HTTP之request请求（注册）

HTTP之request请求

request:请求

    作用:获取浏览器发送过来的数据
    组成部分:请求行 请求头 请求体

操作请求行
    格式: 请求方式 请求资源 协议/版本

        常用方法:HttpServletRequest
            掌握
                String getMethod():获取请求方式
                String getRemoteAddr():获取ip地址
                String getContextPath() :在java中获取项目名称  (/day10)

            了解:
                getRequestURI():获取的是 从项目名到参数之前的内容  /day10/regist
                getRequestURL():获取的带协议的完整路径   http://localhost/day10/regist
                String getQueryString():get请求的所有参数   username=tom&password=123
                String getProtocol():获取协议和版本

        例如:请求行
            GET /day10/row?username=tom&password=123 HTTP/1.1

案例1：请求头的方法

　　web.xml的配置

<?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" id="WebApp_ID" version="3.1">

  <servlet>
    <servlet-name>RowServlet</servlet-name>
    <servlet-class>com.hjh.servlet.request.RowServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>RowServlet</servlet-name>
    <url-pattern>/row</url-pattern>
  </servlet-mapping>

</web-app>

　　RowServlet.java源码：

package com.hjh.servlet.request;

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 RowServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //获取请求方式
        String method = request.getMethod();
        System.out.println("请求方式："+method);

        //获取请求资源
        String uri = request.getRequestURI();
       String url = request.getRequestURL().toString();
       System.out.println("uri："+uri+"                "+" url："+url);

        //获取请求参数的字符串
        String query = request.getQueryString();
        System.out.println("请求参数字符串："+query);

        //获取协议版本
        String protocol = request.getProtocol();
        System.out.println("协议版本："+protocol);

        System.out.println("---------------------------以下为重要方法----------------------------");

        //获取请求IP
        String addr = request.getRemoteAddr();
        System.out.println("请求IP:"+addr);

        //获取项目名
        String contextPath = request.getContextPath();
        System.out.println("项目名："+contextPath);
    }

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

　　启动项目，浏览器输入url“http://localhost:8080/Servlet/row?username=hjh&password=12345”，回车，eclipse中console输出为：

请求方式：GET
uri：/Servlet/row                 url：http://localhost:8080/Servlet/row
请求参数字符串：username=hjh&password=12345
协议版本：HTTP/1.1
---------------------------以下为重要方法----------------------------
请求IP:0:0:0:0:0:0:0:1
项目名：/Servlet

操作请求头

　　 格式:key/value(value可以是多个值)

常用方法:
        ★String getHeader(String key):通过key获取指定的value (一个)

       了解:
            Enumeration getHeaders(String name) :通过key获取指定的value(多个)
            Enumeration getHeaderNames() :获取所有的请求头的名称
            int getIntHeader(String key):获取整型的请求头
            long getDateHeader(String key):获取时间的请求头

重要的请求头:
     user-agent:浏览器内核 msie firefox chrome
     referer:页面从那里来 防盗链

案例2：请求头

　　web.xml配置：

 <servlet>
    <servlet-name>HeaderServlet</servlet-name>
    <servlet-class>com.hjh.servlet.request.HeaderServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>HeaderServlet</servlet-name>
    <url-pattern>/header</url-pattern>
  </servlet-mapping>

　　HeaderServlet.java源码：

package com.hjh.servlet.request;

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 HeaderServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //获取浏览器内核
        String user_agent = request.getHeader("user-agent");
        System.out.println("浏览器内核："+user_agent);

        //获取referer
        String referer = request.getHeader("referer");
        if(referer==null) {
            System.out.println("直接在地址栏输入的");
        }else if(referer.contains("localhost")) {
            System.out.println("本机输入");
        }else if(referer.contains("192.167.23.156")) {
            System.out.println("其他人的");
        }else {
            System.out.println("兄弟，盗链可耻");
        }
    }

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

}

　　启动项目，在浏览器中输入url  “http://localhost:8080/Servlet/header”，回车，在eclipse中查看console输出为：

浏览器内核：Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.96 Safari/537.36
直接在地址栏输入的

操作请求参数 ★
        username=tom&password=123&hobby=drink&hobby=sleep
        常用方法:
            String getParameter(String key):获取一个值
            String[] getParameterValues(String key):通过一个key获取多个值
            Map<String,String[]> getParameterMap():获取所有的参数名称和值

案例3：请求参数

　　web.xml配置：

<servlet>
    <servlet-name>ParamServlet</servlet-name>
    <servlet-class>com.hjh.servlet.request.ParamServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>ParamServlet</servlet-name>
    <url-pattern>/param</url-pattern>
  </servlet-mapping>

