HFSJ book - Chapter 8 Q 17

[Kathiresan Chinna]

Which about EL access operators are true?

A. Anywhere the . (dot) operator is used, the [] could be used
instead.

B. Anywhere the [] operator is used, the. (dot)could be used
instead.

C. If the . (dot) operator is used to access a bean property but the
property doesn’t exist, then a runtime exception is thrown.

D. There are some situations where the. (dot)operator must be
used and other situations where the [] operator must be used.

The book answer is A

Is C is not true ?

Thanks
Kathir

[Ashu Jain]

In EL, Null is user friendly. That would mean if bean property does not exist then empty string is printled. Exception is not thrown.

[Kathiresan Chinna]

Hi,

I was understanding the statement C as:

${emp.midName}
here, 'emp' is exist but it does not contain 'midName' property.

So, Is the statement meant by, the actual bean 'emp' does not exist ?

Thanks
Kathir

[Ashu Jain]

I was understanding the statement C as:

${emp.midName} 'midName' property
here, 'emp' is exist but it does not contain .

Statement C meant that 'midName' property does not exist.

Goldern Rule of EL is that - It handles unknown or null values so that the page still displayseven if it can't find a property/attribute/key with the name in the expression.

There will not be any exception even if emp is null or does not exist. you will just see blank output

I hope that helps

[Prashanti Rao]

Hi Ashu,

If you refer Kathy's book second edition page no.370 you will find there is a statement in bold which says "If the object is a bean but the named property doesn't exist, then an excpetion is thrown". Then I guess 'C' should be one of the answers.Please let me know if I am wrong.

[JohnWilliam Fitz]

Kathir is correct.

In the errata for the book it says that the answer for Question 17 on Page 437 should include "C" as one of the answers.

I'm sorry I don't have the link to the errata handy, just a printed copy. But it's a very useful thing to have.

[Ashu Jain]

Guys...i am confused now.

I am refering HFSJ 1st Edition that says C is correct answer(Pg 432) but Erata of the book
"http://oreilly.com/catalog/headservletsjsp/errata/headservletsjsp.confirmed"

says this: -

[432] Question 17, Option C;
option C is invalid and should not be checked.

Can someone please clarify rules related to null key/property in an EL expression.

My understanding is as i said earlier as well -

EL handles unknown or null values gracefully - no exception

Eg- ${foo} - If foo attribute does not exist in any scopes then print nothing
${foo.bar} - If foo Bean/Map exist but if bar does not exist as property than also print nothing

[Kathiresan Chinna]

Hi,

I have a bean in requestScope called "emp"
But, it does not have "midName" property.

In JSP, ${emp.midName} - throws exception

Thank you
Kathir

[Vishal Chugh]

Renu,

Try using : ${emp["midName"]} and please tell me the result.

[Milton Ochoa]

Plese let me know

if empl.property and if property is not define on empl, a exception is thrown???

[Kathiresan Chinna]

Hi Guys,

This is what happened

1. The bean 'emp' is not exist in any scope:
${emp.firstName} - prints nothing
${emp.firstName1} - prints nothing
${emp["firstName"]} - prints nothing


2. The bean 'emp' is exist in requestScope,
but it does not have "firstName1" property

${emp.firstName1} - throws javax.el.PropertyNotFoundException
${emp["firstName1"]} - throws javax.el.PropertyNotFoundException


Kathir

[Vishal Chugh]

Thanks Renu.

[Anket Dhulekar]

Thanks Kathir, I had this doubt too...