JavaEE：response响应和request请求

时间：2023-11-11 20:04:50

Web服务器接收到客户端的http请求，会针对每一次请求，分别创建一个用于代表请求的request对象、和代表响应的response对象。
request和response对象既然代表请求和响应，那么我们要获取客户机提交过来的数据，只需要找request对象，就行了。要向客户机输出数据，只需要找response对象就行了。

HttpServletRequest封装客户端相关信息，服务器Servlet程序可以通过request对象操作客户端信息
HttpServletResponse封装服务器向客户端发送响应数据信息，Servlet程序通过response对象向客户端发送响应

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

Request
HttpServletRequest相比ServletRequest添加与协议相关的API
HttpServletRequest对象代表客户端的请求，当客户端通过HTTP协议访问服务器时，HTTP请求中的所有信息都封装在这个对象中，可通过这个对象的方法，获取客户这些信息。
HttpServletRequest分为四个部分
1.获取客户机信息
1）几个方法：
getRequestURL方法返回客户端发出请求完整URL
getRequestURI方法返回请求行中的资源名部分
getQueryString方法返回请求行中的参数部分
getRemoteAddr方法返回发出请求的客户机的IP地址
getMethod得到客户机请求方式
getContextPath获得工程虚拟目录名称

eg:

package cn.lsl.request;

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 RequestServlet1 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        System.out.println("url:" + request.getRequestURL());

        System.out.println("uri:" + request.getRequestURI());

        //通过getQueryString可以获得get方式提交查询串url中？后面部分

        System.out.println("querystring:" + request.getQueryString());

        //获得客户端ip

        System.out.println("ip:" + request.getRemoteAddr());

        //通过getContextPath获得工程虚拟目录名称

        System.out.println(request.getContextPath());

        //通过getMethod获取请求方式

        System.out.println("请求方式:" + request.getMethod());

        //获得当前访问资源路径  --- /request1

        System.out.println("当前访问资源路径:" + request.getRequestURI().substring(request.getContextPath().length()));

    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        doGet(request,response);

    }

}

URI和URL区别
url:http://localhost:8080/Request/request1  （完整）
uri:/Request/request1  （部分）

URI包含URL的
http://localhost:8080/Request/request1 是一个URL，同时也是URI
./hello  /day06/request1 都是URI，不是URL

2.获取请求头信息
getHeader获得头信息的值，转换一个字符串
getHeaders获得头信息值，返回Enumeration
getHeaderNames获得所有头信息名称，返回Enumeration

eg:

package cn.lsl.request;

import java.io.IOException;

import java.util.Enumeration;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

public class RequestServlet2 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        String value = request.getHeader("Accept-Encoding");

        System.out.println(value);

        System.out.println("--------------");

        Enumeration<String> enumeration = request.getHeaderNames();

        while(enumeration.hasMoreElements()){

            String name = enumeration.nextElement();

            System.out.println(name + ":" + request.getHeader(name));

        }

    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        doGet(request,response);

    }

}

案例：
编写防盗链程序，存在合法referer不是盗链，否则控制目标资源无法访问！

package cn.lsl.request;

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 RequestServlet3 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        String referer = request.getHeader("referer");

        response.setContentType("text/html;charset=utf-8");

        if(referer == null || !referer.startsWith("http://localhost")){

            response.getWriter().println("是盗链");

        }else{

            response.getWriter().println("不是盗链");

        }

    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        doGet(request,response);

    }

}

3.获取请求参数
什么是请求参数？
用户用过请求提交服务器一些数据

四个常用API
getParameter
getParameterValues
getParameterNames
getParameterMap

eg:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>

  <head>

    <title>request.html</title>

  </head>

  <body>

    <h1>分别以get和post方式提交数据</h1>

    <h1>第一种 通过超链接提交数据 以？方式</h1>

    <a href="/Request/request4?name=zhangsan&&city=beijing"">超链接提交数据</a>

    <h1>第二种 通过form的post方式提交数据</h1>

    <form action="/Request/request4" method="post">

        请输入姓名<input type="text" name="name" /><br/>

        请输入城市<input type="text" name="city" /><br/>

        <input type="submit" value="提交" />

    </form>

  </body>

</html>
package cn.lsl.request;

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 RequestServlet4 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        //通过getParameter获得请求数据

        String name = request.getParameter("name");

        System.out.println(name);

        String city = request.getParameter("city");

        System.out.println(city);

    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        doGet(request,response);

    }

}

乱码问题
post --- request.setCharacterEncoding("客户端编码集");

get乱码手动解决：
username = URLEncoder.encode(username, "ISO-8859-1");// 用ISO编码
username = URLDecoder.decode(username, "utf-8"); // 用utf-8解码
简化上面写法 ： username = new String(username.getBytes("ISO-8859-1"), "utf-8")

get乱码 配置tomcat默认解码字符集
在tomcat/conf/server.xml
Connector中 添加一个属性 URIEncoding="utf-8"

结论：开发时，尽量不要修改tomcat默认解码集，提交请求尽量使用post，如果非要使用get，手动编码

问题：http://localhost/day06/servlet?username=zhangsan+lisi
在服务器端 通过 request.getParameter("username") 结果是 ？？？ ----- zhangsan lisi

