response响应

郭晨 软件151 1531610114

response
1.response常用API
setStatus：设置响应行当中的状态码
setHeader：设置响应头信息
getOutputStream：获得字节流 --- 输出响应体内容
getWriter：获得字符流 --- 输出响应体内容
2.HttpServletResponse继承ServletResponse接口，ServletResponse并没有提供与HTTP协议相关API，HttpServletResponse添加了与协议相关API
JavaEE API 中并没有提供HttpServletResponse实现类---实现类由tomcat服务器提供的
3.常用状态码：200 302 304 404 500
200 请求处理成功
302 客户端重定向
304 客户端访问资源没有被修改，客户端访问本地缓存
404 访问资源不存在
500 服务器内部出错
4.案例一：通过302+Location头信息实现页面重定向

package cn.lsl.response;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ResponseServlet1 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        //302客户端重定向 --- 结合Location头信息一起使用
        response.setStatus(302);
        //通知浏览器定向到哪个页面
        response.setHeader("Location", "/Response/welcome.html");
    }

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

}

response.setStatus(302);
response.setHeader("Location", "/Response/welcome.html");    //由客户端定向到服务器，必须添加工程虚拟目录

案例二：登陆重定向
在response API中提供sendRedirect() --- 完成302+Location重定向效果
例如：response.sendRedirect("/day06/welcome.html");

eg：

package cn.lsl.response;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ResponseServlet2 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        String username = request.getParameter("username");
        String password = request.getParameter("password");

        if("admin".equals(username) && "admin".equals(password)){
//            response.setStatus(302);
//            response.setHeader("Location", "/Response/welcome.html");
            //使用response.sendRedirect完成重定向
            response.sendRedirect("/Response/welcome.html");
        }else{
//            response.setStatus(302);
//            response.setHeader("Location", "/Response/login.html");
            response.sendRedirect("/Response/login.html");
        }

    }

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

}

案例三：自动刷新网页
*登陆成功，5秒后自动跳转XX页面
原理：通过refresh头信息
格式 --- refresh:时间;url=跳转路径
例如：refresh:3;url=http://www.baidu.com  --- 3秒后自动跳转http://www.baidu.com网站

eg:

package cn.lsl.response;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ResponseServlet3 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setHeader("refresh", "3;url=http://www.baidu.com");
        response.setContentType("text/html;charset=utf-8");
        response.getWriter().println("3秒后跳转到百度");
    }

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

}

在HTML页面中存在一类非常特殊标签<meta>,<meta>起到设置头信息作用
<meta content="3;url=http://www.baidu.com" http-equiv="refresh">  ---- 完成自动跳转

案例四：通过response头信息设置浏览器禁止缓存
原理：和禁止缓存相关头信息（三个）
Cache-Control:no-cache
Expires:-1
Pragma:no-cache
eg:

package cn.lsl.response;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ResponseServlet4 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setHeader("Cache-Control", "no-cache");
        response.setHeader("Pragma", "no-cache");
        response.setDateHeader("expires", -1);
        response.getWriter().println("Hello");
    }

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

}

中文乱码问题
通过response生成客户端响应体，通过字节流和字符流两种输出方式
*哪些情况用字节流？哪些情况用字符流？
拷贝文件 --- 字节流
分析文件内容 --- 字符流  （中文操作 字符流）

案例五：输出中文信息

package cn.lsl.response;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ResponseServlet5 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        //需要通知浏览器查看编码
        response.setContentType("text/html;charset=utf-8");    //设置响应编码与浏览器查看编码
        PrintWriter out = response.getWriter();
        out.println("我很好！");
    }

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

}

setCharacterEncoding 和 setContentType区别？
setCharacterEncoding 设置响应内容编码，无法设置浏览器查看编码
setContentType设置响应内容编码，同时通知浏览器查看编码
*在响应头信息中 Content-Type:text/html;charset=utf-8
结论：setContentType具备setCharacterEncoding编码功能，现实开发中，只需要使用setContentType就可以了

注意：
1）getOutputStream和getWriter不能同时使用
2）必须在getOutputStream喝getWriter之前设置响应编码
3）getOutputStream和getWriter输出内容是HTTP响应体
4）getOutputStream和getWriter存在缓冲区，在service方法结束时，自动关闭流，flush缓冲区内容

案例六：文件下载
第一种：通过超链接完成文件下载
*如果浏览器可以识别该文件格式，直接打开，只有链接文件浏览器不识别文件格式，才会实现下载
第二种：通过Servlet程序实现下载
原理：通过Servlet读取目标程序，将资源返回客户端
通过程序下载文件，设置两个头信息Content-Type Content-Disposition

response.setContentType(getServletContext().getMimeType(filename));     ----设置文件类型
response.setHeader("Content-Disposition","attachment;filename="+filename); ----设置文件以附件形式下载（对于浏览器识别格式文件）
eg:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <title>download.html</title>
  </head>

