HttpServlet

HttpServlet(开发使用)

1). 是一个 Servlet, 继承自 GenericServlet. 针对于 HTTP 协议所定制.

2). 在 service() 方法中直接把 ServletReuqest 和 ServletResponse 转为 HttpServletRequest

    和 HttpServletResponse. 并调用了重载的 service(HttpServletRequest, HttpServletResponse)

     在 service(HttpServletRequest, HttpServletResponse) 获取了请求方式: request.getMethod().

     根据请求方式有创建了 doXxx() 方法(xxx 为具体的请求方式, 比如 doGet, doPost)

package com.aff.java;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
 * 针对于http协议定义的一个Servlet基类
 * @author lz
 *
 */
public class MyHttpServlet extends MyGenericServlet {

    @Override
    public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {

        HttpServletRequest request;
        HttpServletResponse response;
        try {
            request = (HttpServletRequest) req;
            response = (HttpServletResponse) res;
        } catch (ClassCastException e) {
            throw new ServletException("non-HTTP request or response");
        }
        service(request, response);
    }

    
    public void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 1. 获取请求方式.
        String method = request.getMethod();

        // 2. 根据请求方式再调用对应的处理方法
        if ("GET".equalsIgnoreCase(method)) {
            doGet(request, response);
        } else if ("POST".equalsIgnoreCase(method)) {
            doPost(request, response);
        }
    }

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

    }

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

    }
}

3). 实际开发中, 直接继承 HttpServlet, 并根据请求方式复写 doXxx() 方法即可.(主要指doGet 和 doPost)

4). 优点: 直接由针对性的覆盖 doXxx() 方法; 直接使用 HttpServletRequest 和 HttpServletResponse, 不再需要强转.

练习：定义一个 login.html, 里边定义两个请求字段: user, password. 发送请求到 loginServlet

           在创建一个 LoginServlet(需要继承自 HttpServlet, 并重写其 doPost 方法), 

           在其中获取请求的 user, password.

           利用 JDBC 从 test_users 中查询有没有和页面输入的 user, password 对应的记录

           SELECT count(id) FROM test_users WHERE user = ? AND password = ?

           若有, 响应 Hello:xxx, 若没有, 响应 Sorry: xxx xxx 为 user.

准备： 在 MySQL 数据库中创建一个 users 数据表, 添加 3 个字段:

            id, username, password. 并录入几条记录. 

Loginservlet3

package com.aff.java;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.aff.util.JDBCUtilsC3P0;

public class Loginservlet3 extends HttpServlet {
    private static final long serialVersionUID = -2287053550217699690L;

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String username = req.getParameter("username");
        String password = req.getParameter("password");

        Connection conn = null;
        PreparedStatement ps = null;
        ResultSet rs = null;
        PrintWriter out = resp.getWriter();
        try {    
                conn =JDBCUtilsC3P0.getConnection();
                String sql = "SELECT count(id) FROM users WHERE username = ? and password = ?" ;
                    ps = conn.prepareStatement(sql);
                    ps.setString(1, username);
                    ps.setString(2, password);
                    rs = ps.executeQuery();
                    if (rs.next()) {
                        int count = rs.getInt(1);
                        if (count>0) {
                            out.print("hello:"+username);
                        }else{
                            out.print("sorry:"+username);
                        }
                    }
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            JDBCUtilsC3P0.closeResource(conn, ps, rs);
        }
    }
}

login.html

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>

<form action="loginServlet" method="post">
user:<input type="text"  name="username"/>
password:<input type="password" name="password"/>
<input type="submit" value="Submit"/>
</form>

</body>
</html>

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://xmlns.jcp.org/xml/ns/javaee"
    xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
    version="3.1">
    <!--配置当前web应用的初始化参数 全局的 -->
    <context-param>
        <param-name>user</param-name>
        <param-value>hmm</param-value>
    </context-param>

    <context-param>
        <param-name>password</param-name>
        <param-value>123456</param-value>
    </context-param>

    <servlet>
        <servlet-name>loginServlet</servlet-name>
        <servlet-class>com.aff.java.Loginservlet3</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>loginServlet</servlet-name>
        <url-pattern>/loginServlet</url-pattern>
    </servlet-mapping>

</web-app>