Request

1. request对象和response对象的原理
    1. request和response对象是由服务器创建的。我们来使用它们
    2. request对象是来获取请求消息，response对象是来设置响应消息

2. request对象继承体系结构：    
    ServletRequest        --    接口
        |    继承
    HttpServletRequest    -- 接口
        |    实现
    org.apache.catalina.connector.RequestFacade 类(tomcat)

1. 获取请求消息数据
    1. 获取请求行数据
        * GET /day14/demo1?name=zhangsan HTTP/1.1
        * 方法：
            1. 获取请求方式 ：GET
                * String getMethod()  
            2. (*)获取虚拟目录：/day14
                * String getContextPath()
            3. 获取Servlet路径: /demo1
                * String getServletPath()
            4. 获取get方式请求参数：name=zhangsan
                * String getQueryString()
            5. (*)获取请求URI：/day14/demo1
                * String getRequestURI():        /day14/demo1
                * StringBuffer getRequestURL()  :http://localhost/day14/demo1

                * URL:统一资源定位符 ： http://localhost/day14/demo1    中华人民共和国
                * URI：统一资源标识符 : /day14/demo1                    共和国
            
            6. 获取协议及版本：HTTP/1.1
                * String getProtocol()

            7. 获取客户机的IP地址：
                * String getRemoteAddr()


---------------------------------
package cn.itcast.web.request;

import com.sun.scenario.effect.impl.sw.sse.SSEBlend_SRC_OUTPeer;

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("/requestDemo1")
public class RequestDemo1 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //获取请求方式
        String method = request.getMethod();
        System.out.println(method);
        //获取虚拟目录
        String contextPath = request.getContextPath();
        System.out.println(contextPath);
        //获取Servlet路径
        String servletPath = request.getServletPath();
        System.out.println(servletPath);
        //获取get方式请求参数
        String queryString = request.getQueryString();
        System.out.println(queryString);
        //获取请求URI
        String requestURI = request.getRequestURI();
        System.out.println(requestURI);
        StringBuffer requestURL = request.getRequestURL();
        System.out.println(requestURL);
        //获取协议及版本
        String protocol = request.getProtocol();
        System.out.println(protocol);
        //获取客户机的IP地址
        String remoteAddr = request.getRemoteAddr();
        System.out.println(remoteAddr);
    }
}

* 方法：
    * (*)String getHeader(String name):通过请求头的名称获取请求头的值
    * Enumeration<String> getHeaderNames():获取所有的请求头名称

----------------------------------
@WebServlet("/requestDemo2")
public class RequestDemo2 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //演示获取请求头数据：user-agent
        String agent = request.getHeader("user-agent");
        //判断agent的浏览器版本
        if(agent.contains("Chrome")) {
            //谷歌
            System.out.println("谷歌...");
        } else if(agent.contains("Firefox")) {
            System.out.println("火狐...");
        }

    }
}


----------------------------------
@WebServlet("/requestDemo4")
public class RequestDemo4 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //演示获取请求头数据：referer
        String referer = request.getHeader("referer");
        System.out.println(referer);

        //防盗链
        if(referer != null) {
            if(referer.contains("/day14")) {
                System.out.println("正常的");
            }else {
                System.out.println("盗链");
            }
        }
    }
}

* 请求体：只有POST请求方式，才有请求体，在请求体中封装了POST请求的请求参数
    * 步骤：
        1. 获取流对象
            *  BufferedReader getReader()：获取字符输入流，只能操作字符数据
            *  ServletInputStream getInputStream()：获取字节输入流，可以操作所有类型数据
                * 在文件上传知识点后讲解

        2. 再从流对象中拿数据


-----------------------------------
@WebServlet("/requestDemo5")
public class RequestDemo5 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //获取请求消息体--请求参数

        //1.获取字符流
        BufferedReader br = request.getReader();
        //2.读取数据
        String line = null;
        while ((line = br.readLine()) != null) {
            System.out.println(line);
        }
    }

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

    }
}

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=zs&password=123
    2. String[] getParameterValues(String name):根据参数名称获取参数值的数组  hobby=xx&hobby=game
    3. Enumeration<String> getParameterNames():获取所有请求的参数名称
    4. Map<String,String[]> getParameterMap():获取所有参数的map集合

--------------------------------
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("/requestDemo6")
public class RequestDemo6 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //post 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("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);
        }

        //获取所有请求的参数名称
        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) {
            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("post");
//        System.out.println(username);
        this.doPost(request,response);
    }
}

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

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对象获取请求转发器对象：RequestDispatcher getRequestDispatcher(String path)
        2. 使用RequestDispatcher对象来进行转发：forward(ServletRequest request, ServletResponse 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
        
    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：代表一次请求的范围，一般用于请求转发的多个资源中共享数据
        * 方法：
            1. void setAttribute(String name,Object obj):存储数据
            2. Object getAttitude(String name):通过键获取值
            3. void removeAttribute(String name):通过键移除键值对

    4. 获取ServletContext：
        * ServletContext getServletContext()


------------------------------------
@WebServlet("/requestDemo8")
public class RequestDemo8 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("demo8888被访问了。。。");
        //转发到demo9资源
/*
        RequestDispatcher requestDispatcher = request.getRequestDispatcher("/requestDemo9");
        requestDispatcher.forward(request,response);
        */

        //存储数据到request域中
        request.setAttribute("msg","hello");

        request.getRequestDispatcher("/requestDemo9").forward(request,response);
        //request.getRequestDispatcher("http://www.itcast.cn").forward(request,response);

    }

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

        this.doPost(request,response);
    }
}



@WebServlet("/requestDemo9")
public class RequestDemo9 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("demo9999被访问了。。。");

    }

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

        this.doPost(request,response);
    }
}


---------------------------
获取ServletContext

@WebServlet("/requestDemo10")
public class RequestDemo10 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);
    }
}