Comparing Two Strings give java.lang.NullPointerException

Question

I'm trying to get checkbox value from HTML post. My problem is that the post return on or null instead of true or false so I need to convert it to a true of false to insert in the database.

 Boolean hasProfile7 = Boolean.valueOf(request.getParameter("hasProfile7"))

hasProfile7 is false even when it's "on"

 Boolean hasProfile7 = (request.getParameter("hasProfile7").equals("on")) ? true : false;

This crashes my application giving java.lang.NullPointerException when the checkbox is not ticked (false)

 Boolean hasProfile7 = (request.getParameter("hasProfile7") == "on") ? true : false;

and this gives me always false.

What can I do?? I just want the bool to be True when "on" and false when "null"

You could use "on".equals(request...) to avoid the NPE.

assylias
– assylias

2017-10-03 14:44:40 +00:00
Commented Oct 3, 2017 at 14:44 — assylias
– assylias, Commented Oct 3, 2017 at 14:44

zappee · Accepted Answer · 2017-10-03 15:07:59Z

3

This is the null safe way to compare constant with String:

"some-value".equals(variable) // ok

The following code snippet will throw a null pointer exception if variable is null because you are not allowed to call equals method on null value:

variable.equals("some-value") // not recomended

This method will return true if value contains "on", otherwise false will be returned:

public boolean isChecked(final String value) {
    if (Objects.isNull(value)) {
        return false;
    }

    if ("on".equals(value.toLowerCase())) {
        return true;
    }

    return false;
}

edited Oct 3, 2017 at 15:07

answered Oct 3, 2017 at 14:56

zappee

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Comments

Erwan C. · Accepted Answer · 2017-10-03 15:00:35Z

First point

Boolean hasProfile7 = Boolean.valueOf(request.getParameter("hasProfile7"))

You are doing

Boolean.valueOf(<A String>)

According to https://docs.oracle.com/javase/7/docs/api/java/lang/Boolean.html#valueOf(java.lang.String) public static Boolean valueOf(String s) "Returns a Boolean with a value represented by the specified string. The Boolean returned represents a true value if the string argument is not null and is equal, ignoring case, to the string "true"."

Second point

Boolean hasProfile7 = (request.getParameter("hasProfile7").equals("on")) ? true : false;

Here you are close to the rigth thing to do. Your problem is that request.getParameter("hasProfile7") returns null and so you have *null*.equals("on")and thats why you get the NPE.

When you have a predefined String, always put it on the left size:

Boolean hasProfile7 = ("on".equals(request.getParameter("hasProfile7"))) ? true : false;

Here, even if request.getParameter("hasProfile7") is null you have any exception and it will simply return false

Third point

 Boolean hasProfile7 = (request.getParameter("hasProfile7") == "on") ? true : false;

Here you are comparing the object "on" to the object request.getParameter("hasProfile7"). If the values are the sames, the objects are not.

For the last point, why do you use a ternary expression (request.getParameter("hasProfile7").equals("on")) ? true : false; can be translated to

if true --> true 
if false --> false

You can just write

Boolean hasProfile7 = "on".equals(request.getParameter("hasProfile7"))

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