Servlet笔记

1 Servlet的快速入门

1 web.xml配置文件

<?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_2_5.xsd" id="WebApp_ID" version="2.5">
  <display-name>WEBTest13</display-name>
  
  <servlet>
      <servlet-name>myservlet</servlet-name>
      <servlet-class>p1.servlet.MyFirstServlet</servlet-class>
  </servlet>
  <servlet-mapping>
      <servlet-name>myservlet</servlet-name>
      <url-pattern>/fist</url-pattern>
  </servlet-mapping>
  
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
</web-app>

2 servlet代码

package p1.servlet;

import java.io.IOException;

import javax.servlet.Servlet;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletResponse;

/*
 * 1 创建类实现servlet接口
 * 2 添加里面没有实现的方法，并重写service方法
 * 3 配置web.xml文件。
 */
public class MyFirstServlet implements Servlet{

    /**
     * 重写service方法
  */
    @Override
    public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {
    
        HttpServletResponse response = (HttpServletResponse) res;
        res.getWriter().write("this is my first servlet");
    }

    @Override
    public void init(ServletConfig config) throws ServletException {
    }

    @Override
    public ServletConfig getServletConfig() {
        
        return null;
    }

    
    @Override
    public String getServletInfo() {
        
        return null;
    }

    @Override
    public void destroy() {
    }

    
}

2 Servlet的生命周期

3 Servlet的配置

3 HttpServlet

package p1.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 MyServlet extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.getWriter().write("");
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

}

4 servletContext 概念

5 servletContext 作用

 1获取web应用全局的初始化参数

1）web.xml配置

  <!-- 配置全局的初始化参数 -->
  <context-param>
      <param-name>driver</param-name>
      <param-value>com.jdbc.mysql.Driver</param-value>
  </context-param>

<?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_2_5.xsd" id="WebApp_ID" version="2.5">
  <display-name>WEBTest13</display-name>
  <!-- 配置全局的初始化参数 -->
  <context-param>
      <param-name>driver</param-name>
      <param-value>com.jdbc.mysql.Driver</param-value>
  </context-param>
  
  <servlet>
    <servlet-name>myservlet</servlet-name>
    <servlet-class>p1.servlet.MyFirstServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>myservlet</servlet-name>
    <url-pattern>/first</url-pattern>
  </servlet-mapping>
  <welcome-file-list>
    <welcome-file>1.html</welcome-file>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  <servlet>
    <description></description>
    <display-name>MyServlet</display-name>
    <servlet-name>MyServlet</servlet-name>
    <servlet-class>p1.servlet.MyServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>MyServlet</servlet-name>
    <url-pattern>/servlet</url-pattern>
  </servlet-mapping>
</web-app>

2）Servlet代码

package p1.servlet;

import java.io.IOException;

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

public class MyServlet extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //获取ServletContext对象
        ServletContext context = this.getServletContext();
        //获得初始化参数
        String initParameter = context.getInitParameter("driver");
        response.getWriter().write(initParameter);
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

}

2 获取web应用中任何资源的绝对路径

//1 获取ServletContext对象
ServletContext context = getServletContext();
        
//2 Returns the context path of the web application.
String contextPath = context.getContextPath();//  /WEBTest13
response.getWriter().write(contextPath);
        
// 3 获取绝对路径 getRealPath("1.html")地址相对于web应用
String path = context.getRealPath("1.html");
response.getWriter().write(path);//D:apache-tomcat-7.0.52webappsWEBTest131.html

3 ServletContext是一个域对象

 6 案例记录成功登录系统的人数

package p2.login_servlet;

import java.io.IOException;
import java.sql.SQLException;

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

import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.BeanHandler;

import p1.utils.C3P0Utils;
import p3.domain.User;

public class LoginServlet extends HttpServlet {
    
    
    
    @Override
    public void init() throws ServletException {
        //在Seveltcontext域中存一个数据count
         int count = 0;
         this.getServletContext().setAttribute("count", count);
         
    }
    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1 获取用户名和密码
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        // 2查询数据库中是否有相应的用户名和密码
        QueryRunner qr = new QueryRunner(C3P0Utils.getDataSource());
        String sql = "select * from user where username=? and upassword=?";
        Object[] params = {username,password};
        User user = null;
        try {
            user = qr.query(sql, new BeanHandler<User>(User.class), params);
        } catch (SQLException e) {
            
            e.printStackTrace();
        }
        // 3 根据返回结果给用户不同的显示信息
        if(user!=null){
            //从servletcontext中取出count进行++运算
            ServletContext context = this.getServletContext();
            Integer count = (Integer) context.getAttribute("count");
            count++;
            response.getWriter().write(user.toString());
            response.getWriter().write(user.getUsername()+":success"+count);
        }else{
            response.getWriter().write("sorry");
        }
    }
    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

}