JSP Getting Started

First read this one.
Then get this one which is free from sun for the more serious stuff.

First read this one.
Then get this one which is free from sun for the more serious stuff.

Thanks for the URL r035198x....
Im on my way.....

Thanks for the URL r035198x....
Im on my way.....

I have created a jar named Checker.jar
saved on WEB-INF\lib\

my problem is i cannot access the Checker.jar
with content dma.Checker.class

i've attempt:

<jsp:useBean id="Checker" scope="page" class="Checker" />

attempting to replace class into jar ==> invalid attribute

But i really have no idea how to fix this.....

Can you show me an example about this?
The url above does only explains how to deal with classes...( not jar )

Is this possible?

I would like to add a text file together with the classes folder inside WEB-INF
And that text-file is the source to be extracted for calculations and i will try to open that textfile from my java-bean.... possible? or not?

for example,
I have a text file that contains the list of all countries....
That is really disapointing on my part that all the countries will be coded on
bean. so i decided not to do it inside the code, instead on the database....
But for that it is just a constant data, having it on the database will add
another table and it will consume another bean that has 100 lines of code
(Approximately). Before attempting it into database, i need your advice, and
the answer on the above questions experts....

Looking forward on your replies,
sukatoa....

Im currently doing some experiments in JSP........

and I fail to debug my code.....

Here is the stacktrace:
I am curious about that inputString.........

Here is the JSP code.

Im loosing hope with this problem.....

Im using DreamWeaverMX, manual set-up of Apache Tomcat........

Can you experts tell me where is it on the code?
Or can you suggest any alternatives for this?

waiting,
sukatoa

Im always late to realize.........

ArrayList indexOf(Object o) uses the equals method that can't be used to compare null values........

Gotcha!!!!!!!

I wonder what implementation did lastIndexOf method used in ArrayList?
Is that only uses the reverse value arrangement then apply the indexOf method?

I wonder what implementation did lastIndexOf method used in ArrayList?
Is that only uses the reverse value arrangement then apply the indexOf method?

If you wonder how those standard classes implemented things go to your jdk
directory and find the file src.zip. It's a zip file that contains all the source code
files for all the publicly available classes in your Java installation.

kind regards,

Jos

Just a quick,

I've planned to implement all the necessary validations using JSP,

Now, may i know what are the disadvantages of doing such thing?
except for the passing parameters?( takes a little bit of time ) through form.....

Unlike JS, that it runs on the browser as it validates the form just in time.......

Just a quick,

I've planned to implement all the necessary validations using JSP,

Now, may i know what are the disadvantages of doing such thing?
except for the passing parameters?( takes a little bit of time ) through form.....

Unlike JS, that it runs on the browser as it validates the form just in time.......

I think by validations you mean form validations? I normally do it in the client side as well as in the server side(just to be doubly sure, and thats the way it should be :)). I dont see it as a disadvantage because those are the things a web developer should do, lets say what happens when a ignorant(or any user) turns the javaScript off in the browser? I as a web developer ensure that the user doesnt skip the mandatory things that he needs to fill. I dont think that it comes down to performance, its a securuty thing for me.

regards,

ajos

I think by validations you mean form validations? I normally do it in the client side as well as in the server side(just to be doubly sure, and thats the way it should be :)). I dont see it as a disadvantage because those are the things a web developer should do, lets say what happens when a ignorant(or any user) turns the javaScript off in the browser? I as a web developer ensure that the user doesnt skip the mandatory things that he needs to fill. I dont think that it comes down to performance, its a securuty thing for me.

regards,

ajos

Yes, always do validations both client side and server side. It's one of the golden rules of web programming.

Yes, always do validations both client side and server side. It's one of the golden rules of web programming.

Just a question: while I do understand that just client side validation would be
silly (no Javascript, request synthesis etc.) but what's wrong with just having
server side validation? (except for the server load).

kind regards,

Jos

ps. sorry for the hijack.

If there's client side validations as well then the user doesn't have to wait for the page to be posted to the server just to be told that they left a field blank.

If there's client side validations as well then the user doesn't have to wait for the page to be posted to the server just to be told that they left a field blank.

