Response 的学习

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  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
    技术图片

     

     

    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()
                //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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