRegistrationBeans);
        Assert.notNull(filter, "Filter must not be null");
        this.filter = filter;
}
 
super的实例化
AbstractFilterRegistrationBean(ServletRegistrationBean... servletRegistrationBeans) {
        Assert.notNull(servletRegistrationBeans, "ServletRegistrationBeans must not be null");
        Collections.addAll(this.servletRegistrationBeans, servletRegistrationBeans);
}

可知FilterRegistrationBean得实例化过程就是将Filter保存到servletRegistrationBeans（一个set）中

再分析FilterRegistrationBean类

FilterRegistrationBean的父类是一个ServletContextInitializer，他有一个方法onStartup(ServletContext servletContext)
其结果最终会调用
servletContext.addFilter(this.getOrDeduceName(filter), filter)
现在看看ServletContextInitializer.onStartup的调用地方
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springboot启动
new SpringApplication(XXApplication.class).run(XXApplication.class,args)
调用
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());
}

再分析getSelfInitializer方法

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prepareWebApplicationContext(servletContext);
        registerApplicationScope(servletContext);
        WebApplicationContextUtils.registerEnvironmentBeans(getBeanFactory(),servletContext);
        for (ServletContextInitializer beans :getServletContextInitializerBeans()) {　　　　　　　　　　　　　　
       //调用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) 代码如下：
MultipartConfigElement multipartConfig = getMultipartConfig(beanFactory);
//将servlet类的bean包装为ServletRegistrationBean
addAsRegistrationBean(beanFactory, Servlet.class,new ServletRegistrationBeanAdapter(multipartConfig));
//将Filter的bean包装为FilterRegistrationBean
addAsRegistrationBean(beanFactory, Filter.class,new FilterRegistrationBeanAdapter());
for (Class<?> listenerType : ServletListenerRegistrationBean.getSupportedTypes())
{       　　
addAsRegistrationBean(beanFactory, EventListener.class,(Class<EventListener>) listenerType,new ServletListenerRegistrationBeanAdapter());
}

 这里提一下，如果Servlet的bean实例名为dispatcherServlet，且该实例在seen集合中（seen集合为自定义配置的实例，通过ServletContextInitializerBeans.addServletContextInitializerBean入口可以查看源码），则设置默认值为  /

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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;

　

总结：springboot启动时，会将所有的 FilterRegistrationBean、ServletRegistrationBean以及被spring管理的Servlet和Filter的实例，通过　　　　      ServletContext注册Servlet以及Filter

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原文地址：https://www.cnblogs.com/kelelipeng/p/11494005.html