ParamServlet.java源码：

package com.hjh.servlet.request;

import java.io.IOException;
import java.util.Arrays;
import java.util.Map;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * 请求参数
 */
public class ParamServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            //获取username
        String username = request.getParameter("username");
        System.out.println("用户名："+username);

        //获取爱好hobby,多个
        String[] hobby = request.getParameterValues("hobby");
        System.out.println("爱好hobby:"+Arrays.toString(hobby));

        //获取所有的请求参数
        Map<String, String[]> map = request.getParameterMap();
        for (String key : map.keySet()) {
            System.out.println(key+":"+Arrays.toString(map.get(key)));
        }
    }

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

}

　　浏览器中输入以下url，回车：

http://localhost:8080/Servlet/param?username=hjh&password=8888&hobby=swimming&hobby=sport

　　eclipse中console输出为：

用户名：hjh
爱好hobby:[swimming, sport]
username:[hjh]
password:[8888]
hobby:[swimming, sport]

请求的中文乱码

        对于get请求:参数追加到地址栏,会使用utf-8编码,服务器(tomcat7)接受到请求之后,使用iso-8859-1解码,所以会出现乱码
        对于post请求,参数是放在请求体中,服务器获取请求体的时候使用iso-8859-1解码,也会出现乱码

        通用的方法:
            new String(参数.getBytes("iso-8859-1"),"utf-8");
        针对于post请求来说:只需要将请求流的编码设置成utf-8即可
            request.setCharacterEncoding("utf-8");

案例1：乱码问题

　　web.xml配置：

<servlet>
    <servlet-name>MessyCodeServlet</servlet-name>
    <servlet-class>com.hjh.servlet.request.MessyCodeServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>MessyCodeServlet</servlet-name>
    <url-pattern>/mcode</url-pattern>
  </servlet-mapping>

MessyCodeServlet.java源码

package com.hjh.servlet.request;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * 请求中文乱码问题
 */
public class MessyCodeServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

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

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        System.out.println(username+":"+password);
    }
}

　　 messyCode.html页面：

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
    <form action="/Servlet/mcode" method="post">
        用户名：<input name="username"><br/>
        密码：<input name="password"><br/>
        <input type="submit">
    </form>
</body>
</html>

　　启动项目，浏览器中输入如下url，页面显示如下，输入“hjh 88888”,回车

　　点击提交按钮，eclipse中console打印如下：

　　浏览器中输入如下url，页面显示如下，输入“王大锤  12345”,回车

　　点击提交按钮，eclipse中console打印如下，中文出现乱码：

　　解决方式：在方法第一行加入以下代码：

//设置编码
request.setCharacterEncoding("utf-8");

域对象:
    request:
        创建:一次请求来的时候
        销毁:响应生成的时候
        作用:
            一次请求里面的数据
        请求转发(请求链,请求串)
            request.getRequestDispatcher("内部路径").forward(request,response);

案例：请求转发，url不变

　　web.xml配置：

<?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" id="WebApp_ID" version="3.1">
  <servlet>
    <servlet-name>TransmitServlet1</servlet-name>
    <servlet-class>com.hjh.servlet.request.TransmitServlet1</servlet-class>
  </servlet>

  <servlet>
    <servlet-name>TransmitServlet2</servlet-name>
    <servlet-class>com.hjh.servlet.request.TransmitServlet2</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>TransmitServlet2</servlet-name>
    <url-pattern>/transmit2</url-pattern>
  </servlet-mapping>

  <servlet-mapping>
    <servlet-name>TransmitServlet1</servlet-name>
    <url-pattern>/transmit1</url-pattern>
  </servlet-mapping>
</web-app>

　　

TransmitServlet1.java源码：

package com.hjh.servlet.request;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * 请求转发:浏览器需某个资源，访问这个servlet 中没有，但是这个servlet知道哪里有；
 * 这个servlet将路径告诉浏览器，浏览器根据这个路径再次访问资源
 *
 */
public class TransmitServlet1 extends HttpServlet {
    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //将请求者的姓名放入username
        request.setAttribute("username", "hjh");

        System.out.println(request.getServletPath()+":我这没你要的东西,去找XXX");

        //请求转发
        request.getRequestDispatcher("/transmit2").forward(request, response);
    }

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

TransmitServlet2.java源码：

package com.hjh.servlet.request;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * 请求转发
 */
public class TransmitServlet2 extends HttpServlet {
    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println(request.getServletPath()+"：是谁在找资源呀？是："+
                                                                                request.getAttribute("username")+";来来来，我给你");
    }

