Servlet:Response响应:服务器端发送给客户端的数据

其他 2020-02-07 18:22:31 阅读次数: 0

文章目录

1.响应response的原理

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1.1 重定向(302)

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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
2.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
3.面试问 forward 和 redirect 区别

代码1：responseDemo1与responseDemo2重定向不能共享

//4.动态获取虚拟目录,当更改虚拟目录时，程序可以自动更改
String contextPath = request.getContextPath();
//简单重定向的写法
response.sendRedirect(contextPath+"/responseDemo2");

package com.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("/responseDemo1")
public class ResponseDemo1 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("ResponseDemo1......");
        //重定向：访问/responseDemo1,会自动跳转到/responseDemo2资源
        /*//1.设置重定向状态码302
        response.setStatus(302);
        //2.设置响应头location      response.setHeader("location","/Servlet_war_exploded/responseDemo2");//结果是访问ResponseDemo1的同时，也访问ResponseDemo2*/
        //3.结果为null,故重定向不能共享数据
        request.setAttribute("msg","response");
        //4.动态获取虚拟目录,当更改虚拟目录时，程序可以自动更改
        String contextPath = request.getContextPath();
        //简单重定向的写法
        response.sendRedirect(contextPath+"/responseDemo2");
        //重定向可以访问其他站点(服务器)的资源
        //response.sendRedirect("http://www.baidu.com");
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

package com.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("ResponseDemo2开始...");
        Object msg=request.getAttribute("msg");
        System.out.println(msg);
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

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2. response应用

代码2：responseDemo3转发到responseDemo2

package com.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;
/**
 * 则：判断定义的路径是给谁用的？判断请求将来从哪儿发出
 * 	  1. 给客户端浏览器使用：需要加虚拟目录(项目的访问路径)
 * 	     -- <a> , <form>表单，重定向...
 * 	  2. 给服务器使用：不需要加虚拟目录
 * 	     -- 转发路径
 * */
@WebServlet("/responseDemo3")
public class ResponseDemo3 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //转发,不更改地址栏地址
        request.getRequestDispatcher("/responseDemo2").forward(request,response);
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

代码3：
解决响应中文乱码：response.setContentType(“text/html;charset=utf-8”);
获取字符流:PrintWriter pw = response.getWriter();

package com.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 {
        //解决中文乱码问题：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(以后不论英文输出，也写)
        response.setContentType("text/html;charset=utf-8");
        //1.获取字符输出流
        //响应会每次响应结束都自动刷新
        PrintWriter pw=response.getWriter();
        //2.输出数据
        //print输出流本身刷新
        //pw.println("hello,response!!!");
        //write输出流本身不刷新，但是响应已经刷新，所以2者皆可
        pw.write("<h1>hello,response</h1>");//标题<h1>
        //中文输出
        pw.write("我是安徽人，hello!");
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

在这里插入图片描述

代码4：获取字节输出流
ServletOutputStream outputStream=response.getOutputStream();

package com.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;
import java.io.PrintWriter;
@WebServlet("/responseDemo5")
public class ResponseDemo5 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //避免中文乱码：先在获取流之前，告诉浏览器，服务器用的编码，即设置编码格式
        response.setContentType("text/html;charset=utf-8");
        //1.获取字节输出流
        ServletOutputStream outputStream = response.getOutputStream();
        //2.输出数据,将字符串转换成字节数组存放，服务器以utf-8编码
        outputStream.write("你好啊啊".getBytes("utf-8"));
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

代码5：状态码：500的检测

package com.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("/servletDemo1")
public class ServletDemo1 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doGet(request,response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //这是检验状态码 500 的错误
        int i= 3/0;
    }
}

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代码6:字节输出流，用图片来验证
register.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>验证码图片与事件点击</title>
</head>
<script type="text/javascript">
    /**
     * 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="/Servlet_war_exploded/checkCodeServlet?"+date;
        }
        document.getElementById("change").onclick=function () {
            img.src="/Servlet_war_exploded/checkCodeServlet?"+date;
        }
    }
</script>
<body>
    <img id="checkCode" src="/Servlet_war_exploded/checkCodeServlet" />
    <a id="change" href="">看不清换一张？</a>
</body>
</html>

checkCodeServlet

package com.Servlet;
import javax.imageio.ImageIO;
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.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.创建一个对象，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.yellow);//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="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
        //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 <6 ; 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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