1.获取请求参数通用方式：不论get还是post请求方式都可以使用下列方法来获取请求参数

    1.String getParameter(String name)：根据参数名称获取参数值  username=zhangsan&password=123

    2.String[] getParameterValues(String name)：根据参数名称获取参数值的数组  hobby=xx&hobby=xxxx (多用于复选框)

    3.Enumeration<String> getParameterNames()：获取所有请求参数名称

    4.Map<String,String[]> getParameterMap()：获取所有参数的Map集合

    中文乱码情况：

        get方式：tomcat 8 已经将get方式乱码问题解决了

        post方式：会乱码

            解决方法：在获取参数前，设置request的编码  request.setCharacterEncoding("utf-8");

定义一个注册页面：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>注册页面</title>
</head>
<body>
    <form action="/Tomcat_servlet/RequestDemo4" method="post">
        <input type="text" placeholder="请输入用户名" name="username"><br>
        <input type="text" placeholder="请输入密码" name="password"><br>

        <input type="checkbox" name="hobby" value="game">游戏
        <input type="checkbox" name="hobby" value="study">学习
        <input type="checkbox" name="hobby" value="speak">说话
        <br>

        <input type="submit" value="提交">
    </form>
</body>
</html>
定义一个类：

package cn.itcast.web.request;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.BufferedReader;
import java.io.IOException;
import java.util.Enumeration;
import java.util.Map;
import java.util.Set;

@WebServlet("/RequestDemo4")
public class RequestDemo4 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        
        //1.设置流的编码
        request.setCharacterEncoding("utf-8");

        //post 获取请求参数

        //根据参数名称获取参数值的数组
        String username = request.getParameter("username");
        /*System.out.println("post");
        System.out.println(username);*/

        //根据参数名称获取参数值的数组
        String[] hobbies = request.getParameterValues("hobby");
        /*for (String hobby : hobbies) {
            System.out.println(hobby);
        }*/

        //获取所有请求参数名称
        Enumeration<String> parameterNames = request.getParameterNames();
        /*while (parameterNames.hasMoreElements()){
            String name = parameterNames.nextElement();
            System.out.println(name);
            String value = request.getParameter(name);
            System.out.println(value);
            System.out.println("----------");
        }*/

        //获取所有参数的Map集合
        Map<String, String[]> parameterMap = request.getParameterMap();
        //遍历
        Set<String> keySet = parameterMap.keySet();
        for (String name : keySet) {
            //根据键获取值
            String[] values = parameterMap.get(name);
            System.out.println(name);
            for (String value : values) {
                System.out.println(value);
            }
            System.out.println("----------");
        }
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //get 获取请求参数

        //根据参数名称获取参数值
        /*String username = request.getParameter("username");
        System.out.println("get");
        System.out.println(username);*/
        this.doPost(request,response);
    }
}




2.请求转发：一种在服务器内部的资源跳转方式

    1.步骤：

        1.通过request对象获取请求转发的对象：RequestDispatcher getRequestDispatcher(String path)

        2.通过RequestDispatcher对象来进行转发： forward(request,response);

    2.特点：

        1.浏览器地址栏路径不发生变化

        2.只能转发到当前服务器内部资源中

        3.转发是一次请求

定义一个类：

package cn.itcast.web.request;

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

@WebServlet("/RequestDemo6")
public class RequestDemo6 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("Demo666被访问了....");
        //转发到demo7中

       /* RequestDispatcher requestDispatcher = request.getRequestDispatcher("/RequestDemo7");
        requestDispatcher.forward(request,response);*/

       request.getRequestDispatcher("/RequestDemo7").forward(request,response);
    }

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

        this.doPost(request,response);
    }
}
定义另一个类：

package cn.itcast.web.request;

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

@WebServlet("/RequestDemo7")
public class RequestDemo7 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("Demo777被访问了....");
}

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

        this.doPost(request,response);
    }
}
3.共享数据

    域对象：一个有作用范围的对象，可以在范围内共享数据

    request域：代表一次的请求范围，一般用于请求转发的多个资源***享数据

    方法：

        1.void setAttribute(String name,Object obj)：存储数据

        2.Object getAttribute(String name)：通过键获取值

        3.void removeAttribute(String name)：通过键移除键值对

定义一个类：

package cn.itcast.web.request;

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

@WebServlet("/RequestDemo6")
public class RequestDemo6 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("Demo666被访问了....");
        //转发到demo7中
        
       //储存数据到request域中
        request.setAttribute("msg","hello");

       request.getRequestDispatcher("/RequestDemo7").forward(request,response);
    }

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

        this.doPost(request,response);
    }
}
定义另一个类：

package cn.itcast.web.request;

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

@WebServlet("/RequestDemo7")
public class RequestDemo7 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //获取数据
        Object msg = request.getAttribute("msg");
        System.out.println(msg);

        System.out.println("Demo777被访问了....");
}

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

        this.doPost(request,response);
    }
}
4.获取ServletContext

    ServletContext getServletContext()

定义一个类：

package cn.itcast.web.request;

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

@WebServlet("/RequestDemo8")
public class RequestDemo8 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        ServletContext servletContext = request.getServletContext();
        System.out.println(servletContext);
    }

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

        this.doPost(request,response);
    }
}