java 如何检查文本字段的空值并将其放入 if else 语句以将其重定向到错误页面？
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How to check null values of text fields and put it in if else statements to redirect it to error page?
提问by a k
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?
在以下代码中，If Else 语句中存在问题。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 中文本字段的空值？
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);
}
}
回答by Ravi Wallau
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.
我喜欢在 commons-lang ( http://commons.apache.org/lang) 中使用StringUtils.isBlank(String)方法进行此类检查。它检查字符串是否为空、空或是否仅包含空格。
回答by Viswanadh Kumar Reddy Vuggumud
I think the parameters become nullonly if the formdoes not send them at all.
我认为只有当表单根本不发送参数时，参数才会变为空。
Suppose your form is like this:
假设你的表格是这样的：
input type=text name="pass" (not password)
then the parameter you are using in request.getParameteris not present so it is null.
那么你使用的参数request.getParameter不存在所以它是null。
回答by Tommi
Perhaps the values are (non-null) empty strings? Try:
也许这些值是（非空）空字符串？尝试：
if (Email == null || Password == null || Email.equals("") || Password.equals("")){
回答by Don Roby
Likely the fields are coming in as empty strings rather than nulls, but we can't tell that for sure without seeing more code.
很可能这些字段是作为空字符串而不是空值出现的，但如果没有看到更多代码，我们就无法确定。
Running it in a debugger or adding debug prints would clarify.
在调试器中运行它或添加调试打印会澄清。