数据获取和乱码解决的案例：

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

<html>

<head>

<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">

<title>Insert title here</title>

</head>

<body>

<!-- 最复杂form表单 -->

<!-- 用户注册 -->

<form action="/Request/request5" method="post">

    <table>

        <!-- 文本输入框 -->

        <tr>

            <td>用户名</td>

            <td><input type="text" name="username"/></td>

        </tr>

        <!-- 密码框 -->

        <tr>

            <td>密码</td>

            <td><input type="password" name="password" /></td>

        </tr>

        <!-- 单选按钮 -->

        <tr>

            <td>性别</td>

            <td>

                <input type="radio" name="gender" value="male" /> 男

                <input type="radio" name="gender" value="female" />女

            </td>

        </tr>

        <!-- 复选框  -->

        <tr>

            <td>爱好</td>

            <td>

                <input type="checkbox" name="hobby" value="sport" /> 体育

                <input type="checkbox" name="hobby" value="music" /> 音乐

                <input type="checkbox" name="hobby" value="game" /> 游戏

            </td>

        </tr>

        <!-- 下拉框 -->

        <tr>

            <td>城市</td>

            <td>

                <select name="city">

                    <option value="beijing">北京</option>

                    <option value="shanghai">上海</option>

                    <option value="shenzhen">深圳</option>

                </select>

            </td>

        </tr>

        <!-- 多行文本框 -->

        <tr>

            <td>个人简介</td>

            <td>

                <textarea rows="5" cols="60" name="introduce"></textarea>

            </td>

        </tr>

        <tr>

            <td colspan="2"><input type="submit" value="注册"/></td>

        </tr>

    </table>

</form>

</body>

</html>
package cn.lsl.request;

import java.io.IOException;

import java.net.URLDecoder;

import java.net.URLEncoder;

import java.util.Arrays;

import java.util.Enumeration;

import java.util.Map;

import java.util.Set;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

public class RequestServlet5 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        //解决post乱码

        request.setCharacterEncoding("utf-8");

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

        System.out.println(username);

//        解决get乱码 --- 使用手动编码

//        username = URLEncoder.encode(username, "ISO-8859-1");    //用ISO编码

//        username = URLDecoder.decode(username, "utf-8");    //用utf-8解码

        //以下一句等效于上面两句

//        username = new String(username.getBytes("ISO-8859-1"), "UTF-8");

        System.out.println(username);

        String[] hobbies = request.getParameterValues("hobby");

        System.out.println(Arrays.toString(hobbies));

        //打印所有请求提交参数

        //方式一：先获得所有参数name，然后通过name获得value

        Enumeration<String> names = request.getParameterNames();

        while(names.hasMoreElements()){

            String name = names.nextElement();    //获得每一参数名称

            System.out.println(name + Arrays.toString(request.getParameterValues(name)));

        }

        System.out.println("--------------");

        Map<String, String[]> paramterMap = request.getParameterMap();

        Set<String> keys = paramterMap.keySet();

        for(String key : keys){

            System.out.println(key + ":" + Arrays.toString(paramterMap.get(key)));

        }

    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        doGet(request,response);

    }

}

4.利用请求域传递对象
HttpServletRequest和ServletContext类似，都是数据域对象，以Map方式保存数据
区分：
ServletContext对象：服务器启动对象创建，服务器停止对象销毁
ServletRequest对象：当产生一次请求时创建，当响应结束后，对象销毁

eg:

package cn.lsl.request;

import java.io.IOException;

import java.io.PrintWriter;

import javax.servlet.RequestDispatcher;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

public class AServlet extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        //通过request对象传递

        //向request域对象保存一个属性

        request.setAttribute("name", "lsl");

        //传递数据给BServlet必须使用请求转发

        RequestDispatcher dispatcher = request.getRequestDispatcher("/b");

        dispatcher.forward(request, response);

    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        doGet(request,response);

    }

}
package cn.lsl.request;

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 BServlet extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        System.out.println(request.getAttribute("name"));

    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        doGet(request,response);

    }

}

注意事项：
1）在使用forward之前，不能将响应内容传输到客户端
情况一：response输出流输出流执行flush，导致内容不能输出
情况二：同一个Servlet不能连续使用forward和redirect
2）在执行forward和redirect时，清除之前写入响应流数据
3）ServletContext进行转发路径必须以/开始，request进行转发路径可以使用相对路径

转发和重定向区别：
1、转发一次请求、一次响应，重定向 两次请求 两次响应
2、转发只能跳转站内程序，重定向定向任何站点
3、转发 URL地址不变 ，重定向URL地址改变
4、转发 对客户端不可见，重定向对客户端可见
5、转发共享同一个Request中数据，重定向两次请求，不同Request对象，不能共享Request数据

* request.setAttribute 必须和 request.getRequestDispatcher().forward 一起使用

RequestDispatcher 的 include 方法 用来做页面布局 ------ <%@include%> <jsp:include>
将页面公共部分抽取出来，通过include 引用到页面中 ---- 更加方便维护

package cn.lsl.request;

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 MainServlet1 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        request.getRequestDispatcher("/logo.html").include(request, response);

        response.getOutputStream().println("<h1>A</h1>");

        request.getRequestDispatcher("/footer.html").include(request, response);

    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        doGet(request,response);

    }

}
package cn.lsl.request;

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 MainServlet2 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        request.getRequestDispatcher("/logo.html").include(request, response);

        response.getOutputStream().println("<h1>B</h1>");

        request.getRequestDispatcher("/footer.html").include(request, response);

    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        doGet(request,response);

    }

}

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