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

　　浏览器中输入以下url，回车：

http://localhost:8080/Servlet/transmit1

　　 eclipse中console输出为：

/transmit1:我这没你要的东西,去找XXX
/transmit2：是谁在找资源呀？是：hjh;来来来，我给你

　　web.xml配置：

<?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" id="WebApp_ID" version="3.1">
  <servlet>
    <servlet-name>TransmitServlet1</servlet-name>
    <servlet-class>com.hjh.servlet.request.TransmitServlet1</servlet-class>
  </servlet>
  <servlet>
    <servlet-name>TransmitServlet2</servlet-name>
    <servlet-class>com.hjh.servlet.request.TransmitServlet2</servlet-class>
  </servlet>
   <servlet>
    <servlet-name>MsgServlet</servlet-name>
    <servlet-class>com.hjh.servlet.request.MsgServlet</servlet-class>
  </servlet>
   <servlet>
    <servlet-name>RegisterServlet</servlet-name>
    <servlet-class>com.hjh.servlet.request.RegisterServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>RegisterServlet</servlet-name>
    <url-pattern>/register</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>MsgServlet</servlet-name>
    <url-pattern>/msg</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>TransmitServlet2</servlet-name>
    <url-pattern>/transmit2</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>TransmitServlet1</servlet-name>
    <url-pattern>/transmit1</url-pattern>
  </servlet-mapping>
</web-app>

注册案例：

例2-步骤分析:
    1.数据库和表(day09)
    2.页面(表单)
        给每个字段添加name属性
        还需修改表单提交的路径 method=post
    3.表单提交到一个servlet(RegistServlet)
    4.RegistServlet:
        操作:
            接受数据,封装成一个user
            调用UserSerivce完成保存操作  int regist(User user)
            判断结果是否符合我们预期
                若int=1; 插入成功
                若int!=1; 插入失败
            相应的提示信息在当前的servlet不做处理,将信息转发给另一个servlet展示(MsgServlet);
    5.UserService
        调用dao
    6.userdao 通过dbutils在数据库中插入一条记录.

　　建表：

　　 DataSourseUtils.java源码：

package com.hjh.util;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import javax.sql.DataSource;
import com.mchange.v2.c3p0.ComboPooledDataSource;

public class DataSourseUtils {
    //建立连接池ds
    private static ComboPooledDataSource ds =     new ComboPooledDataSource();

    //获取数据源
    public static DataSource getDataSourse() {
        return ds;
    }

    //获取连接
    public static Connection getConnection() throws SQLException {
        return ds.getConnection();
    }

    //释放资源
    public static void closeResourse(Connection conn,Statement st) {
        try {
            if(st!=null) {
                st.close();
            }else {
                st = null;
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
        try {
            if(conn!=null) {
                conn.close();
            }else {
                conn = null;
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    /**释放资源closeResourse（conn,ps）*/
    public static void closeResourse(Connection conn,PreparedStatement ps) {
        try {
            if(ps!=null) {
                ps.close();
            }else {
                ps = null;
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
        try {
            if(conn!=null) {
                conn.close();
            }else {
                conn = null;
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
    /**释放资源closeResourse（rs）*/
    public static void closeResourse(ResultSet rs) {
        try {
            if(rs!=null) {
                rs.close();
            }else {
                rs = null;
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

　　c3p0-config.xml，根据实际连接数据库配置，jdbcUrl加“?characterEncoding=UTF-8”是为了解决插入数据库数据中文乱码的问题：

<c3p0-config>
    <!-- 默认配置，如果没有指定则使用这个配置 -->
    <default-config>
        <!-- 基本配置 -->
        <property name="driverClass">com.mysql.jdbc.Driver</property>
        <property name="jdbcUrl">jdbc:mysql://localhost/hejh?characterEncoding=UTF-8</property>
        <property name="user">root</property>
        <property name="password">root</property>

        <!--扩展配置-->
        <property name="checkoutTimeout">30000</property>
        <property name="idleConnectionTestPeriod">30</property>
        <property name="initialPoolSize">10</property>
        <property name="maxIdleTime">30</property>
        <property name="maxPoolSize">100</property>
        <property name="minPoolSize">10</property>
        <property name="maxStatements">200</property>
    </default-config> 

    <!-- 命名的配置 -->
    <named-config name="XXX">
        <property name="driverClass">com.mysql.jdbc.Driver</property>
        <property name="jdbcUrl">jdbc:mysql://127.0.0.1:3306/xxxx</property>
        <property name="user">root</property>
        <property name="password">1234</property>

        <!-- 如果池中数据连接不够时一次增长多少个 -->
        <property name="acquireIncrement">5</property>
        <property name="initialPoolSize">20</property>
        <property name="minPoolSize">10</property>
        <property name="maxPoolSize">40</property>
        <property name="maxStatements">20</property>
        <property name="maxStatementsPerConnection">5</property>
    </named-config>
</c3p0-config> 

　　register.html:

