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web框架的前生今世--从servlet到spring mvc到spring boot

發布時間：2025/4/5 c/c++ 35 豆豆

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背景
上世紀90年代，隨著Internet和瀏覽器的飛速發展，基于瀏覽器的B/S模式隨之火爆發展起來。最初，用戶使用瀏覽器向WEB服務器發送的請求都是請求靜態的資源，比如html、css等。??但是可以想象：根據用戶請求的不同動態的處理并返回資源是理所當然必須的要求。 ??

servlet的定義

Servlet is a technology which is used to create a web application. servlet是一項用來創建web application的技術。
Servlet is an API that provides many interfaces and classes including documentation. servlet是一個提供很多接口和類api及其相關文檔。
Servlet is an interface that must be implemented for creating any Servlet.servlet是一個接口，創建任何servlet都要實現的接口。
Servlet is a class that extends the capabilities of the servers and responds to the incoming requests. It can respond to any requests. servlet是一個實現了服務器各種能力的類，對請求做出響應。它可以對任何請求做出響應。
Servlet is a web component that is deployed on the server to create a dynamic web page.servlet是一個web組件，部署到一個web server上（如tomcat，jetty），用來產生一個動態web頁面。

servlet的歷史

版本	日期	JAVA EE/JDK版本	特性
Servlet 4.0	2017年10月	JavaEE 8	HTTP2?[1]?
Servlet 3.1	2013年5月	JavaEE 7	Non-blocking I/O, HTTP protocol upgrade mechanism
Servlet 3.0	2009年12月	JavaEE 6, JavaSE 6	Pluggability, Ease of development, Async Servlet, Security, File Uploading
Servlet 2.5	2005年10月	JavaEE 5, JavaSE 5	Requires JavaSE 5, supports annotation
Servlet 2.4	2003年11月	J2EE 1.4, J2SE 1.3	web.xml uses XML Schema
Servlet 2.3	2001年8月	J2EE 1.3, J2SE 1.2	Addition of Filter
Servlet 2.2	1999年8月	J2EE 1.2, J2SE 1.2	Becomes part of J2EE, introduced independent web applications in .war files
Servlet 2.1	1998年11月	未指定	First official specification, added RequestDispatcher, ServletContext
Servlet 2.0	?	JDK 1.1	Part of Java Servlet Development Kit 2.0
Servlet 1.0	1997年6月	?	?

web Container

web容器也叫servlet容器，負責servlet的生命周期，映射url請求到相應的servlet。

A web container (also known as a servlet container;[1] and compare "webcontainer"[2]) is the component of a web server that interacts with Java servlets. A web container is responsible for managing the lifecycle of servlets, mapping a URL to a particular servlet and ensuring that the URL requester has the correct access-rights.A web container handles requests to servlets, JavaServer Pages (JSP) files, and other types of files that include server-side code. The Web container creates servlet instances, loads and unloads servlets, creates and manages request and response objects, and performs other servlet-management tasks.A web container implements the web component contract of the Java EE architecture. This architecture specifies a runtime environment for additional web components, including security, concurrency, lifecycle management, transaction, deployment, and other services.

常見的web容器如下：

在web容器中，web應用服務器的結構如下：

1.普通servlet實現頁面訪問

1.1 實例1：使用web.xml實現一個http服務

實現一個簡單的servlet

package com.howtodoinjava.servlets;import java.io.IOException; import java.io.PrintWriter;import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse;public class MyFirstServlet extends HttpServlet {private static final long serialVersionUID = -1915463532411657451L;@Overrideprotected void doGet(HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException{response.setContentType("text/html;charset=UTF-8");PrintWriter out = response.getWriter();try {// Write some contentout.println("<html>");out.println("<head>");out.println("<title>MyFirstServlet</title>");out.println("</head>");out.println("<body>");out.println("<h2>Servlet MyFirstServlet at " + request.getContextPath() + "</h2>");out.println("</body>");out.println("</html>");} finally {out.close();}}@Overrideprotected void doPost(HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException {//Do some other work }@Overridepublic String getServletInfo() {return "MyFirstServlet";} }

web.xml配置servlet

<?xml version="1.0"?> <web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaeehttp://xmlns.jcp.org/xml/ns/javaee/web-app_3_0.xsd"version="3.0"><welcome-file-list><welcome-file>/MyFirstServlet</welcome-file></welcome-file-list><servlet><servlet-name>MyFirstServlet</servlet-name><servlet-class>com.howtodoinjava.servlets.MyFirstServlet</servlet-class></servlet><servlet-mapping><servlet-name>MyFirstServlet</servlet-name><url-pattern>/MyFirstServlet</url-pattern></servlet-mapping></web-app>

