HttpServletResponse的学习

关于Response对象的一些方法和属性可以查看官方文档：https://javaee.github.io/javaee-spec/javadocs/

比如里面定义了许多常量：

这些都是服务器向浏览器返回的一些状态码，我们把它定义成常量，之后就不要写数字！

还有一些方法：

1、示例：向浏览器输出中文：

package test;

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

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

/**
 * Servlet implementation class ServletContextDemo2
 */
@WebServlet("/ServletContextDemo2")    //注意有了这个就不需要往web.xml文件里面添加路径映射
public class ServletContextDemo2 extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub大小写要注意好了
        response.setHeader("Content-type", "text/html;charset=UTF-8"); //要告诉浏览器以什么编码打开
        String s = "中国";
        OutputStream out = response.getOutputStream();
        out.write(s.getBytes("UTF-8"));  //为了兼容性，我们设置字符编码为utf-8
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

还可以：

package test;

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

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

/**
 * Servlet implementation class ServletContextDemo2
 */
@WebServlet("/ServletContextDemo2")    //注意有了这个就不需要往web.xml文件里面添加路径映射
public class ServletContextDemo2 extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        String s = "中国";
        OutputStream out = response.getOutputStream();
        //使用html的meta标签模拟一个http响应头，来控制浏览器行为
        out.write("<meta http-equiv='content-type' content='text/html;charset=UTF-8'>".getBytes());
        out.write(s.getBytes("UTF-8"));  //为了兼容性，我们设置字符编码为utf-8
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

注意：下面这种方式对于谷歌浏览器不可以，对于IE浏览器可以

package test;

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.util.Properties;

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

/**
 * Servlet implementation class ServletContextDemo2
 */
@WebServlet("/ServletContextDemo2")    //注意有了这个就不需要往web.xml文件里面添加路径映射
public class ServletContextDemo2 extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        String s = "中国";
        response.setCharacterEncoding("UTF-8");  //设置response的默认编码，控制response以什么码表像浏览器输出数据
        response.setHeader("Content-type", "text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        out.write(s);  //通过字符方式写数据
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

//下面两个语句一样的效果
response.setHeader("Content-type", "text/html;charset=UTF-8");
response.setContentType("text/html;charset=UTF-8");  这样也可以

2、文件下载

package test;

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.util.Properties;

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

/**
 * Servlet implementation class ServletContextDemo2
 */
@WebServlet("/ServletContextDemo2")    //注意有了这个就不需要往web.xml文件里面添加路径映射
public class ServletContextDemo2 extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        String path = this.getServletContext().getRealPath("/download/1.txt");
        String file_name = path.substring(path.lastIndexOf("\\")+1);
        response.setHeader("content-disposition", "attachment;filename="+file_name);
        //文件写入response
        InputStream in = null;
        OutputStream out = null;
        try {
            in = new FileInputStream(path);
            int len=0;
            byte buffer[] = new byte[1024];
            out = response.getOutputStream();
            while((len = in.read(buffer))>0) {
                out.write(buffer,0,len);
            }
        }finally {  
            if(in!=null) {
                try {
                    in.close();
                }catch(Exception e){
                    e.printStackTrace();
                }
            }
        }
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

如果文件名是中文的需要经过URL编码

package test;

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.net.URLEncoder;
import java.util.Properties;

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

/**
 * Servlet implementation class ServletContextDemo2
 */
@WebServlet("/ServletContextDemo2")    //注意有了这个就不需要往web.xml文件里面添加路径映射
public class ServletContextDemo2 extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        String path = this.getServletContext().getRealPath("/download/你好.txt");
        String file_name = path.substring(path.lastIndexOf("\\")+1);
        response.setHeader("content-disposition", "attachment;filename="+URLEncoder.encode(file_name,"UTF-8"));
        //文件写入response
        InputStream in = null;
        OutputStream out = null;
        try {
            in = new FileInputStream(path);
            int len=0;
            byte buffer[] = new byte[1024];
            out = response.getOutputStream();
            while((len = in.read(buffer))>0) {
                out.write(buffer,0,len);
            }
        }finally {  
            if(in!=null) {
                try {
                    in.close();
                }catch(Exception e){
                    e.printStackTrace();
                }
            }
        }
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