Ah, ok; so the reason for double sided validation is just speed. But then you have
to keep both validations in sync with each other. (just wondering)

kind regards,

Jos

Ah, ok; so the reason for double sided validation is just speed. But then you have
to keep both validations in sync with each other. (just wondering)

kind regards,

Jos

Can become a nightmare right? Generally the server side validator must not assume any client side validators. So his job is easier. He doesn't need to sync with anyone. The client side validator only needs to do the best he can to make sure that the server code is not called unnccessarily.

Would you experts recommend me an article that discuss about creating effective javabeans or bugs of tomcat 5.5.x,

Im not sure about google's suggested.......

I've encountered errors on getting the exact value from my bean........
If im gonna restart the tomcat, the errors gone, but when im going to add additional jsp code that filters the input, then the errors came back again.......

Would you experts recommend me an article that discuss about creating effective javabeans or bugs of tomcat 5.5.x,

Im not sure about google's suggested.......

I've encountered errors on getting the exact value from my bean........
If im gonna restart the tomcat, the errors gone, but when im going to add additional jsp code that filters the input, then the errors came back again.......

That problem specifically, i've used an arraylist......

Base on my observation, when i used the class arraylist on my bean, a random interval will fail the updated value to be retrieved......

Is this problem already exists?

That problem specifically, i've used an arraylist......

Base on my observation, when i used the class arraylist on my bean, a random interval will fail the updated value to be retrieved......

Is this problem already exists?

I got it,

For me, there is a conflict when creating a bean that extends/contains an Object type ArrayList that will be used for storing some data that represents a String value.....

I don't know what's the real reason, but when i try to convert an Object type list into String type list

The conflict occurs, in any time interval, the conversion fails........
Just for sure, i restarted the tomcat for the class files to be refreshed......

Hence, changing the type of the List into String resolves the issue........

This is my first time to have IF/ELSE statements more than i've expected on a single file..........

Is it natural to have more if/else statement on just a single JSP file?
or can you recommend to me experts how to reduce such structure? ( URL )

Looking forward on your replies,
sukatoa

...

The conflict occurs, in any time interval, the conversion fails........
...

What was the exact error message?

This is my first time to have IF/ELSE statements more than i've expected on a single file..........

Is it natural to have more if/else statement on just a single JSP file?
or can you recommend to me experts how to reduce such structure? ( URL )

Looking forward on your replies,
sukatoa

You can reduce such a structure by making a decision table. And put the long expression in a function!
Example (Wrong way):
[HTML]<HTML>
<FONT color=<% if(a==7) out. write("red") else {if (b==1) out.write("yellow") else if (b==2) out.write("red") else out.write("green")}%> Hello World </FONT>
</HTML>[/HTML]
Example(Right way):
[HTML]<%!
private String getColor(int a, int b)
{
if (a==7 || b==2) return "red";
if (b==1) return "yellow";
return "green";
}
%>
<HTML>
<FONT color=<%= getColor(a,b) %> Hello World </FONT>
</HTML>[/HTML]


Just a sidenote:
Every if-else can be reduced to a formula. Fore example:
can be written as
or as a formula:
The last expression evaluates to
case x==7 --> 0*2+3 --> 3
case x !=7 --> 1*2+3 --> 5

What was the exact error message?

@ reply#16(mine), that error occured due to typo.......

@reply#17
Error fixed, yet the problem persist, only the Object type ArrayList when converted to String on JSP page, well i don't know the reason but not all values are set on the said bean........

Before i've come-up the alternative way, my bean has an Object-type ArrayList that stores all the String representation value from my sign-up form.....

In any time, all the values that i was trying to store on that bean from the validation.jsp fails, no error message issued...

My first approach was it is a known/unknown bug, then i tried to rewrite the type of that ArrayList into String instead of Object since all the values are Strings........

Here is my previous algo:
scope=session.

catch all values from the form through request.getParameter() method
store them in a temporary String type ArrayList.

If there is an invalid input, blank or unmatched values, then erase the password, retypepassword,emailaddress,retypeemail and confirmation code values from that temporary String List and replace them with a value "invalid".
else, persist.

Convert the temp list into Object type List then upload to the bean.....

Redirect into the signup page to fill-up correctly all the necessary fields.

Initialize a temp String type arraylist and store all the values from the bean(Object type, assumed it was converted again down to String)

Now, here is the problem.

alternately, all values that was stored by the validation.jsp into bean is not exactly received by the signup form(JSP page)...... I've list down the behavior of the beans,

first attempt:
Lacking: username, creditcard number
second attempt:
Not exact: password & retypepassword
third attempt:
validation code
fourth attempt:
etc & etc.......