<!doctype html>

<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>用户注册</title>
</head>
<body>
<form action="/Servlet/register" method="post">
    用户名：<input type="text" name="username"><br/>
    密码：<input type="password" name="password"><br/>
    <input type="submit" value="register"><br/>
</form>

</body>

　　RegisterServlet.java源码：

package com.hjh.servlet.request;

import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.commons.beanutils.BeanUtils;
import com.hjh.domain.User;
import com.hjh.service.UserService;

/**
 * 用户注册
 */
public class RegisterServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1.设置编码，防止中文乱码
        request.setCharacterEncoding("utf-8");

        //2.封装数据
        //推荐使用beanutils封装对象
        User user  = new User();
        try {
            BeanUtils.populate(user, request.getParameterMap());

            //3.调用userService.register(user)方法，返回int
            int i = new UserService().register(user);

            //4.判断int，将信息转发答msgServlet类，交由它处理
            if(i==1) {
                request.setAttribute("msg", "注册成功");
                request.getRequestDispatcher("/msg").forward(request, response);
            }else {
                request.setAttribute("msg", "注册失败");
                request.getRequestDispatcher("/msg").forward(request, response);
            }
        } catch (Exception e) {
            e.printStackTrace();
            throw new RuntimeException();
        }
    }

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

　　MsgServlet.java源码：

package com.hjh.servlet.request;

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 MsgServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1、设置编码
        response.setContentType("text/html;charset=utf-8");

        //2.从request域中获取msg信息
        String msg = (String)request.getAttribute("msg");

        //3.将msg打印到浏览器页面上
        response.getWriter().print(msg);
    }

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

　　UserService.java

package com.hjh.service;

import java.sql.SQLException;
import com.hjh.dao.UserDao;
import com.hjh.domain.User;

public class UserService {

    public User login(String username, String password) {
        User user = null;
        try {
            user = new UserDao().findUserByUsernameAndPassword(username,password);
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return user;
    }

    public int register(User user) throws Exception {
        //调用UserDao
        UserDao dao = new UserDao();
        return dao.register(user);
    }
}

　　UserDao.java源码

package com.hjh.dao;

import java.sql.SQLException;
import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.BeanHandler;
import com.hjh.domain.User;
import com.hjh.util.DataSourseUtils;

public class UserDao {

    public User findUserByUsernameAndPassword(String username, String password) throws SQLException {
        //创建QueryRunner对象，操作sql语句
        QueryRunner qr  = new QueryRunner(new DataSourseUtils().getDataSourse());

        //编写sql语句
        String sql  = "select * from user where username=? and password=?";

        //执行sql      BeanHandler, 将查询结果的第一条记录封装成指定的bean对象,返回
        User user = qr.query(sql, new BeanHandler<User>(User.class),username,password);

        //返回user对象
        return user;
    }

    public int register(User user) throws Exception {
        //创建QueryRunner对象，操作sql语句
        QueryRunner qr  = new QueryRunner(new DataSourseUtils().getDataSourse());
        //编写sql语句
        String sql  = "insert into user(username,password) values(?,?)";
        //执行sql
        int i = qr.update(sql,user.getUsername(),user.getPassword());
        return i;
    }
}

　　User.java源码

package com.hjh.domain;

public class User {

    private int id;
    private String username;
    private String password;

    public User() {}
    public User(int id,String username,String password) {
        this.id = id;
        this.username = username;
        this.password = password;
    }

    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }

    @Override
    public String toString() {
        return "User [id=" + id + ", username=" + username + ", password=" + password + "]";
    }
}

　　web.xml配置：

 <servlet>
    <servlet-name>RegisterServlet</servlet-name>
    <servlet-class>com.hjh.servlet.request.RegisterServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>RegisterServlet</servlet-name>
    <url-pattern>/register</url-pattern>
  </servlet-mapping>

  <servlet-mapping>
    <servlet-name>MsgServlet</servlet-name>
    <url-pattern>/msg</url-pattern>
  </servlet-mapping>

　　浏览器中输入以下url:

　　 输入框输入：王大锤，12345

　　点击register按钮，url显示：

　　查看数据库表数据：

请求转发和重定向区别:
    重定向发送两次请求,请求转发一次请求

    重定向地址栏发生该表,请求转发不变

    重定向是从浏览器发送,请求转发是服务器内部

    重定向不存在request域对象,请求转发可以使用request域对象

    重定向是response的方法,请求转发是request的方法

    重定向可以请求站外资源,请求转发不可以