?1.2 編程方式實現一個http服務請求

?不需要xml

package com.journaldev.first;import java.io.IOException; import java.io.PrintWriter; import java.util.Date;import javax.servlet.ServletException; import javax.servlet.annotation.WebInitParam; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse;/*** Servlet implementation class FirstServlet*/ @WebServlet(description = "My First Servlet", urlPatterns = { "/FirstServlet" , "/FirstServlet.do"}, initParams = {@WebInitParam(name="id",value="1"),@WebInitParam(name="name",value="pankaj")}) public class FirstServlet extends HttpServlet {private static final long serialVersionUID = 1L;public static final String HTML_START="<html><body>";public static final String HTML_END="</body></html>";/*** @see HttpServlet#HttpServlet()*/public FirstServlet() {super();// TODO Auto-generated constructor stub }/*** @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)*/protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {PrintWriter out = response.getWriter();Date date = new Date();out.println(HTML_START + "<h2>Hi There!</h2><br/><h3>Date="+date +"</h3>"+HTML_END);}/*** @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)*/protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {// TODO Auto-generated method stub }}

?2.spring mvc實現頁面訪問

2.1 web.xml方式

示例：

<web-app xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"version="2.5"><display-name>Gradle + Spring MVC Hello World + XML</display-name><description>Spring MVC web application</description><servlet><servlet-name>hello-dispatcher</servlet-name><servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class><init-param><param-name>contextConfigLocation</param-name><param-value>/WEB-INF/spring-mvc-config.xml</param-value></init-param><load-on-startup>1</load-on-startup></servlet><servlet-mapping><servlet-name>hello-dispatcher</servlet-name><url-pattern>/</url-pattern></servlet-mapping><listener><listener-class>org.springframework.web.context.ContextLoaderListener</listener-class></listener><context-param><param-name>contextConfigLocation</param-name><param-value>/WEB-INF/spring-core-config.xml</param-value></context-param></web-app>

?2.2 編碼方式

public class MyWebAppInitializer implements WebApplicationInitializer {@Overridepublic void onStartup(ServletContext container) {// Create the 'root' Spring application contextAnnotationConfigWebApplicationContext rootContext =new AnnotationConfigWebApplicationContext();rootContext.register(AppConfig.class);// Manage the lifecycle of the root application contextcontainer.addListener(new ContextLoaderListener(rootContext));// Create the dispatcher servlet's Spring application contextAnnotationConfigWebApplicationContext dispatcherContext =new AnnotationConfigWebApplicationContext();dispatcherContext.register(DispatcherConfig.class);// Register and map the dispatcher servletServletRegistration.Dynamic dispatcher =container.addServlet("dispatcher", new DispatcherServlet(dispatcherContext));dispatcher.setLoadOnStartup(1);dispatcher.addMapping("/");}}

內部實現

3.spring boot

? 繼承了spring mvc的框架，實現SpringBootServletInitializer

package com.mkyong;import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import org.springframework.boot.builder.SpringApplicationBuilder; import org.springframework.boot.web.support.SpringBootServletInitializer;@SpringBootApplication public class SpringBootWebApplication extends SpringBootServletInitializer {@Overrideprotected SpringApplicationBuilder configure(SpringApplicationBuilder application) {return application.sources(SpringBootWebApplication.class);}public static void main(String[] args) throws Exception {SpringApplication.run(SpringBootWebApplication.class, args);}}

然后controller

package com.mkyong;import java.util.Map;import org.springframework.beans.factory.annotation.Value; import org.springframework.stereotype.Controller; import org.springframework.web.bind.annotation.RequestMapping;@Controller public class WelcomeController {// inject via application.properties@Value("${welcome.message:test}")private String message = "Hello World";@RequestMapping("/")public String welcome(Map<String, Object> model) {model.put("message", this.message);return "welcome";}}

總結：

1.servlet的本質沒有變化，從web框架的發展來看，web框架只是簡化了開發servlet的工作，但還是遵循servlet規范的發展而發展的。

2.servlet的歷史發展，從配置方式向編程方式到自動配置方式發展

3.spring mvc框架的分組：root和child(可以有多個dispatcherservlet)，多個child可以共享root，child直接不共享

參考文獻：

【1】https://en.wikipedia.org/wiki/Web_container

【2】https://baike.baidu.com/item/servlet/477555?fr=aladdin

【3】https://www.javatpoint.com/servlet-tutorial

【4】https://www.journaldev.com/1854/java-web-application-tutorial-for-beginners#deployment-descriptor

【5】https://blog.csdn.net/qq_22075041/article/details/78692780

【6】http://www.mkyong.com/spring-mvc/gradle-spring-mvc-web-project-example/

【7】http://www.mkyong.com/spring-boot/spring-boot-hello-world-example-jsp/

轉載于:https://www.cnblogs.com/davidwang456/p/10297476.html

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