String null check
I have tried this for 2 hours , but I've given up. I am checking the value of a String this way:
if(value.equals("")||value.length()<0||value==null)
{
value = "Anynomous"
}
But still the string is printing the value null.
Please see this program code here
<HTML>
<BODY&g开发者_如何学运维t;
<%!
String value ;
%>
<%
value = (String)request.getAttribute("retunval");
System.out.println("Inside New fgdf JSP");
if(value.equals("")||value.length()<0||value==null)
value = "Anonymuos";
%>
Hello <%=value%>
<BR>
</BR>
<BR>
</BR>
<a href="Test.jsp">Try Again</a>
</BODY>
</HTML>
Check whether value is null first. Otherwise value.equals() will throw a NullPointerException.
if (value == null || value.equals("")) {
value = "Anonymous";
}
First you need to reorder your if condition, otherwise you could run into NPEs. Additionally, the string length can never be lower than 0, so that check is not needed:
value==null||value.equals("")
Alternatively, if you can use Apache Commons Lang you could use StringUtils.isEmpty(value) which handles all the relevant cases for you.
You need to add
||value.equals("null")
Somewhere something already did a toString() on the null value. Note the other answers as well - but this is the cause of the specific problem you're reporting.
So you'd end up with, as one option:
if ( value==null || value.isEmpty() || "null".equals(value) )
Because of the null-check, inverting the .equals() isn't necessary in this case - but it's a good habit to get into.
i think
value = (String)request.getAttribute("retunval");
is returning you a "null" string. When you try to do if tests that you have mentioned, it will return false because you are not checking
value.equals("null")
so that's why you get output as null.
if(value.equals("")||value.length()<0||value==null)
value = "Anynomous"
The second and third condition can never evaluate to true!
(A String's length can never be less than zero, and if value was null, value.equals("") would have caused a NullPointerException)
try this instead:
if(value==null||"".equals(value))
value.length()<0 will never be true - use value.length()==0 instead. However, in this case, the previous check (value.equals("")) is equivalent to this one, so you can omit it. Apart from this, the condition should detect empty/null strings (except that the null check should be first, to avoid dereferencing a null pointer).
Is it possible that value contains the text "null"?
Is it possible that the value of the string is 'null'? (That is, not null, but a string which reads 'null')
Reorder as Thomas and ig0774 suggested or use the StringUtils.isEmpty() method of Apache Commons Lang.
Use this :
if(value == null || value.trim().length() <=0 || value.trim().equals("null")){
value ="Ananymous";
}
I think this would be the best condition to check for it
if(value==null || value.trim().length()==0 || value.equals("null"))
it also eliminate fact if value=" " contains spaces.
加载中,请稍侯......
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