servlet的实现

1.servelt的作用
接受请求，对请求进行处理，并发送响应。
2.编写servlet
a.继承HttpServlet这个类(此类实现了Servlet接口)

package servlet;

import java.io.IOException;
import java.io.UnsupportedEncodingException;

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

public class FirstServlet extends HttpServlet{

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // TODO Auto-generated method stub
        this.log("执行了doGet方法");
        //调用servlet自带的日志输出信息到控制台
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // TODO Auto-generated method stub
        this.log("执行了doPost方法");
    }

    @Override
    protected long getLastModified(HttpServletRequest req) {
        // TODO Auto-generated method stub
        this.log("执行了lastModified方法");
        return -1;
    }

    private void execute(HttpServletRequest req,HttpServletResponse resp) throws Exception{
        resp.setCharacterEncoding("UTF-8");
        req.setCharacterEncoding("UTF-8");
        String requestURI=req.getRequestURI();
        String method=req.getMethod();
        //访问该servlet的方式，get或者method
        String param=req.getParameter("param");
        //客户提交的参数param值
    }

}

b.在web.xml中配置servlet

<!-- 配置servlet -->
  <servlet>
    <servlet-name>FirstServlet</servlet-name>
    <servlet-class>servlet.FirstServlet</servlet-class>
    <!-- 初始化参数 -->
    <init-param>
        <param-name>message</param-name>
        <param-value>welcome to FirstServlet</param-value>
    </init-param>
    <init-param>
        <param-name>encoding</param-name>
        <param-value>UTF-8</param-value>
    </init-param>
    <!-- 配置servlet的加载方式,如果是1的话，tomcat会在启动的时候加载该servlet，否则在有人第一次请求时加载该servlet -->
    <load-on-startup>1</load-on-startup>
  </servlet>

c.在web.xml中配置servlet-mapping

  <!-- 配置servlet-mapping -->
  <servlet-mapping>
    <servlet-name>FirstServlet</servlet-name>
    <!-- 配置servlet的访问路径 -->
    <url-pattern>/FirstServlet</url-pattern>
  </servlet-mapping>