HttpServletResponceHttpServletResponse对象是有关于对客户端请求之响应，您可以利用它来设定一些要响应的讯息，例如标题信息、响应状态码等response的常用方法:　　1.向客户端输出中文数据(OutputStream和PrintWriter)    response.setHeader("Content-Type","text/html;charset=utf-8");    String data = "中国";    OutputStream out =  response.getOutputStream();    out.write(data.getBytes("utf-8"));    /********************************************************************************/    String data = "中国";    OutputStream out = response.getOutputStream();    out.write("<meta http-equiv=‘content-type‘ content=‘text/html;charset=utf-8‘>".getBytes());    out.write(data.getBytes("utf-8"));    /********************************************************************************/    response.setCharacterEncoding("utf-8");    response.setHeader("Content-Type","text/html;charset=utf-8");    String data = "中国";    PrintWriter out =  response.getWriter();    out.write(data);    /********************************************************************************/    response.setContentType("text/html;charset=utf-8");    String data = "中国";    PrintWriter out = response.getWriter();    out.write(data);    /********************************************************************************/    String data = "中国";    PrintWriter out = response.getWriter();    out.write("<meta http-equiv=‘content-type‘ content=‘text/html;charset=utf-8‘>");    out.write(data);    /********************************************************************************/    2.文件下载与中文文件下载      // String filePath = this.getServletContext().getRealPath("/Download/呵呵.jpg");      String filePath = this.getServletContext().getRealPath("/Download/呵呵.txt");        String fileName = filePath.substring(filePath.lastIndexOf("\\") + 1);        System.out.println(fileName);        // 设置回送数据打开方式        response.setHeader("content-disposition", "attachment;filename="+ URLEncoder.encode(fileName, "utf8"));        InputStream inS = null;        OutputStream outS = null;        try {            inS = new FileInputStream(filePath);            int len = 0;            byte[] buff = new byte[1024];            outS = response.getOutputStream();            while ((len = inS.read(buff)) > 0) {                outS.write(buff, 0, len);            }        } catch (IOException e) {            try {                if (inS != null) {                    inS.close();                }            } catch (IOException e2) {            }            try {                if (outS != null) {                    outS.close();                }            } catch (IOException e3) {            }        }    3.输出随机图片(验证码)    protected void doGet(HttpServletRequest request,            HttpServletResponse response) throws ServletException, IOException {        BufferedImage image = new BufferedImage(//                WIDTH//                , HEIGHT//                ,BufferedImage.TYPE_INT_RGB);        Graphics g = image.getGraphics();        // 1.设置背景色        setBackGround(g);        // 2.设置边框        setBorder(g);        // 3.画干扰线        drawRandomLine(g);        // 4.写随机数        drawRandomNum((Graphics2D) g);        // 5.输出到浏览器        response.setContentType("image/jpeg");        // 发表头控制浏览器不要缓存        response.setDateHeader("expries", -1);        response.setHeader("Cache-Control", "no-cache");        response.setHeader("Pragma", "no-cache");        //        ImageIO.write(image, "jpg", response.getOutputStream());    }    private void setBackGround(Graphics g) {        g.setColor(Color.WHITE);        g.fillRect(0, 0, WIDTH, HEIGHT);    }    private void setBorder(Graphics g) {        g.setColor(Color.BLUE);        g.drawRect(1, 1, WIDTH - 2, HEIGHT - 2);    }    private void drawRandomLine(Graphics g) {        g.setColor(Color.GREEN);        for (int i = 0; i < 5; i++) {            int x1 = new Random().nextInt(WIDTH);            int y1 = new Random().nextInt(HEIGHT);            int x2 = new Random().nextInt(WIDTH);            int y2 = new Random().nextInt(HEIGHT);            g.drawLine(x1, y1, x2, y2);        }    }    private void drawRandomNum(Graphics2D g) {        g.setColor(Color.RED);        g.setFont(new Font("宋体", Font.BOLD, 20));        //常用中文的Unicode编码        String base = 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       for (int i = 0; i < 4; i++) {            int degree = new Random().nextInt() % 30;            String ch = base.charAt(new Random().nextInt(base.length())) + "";            int x1 = 5 + i * 30;// +(new Random().nextInt()%5);            int y1 = 20;            g.rotate(degree * Math.PI / 180, x1, y1);// degree*Math.PI/180            // 设置旋转的弧度            g.drawString(ch, x1, y1);            // 将旋转返回原点            g.rotate(-degree * Math.PI / 180, x1, y1);        }    }    //使用方法    <img style="cursor:hand" alt="刷新" src="http://www.mamicode.com/ServletDemo/responseDemo4" onclick="fincton(this.src = http://www.mamicode.com/this.src +‘?time=‘+ new Date().getTime)"><br />    4.发送HTTP响应头    //解释为图片    response.setContentType("image/jpeg");    // 发表头控制浏览器不要缓存    response.setDateHeader("expries", -1);    response.setHeader("Cache-Control", "no-cache");    response.setHeader("Pragma", "no-cache");    //控制页面刷新    String message = "<meta http-equiv=‘refresh‘ content=‘3;url=/ServletDemo/register.html‘>3秒后跳到首页,如果没有跳转，请3秒后点击<a href=http://www.mamicode.com/‘/ServletDemo/register.html‘>超链接";    this.getServletContext().setAttribute("message",message);    //控制页面刷新,假设程序运行到此，用户登录成功了。    response.setCharacterEncoding("UTF-8");    response.setContentType("text/html;charset=UTF-8");    response.setHeader("refresh","3;url=‘/ServletDemo/register.html‘");    response.getWriter().write("3秒后跳到首页,如果没有跳转，请3秒后点击<a href=http://www.mamicode.com/‘/ServletDemo/register.html‘>超链接");    //控制页面刷新    response.setHeader("refresh","3");            String data = new Random().nextInt(100000)+"";        response.getWriter().write(data);    //设置缓存一小时。设置了缓存后一小时内不会向服务器重新加载而是在本地加载。 这个技术可以用于网站加载js文件、图片、等固定的元素，减轻服务器负载    response.setDateHeader("expires",System.currentTimeMillis()+1000*3600);    5.实现请求重定向    重定向的特点：    1.浏览器会向服务器发送两次请求，这意味着就用两个不同servlet、response、request    2.用重定向技术后，浏览器的地址栏会发生变化        response.setStatus(302);    response.setHeader("location", "/ServletDemo/index.jsp");*/    /********************************************************************************/    response.sendRedirect("/ServletDemo/index.jsp");    6.response细节     1.getOutputStream 和 getWriter 方法两者相互排斥，调用了这个就不能再调用另一个了。//IllegalStateException     2.getOutputStream 和 getWriter 不用手动关闭否则会出错，因为 Servlet会自动调用close关闭。