  <body>
    <h1>通过超链接实现文件下载</h1>
    <a href="/Response/download/xpp3.zip">zip压缩包下载</a>
    <a href="/Response/download/mm.jpg">jpg图片下载</a>
    <!-- 通过?在url地址里拼接参数 get方式提交 -->
    <h1>通过程序实现下载</h1>
    <a href="/Response/response6?filename=xpp3.zip">zip压缩包下载</a>
    <a href="/Response/response6?filename=mm.jpg">jpg图片下载</a>
  </body>
</html>

package cn.lsl.response;

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ResponseServlet6 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        //获得文件名
        String filename = request.getParameter("filename");
        response.setContentType(getServletContext().getMimeType(filename));    //设置MIME类型
        response.setHeader("Content-Disposition", "attachment;filename=" + filename);

        //绝对磁盘路径
        String fullFilename = getServletContext().getRealPath("/download/" + filename);
        InputStream in = new FileInputStream(fullFilename);
        OutputStream out = response.getOutputStream();
        int b;
        while((b=in.read())!=-1){
            out.write(b);
        }
        in.close();
        out.close();
    }

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

}

案例七：验证码输出案例
Java图形API生成验证码图片
为什么需要验证码？防止有人通过程序恶意攻击网站
eg：

package cn.lsl.response;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ResponseServlet7 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        int width = 120;
        int height = 30;
        //创建一张内存中缓冲图片
        BufferedImage bufferedImage = new BufferedImage(width, height, BufferedImage.TYPE_INT_BGR);
        //背景色
        Graphics graphics = bufferedImage.getGraphics();    //通过graphics对象绘制图片
        graphics.setColor(Color.YELLOW);
        graphics.fillRect(0, 0, width, height);

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

        //写验证内容
        Graphics2D graphics2d = (Graphics2D)bufferedImage.getGraphics();
        graphics2d.setColor(Color.RED);
        graphics2d.setFont(new Font("宋体",Font.BOLD,18));

