I have a subject that covers JSP(new to me), accessing database through JSP(new to me), applets, UML(also new to me)
So, as im learning java, all i did to learn faster is i've created some applications(wi th sense). With my style of self learning, i hope it could be effective in JSP too....
I like to be advanced on the planned topic to be discussed by our instructor(He is not a certified Java Programmer though)
So now, all i know about JSP is the following:
-basic tags
expression <%= something%>
declaration <%! something%>
i dont know the term <% something %> I think it is an invocation
equivalent to java (Please correct me on that part)
-Setting up tomcat.
-The ROOT folder
-WEB-INF theoritically knew where to put classes/jars etc....
(though im not tested them yet)
-getting the value of a html form through request.getPara meter("form input-type name)
Those are basics obviously...( I learned them through surfing)
And im planning to create a simple application.
What comes on my mind is to reimplement my previous project (Simple Hotel FrontDesk System) into Online Hotel Reservation System
-the registration is obviously done by the hotel frontdesk only....
-Maybe the BlackList feature would be added if i knew the real ( Deep )
Actually, we have proposed a project "Online Entrance Exam" to our instructor and he likes it... so he approved our proposal.....( Not Thesis )
But before we start banging that project, deadline is on October ( Final week in this semester )
I like to grasp the essentials of JSP and also the other techniques, new way, and theory behind that architectural design for web application platform....
(Please correct me on the phrase above)
Actually, the faculty decided to order a J2EE book from Sun( i think the book base is in Singapore) for about 2500php or $56.00
Unfortunately, that book is expected to be arrived on midterms.... unbelievable scenario(but that was true)....
I did attempt to buy a new book instead of waiting that precious book, but i doubt for having such book....(for $40.99)....
So i decided to wait that precious book, yet learning in advance from this forum and the other web resources....
What a long story :)
Well, anyway,
Here is what i suppose to know in JSP as im building my experimental application for the supplement on my final project( Not thesis though )
I like to know about the JSP Beans,
for example, i have a java class that contains setter and getter methods,
i like to jar them, unfortunately, i didn't found the right tutorial for it on the web...
so can you post a helpful url that would teach me how to do that?
and also, about how to access the jar file from the jsp container( doubt of terms )Please correct me....
Or can you show an example?
For example, i have a jar file in WEB-INF/lib/JARZKY.jar
and the content is com\myclass.cla ss(with setSetter() and getGetter() methods)
How can you invoke that class through JSP?
A sincere Java Lover,
sukatoa
Jul 3 '08
35  3667 
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("yell ow") else if (b==2) out.write("red" ) else out.write("gree n")}%> 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: - z=0;
-
if (x=7) z=3; else z=5;
can be written as
or as a formula: - 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 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.getPara meter() 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,re typeemail 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("yell ow") else if (b==2) out.write("red" ) else out.write("gree n")}%> 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:
- z=0;
-
if (x=7) z=3; else z=5;
can be written as
or as a formula:
- 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: - if this is,
-
then do this,
-
else,
-
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
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:
- if this is,
-
then do this,
-
else,
-
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: - if this is,
-
then do this,
-
else,
-
do also this,
it is better to use - if this is,
-
then do this and return,
-
do also this,
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: - if this, then do that
-
if this, then do also that
is reduced to - if this or this then do that
.
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 IllegalStateExc eption 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
JosAH 11,448
Recognized Expert MVP
Im just wondering.....
I have observed the behavior of my JavaServer Pages such that it will encounter an IllegalStateExc eption 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: - <%@ 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: - <% session.setMaxInactiveInterval(240*60); %>
2.) write in your web.xml - <session-config>
-
<session-timeout>240</session-timeout>
-
</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 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 - <session-config>
-
<session-timeout>100</session-timeout>
-
</session-config>
that is 100 minutes
For a particular session then that would be
int seconds = ....//your required timeout - session.setMaxInactiveInterval(seconds);
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:
- <%@ 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:
- <% session.setMaxInactiveInterval(240*60); %>
2.) write in your web.xml
- <session-config>
-
<session-timeout>240</session-timeout>
-
</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 - <session-config>
-
<session-timeout>240</session-timeout>
-
</session-config>
I expect that it was there, yet, it should be added.....
So, Here is the content of the web.xml - <?xml version="1.0" encoding="ISO-8859-1"?>
-
<!--
-
Copyright 2004 The Apache Software Foundation
-
-
Licensed under the Apache License, Version 2.0 (the "License");
-
you may not use this file except in compliance with the License.
-
You may obtain a copy of the License at
-
-
http://www.apache.org/licenses/LICENSE-2.0
-
-
Unless required by applicable law or agreed to in writing, software
-
distributed under the License is distributed on an "AS IS" BASIS,
-
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-
See the License for the specific language governing permissions and
-
limitations under the License.
-
-->
-
-
<web-app xmlns="http://java.sun.com/xml/ns/j2ee"
-
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"
-
version="2.4">
-
-
<display-name>Welcome to Tomcat</display-name>
-
<description>
-
Welcome to Tomcat
-
</description>
-
-
<!-- JSPC servlet mappings start -->
-
-
<servlet>
-
<servlet-name>org.apache.jsp.index_jsp</servlet-name>
-
<servlet-class>org.apache.jsp.index_jsp</servlet-class>
-
</servlet>
-
-
<servlet-mapping>
-
<servlet-name>org.apache.jsp.index_jsp</servlet-name>
-
<url-pattern>/index.jsp</url-pattern>
-
</servlet-mapping>
-
-
<!-- JSPC servlet mappings end -->
-
-
</web-app>
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)
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