Lecture3x - Francisco R. Ortega

Today’s Lecture
–

05/16/12

•
Some Java questions to do at home.

•
Chapter 2

•
Remember I have office hours Today!

Java Questions (@home)

•
Write logic for a controller using JSP that
calls
confirm.jsp

if:

–
Button was pressed and amount of total users
currently requesting the page is less that 10000

•
Hint USE static variable to add or remove users.

–
Otherwise, send to
Busy.jsp


Java Questions (@home)

•
Write logic for a controller using JSP that
calls
sold.jsp

if

–
Button buy was pressed and textbox quantity is
greater than 1.

–
Check that value of textbox is present before
asking if > 1

Java Questions (@home)

•
Write
a controller using a servlet that checks
to see if
edit,confirm

or cancel was pressed

–
If none pressed, send them to
BadQuery.jsp

–
If any of them pressed send them to their page.

–
Check that the button was pressed and that
value is not an empty string.

Java Questions(@home)

•
How do you open a
PrintWriter

and write
something to it in Java?

•
How do you read a file using a scanner?

•
Write the code that will do the following: if a
number is less than 0, display 'negative'; if a
number is greater than 100, display 'over 100';
for all other numbers, display 'valid grade'.

•
How do you test if a string is empty as opposed
to not existing?


Java Questions(@home)

•
How do you define a variable for a class
named
ShoppingCart
?

•
How do you create a new object for a class
named
ShoppingCart
?

–
Assume it takes
CartList

as parameter


Java Questions(@home)

•
What is an abstract class?

•
What is an interface ?

•
Create some classes (and extend them) to
show:

–
Abstract Classes

–
Use of interface

•
Create a class person and then student.

–
How do you call the base constructor of person?


File Structure

Tutorials/

WEB
-
INF/

classes/


*.class

lib/

*.jar

web.xml

index.jsp

edit.jsp

confirm.jsp

Web Applications

•
Web application can have many properties in
common

•
For the rest of the chapter, we will see

–
Edit page

–
Confirm page

–
Process page

•
For a more smooth operation

–
Controller class will be needed

•
A servlet page

Sending Data

•
<form
action=“
Confirm.jsp
">



Sending Data


<form
action
=“
Confirm.jsp
">


<p> Test
<
br
>



<
input type
=“text"
name="hobby"



value="${
param.hobby
}">



<
input type="
submit“ name=“
confirmBtn
"


value=“Confirm">


</
form>


Relative and Absolute Reference

•
Same as we sow in HTML

•
Questions

–
http://server.com/path/Edit.jsp

–
http://
server.com/path/Confirm.jsp

–
http://
server.com/utils/files/validate.jsp

•
What is the absolute and relative reference
for
Confirm.jsp

if called from
Edit.jsp

?

•
What is the absolute and relative reference
for
validate.jsp

if called from
Confirm.jsp

?

Retrieving Values (Form Element)

•
${
param.field
}

•
For example

–
${
param.hobby
}

•
Try
Edit.jsp

from book (page 38)

Hidden Field Technique

•
Edit.jsp

sends data to
Confirm.jsp

–
How to send data back to
Edit.jsp
?

•
Hidden Fields

–
<input type=“
hidden
” name=“hobby”


value = “${
param.hobby
}”>

Hidden Fields! Let’s Compare

•
Edit

–
<
input type
=“
text
”
name=“hobby”


value = “${
param.hobby
}”>

•
Confirm

–
<input
type=“
hidden
” name=“hobby”


value = “${
param.hobby
}”>


More in Sending Data!

•
How do we send data to either
edit.jsp

or
process.jsp
?


Inefficient Solution

<
form action="
Edit.jsp
">


<input type="hidden" name="hobby"


value="${
param.hobby
}">


<input type="submit" name="
editButton
"


value="Edit">

</
form>

<
form action="
Process.jsp
">


<input type="hidden" name="hobby"


value="${
param.hobby
}">


<input type="submit" name="
processButton
"


value="Process">

</
form>

Better Solution: Controller

•
Using a controller is better solution


Example:
Confirm.jsp


<form action="
Controller.jsp
">


<p>


<input type="hidden" name="hobby"


value="${
param.hobby
}">


<input type="submit" name="
editButton
"


value="Edit">


<input type="submit" name="
processButton
"


value="Process">




</
form>

Controller

•
It only contains java code

•
Each JSP will send its data to the controller

•
First, it will be shown as a JSP (for simplicity)

•
Objects:

