在try/catch中没有捕获NumberFormatException

Question

我正在创建一个.jsp页面的问题.对于那些担心的人来说,该网站是为了完成家庭作业,但是,我试图超越所需要的,并且不会要求任何与评分相关的内容.这完全是为了我自己的利益.

开始营业:我从用户那里得到一个输入,执行方法="发布"并刷新页面,并且在理想的情况下它起作用(这是作业.)但是,我正在尝试尝试/捕获在用户将字符串输入int字段的情况下阻止.

int Svolt = 0;
double Amperes = 0.0;
double LEDdrop = 0.0;

if (request.getParameter("Svolt") != null) {
try {
    Svolt = Integer.parseInt(request.getParameter("Svolt")); 
} catch ( NumberFormatException e ) {
    %>
    <script type ="text/javascript">
        alert("The source voltage must be an integer. Please fix this.");
    </script>
    <%                                                    
}

我已经尝试将"NumberFormatException"切换为"Exception",但它返回了相同的错误代码.早些时候,我在if()语句之前尝试了catch,它运行了,但是没有显示我想要的警告框.

该代码如下:

final double MA_TO_A = 0.001;
int Svolt = 0;
double Amperes = 0.0;
double LEDdrop = 0.0;

try {
    if (request.getParameter("Svolt") != null) {
        try {
            Svolt = Integer.parseInt(request.getParameter("Svolt"));
        } catch (Exception e) 
        {
            %>
            <script type ="text/javascript">
                alert("The source voltage must be an integer. Please fix this.");
            </script>
            <%
        }
        Amperes = Double.parseDouble(request.getParameter("Amperes"));
        LEDdrop = Double.parseDouble(request.getParameter("LEDdrop"));

        out.println("Ideal resistance is: " + ((Svolt - LEDdrop) / (Amperes * MA_TO_A)) + " Ohms.");   
    }
} catch (Exception e) {
        out.println("Please make sure your inputs are correct.");
}

任何帮助表示赞赏,您的时间也是如此.非常感谢你!

编辑:对不起,意思是复制粘贴错误代码:

org.apache.jasper.JasperException: java.lang.NumberFormatException: For input string: "a"

测试输入为字符串"a"的位置

EDIT2:备份/编辑/测试@ Nambari的建议

final double MA_TO_A = 0.001;
int Svolt = 0;
double Amperes = 20.0;
double LEDdrop = 1.8;

try {
    if (request.getParameter("Svolt") != null) {
        try {
            Svolt = Integer.parseInt(request.getParameter("Svolt"));
        } catch (Exception e) 
        {
            %>
            <script type ="text/javascript">
                alert("The source voltage must be an integer. Please fix this.");
            </script>
        <%
        }
        out.println("Ideal resistance is: " + ((Svolt - LEDdrop) / (Amperes * MA_TO_A)) + " Ohms.");   
    }
} catch (Exception e) {
    out.println("Please make sure your inputs are correct.");
}

输出:理想电阻为:-90.0欧姆

警报框说("源电压必须是整数.请修复此问题.")

没有错误代码.

没有out.println说("请确保您的输入正确").

最终编辑:

代码现在几乎按照需要工作,但足够好.

                    final double MA_TO_A = 0.001;
                    int Svolt;
                    double Amperes;
                    double LEDdrop;

                    if (request.getParameter("Svolt") != null) 
                    {
                        try 
                        {

                            try 
                            {
                                Svolt = Integer.parseInt(request.getParameter("Svolt"));
                            } catch (Exception e) 
                            {
                            %>
                            <script type ="text/javascript">
                                alert("The source voltage must be an integer. Please fix this.");
                            </script>
                            <%  
                            Svolt = 0;
                            }
                            try 
                            {
                                Amperes = Double.parseDouble(request.getParameter("Amperes"));
                            } catch (Exception e) 
                            {
                                %>
                                <script  type = "text/javascript"> 
                                    alert("The source voltage must be an integer. Please fix this.");
                                </script> 
                                <% 
                                Amperes = 0.0;
                            }
                            try 
                            {
                                LEDdrop = Double.parseDouble(request.getParameter("LEDdrop"));
                            } catch (Exception e) 
                            {
                            %>
                                <script  type = "text/javascript"> 
                                    alert("The source voltage must be an integer. Please fix this.");
                                </script> 
                            <%
                            LEDdrop = 0.0;
                            }
                            out.println("Ideal resistance is: " + ((Svolt - LEDdrop) / (Amperes * MA_TO_A)) + " Ohms.");
                        } catch (Exception e)
                        { 
                            out.println("Please make sure your inputs are correct."); 
                        }   
                    }

我知道很多术语,但那是最终的结果.不知何故,这一切都有效.感谢所有帮助过的人!

Answer 1

这是根据我的评论发布的答案：

我建议删除表单上除 Svolt 相关代码之外的所有内容并尝试。我认为还有比这更糟糕的事情。备份现有代码。删除除 Svolt 之外的所有内容，看看我们可以解决问题。

确保 try/catch 块与上面注释中建议的代码流正确同步。