背景
上世纪90年代,随着Internet和浏览器的飞速发展,基于浏览器的B/S模式随之火爆发展起来。最初,用户使用浏览器向WEB服务器发送的请求都是请求静态的资源,比如html、css等。 但是可以想象:根据用户请求的不同动态的处理并返回资源是理所当然必须的要求。
servlet的定义
- Servlet is a technology which is used to create a web application. servlet是一项用来创建web application的技术。
- Servlet is an API that provides many interfaces and classes including documentation. servlet是一个提供很多接口和类api及其相关文档。
- Servlet is an interface that must be implemented for creating any Servlet.servlet是一个接口,创建任何servlet都要实现的接口。
- Servlet is a class that extends the capabilities of the servers and responds to the incoming requests. It can respond to any requests. servlet是一个实现了服务器各种能力的类,对请求做出响应。它可以对任何请求做出响应。
- Servlet is a web component that is deployed on the server to create a dynamic web page.servlet是一个web组件,部署到一个web server上(如tomcat,jetty),用来产生一个动态web页面。
servlet的历史
web容器也叫servlet容器,负责servlet的生命周期,映射url请求到相应的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.
常见的web容器如下:
实现一个简单的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 编程方式实现一个http服务请求
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;
- @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>”;
- public FirstServlet() {
- super();
- // TODO Auto-generated constructor stub
- }
- 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);
- }
- protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
- // TODO Auto-generated method stub
- }
- }
2.spring mvc实现页面访问
2.1 web.xml方式
- <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 编码方式
- 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(“/”);
- }
- }
内部实现
继承了spring mvc的框架,实现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”;
- }
- }
总结:
1.servlet的本质没有变化,从web框架的发展来看,web框架只是简化了开发servlet的工作,但还是遵循servlet规范的发展而发展的。
2.servlet的历史发展,从配置方式向编程方式到自动配置方式发展
3.spring mvc框架的分组:root和child(可以有多个dispatcherservlet),多个child可以共享root,child直接不共享
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