为什么我做的登录页面的验证码，第一次总是加载不出来，要点击刷新才行？

Question

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<%@ page contentType="text/html;charset=UTF-8" language="java" %>

Title


<br> &lt;%-- 当窗口加载完毕 --%&gt;<br> window.onload = function (ev) {<br> document.getElementById(&quot;img&quot;).onclick = function (ev1) {<br> this.src = &quot;./checkCodeServlet?time=&quot;+new Date().getTime();<br> }<br> }<br>

<form action="./loginServlet">
    <table>
        <tr>
            <td>账号</td>
            <td><input type="text" name="username"></td>
        </tr>
        <tr>
            <td>密码</td>
            <td><input type="password" name="password"></td>
        </tr>
        <tr>
            <td>验证码</td>
            <td><input type="text" name="checkCode"></td>
        </tr>
        <tr>
            <td colspan="2"><img id="img" src="com.test.pro.CheckCodeServlet"></td>
        </tr>
        <tr>
            <td>提交</td>
            <td colspan="2"><input type="submit" value="登录"></td>
        </tr>
        <tr>
            <td></td>
            <td></td>
        </tr>
    </table>
</form>

<div><%=request.getAttribute("cc_error") == null ? "" : request.getAttribute("cc_error") %></div>
<div><%=request.getAttribute("login_error") == null ? "" : request.getAttribute("login_error")%></div>

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@WebServlet("/checkCodeServlet")
public class CheckCodeServlet extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    int width = 100;
    int height = 50;

    //1.创建一对象，在内存中图片(验证码图片对象)
    BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);


    //2.美化图片
    //2.1 填充背景色
    Graphics g = image.getGraphics();//画笔对象
    g.setColor(Color.PINK);//设置画笔颜色
    g.fillRect(0,0,width,height);

    //2.2画边框
    g.setColor(Color.BLUE);
    g.drawRect(0,0,width - 1,height - 1);

    String str = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghigklmnopqrstuvwxyz0123456789";
    //生成随机角标
    Random ran = new Random();
    StringBuilder sb = new StringBuilder();
    for (int i = 1; i <= 4; i++) {
        int index = ran.nextInt(str.length());
        //获取字符
        char ch = str.charAt(index);//随机字符
        // 把生成的验证码存进sb
        sb.append(ch);

        //2.3写验证码
        g.drawString(ch+"",width/5*i,height/2);
    }
    // 转换sb的格式？
    String checkCode_session = sb.toString();
    //将验证码存入session
    request.getSession().setAttribute("checkCode_session",checkCode_session);

    //2.4画干扰线
    g.setColor(Color.GREEN);

    //随机生成坐标点

    for (int i = 0; i < 10; i++) {
        int x1 = ran.nextInt(width);
        int x2 = ran.nextInt(width);

        int y1 = ran.nextInt(height);
        int y2 = ran.nextInt(height);
        g.drawLine(x1,y1,x2,y2);
    }


    //3.将图片输出到页面展示
    ImageIO.write(image,"jpg",response.getOutputStream());


}

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

}

Answer 1

不是，是 src 路径错误了，把页面的 src 写成 onload 里面那个点击事件时重新设置的 src 的值一样。
默认的你写的是一个类名，是不对的，应该写这个类名对应的 Servlet 请求路径才对。

./checkCodeServlet?time=new Date()