JSP请求get参数抛出异常

Question

我正在开始JSP.我有以下HTML表单.

<form method='POST' enctype='multipart/form-data'>
    <input type="text" name="sittingPlaces">
    <textarea name="invitees"></textarea>
    <input type="submit" value="Submit">
</form>

以及以下java代码.

if (request != null && request.getContentType() != null) {
    int sittingPlaces = Integer.parseInt(request.getParameter("sittingPlaces"));
    String invites = request.getParameter("invitees");
}

我收到错误

int sittingPlaces = Integer.parseInt(request.getParameter("sittingPlaces"));

知道为什么吗？谢谢负载.

Answer 1

request.getParameter("sittingPlaces")使用以下方法检查字符串是否为有效数字:

public boolean isInteger(String str) {
    try {
        Integer.parseInt(str);
    } catch (NumberFormatException e) {
        return false; // The string isn't a valid number
    }
    return true; // The string is a valid number
}

或者您可以在代码中实现它:

if (request != null && request.getContentType() != null) {
    String sittingPlacesStr = request.getParameter("sittingPlaces");
    try {
        int sittingPlaces = Integer.parseInt(sittingPlacesStr);
        String invites = request.getParameter("invitees");
    } catch (NumberFormatException | NullPointerException e) {
        // handle the error here
    }
}

您遇到的问题NumberFormatException是抛出,因为Java无法转换为您String,Integer因为它不代表有效的Integer.您应该使用try-catch语句(就像上面的示例方法一样)来过滤该异常,因为您无法控制来自客户端的请求.

Additionaly:

您还应检查request.getParameter("sittingPlaces")表达式是否返回有效字符串,而不是null:String.Staces = request.getParameter("sittingPlaces");

if (sittingPlaces != null {
    // Continue your code here
} else {
    // The client request did not provide the parameter "sittingPlaces"
}