Spring MVC Servlet 的实现对比

女爷i 2022-03-11 19:22 210阅读 0赞

[Demo 下载 Github][Demo _ Github]

实现Servlet的三种方式

1.  编写一个类去实现 `Servlet` 接口(必须重写`Servlet`接口里面所有的抽象方法)
2.  编写一个类去继承 `GenericServlet` 抽象类(重写生命周期的`service`方法（抽象方法）)`GenericServle`抽象类它实现了`Servlet`接口，还实现了ServletConfig接口(这个接口中提供了一个`getServletContext`方法)可以在编写一个类中直接调用`getServletContext`方法就可以获得`ServletContext`对象。（开发中不常用）
3.  编写一个类去继承 `HttpServlet` 抽象类(没有抽象方法！根据页面的提交方式决定重写doGet或者doPost方法)

通过三个Demo演示了Servlet的进化。

1.  Demo1直接使用`Servlet`接口
2.  Demo2继承`GenericServlet`类
3.  Demo3继承`HttpServlet`类

## 1.Servlet ##

public class ServletDemo1 implements Servlet { 
    
        private final Logger logger = Logger.getLogger("ServletDemo1");
    
        public void init(ServletConfig servletConfig) throws ServletException { 
            logger.info("ServletDemo1 - init()");
        }
    
        public ServletConfig getServletConfig() { 
            logger.info("ServletDemo1 - getServletConfig()");
            return null;
        }
    
        public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException { 
            logger.info("ServletDemo1 - service()");
            servletResponse.getWriter().write("ServletDemo1 - Hello World");
        }
    
        public String getServletInfo() { 
            logger.info("ServletDemo1 - getServletInfo()");
            return null;
        }
    
        public void destroy() { 
            logger.info("ServletDemo1 - destroy()");
    
        }
    }

## 2.GenericServlet ##

public class ServletDemo2 extends GenericServlet { 
    
        private final Logger logger = Logger.getLogger("ServletDemo3");
    
        @Override
        public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException { 
            logger.info("ServletDemo2 - service()");
            servletResponse.getWriter().write("ServletDemo2 - Hello World");
        }
    }

## 3.HttpServlet ##

public class ServletDemo3 extends HttpServlet { 
    
        private final Logger logger = Logger.getLogger("ServletDemo3");
    
        @Override
        protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 
            logger.info("ServletDemo3 - doGet()");
            response.getWriter().write("ServletDemo3 - Hello World");
        }
    
    }

## 4.web配置 ##

web.xml

<?xml version="1.0" encoding="UTF-8"?>
    <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
    
        <display-name>ServletDemo</display-name>
    
        <servlet>
            <servlet-name>servletDemo1</servlet-name>
            <servlet-class>com.jeiker.ServletDemo1</servlet-class>
        </servlet>
        <servlet-mapping>
            <servlet-name>servletDemo1</servlet-name>
            <url-pattern>/demo1</url-pattern>
        </servlet-mapping>
    
        <servlet>
            <servlet-name>servletDemo2</servlet-name>
            <servlet-class>com.jeiker.ServletDemo2</servlet-class>
        </servlet>
        <servlet-mapping>
            <servlet-name>servletDemo2</servlet-name>
            <url-pattern>/demo2</url-pattern>
        </servlet-mapping>
    
        <servlet>
            <servlet-name>servletDemo3</servlet-name>
            <servlet-class>com.jeiker.ServletDemo3</servlet-class>
        </servlet>
        <servlet-mapping>
            <servlet-name>servletDemo3</servlet-name>
            <url-pattern>/demo3</url-pattern>
        </servlet-mapping>
    
        <welcome-file-list>
            <welcome-file>index.html</welcome-file>
        </welcome-file-list>
    </web-app>

## 访问测试 ##

1.  GET [http://localhost:8080/demo1][http_localhost_8080_demo1]
2.  GET [http://localhost:8080/demo2][http_localhost_8080_demo2]
3.  GET [http://localhost:8080/demo3][http_localhost_8080_demo3]

[Demo _ Github]: https://github.com/jeikerxiao/spring-mvc/tree/master/spring-mvc-servlet
[http_localhost_8080_demo1]: http://localhost:8080/demo1
[http_localhost_8080_demo2]: http://localhost:8080/demo2
[http_localhost_8080_demo3]: http://localhost:8080/demo3