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  • Response 的学习

    1. Response对象
      功能：设置响应消息（回应浏览器的数据）
      1. 设置响应行
                  1. 格式：HTTP/1.1 200 ok
                  2. 设置状态码：setStatus(int sc)

      2. 设置响应头：setHeader(String name, String value)

      3. 设置响应体：
                  * 使用步骤：
                      1. 获取输出流
                          * 字符输出流：PrintWriter getWriter()

                          * 字节输出流：ServletOutputStream getOutputStream()

                      2. 使用输出流，将数据输出到客户端浏览器

      4.例子：使用完成重定向（302）
      思路解析：也是资源跳转，要告知浏览器状态码为302，还要告知跳转资源路径
      package cn.itcast.web.servlet;

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;

/**
 * 重定向
 */

@WebServlet("/responseDemo1")
public class ResponseDemo1 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        System.out.println("demo1........");



        //访问/responseDemo1，会自动跳转到/responseDemo2资源
       /* //1. 设置状态码为302
        response.setStatus(302);
        //2.设置响应头location
        response.setHeader("location","/day15/responseDemo2");*/

        request.setAttribute("msg","response");

        //动态获取虚拟目录
        String contextPath = request.getContextPath();

        //简单的重定向方法
        response.sendRedirect(contextPath+"/responseDemo2");
        //response.sendRedirect("http://www.itcast.cn");

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}
      package cn.itcast.web.servlet;

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("/responseDemo2")
public class ResponseDemo2 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("demo2222222........");

        Object msg = request.getAttribute("msg");
        System.out.println(msg);
    }

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


      4.重定向和转发的特点比较

      * 重定向的特点:redirect
                      1. 地址栏发生变化
                      2. 重定向可以访问其他站点(服务器)的资源
                      3. 重定向是两次请求。不能使用request对象来共享数据
      * 转发的特点：forward
                      1. 转发地址栏路径不变
                      2. 转发只能访问当前服务器下的资源
                      3. 转发是一次请求，可以使用request对象来共享数据
                 


    2. 路径的写法
      1.分类：相对路径/绝对路径

      绝对路径：用一个路径确定唯一资源
      * 如：http://localhost/day15/responseDemo2        /day15/responseDemo2
      * 以/开头的路径【一定是绝对路径】
      * 规则：判断定义的路径是给谁用的？判断请求将来从哪儿发出
                                  * 给客户端浏览器使用：需要加虚拟目录(项目的访问路径)
                                      * 建议虚拟目录动态获取：request.getContextPath()
                                      *例如 <a> , <form> 重定向...
                                  * 给服务器使用：不需要加虚拟目录
                                      * 例如 转发路径

      相对路径：通过相对路径不可以确定唯一资源
      * 如：./index.html
      * 不以/开头，以.开头路径
      * 规则：找到当前资源和目标资源之间的相对位置关系
                   * ./：当前目录
                   * ../:后退一级目录

    3. 服务器输出字符数据到浏览器
      步骤:
                      1. 获取字符输出流
                      2. 输出数据【PrintWriter pw = response.getWriter();     pw.write("~~~~~");】
      * 乱码问题：
                          1. PrintWriter pw = response.getWriter();获取的流的默认编码是ISO-8859-1
                          2. 设置该流的默认编码
                          3. 告诉浏览器响应体使用的编码

                          //简单的形式，设置编码，是在获取流之前设置
                          response.setContentType("text/html;charset=utf-8");
      package cn.itcast.web.servlet;

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;
import java.io.PrintWriter;

@WebServlet("/responseDemo4")
public class ResponseDemo4 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        //获取流对象之前，设置流的默认编码：ISO-8859-1 设置为：GBK
       // response.setCharacterEncoding("utf-8");

        //告诉浏览器，服务器发送的消息体数据的编码。建议浏览器使用该编码解码
        //response.setHeader("content-type","text/html;charset=utf-8");

        //简单的形式，设置编码
        response.setContentType("text/html;charset=utf-8");

        //1.获取字符输出流
        PrintWriter pw = response.getWriter();
        //2.输出数据
        //pw.write("<h1>hello response</h1>");
        pw.write("你好啊啊啊 response");
    }

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


    4.  服务器输出字节数据到浏览器
                  * 步骤：
                      1. 获取字节输出流
                      2. 输出数据
      package cn.itcast.web.servlet;

import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
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("/responseDemo5")
public class ResponseDemo5 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html;charset=utf-8");

        //1.获取字节输出流
        ServletOutputStream sos = response.getOutputStream();
        //2.输出数据
        sos.write("你好".getBytes("utf-8"));
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}
    5. Response 验证码的使用（字节）
      1. 本质：图片
      2. 目的：防止恶意表单注册

      package cn.itcast.web.servlet;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;

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


        int width = 100;
        int height = 50;

        //1.创建一对象，在内存中图片(验证码图片对象)
        BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);


        //2.美化图片
        //2.1 填充背景色
        Graphics g = image.getGraphics();//画笔对象
        g.setColor(Color.PINK);//设置画笔颜色
        g.fillRect(0,0,width,height);

        //2.2画边框
        g.setColor(Color.BLUE);
        g.drawRect(0,0,width - 1,height - 1);

        String str = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghigklmnopqrstuvwxyz0123456789";
        //生成随机角标
        Random ran = new Random();

        for (int i = 1; i <= 4; i++) {
            int index = ran.nextInt(str.length());
            //获取字符
            char ch = str.charAt(index);//随机字符
            //2.3写验证码
            g.drawString(ch+"",width/5*i,height/2);
        }


