JSP doubt

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posted 15 years ago

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you are creating a new JSP page and you need to execute some code that acts when the page is first executed, but only once. which three are possible mechanisms for performing the initialization code? (choose 3)
A. in the init method
B. in the jspInit mehtod
C. in the constructor of the JSP's java code
D. in a JSP declaration, which includes an initializer block
E. in a JSP declaration, which includes a static initializer block

SCBCD5, SCWCD5, SCJP5
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Deepak Jain

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posted 15 years ago

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a) in the init method : JSP do not have a method named init(). Its only for servlet that are written by implementing Servlet interface.
b) In the jspInit mehtod : This is a correct answer. Write down a JSP for yourself. As you know JSP are converted into servlets, the servlet container will have a jspInit() method that behaves excatly same as init() of servlet. jspInit() is invoked only once during the lifetime of a servlet [jsp converted servlet]
c) In the constructor of the JSP's java code : Since most of the containers create only one instance of the servlet , this code will also run only once. Containers use the same instance to serve multiple requests.
d) in a JSP declaration, which includes an initializer block: Same explanation as above
e) In a JSP declaration, which includes a static initializer block Same explanation as above

Try it yourself

Result can be seen in logs\stdout.log

So actually there are 4 options that are correct.

SCJP, SCWCD, SCBCD

Ralf Wahner

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Posts: 21

posted 15 years ago

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Dear Colleagues

Answer A: method init(). It it not true, that a servlet generated from a JSP page has no init() method, because the servlets type (HttpJspBase with Tomcat) derives from GenericServlet, where init() is implemented (defined in interface Servlet). Therefore, it is possible to override init() by means of a JSP declaration. Bridgewater actually goes further (abbreviated from pp. 57f): "Initialization code for a servlet could go in the constructor [...] but it's more usual to override the public void init() method and place initialization code there. The servlet container is guaranteed to call this method once - and only once - on instantiation of the servlet."

So, why is init() deemed not to be a correct answer? Potentially, overriding init() in a JSP-generated servlet is not regarded best practice? Bridgewater says in Chapter 6 JavaServer Pages (p.384): "You can also use declarations to override some methods that appear further up in the JSP servlet hierarchy - namely jspInit() and jspDestroy()." (Method init() not mentioned.)

Answers C and D: constructor vs. dynamic initialization block. Constructor and non-static initialization blocks both execute when a new object is created. What can a constructor possibly do, what an init block can not (or vice versa)? Why is the one correct and the other is wrong?

Please let me off the hook, if these are recurring items. I couldn't proof so. I'm looking forward to read your comments.

Best regards,

Ralf Wahner

SCJP (SE6), SCWCD (EE5)

Parth Twari

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Posts: 163

posted 14 years ago

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this question brings out , how irresponsibly the free mock exams are rewritten .

This shows that they just search forum for questions and copy them they never test it.

see this question

you are creating a new JSP page and you need to execute some code that acts when the page is first executed, but only once. which three are possible mechanisms for performing the initialization code? (choose 3)
A. in the init method
B. in the jspInit mehtod
C. in the constructor of the JSP's java code
D. in a JSP declaration, which includes an initializer block
E. in a JSP declaration, which includes a static initializer block

they ask for 3 options but actually all are correct

i tested it myself with this code , tell me if I am wrong

which prooves that all the options are correct!

But can someone tell me why does initializer run before constructor?

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