And before i click the submit button, i've wrote all the values exactly what my naked eyes could see.....

And, it appears that there is a problem on my inputs..(i've created an indicator that tells the guests about their wrong input/leaved blank)......

I get stuck on this experiment(last day). I've exert all of my efforts on debugging, and it is proven that there should be no error, typo, mistakes on my code.....

my last option was to use my common sense.
Since all the values are being treated as String and absolutely a pure string data type, then i've changed the Object type ArrayList into String type ArrayList.

Then it solves my problem......

You may not believe on this kind of scenario, but it really happens on my part.......

You can reduce such a structure by making a decision table. And put the long expression in a function!
Example (Wrong way):
[HTML]<HTML>
<FONT color=<% if(a==7) out. write("red") else {if (b==1) out.write("yellow") else if (b==2) out.write("red") else out.write("green")}%> Hello World </FONT>
</HTML>[/HTML]
Example(Right way):
[HTML]<%!
private String getColor(int a, int b)
{
if (a==7 || b==2) return "red";
if (b==1) return "yellow";
return "green";
}
%>
<HTML>
<FONT color=<%= getColor(a,b) %> Hello World </FONT>
</HTML>[/HTML]


Just a sidenote:
Every if-else can be reduced to a formula. Fore example:

Expand|Select|Wrap|Line Numbers

1. z=0;
2. if (x=7) z=3; else z=5;

can be written as

Expand|Select|Wrap|Line Numbers

1. z = (x=7) ? 3 : 5

or as a formula:

Expand|Select|Wrap|Line Numbers

1. z =  Math.abs(Math.signum(x-7)) * 2 + 3;

The last expression evaluates to
case x==7 --> 0*2+3 --> 3
case x !=7 --> 1*2+3 --> 5

What always come to my mind is that "z = (x=7)? 3: 5"
But the methods are all created for validation only........

All conversion, db access, constants, encoders/decoders are in a bean.....
and all elseif statements are forcely implemented for validations......
(my last option)

Like:

Unless, if it is an assignment operation with two options to choose with respect to its (logically tested)value, then this "z = (x=7)? 3: 5" pattern should be used.........

Thanks for the examples,
i will try it.....

JSP beginner,
sukatoa

What always come to my mind is that "z = (x=7)? 3: 5"
But the methods are all created for validation only........

All conversion, db access, constants, encoders/decoders are in a bean.....
and all elseif statements are forcely implemented for validations......
(my last option)

Like:

Expand|Select|Wrap|Line Numbers

1. if this is, 
2.     then do this, 
3. else, 
4.     do also this,

Unless, if it is an assignment operation with two options to choose with respect to its (logically tested)value, then this "z = (x=7)? 3: 5" pattern should be used.........

Thanks for the examples,
i will try it.....

JSP beginner,
sukatoa

There is a mistying on my side, the corrected version is:
Please note the double-equal sign after "x", or else it will not work as intended.

My example with decision table and function should show you that instead of using:
it is better to use
This reduces complexity of your if-else nesting.
Please note that a "decision table" puts cases which are the same together, which also reduces your if-else-nesting.
Like in the example:
is reduced to
.
This is just a simple part of this matter. There is a whole course at university only how to make decision tables and it can be a complex matter, but it is worth it. It makes your programs smaller (=faster) and easier to understand.

Im just wondering.....

I have observed the behavior of my JavaServer Pages such that it will encounter an IllegalStateException when this application not modified(not roaming around the site) for 20 to 30 mins(minimum).... (After logging-in)

Why?

Can this be avoided?
All of my beans are session scoped.....

Please let me know experts,
sukatoa

Im just wondering.....

I have observed the behavior of my JavaServer Pages such that it will encounter an IllegalStateException when this application not modified(not roaming around the site) for 20 to 30 mins(minimum).... (After logging-in)

Why?

Can this be avoided?
All of my beans are session scoped.....

Please let me know experts,
sukatoa

On a Tomcat Servlet container a Session times out after 30 minutes (by default)
if I remember correctly. If you don't want that you should anticipate for it like
extending the timeout time for the Session object.

kind regards,

Jos

thanks for your reply Jos,

But, how can i modify its default value?

Can you recommend me where to read that one?

regards,
sukatoa

thanks for your reply Jos,

But, how can i modify its default value?