        //2.4画干扰线
        g.setColor(Color.GREEN);

        //随机生成坐标点

        for (int i = 0; i < 10; i++) {
            int x1 = ran.nextInt(width);
            int x2 = ran.nextInt(width);

            int y1 = ran.nextInt(height);
            int y2 = ran.nextInt(height);
            g.drawLine(x1,y1,x2,y2);
        }


        //3.将图片输出到页面展示
        ImageIO.write(image,"jpg",response.getOutputStream());


    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}
      <!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>

    <script>
        /*
            分析：
                点击超链接或者图片，需要换一张
                1.给超链接和图片绑定单击事件

                2.重新设置图片的src属性值

         */
    window.onload = function(){
        //1.获取图片对象
        var img = document.getElementById("checkCode");
        //2.绑定单击事件
        img.onclick = function(){
            //加时间戳
            var date = new Date().getTime();

            img.src = "/day15/checkCodeServlet?"+date;
        }

    }


    </script>


</head>
<body>


    <img id="checkCode" src="/day15/checkCodeServlet" />

    <a id="change" href="">看不清换一张？</a>

</body>
</html>
    6. ServletContext对象
      1. 概念：代表整个web应用，可以和程序的容器(服务器)来通信
      2. 获取：【这两个方法都是一样的】
              1. 通过request对象获取
                  request.getServletContext();
              2. 通过HttpServlet获取
                  this.getServletContext();
      package cn.itcast.web.servletcontext;

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("/servletContextDemo1")
public class ServletContextDemo1 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        /*

            ServletContext对象获取：
                1. 通过request对象获取
                    request.getServletContext();
                2. 通过HttpServlet获取
                    this.getServletContext();
         */
        
        //1. 通过request对象获取
        ServletContext context1 = request.getServletContext();
        //2. 通过HttpServlet获取
        ServletContext context2 = this.getServletContext();

        System.out.println(context1);
        System.out.println(context2);

        System.out.println(context1 == context2);//true


    }

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


      3. 功能：
              1. 获取MIME类型：
                  * MIME类型:在互联网通信过程中定义的一种文件数据类型
                      * 格式： 大类型/小类型   text/html        image/jpeg

                  * 获取：String getMimeType(String file)  
      package cn.itcast.web.servletcontext;

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("/servletContextDemo2")
public class ServletContextDemo2 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        /*

            ServletContext功能：
               1. 获取MIME类型：
                * MIME类型:在互联网通信过程中定义的一种文件数据类型
                    * 格式： 大类型/小类型   text/html        image/jpeg

                * 获取：String getMimeType(String file)
                2. 域对象：共享数据
                3. 获取文件的真实(服务器)路径
         */
        
        //2. 通过HttpServlet获取
        ServletContext context = this.getServletContext();

        //3. 定义文件名称
        String filename = "a.jpg";//image/jpeg


        //4.获取MIME类型
        String mimeType = context.getMimeType(filename);
        System.out.println(mimeType);


    }

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


              2. 域对象：共享数据
                  1. setAttribute(String name,Object value)
                  2. getAttribute(String name)
                  3. removeAttribute(String name)

                  * ServletContext对象范围：所有用户所有请求的数据
      package cn.itcast.web.servletcontext;

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("/servletContextDemo3")
public class ServletContextDemo3 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        /*

            ServletContext功能：
               1. 获取MIME类型：

                2. 域对象：共享数据
                3. 获取文件的真实(服务器)路径
         */
        
        //2. 通过HttpServlet获取
        ServletContext context = this.getServletContext();

        //设置数据
        context.setAttribute("msg","haha");


    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}
      package cn.itcast.web.servletcontext;

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("/servletContextDemo4")
public class ServletContextDemo4 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        /*

            ServletContext功能：
               1. 获取MIME类型：

                2. 域对象：共享数据
                3. 获取文件的真实(服务器)路径
         */
        
        //2. 通过HttpServlet获取
        ServletContext context = this.getServletContext();

        //获取数据
        Object msg = context.getAttribute("msg");
        System.out.println(msg);

    }

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

      思路：先在某浏览器访问D3，后在其他浏览器上访问D4，可以显示出D3的共享数据；


              3. 获取文件的真实(服务器)路径
                  1. 方法：String getRealPath(String path)  
                       String b = context.getRealPath("/b.txt");//web目录下资源访问
                       System.out.println(b);
              
                      String c = context.getRealPath("/WEB-INF/c.txt");//WEB-INF目录下的资源访问
                      System.out.println(c);
              
                      String a = context.getRealPath("/WEB-INF/classes/a.txt");//src目录下的资源访问
                      System.out.println(a);

      package cn.itcast.web.servletcontext;

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.File;
import java.io.IOException;

@WebServlet("/servletContextDemo5")
public class ServletContextDemo5 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        /*

            ServletContext功能：
               1. 获取MIME类型：

                2. 域对象：共享数据
                3. 获取文件的真实(服务器)路径
         */
        
        // 通过HttpServlet获取
        ServletContext context = this.getServletContext();


        // 获取文件的服务器路径
        String b = context.getRealPath("/b.txt");//web目录下资源访问
        System.out.println(b);
       // File file = new File(realPath);

        String c = context.getRealPath("/WEB-INF/c.txt");//WEB-INF目录下的资源访问
        System.out.println(c);

        String a = context.getRealPath("/WEB-INF/classes/a.txt");//src目录下的资源访问
        System.out.println(a);


    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}
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  • 原文地址：https://www.cnblogs.com/YanZhuDL/p/11619510.html
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