JSP, Integer.parseInt throw error even when testing for null

Question

here is the code

if(var!=null) {
                        int varInt= Integer.parseInt(var);
                        method.setProp(varInt);
              }

After some reseach it normally throw error when we're not testing for null, but I am, so what's the problem?

The Error

org.apache.jasper.JasperException: An exception occurred processing JSP page /TravelSearch.jsp at line 81               
80:                    if(var!=null) {
81:                         int varInt= Integer.parseInt(var);
82:                         method.setProp(varInt);
83:                     }
84:                     
Stacktrace:
    org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:567)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:469)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:396)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:340)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:725)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
cause mère
java.lang.NumberFormatException: For input string: ""

Whats the exception? A `null` check will not prevent invalid values in `var` that can't be parsed to an integer — Chetan Kinger, May 01 '15 at 17:04
but the i'm puting nothing in the field so i'm supposed to test for null not "" — Lola Loulita, May 01 '15 at 17:13
testing for null is not enough you have to check it if it has a valid int chracter becaue `""` is not int — singhakash, May 01 '15 at 17:13
That's the exact thing you're told in the exception: java.lang.NumberFormatException: For input string: "" What number is empty string? - what you want is a method equivalent to Int.TryParse() in C#. — Jesper Bangsholt, May 01 '15 at 17:14

score 0 · Answer 1 · edited May 23 '17 at 12:21

0

Take a look at this answer by Jon Skeet.

https://stackoverflow.com/a/1486082/891261

This is what you want - a method that checks if the string can be parsed to a number and returns an obvious illegal value when it does not, which you then can check for and act on.

edited May 23 '17 at 12:21

Community

1
1

answered May 01 '15 at 17:18

Jesper Bangsholt

544
4
11

tddmonkey · Accepted Answer · 2015-05-01T17:28:22.593

-1

The number you're trying to parse isn't null, it's an empty string "". The stacktrace was telling you this here:

java.lang.NumberFormatException: For input string: ""

Change your test to do this:

if(var!=null && !"".equals(var)) {

edited May 01 '15 at 17:28

answered May 01 '15 at 17:13

tddmonkey

20,798
10
58
67

Thank you all for your answers, this one work for me – Lola Loulita May 01 '15 at 17:25

JSP, Integer.parseInt throw error even when testing for null

2 Answers2