2、生成随机验证图片，并向浏览器输出

目录为：

ServletContextDemo2.Java内容：

package test;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.net.URLEncoder;
import java.util.Properties;
import java.util.Random;

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;

/**
 * Servlet implementation class ServletContextDemo2
 */
@WebServlet("/ServletContextDemo2")    //注意有了这个就不需要往web.xml文件里面添加路径映射
public class ServletContextDemo2 extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    public static final int WIDTH = 120;
    public static final int HEIGHT = 35;
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        BufferedImage image = new BufferedImage(WIDTH,HEIGHT,BufferedImage.TYPE_INT_RGB);
        Graphics g = image.getGraphics();
        //背景色
        setBackGround(g);
        //边框
        setBorder(g);
        //干扰线
        drawRandomLine(g);
        //画随机数\字体旋转
        drawRandomNum((Graphics2D)g);
        
        //图形写给浏览器
        response.setContentType("image/jpeg");
        //控制浏览器不要缓存随机图片
        response.setHeader("Cache-Control", "no-cache");
        response.setHeader("Pragma", "no-cache");
        ImageIO.write(image, "jpg", response.getOutputStream());
    }

    private void drawRandomNum(Graphics2D g) {
        // TODO Auto-generated method stub
        g.setColor(Color.red);
        //设置字体为加粗宋体，高度20
        g.setFont(new Font("宋体",Font.BOLD,20));
        //在UTF-8码表中，所有汉字都在[4e00-9fa5]这个区间内
        //char c = '\u4e00'; Java内内置编码为UTF-8 ，所以\u4e00就相当于一个汉字
        //常用汉字编码utf-8编码
        String data = "\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";
        int x=5;
        for(int i=0;i<4;++i)
        {
            int degree = new Random().nextInt()%30; //生成-30-30的随机数
            String ch = data.charAt(new Random().nextInt(data.length()))+"";
            //degree*Math.PI/180角度变弧度,设置旋转角度
            g.rotate(degree*Math.PI/180,x,20); //基于(x,20)点旋转
            g.drawString(ch, x, 20);
            g.rotate(-degree*Math.PI/180,x,20); //调回旋转角度
            x+=30;
        }
    }

    private void drawRandomLine(Graphics g) {
        // TODO Auto-generated method stub
        g.setColor(Color.GREEN);
        for(int i=0;i<5;++i) {
            int x1 = new Random().nextInt(WIDTH); //生成[0,WIDTH)的随机数
            int y1 = new Random().nextInt(HEIGHT);
            
            int x2 = new Random().nextInt(WIDTH); //生成[0,WIDTH)的随机数
            int y2 = new Random().nextInt(HEIGHT);
            g.drawLine(x1, y1, x2, y2);
        }
    }

    private void setBorder(Graphics g) {
        // TODO Auto-generated method stub
        g.setColor(Color.BLUE);
        g.drawRect(1, 1, WIDTH-2, HEIGHT-2);
    }

    private void setBackGround(Graphics g) {
        // TODO Auto-generated method stub
        g.setColor(Color.WHITE);
        g.fillRect(0, 0, WIDTH, HEIGHT);
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

还有html内容：

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
    <form action="">
        用户名：<input type="text" name="username">
        密码：<input type="password" name="password">
        认证码：<input type="text" name="checkcode"><img src="/day02/ServletContextDemo2"><br/>
        <input type="submit" value="注册">
    </form>
</body>
</html>