Can you recommend me where to read that one?

regards,
sukatoa

If your page does not use session, you can use a jsp-directive. Just write at the top of your jsp-page:
If you want to use a session and want to modify its timeout (e.g. 4 hours=240 minutes), there are several ways.
1.)
write in your jsp-page:
2.) write in your web.xml
The file is there two times: in tomcat's "conf" folder (default value for all applications) or in your application's "WEB-INF" folder. (default value for all jsp-pages of your application)

thanks for your reply Jos,

But, how can i modify its default value?

Can you recommend me where to read that one?

regards,
sukatoa

The place to read would be the Servlet Specification

You can change it for the whole application or for a particular session only.
When changing for the whole application then you set the value in your application's web.xml with something like

that is 100 minutes

For a particular session then that would be
int seconds = ....//your required timeout
Edit: Since when did chaar get a faster keyboard than mine?

If your page does not use session, you can use a jsp-directive. Just write at the top of your jsp-page:

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1. <%@ page session="true" %>

If you want to use a session and want to modify its timeout (e.g. 4 hours=240 minutes), there are several ways.
1.)
write in your jsp-page:

Expand|Select|Wrap|Line Numbers

1. <% session.setMaxInactiveInterval(240*60); %>

2.) write in your web.xml

Expand|Select|Wrap|Line Numbers

1. <session-config>
2.        <session-timeout>240</session-timeout>
3. </session-config>

The file is there two times: in tomcat's "conf" folder (default value for all applications) or in your application's "WEB-INF" folder. (default value for all jsp-pages of your application)

Thanks, that was interesting to read,
But, i have modified the web.xml in WEB-INF folder, and i couldn't see

I expect that it was there, yet, it should be added.....

So, Here is the content of the web.xml

Can you point me where to put your suggested xml code in the xml above?
This was my first time to modify such config file.....

P.S i just don't want to commit mistake specially on this type of file... because i believe that if there is something wrong with this, i can't trace whatever error/bug may exists later......

sukatoa

Can you point me where to put your suggested xml code in the xml above?
This was my first time to modify such config file.....

sukatoa

Inside your web-app element. (line 22)

Thank you Jos, r035198x and chaarmann.....

Now, new problem i have noticed on my page,

I can't compare the values between the content of my bean and the parameter value received in my controller,

How come? I remembered the Collator class or converting the two values into hashcode then compare, but before i'll start banging here, please let me know why is it happening?

curious,
sukatoa

I've always encounter IllegalStateException when the server executes the code below,

stacktrace from apache tomcat logs
Could you experts realize me how to avoid such exception?
and any comment about the code above is greatly accepted....
worst/better or suggestions about redesigning the code, it will be greatly appreciated.....

This was my first time to dive into a real application using JSP

get stucked,
sukatoa

Gotcha!!!

if forgot to think about MVC architecture......

Controller 1
Controller 2
always late to realize.....

I doubt about the following scenario,

Im going to add the naming-factory-dbcp.jar on my WEB-INF/lib to be able to run my beans that implements tablehandler classes.... (accessing database)
and im going to test it on some jsp hosting site....

What if the naming-factory-dbcp.jar already been exists in there server?
(found in common/lib/ directory)

So, that means, 2 the same jar appears,
What will happened when im going to use transaction with my tablehandler?
Is there any predictable conflicts? or something?

But before im going to test it, i wan't to know from you experts....

I doubt about the following scenario,

Im going to add the naming-factory-dbcp.jar on my WEB-INF/lib to be able to run my beans that implements tablehandler classes.... (accessing database)
and im going to test it on some jsp hosting site....

What if the naming-factory-dbcp.jar already been exists in there server?
(found in common/lib/ directory)

So, that means, 2 the same jar appears,
What will happened when im going to use transaction with my tablehandler?
Is there any predictable conflicts? or something?

But before im going to test it, i wan't to know from you experts....

The first jar-file included is the one from your common/lib directory.
If you try to add any class (contained in second jar) later on that was included already in your first jar, then this second jar will not be included and you get an error message:

15.09.2008 08:54:31 org.apache.catalina.loader.WebappClassLoader validateJarFile
INFO: validateJarFile(D:\myDir\webapps\myApp\WEB-INF\lib\myJar.jar) - jar not loaded. Offending class: myPackage/MyClass.class