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  • 08Response

    1.HTTP协议

    1. 请求消息:客户端发送给服务器端的数据
      数据格式:
        1. 请求行
        2. 请求头
        3. 请求空行
        4. 请求体
    2. 响应消息:服务器端发送给客户端的数据
      数据格式:
        1. 响应行
          1. 组成:协议/版本 响应状态码 状态码描述
          2. 响应状态码:服务器告诉客户端浏览器本次请求和响应的一个状态。
            1. 状态码都是3位数字
            2. 分类:
              1. 1xx:服务器就收客户端消息,但没有接受完成,等待一段时间后,发送1xx多状态码
              2. 2xx:成功。代表:200
              3. 3xx:重定向。代表:302(重定向),304(访问缓存)
              4. 4xx:客户端错误。
                代表:
                  404(请求路径没有对应的资源)
                  405:请求方式没有对应的doXxx方法
              5. 5xx:服务器端错误。代表:500(服务器内部出现异常)

        2. 响应头:
          1. 格式:头名称: 值
          2. 常见的响应头:
            1. Content-Type:服务器告诉客户端本次响应体数据格式以及编码格式
            2. Content-disposition:服务器告诉客户端以什么格式打开响应体数据
              值:
                in-line:默认值,在当前页面内打开
                attachment;filename=xxx:以附件形式打开响应体。文件下载
        3. 响应空行
        4. 响应体:传输的数据


      响应字符串格式
        HTTP/1.1 200 OK
        Content-Type: text/html;charset=UTF-8
        Content-Length: 101
        Date: Wed, 06 Jun 2018 07:08:42 GMT

      <html>
        <head>
          <title>$Title$</title>
        </head>
        <body>
          hello , response
        </body>
      </html>

    2.功能:设置响应消息 

    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

    3.案例

    3.1 完成重定向

      重定向:资源跳转的方式

    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","/day15Response/ResponseDemo2");
    
    
        }
    
        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........");
    
        }
    
        protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            this.doPost(request,response);
        }
    }

    另外一种简单的方法

    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
    
            request.setAttribute("msg","response");
    
            //动态获取虚拟目录
            String contextPath = request.getContextPath();
            System.out.println(contextPath);
            //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);
        }
    }

    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
                
    forward 和  redirect 区别
                
    路径写法:
      1. 路径分类
        1. 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
        2. 绝对路径:通过绝对路径可以确定唯一资源
          如:http://localhost/day15/responseDemo2        /day15/responseDemo2
          以/开头的路径

          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()
                                    * <a> , <form> 重定向...
            给服务器使用:不需要加虚拟目录
                                    * 转发路径
                                     

    3.2 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

    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);
        }
    }


       注意:
        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");

    3.3 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);
        }
    }

    3.4 验证码

      1. 本质:图片
      2. 目的:防止恶意表单注册

    <!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 = "/day15Response/CheckCodeServlet?"+date;
            }
    
        }
    
    
        </script>
    
    
    </head>
    <body>
    
    
        <img id="checkCode" src="/day15Response/CheckCodeServlet" />
    
        <a id="change" href="">看不清换一张?</a>
    
    </body>
    </html>
    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);
        }
    }

        

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  • 原文地址:https://www.cnblogs.com/xinmomoyan/p/11794946.html
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