如何检查文本字段的空值并将其放入 if else 语句中以将其重定向到错误页面？
在下面的代码中，If Else 语句有问题。即使我没有在文本字段中输入任何内容，也只有请求调度程序的其他部分正在执行。另外，如何检查Java内部文本字段的空值？
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String Email = request.getParameter("email");
String Password = request.getParameter("password");
if (Email == null || Password == null){
RequestDispatcher rd = request.getRequestDispatcher("JSP Address");
rd.forward(request, response);
} else {
RequestDispatcher rd = request.getRequestDispatcher("JSP Address");
rd.forward(request, response);
}
}
In following code there is a problem in If Else statement. Only Else part of Request dispatcher is executing even if I don't enter anything in Text Fields. Also, how to check null values of text fields inside Java?
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String Email = request.getParameter("email");
String Password = request.getParameter("password");
if (Email == null || Password == null){
RequestDispatcher rd = request.getRequestDispatcher("JSP Address");
rd.forward(request, response);
} else {
RequestDispatcher rd = request.getRequestDispatcher("JSP Address");
rd.forward(request, response);
}
}
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我喜欢使用方法 StringUtils.isBlank(String) (http://commons.apache.org/lang) 用于此类检查。它检查字符串是否为 null、空或者是否仅包含空格。
I like to use the method StringUtils.isBlank(String) in the commons-lang (http://commons.apache.org/lang) for this type of checking. It checks if the string is null, empty, or if it contains only whitespaces.
我认为只有当表单根本不发送参数时，参数才会变成null。
假设您的表单如下所示：
那么您在
request.getParameter中使用的参数不存在，因此它为 null。I think the parameters become null only if the form does not send them at all.
Suppose your form is like this:
then the parameter you are using in
request.getParameteris not present so it is null.也许这些值是（非空）空字符串？尝试：
Perhaps the values are (non-null) empty strings? Try:
这些字段可能以空字符串而不是空值的形式出现，但在没有看到更多代码的情况下我们无法确定这一点。
在调试器中运行它或添加调试打印将会澄清。
Likely the fields are coming in as empty strings rather than nulls, but we can't tell that for sure without seeing more code.
Running it in a debugger or adding debug prints would clarify.