Web框架的前生今世從Servlet到Spring MVC到Spring boot

作者：架構(gòu)師筆記 2019-08-15 10:56:10

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(hù)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(hù)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。

背景

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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(lèi)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(lèi)，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框架的前生今世--從servlet到spring mvc到spring boot

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(fǎng)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(fǎng)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"; 
 } 
}