Web框架的前生今世 從Servlet到Spring MVC到Spring boot
背景
上世紀(jì)90年代，隨著Internet和瀏覽器的飛速發(fā)展，基于瀏覽器的B/S模式隨之火爆發(fā)展起來(lái)。最初，用戶使用瀏覽器向WEB服務(wù)器發(fā)送的請(qǐng)求都是請(qǐng)求靜態(tài)的資源，比如html、css等。 但是可以想象：根據(jù)用戶請(qǐng)求的不同動(dòng)態(tài)的處理并返回資源是理所當(dāng)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(xiàng)用來(lái)創(chuàng)建web application的技術(shù)。
- Servlet is an API that provides many interfaces and classes including documentation. servlet是一個(gè)提供很多接口和類api及其相關(guān)文檔。
- Servlet is an interface that must be implemented for creating any Servlet.servlet是一個(gè)接口，創(chuàng)建任何servlet都要實(shí)現(xiàn)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(gè)實(shí)現(xiàn)了服務(wù)器各種能力的類，對(duì)請(qǐng)求做出響應(yīng)。它可以對(duì)任何請(qǐng)求做出響應(yīng)。
- Servlet is a web component that is deployed on the server to create a dynamic web page.servlet是一個(gè)web組件，部署到一個(gè)web server上(如tomcat，jetty)，用來(lái)產(chǎn)生一個(gè)動(dòng)態(tài)web頁(yè)面。
servlet的歷史
web Container
web容器也叫servlet容器，負(fù)責(zé)servlet的生命周期，映射url請(qǐng)求到相應(yīng)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(jiàn)的web容器如下：
在web容器中，web應(yīng)用服務(wù)器的結(jié)構(gòu)如下：
1.普通servlet實(shí)現(xiàn)頁(yè)面訪問(wèn)
1.1 實(shí)例1：使用web.xml實(shí)現(xiàn)一個(gè)http服務(wù)
實(shí)現(xiàn)一個(gè)簡(jiǎn)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;
- @Override
- protected void doGet(HttpServletRequest request,
- HttpServletResponse response) throws ServletException, IOException
- {
- response.setContentType("text/html;charset=UTF-8");
- PrintWriter out = response.getWriter();
- try {
- // Write some content
- out.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();
- }
- }
- @Override
- protected void doPost(HttpServletRequest request,
- HttpServletResponse response) throws ServletException, IOException {
- //Do some other work
- }
- @Override
- public String getServletInfo() {
- return "MyFirstServlet";
- }
- }
web.xml配置servlet
/MyFirstServlet MyFirstServlet com.howtodoinjava.servlets.MyFirstServlet MyFirstServlet /MyFirstServlet
1.2 編程方式實(shí)現(xiàn)一個(gè)http服務(wù)請(qǐng)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(shí)現(xiàn)頁(yè)面訪問(wèn)
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>
- <!-- For web context -->
- <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>
- <!-- For root context -->
- <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 {
- @Override
- public void onStartup(ServletContext container) {
- // Create the 'root' Spring application context
- AnnotationConfigWebApplicationContext rootContext =
- new AnnotationConfigWebApplicationContext();
- rootContext.register(AppConfig.class);
- // Manage the lifecycle of the root application context
- container.addListener(new ContextLoaderListener(rootContext));
- // Create the dispatcher servlet's Spring application context
- AnnotationConfigWebApplicationContext dispatcherContext =
- new AnnotationConfigWebApplicationContext();
- dispatcherContext.register(DispatcherConfig.class);
- // Register and map the dispatcher servlet
- ServletRegistration.Dynamic dispatcher =
- container.addServlet("dispatcher", new DispatcherServlet(dispatcherContext));
- dispatcher.setLoadOnStartup(1);
- dispatcher.addMapping("/");
- }
- }
內(nèi)部實(shí)現(xiàn)
3.spring boot
繼承了spring mvc的框架，實(shí)現(xiàn)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 {
- @Override
- protected 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(jié)：
1.servlet的本質(zhì)沒(méi)有變化，從web框架的發(fā)展來(lái)看，web框架只是簡(jiǎn)化了開發(fā)servlet的工作，但還是遵循servlet規(guī)范的發(fā)展而發(fā)展的。
2.servlet的歷史發(fā)展，從配置方式向編程方式到自動(dòng)配置方式發(fā)展
3.spring mvc框架的分組：root和child(可以有多個(gè)dispatcherservlet)，多個(gè)child可以共享root，child直接不共享
參考文獻(xiàn)：
【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/
