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
| 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，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：
在web容器中，web应用服务器的结构如下：
1.普通servlet实现页面访问
1.1 实例1：使用web.xml实现一个http服务
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
<?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/javaee
http://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 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;
/**
* 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实现页面访问
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 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
3.spring boot
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
参考文献：
【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/
原文地址：https://www.cnblogs.com/davidwang456/p/10297476.html
时间： 2024-11-10 07:08:16