        //String content = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz1234567890";
        String content = "\u7684\u4e00\u4e86\u662f\u6211\u4e0d\u5728\u4eba\u4eec\u6709\u6765\u4ed6\u8fd9\u4e0a" +
                "\u7740\u4e2a\u5730\u5230\u5927\u91cc\u8bf4\u5c31\u53bb\u5b50\u5f97\u4e5f\u548c\u90a3\u8981\u4e0b" +
                "\u770b\u5929\u65f6\u8fc7\u51fa\u5c0f\u4e48\u8d77\u4f60\u90fd\u628a\u597d\u8fd8\u591a\u6ca1\u4e3a" +
                "\u53c8\u53ef\u5bb6\u5b66\u53ea\u4ee5\u4e3b\u4f1a\u6837\u5e74\u60f3\u751f\u540c\u8001\u4e2d\u5341" +
                "\u4ece\u81ea\u9762\u524d\u5934\u9053\u5b83\u540e\u7136\u8d70\u5f88\u50cf\u89c1\u4e24\u7528\u5979" +
                "\u56fd\u52a8\u8fdb\u6210\u56de\u4ec0\u8fb9\u4f5c\u5bf9\u5f00\u800c\u5df1\u4e9b\u73b0\u5c71\u6c11" +
                "\u5019\u7ecf\u53d1\u5de5\u5411\u4e8b\u547d\u7ed9\u957f\u6c34\u51e0\u4e49\u4e09\u58f0\u4e8e\u9ad8" +
                "\u624b\u77e5\u7406\u773c\u5fd7\u70b9\u5fc3\u6218\u4e8c\u95ee\u4f46\u8eab\u65b9\u5b9e\u5403\u505a" +
                "\u53eb\u5f53\u4f4f\u542c\u9769\u6253\u5462\u771f\u5168\u624d\u56db\u5df2\u6240\u654c\u4e4b\u6700" +
                "\u5149\u4ea7\u60c5\u8def\u5206\u603b\u6761\u767d\u8bdd\u4e1c\u5e2d\u6b21\u4eb2\u5982\u88ab\u82b1" +
                "\u53e3\u653e\u513f\u5e38\u6c14\u4e94\u7b2c\u4f7f\u5199\u519b\u5427\u6587\u8fd0\u518d\u679c\u600e" +
                "\u5b9a\u8bb8\u5feb\u660e\u884c\u56e0\u522b\u98de\u5916\u6811\u7269\u6d3b\u90e8\u95e8\u65e0\u5f80" +
                "\u8239\u671b\u65b0\u5e26\u961f\u5148\u529b\u5b8c\u5374\u7ad9\u4ee3\u5458\u673a\u66f4\u4e5d\u60a8" +
                "\u6bcf\u98ce\u7ea7\u8ddf\u7b11\u554a\u5b69\u4e07\u5c11\u76f4\u610f\u591c\u6bd4\u9636\u8fde\u8f66" +
                "\u91cd\u4fbf\u6597\u9a6c\u54ea\u5316\u592a\u6307\u53d8\u793e\u4f3c\u58eb\u8005\u5e72\u77f3\u6ee1" +
                "\u65e5\u51b3\u767e\u539f\u62ff\u7fa4\u7a76\u5404\u516d\u672c\u601d\u89e3\u7acb\u6cb3\u6751\u516b" +
                "\u96be\u65e9\u8bba\u5417\u6839\u5171\u8ba9\u76f8\u7814\u4eca\u5176\u4e66\u5750\u63a5\u5e94\u5173" +
                "\u4fe1\u89c9\u6b65\u53cd\u5904\u8bb0\u5c06\u5343\u627e\u4e89\u9886\u6216\u5e08\u7ed3\u5757\u8dd1" +
                "\u8c01\u8349\u8d8a\u5b57\u52a0\u811a\u7d27\u7231\u7b49\u4e60\u9635\u6015\u6708\u9752\u534a\u706b" +
                "\u6cd5\u9898\u5efa\u8d76\u4f4d\u5531\u6d77\u4e03\u5973\u4efb\u4ef6\u611f\u51c6\u5f20\u56e2\u5c4b" +
                "\u79bb\u8272\u8138\u7247\u79d1\u5012\u775b\u5229\u4e16\u521a\u4e14\u7531\u9001\u5207\u661f\u5bfc" +
                "\u665a\u8868\u591f\u6574\u8ba4\u54cd\u96ea\u6d41\u672a\u573a\u8be5\u5e76\u5e95\u6df1\u523b\u5e73" +
                "\u4f1f\u5fd9\u63d0\u786e\u8fd1\u4eae\u8f7b\u8bb2\u519c\u53e4\u9ed1\u544a\u754c\u62c9\u540d\u5440" +
                "\u571f\u6e05\u9633\u7167\u529e\u53f2\u6539\u5386\u8f6c\u753b\u9020\u5634\u6b64\u6cbb\u5317\u5fc5" +
                "\u670d\u96e8\u7a7f\u5185\u8bc6\u9a8c\u4f20\u4e1a\u83dc\u722c\u7761\u5174\u5f62\u91cf\u54b1\u89c2" +
                "\u82e6\u4f53\u4f17\u901a\u51b2\u5408\u7834\u53cb\u5ea6\u672f\u996d\u516c\u65c1\u623f\u6781\u5357" +
                "\u67aa\u8bfb\u6c99\u5c81\u7ebf\u91ce\u575a\u7a7a\u6536\u7b97\u81f3\u653f\u57ce\u52b3\u843d\u94b1" +
                "\u7279\u56f4\u5f1f\u80dc\u6559\u70ed\u5c55\u5305\u6b4c\u7c7b\u6e10\u5f3a\u6570\u4e61\u547c\u6027" +
                "\u97f3\u7b54\u54e5\u9645\u65e7\u795e\u5ea7\u7ae0\u5e2e\u5566\u53d7\u7cfb\u4ee4\u8df3\u975e\u4f55" +
                "\u725b\u53d6\u5165\u5cb8\u6562\u6389\u5ffd\u79cd\u88c5\u9876\u6025\u6797\u505c\u606f\u53e5\u533a" +
                "\u8863\u822c\u62a5\u53f6\u538b\u6162\u53d4\u80cc\u7ec6";

        //内容四个字 -- 随机从content中抽取四个字
        Random random = new Random();
        int x=10;
        int y=20;
        for(int i=0; i<4; i++){
            //为字生成旋转角度 -30 -- 30
            double jiaodu = random.nextInt(60) - 30;
            //将旋转角度换算弧度
            double theta = jiaodu/180*Math.PI;
            System.out.println(theta);

            int index = random.nextInt(content.length());
            char letter = content.charAt(index);
            graphics2d.rotate(theta, x, y);
            graphics2d.drawString(letter+"", x, y);
            //将角度还原
            graphics2d.rotate(-theta, x, y);
            x += 30;
        }

        //绘制随机干扰线
        int x1;
        int x2;
        int y1;
        int y2;
        graphics.setColor(Color.LIGHT_GRAY);
        for(int i=0; i<10; i++){
            x1 = random.nextInt(width);
            x2 = random.nextInt(width);
            y1 = random.nextInt(height);
            y2 = random.nextInt(height);
            //根据两点  绘制直线
            graphics.drawLine(x1, y1, x2, y2);
        }

        //内存中资源释放
        graphics.dispose();

        //将图片输出到浏览器 ImageIO
        //将内存的图片通过浏览器输出流写成jpg格式图片
        ImageIO.write(bufferedImage, "jpg", response.getOutputStream());
    }

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

}

分析：
验证码旋转效果
rotate(double theta, double x, double y)  ----- 参数 theta 旋转弧度
2PI 弧度 = 360 角度

-30 ---- 30 角度