实现点验证图片之后换一张图片只需要改一下html内容：

<!DOCTYPE html>
<html>
<head>
    <script type="text/javascript">
        function changeimage(img){
            //img.src = img.src 后面的src是获取html里面img的src属性，赋值给img.src就代表重新访问
            //但是上面的语句不可行是因为浏览器会默认从缓存里面找图片，所以你应该把图片地址换一下
            //这样浏览器在缓存里面找不到就会向服务器发送请求
            img.src=img.src+"?"+new Date().getTime();
        }
    </script>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
    <form action="">
        用户名：<input type="text" name="username">
        密码：<input type="password" name="password">
        认证码：<input type="text" name="checkcode">
        <img src="/day02/ServletContextDemo2" onclick="changeimage(this)" alt="换一张" style="cursor:hand"><br/>
        <input type="submit" value="注册">
    </form>
</body>
</html>

3、控制浏览器定时刷新

package test;

import java.io.IOException;
import java.util.Random;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class ServletContextDemo2
 */
@WebServlet("/ServletContextDemo2")    //注意有了这个就不需要往web.xml文件里面添加路径映射
public class ServletContextDemo2 extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setHeader("refresh", "3"); //3秒刷新一次
        String data = new Random().nextInt(1000000)+"";
        response.getWriter().write(data);  //以字符形式输出数据
    }
    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

3秒之后跳转到指定页面

package test;

import java.io.IOException;
import java.util.Random;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class ServletContextDemo2
 */
@WebServlet("/ServletContextDemo2")    //注意有了这个就不需要往web.xml文件里面添加路径映射
public class ServletContextDemo2 extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setHeader("Content-type", "text/html;charset=utf-8");
        //3秒之后刷新，并跳转到register.html页面
        response.setHeader("refresh", "3;url='/day02/register.html'"); 
        response.getWriter().write("本浏览器在3秒后跳转，若没有跳转，点击<a href=''>超链接</a>");  //以字符形式输出数据
    }
    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

使用expries控制浏览器缓存

package test;

import java.io.IOException;
import java.util.Random;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class ServletContextDemo2
 */
@WebServlet("/ServletContextDemo2")    //注意有了这个就不需要往web.xml文件里面添加路径映射
public class ServletContextDemo2 extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //控制浏览器缓存，浏览器缓存截止于1小时后不可用
        //1000代表一秒，乘于3600就是一小时。System.currentTimeMillis()代表当前时间
        response.setDateHeader("expries", System.currentTimeMillis()+1000*3600);
        String data = "aaaaaa";
        response.getWriter().write(data);
    }
    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

重定向：

package test;

import java.io.IOException;
import java.util.Random;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class ServletContextDemo2
 */
@WebServlet("/ServletContextDemo2")    //注意有了这个就不需要往web.xml文件里面添加路径映射
public class ServletContextDemo2 extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    //重定向会发送两次请求，每一次请求都是不同的servlet处理
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //重定向
        response.setStatus(302);
        response.setHeader("location", "/day02/register.html");
        
        //下面也是重定向
        response.sendRedirect("/day02/register.html");
    }
    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

getWriter和getOutputStream不能用同一个servlet处理，就比如你使用转发，这个时候是一个servlet处理两次请求，所以即使在两个文件却不能同时出现两种输出数据方式，示例：

ServletContextDemo2

package test;

import java.io.IOException;
import java.util.Random;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class ServletContextDemo2
 */
@WebServlet("/ServletContextDemo2")    //注意有了这个就不需要往web.xml文件里面添加路径映射
public class ServletContextDemo2 extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    //重定向会发送两次请求，每一次请求都是不同的servlet处理
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.getOutputStream();
        this.getServletContext().getRequestDispatcher("/ServletContextDemo1").forward(request, response);
    }
    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

ServletContextDemo1

package test;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class ServletContextDemo1
 */
@WebServlet("/ServletContextDemo1")
public class ServletContextDemo1 extends HttpServlet {
    private static final long serialVersionUID = 1L;
    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        response.getWriter();
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

上面这样就会报错，但是换成重定向就没有问题，因为重定向的两次请求不是一个servlet处理的。

posted @ 2020-12-06 13:38 kongbursi 阅读(97) 评论(0) 编辑收藏举报

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