Java 检查整数是否为空
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Check if a Integer is empty
提问by Bogdan
I want to check if a Integervalue is empty.
The value for Integeris completed in a form. Here is my code.
我想检查一个Integer值是否为空。的值以Integer表格形式填写。这是我的代码。
Here the value is introduced:
这里引入了值：
<input name="varsta" placeHolder="Varsta:" type="text" data-constraints='@NotEmpty @Required @AlphaSpecial'> <br/><br/>
Now I want to check if there are data introduced or not.
现在我想检查是否有数据引入。
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
Integer varsta = Integer.parseInt(request.getParameter("varsta"));
request.getSession().setAttribute("varsta", varsta);
try {
DBConnection connection = new DBConnection();
Connection con = connection.Connect();
PreparedStatement ps = con.prepareStatement(
"insert into user(Nume,Prenume,E_mail,Parola,Varsta,Sex,Greutate,Inaltime,Nivel_activitate,Calcul_calorii)" +
"values ('"+nume+"','"+prenume+"','"+email1+"','"+parola+"','"+varsta+"','"+sex+"','"+greutate+"','"+inaltime+"','"+activitate+"','"+calorii+"')"
);
if (varsta == null && "".equals(varsta)) {
String message = "Va rugam completati cu atentie TOATE campurile!";
request.setAttribute("message", message);
request.getRequestDispatcher("/inregistrare.jsp").forward(request, response);
} else {
int i = ps.executeUpdate();
if (i > 0) {
request.getRequestDispatcher("/preferinte.jsp").forward(request, response);
}
}
ps.close();
con.close();
} catch(Exception se) {
se.printStackTrace();
}
}
is not working.
不管用。
Could anyone help me?
有人可以帮助我吗？
采纳答案by Vladimir Vagaytsev
Class Integeris just an wrapper on top of primitive inttype. So it can either be nullor store a valid integer value. There is no obvious "empty" definition for it.
类Integer只是原始int类型之上的包装器。所以它可以是null或存储一个有效的整数值。它没有明显的“空”定义。
If you just compare Integeragainst empty String, you''ll get falseas a result. Always. See Integer.equals(Object o)implementation:
如果您只是Integer与 empty进行比较String，您就会得到false结果。总是。见Integer.equals(Object o)实现：
public boolean equals(Object obj) {
if (obj instanceof Integer) {
return value == ((Integer)obj).intValue();
}
return false;
}
First of all, you can get a NumberFormatExceptionduring parsing integer in the line:
首先，您可以NumberFormatException在行中解析整数期间获得一个：
Integer varsta = Integer.parseInt(request.getParameter("varsta"));
And you are getting it, since For input string: ""looks like a NumberFormatExpectionmessage.
你明白了，因为For input string: ""看起来像一条NumberFormatExpection消息。
In your example you should either check whether the "varsta"attribute value is a number (assume it's a string) and then parse it, or parse it as is and catch NumberFormatExceptionthat Integer.parseInt()throws on incorrect argument.
在您的例子您应该检查是否"varsta"属性值是一个数（假设它是一个字符串），然后分析它，或解析它是和捕获NumberFormatException的是Integer.parseInt()不正确的说法抛出。
First solution:
第一个解决方案：
Integer varsta = null;
String varstaStr = request.getParameter("varsta"); // read string 'varsta' field
if (varstaStr != null && varstaStr.matches("\d+")) { // null-check and regex check to make sure the string contains only digits
varsta = Integer.parseInt(varstaStr);
}
Second solution:
第二种解决方案：
Integer varsta = null;
String varstaStr = request.getParameter("varsta"); // read string 'varsta' field
try {
varsta = Integer.parseInt(varsta);
} catch (NumberFormatException e) {
// handle error
}
After this, you have one more problem in the line:
在此之后，您还有一个问题：
if(varsta == null && "".equals(varsta)){
The varstareference has type Integerhere, so "".equals(varsta)will always return false:
该varsta参考具有类型Integer在这里，所以"".equals(varsta)总是返回false：
(varsta == null && "".equals(varsta)) = [assume varsta is null] =
((null) == null && "".equals(null)) = (true && false) = false
Replace
代替
if(varsta == null && "".equals(varsta)){
with
和
if(varsta == null){
This should help you.
这应该对你有帮助。
P.S.If you use Java of version 7 or higher, consider use try-with-resourcesto manage Connectionand PreparedStatement.
PS如果你使用Java 7或更高版本，可以考虑使用try-with-resources来管理Connection和PreparedStatement。
回答by YCF_L
If you want to check if your field is empty or not than you can use that:
如果您想检查您的字段是否为空，则可以使用：
if (!request.getParameter("varsta").equals("")) {
System.out.println("not empty");
} else {
System.out.println("Empty");
}
But if you want to get the value so you should to be carful:
但是如果你想获得价值，那么你应该小心：
try {
if (!request.getParameter("varsta").equals("")) {
System.out.println("not empty");
Integer varsta = new Integer(request.getParameter("varsta"));
} else {
System.out.println("Exmpty");
}
} catch (NumberFormatException e) {
System.out.println("Number is not correct");
}
what if request.getParameter("varsta") = "4558ez"? this can make a problem.
万一request.getParameter("varsta") = "4558ez"呢？这可能会产生问题。
