Servlet的三种实现方式

第一种：实现javax.servlet.Servlet接口

显见要实现接口未实现的方法。

Java：

package d0322_01_Servlet;

import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.Servlet;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

public class servletDemo1 implements Servlet{

public servletDemo1(){
System.out.println("这是构造方法！");
}

@Override
public void destroy() {
System.out.println("销毁");
}

@Override
public ServletConfig getServletConfig() {
// TODO Auto-generated method stub
return null;
}
@Override
public String getServletInfo() {
System.out.println("没啥用");
return "没啥用";
}
@Override
public void init(ServletConfig arg0) throws ServletException {
System.out.println("这是初始化！");
}
@Override
public void service(ServletRequest arg0, ServletResponse arg1)throws ServletException, IOException {
System.out.println("服务");
PrintWriter pw = arg1.getWriter();
pw.write("Hello!");
}
}

第二种：继承javax.servet.GenericServlet类(适配器模式)

Java：

package d0321_01_servlet;

import java.io.IOException;
import javax.servlet.GenericServlet;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

public class ServletDemo2 extends GenericServlet{

@Override
public void service(ServletRequest arg0, ServletResponse arg1)
throws ServletException, IOException {
System.out.println("服务！");
}
}

第三种：继承javax.servlet.http.HttpServlet类（模板方法设计模式）

Java：

package d0321_01_servlet;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ServletDemo3 extends HttpServlet{
@Override
// 1.处理GET请求
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
System.out.println("---------doGet---------");

}
@Override
//1.处理Post请求
protected void doPost(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
System.out.println("---------doPost---------");
}
}

.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">
<!--创建一个Servlet实例  -->
<servlet>
<servlet-name>servletDemo1</servlet-name>
<servlet-class>d0321_01_servlet.ServletDemo1</servlet-class>
<!-- 让Servlet在服务器启动时就创建 -->
<load-on-startup>2</load-on-startup>
</servlet>

<!-- 给Servlet提供(映射)一个可供客户端访问的URI -->
<servlet-mapping>
<servlet-name>servletDemo1</servlet-name>
<url-pattern>/demo1</url-pattern>
</servlet-mapping>

<!--创建一个Servlet实例  -->
<servlet>
<servlet-name>ServletDemo2</servlet-name>
<servlet-class>d0321_01_servlet.ServletDemo2</servlet-class>
</servlet>
<!-- 给Servlet提供一个可供客户端访问的URI -->
<servlet-mapping>
<servlet-name>ServletDemo2</servlet-name>
<url-pattern>/Demo2</url-pattern>
</servlet-mapping>

<!--创建一个servlet实例  -->
<servlet>
<servlet-name>ServletDemo3</servlet-name>
<servlet-class>d0321_01_servlet.ServletDemo3</servlet-class>
</servlet>
<!-- 给servlet提供一个可供客户端访问的URI -->
<servlet-mapping>
<servlet-name>ServletDemo3</servlet-name>
<url-pattern>/Demo3</url-pattern>
</servlet-mapping>

</web-app>

小提示：Servlet是底层的接口（要实现的方法太多，不常用）

GenericServlet类实现了Servlet接口（只需重写service，也不常用）

HttpServlet类实现了GenericServlet类（只需重写doGet与doPOST，常用）