[Java][Web]Response学习

// 在 http 中，meta 标签可以模拟响应头
response.setHeader("Content-type", "text/html;charset=UTF-8");
String data = "中国";
OutputStream out = response.getOutputStream();
out.write(data.getBytes("UTF-8"));

如果不指定  UTF-8 格式，浏览器默认为 GB2312 格式，此时中文可能出现乱码。

//String pathString = this.getServletContext().getRealPath("/Download/100.gif");
String pathString = this.getServletContext().getRealPath("/Download/中国红.xls");
String filenameString = pathString.substring(pathString.lastIndexOf('\') + 1);

// 如果下载文件是中文名，则文件名需要 url编码
response.setHeader("content-disposition", "attachment;filename="
        + URLEncoder.encode(filenameString, "UTF-8"));
InputStream inputStream = null;
OutputStream outputStream = null;
try {
    inputStream = new FileInputStream(pathString);
    int len = 0;
    byte[] buffer = new byte[1024];
    outputStream = response.getOutputStream();
    while ((len = inputStream.read(buffer)) > 0) {
        outputStream.write(buffer, 0, len);
    }
} finally {
    if (inputStream != null) {
        try {
            inputStream.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    if (outputStream != null) {
        try {
            outputStream.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

这段代码用于下载 WebRoot 目录下的 Download 目录中的中文文件，文件名经过了 url 编码以防乱码。

public static final int WIDTH = 120;
public static final int HEIGHT = 25;

public void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    BufferedImage image = new BufferedImage(WIDTH, HEIGHT,
            BufferedImage.TYPE_INT_BGR);
    Graphics g = image.getGraphics();

    // 1. 设置背景色
    setBackGround(g);

    // 2. 设置边框
    setBorder(g);

    // 3. 设置干扰线
    drawRandomLine(g);

    // 4. 写随机数
    drawRandomNum((Graphics2D)g);

    // 5. 图形输出给浏览器
    response.setContentType("image/jpeg");
    // 发头控制浏览器不要缓存
    response.setDateHeader("expires", -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));
    // 汉字区间 [u4e00-u9fa5]
    // 常用汉字
    String base = "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";
    int x = 5;
    for (int i = 0; i < 4; i++) {
        int degree = new Random().nextInt(36) - 18;
        
        String ch = String.valueOf(    base.charAt(new Random().nextInt(base.length())));
        g.rotate(degree * Math.PI / 180, x, 20);     // 设置旋转角度
        g.drawString(ch, x, 20);
        g.rotate(-degree * Math.PI / 180, x, 20);    // 旋转回来
        x += 30;
    }
}

这段代码用于生成随机验证码（中文常用字），对应页面：

<!DOCTYPE html>
<html>
<head>
<meta charset="gb2312">
<title>注册页面</title>
<script type="text/javascript">
    function changeImage(img) {
        img.src = "/day06/servlet/ResponseDemo4?" + new Date().getMilliseconds();
    }
</script>
</head>
<body>
    <form action="#" method="post">
        <table style="line-height:30px">
            <tr>
                <td>用户名：</td>
                <td><input type="text" name="txtUser" /></td>
            </tr>
            <tr>
                <td>密码：</td>
                <td><input type="password" name="txtPwd" /></td>
            </tr>
            <tr>
                <td>验证码：</td>
                <td><input type="text" name="txtCode" /></td>
                <td><img src="/day06/servlet/ResponseDemo4"
                    style="cursor: pointer" onclick="changeImage(this)" /></td>
            </tr>
            <tr>
                <td colspan="3"><input type="submit" value="提交" /></td>
            </tr>
        </table>
    </form>
</body>
</html>

 这是常用登录页面的简单写法

// 假设登录成功，3秒后自动跳转
response.setCharacterEncoding("UTF-8");
response.setContentType("text/html;charset=UTF-8");

response.setHeader("refresh", "3;url='/day06'");
response.getWriter().write("浏览器会在 3 秒后自动跳转到其它页面。");    

这是登录成功后的自动跳转写法。

String message = "<meta http-equiv='refresh' content='3;url=/day06/'>浏览器会在 3 秒后自动跳转到其它页面。";
this.getServletContext().setAttribute("message", message);
this.getServletContext().getRequestDispatcher("/message.jsp").forward(request, response);

这是另一种写法，message.jsp 页面中写上：

<%
    String message = (String)application.getAttribute("message");
    out.write(message);
 %>

也能实现自动跳转。