java

Servlet中Responce对象的基本使用和验证码图片案例

Nick · 3月18日 · 2020年 · 本文5934字 · 阅读15分钟407

Response对象

  • 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
  • 完成重定向

重定向:资源跳转的方式

* 代码实现:
        //简单的重定向方法
         response.sendRedirect("/day15/responseDemo2");
         * forward 和  redirect 区别
* 重定向的特点:redirect(客户端使用)
        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(服务器端使用)
        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

代码示例如下
1. servlet1.java(发起重定向)

package servlet_response;/*
 *Created by tao on 2020-03-17.
 */

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("/response1")
public class servlet1 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("我是response1");
        request.setAttribute("msg", "request对象共享数据");
        //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 + "/response2");

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}
  1. servlet2.java(重定向接收,并且发起一个转发)
package servlet_response;/*
 *Created by tao on 2020-03-17.
 */

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;

/**
 * 重定向接收
 * 转发
 */

@WebServlet("/response2")
public class servlet2 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("我是response2");
        Object msg = request.getAttribute("msg");
        //重定向是两次请求,获取不到request对象共享数据
        System.out.println("获取到的数据:"+msg);
        //转发
        request.setAttribute("msg", "request对象共享数据");
        request.getRequestDispatcher("/response3").forward(request,response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}
  1. servlet3.java(转发接收)
package servlet_response;/*
 *Created by tao on 2020-03-17.
 */

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;

/**
 * 转发接收
 */

@WebServlet("/response3")
public class servlet3 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("我是response3");
        Object msg = request.getAttribute("msg");
        //转发是一次请求,可以获取到request对象共享数据
        //转发地址栏路径不变
        System.out.println("获取到的数据:"+msg);
    }

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

实现效果如下
Servlet中Responce对象的基本使用和验证码图片案例-左眼会陪右眼哭の博客
验证了上述所说的重定向和转发的区别

向客户端响应数据(字符流和字节流)

1. 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
    * 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");
2. 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

实现代码如下
servlet4.java

package servlet_response;/*
 *Created by tao on 2020-03-17.
 */

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;

//向客户端响应数据
@WebServlet("/response4")
public class servlet4 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //设置响应的编码格式
        response.setContentType("text/html;charset=utf-8");

        /*字符流传输*/
        //1.获取字符输出流
        PrintWriter pw = response.getWriter();
        //2.输出数据
        //pw.write("<h2>hello response</h2>");
        pw.write("我是字符流传输 response");
        //简写方式
        response.getWriter().write("<h2>hello response</h2>");

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

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

实现效果如下
在这里插入图片描述

响应验证码图片案例

验证码
        1. 本质:图片
        2. 目的:防止恶意表单注册
        3. 方式:通过response对象,使用字节流输出图片

实现代码如下

package servlet_response;

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;
/*
* 字节流输出:验证码图片
* */
@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);
    }
}

实现效果如下
Servlet中Responce对象的基本使用和验证码图片案例-左眼会陪右眼哭の博客
刷新会重置验证码

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