–
HttpServletRequest

–
HttpServletResponse

•
Reference Parameters:

–
Request.getParameter
(“hobby”)

Testing Button

•
Button clicked will show in the query string


If (
request.getParameter
(“
processButton
”) != null)

Controller Logic

1.
Each form’s actions is mapped to controller

2.
E
ach submit button has unique name

3.
Controller decides which page to call next

4.
Controller knows URL of all JSP that controls

Controller Logic


if (
request.getParameter
("
processButton
") != null
)


{



address = "
Process.jsp
";


}


else
if (
request.getParameter
("
confirmButton
") != null
)


{



address = "
Confirm.jsp
";


}


else


{



address = "
Edit.jsp
";


}

Forward Control!

•
RequestDispatcher

dispatcher =
request.getRequestDispatcher
(address
);


•
d
ispatcher.forward
(
request,response
)

JSP or Servlet?

•
You can use either one

•
Easier to read in JSP

•
Better performance in Servlet

•
See Controller Code page 50 (or next slide)

Controller Code JSP

<%


String address;




if (
request.getParameter
("
processButton
") != null)


{


address = "
Process.jsp
";


}


else if (
request.getParameter
("
confirmButton
") != null)


{


address = "
Confirm.jsp
";


}


else


{


address = "
Edit.jsp
";


}


RequestDispatcher

dispatcher =

request.getRequestDispatcher
(address
);



dispatcher.forward
(request, response);

%>


Confirm + Controller


<form
action="
Controller.jsp
"
>


<p>


<input type="hidden" name="hobby"


value="${
param.hobby
}">


<input type="submit" name="
editButton
"


value="Edit">


<input type="submit" name="
processButton
"


value="Process">




</form>


JSP
vs

Java Servlet

JSP

•
It will be recreated each
time

•
Prefer when lots of HTML
and little JSP

•
Easy to write HTML

•
Hard to debug

Java Servlet

•
Does not have to recreate

•
Prefer when lots Java and
little HTML

•
Java IDE very useful

More JSP/Servlet

•
If you have lots of HTML and JAVA

–
Redesign your site:

•
Write more code in the controller


JAVA CLASSPATH

•
Windows

–

setx

CLASSPATH=
classpath1
;
classpath2
...

•
Linux/Unix/
MacOsX

–
setenv

CLASSPATH

classpath1
:
classpath2
...



Classpath

+ Packages

•
http://users.cs.fiu.edu/~downeyt/webdev/p
ackages.html

•
http://javarevisited.blogspot.com/2011/01/h
ow
-
classpath
-
work
-
in
-
java.html

•
http://docs.oracle.com/javase/1.4.2/docs/to
oldocs/solaris/classpath.html

•
http://docs.oracle.com/javase/1.4.2/docs/to
oldocs/solaris/classpath.html

More about Packages

•
If your class directory is called “classes”

–
What is the name of the package for
classes/store?

•
Store

–
How about classes/store/hardware ?

•
store.hardware


Controller Servlet

•
Place servlet in a package

–
Location should not be in the
default package

•
Import the following classes:

–
import
java.io.IOException
;

–
import
javax.servlet.ServletException
;

–
import
javax.servlet.http.HttpServlet
;

–
import
javax.servlet.http.HttpServletRequest
;

–
import
javax.servlet.http.HttpServletResponse
;

–
import
javax.servlet.RequestDispatcher
;



Controller Servlet

•
Extend
HttpServlet

–
public class Controller
extends

HttpServlet

{ …. }

–
Override some methods of
HttpServlet

Class

•
Place controller logic in this method:

@Override


protected void
doGet
(
HttpServletRequest

request,


HttpServletResponse

response)


throws
ServletException
,
IOException

{


...


}



Controller Logic

•
Override
doGet

or
doPost

methods

@Override


protected void
doGet
(
HttpServletRequest



request,HttpServletResponse

response)


throws
ServletException
,
IOException

{


...


}


Servlet Controller Code (page 55)

public
class Controller extends
HttpServlet

{


protected void
doGet
(
HttpServletRequest

request,HttpServletResponse

response)




throws
ServletException
,
IOException


{


if
(
request.getParameter
("
processButton
") != null)


{


address
= "../
Process.jsp
";



}



else
if (
request.getParameter
("
confirmButton
") != null)


{



address = "../
Confirm.jsp
";


}



else



{



address
= "../
Edit.jsp
";


}


RequestDispatcher

dispatcher
=
request.getRequestDispatcher
(address);


dispatcher.forward
(request
, response);


}

}

Jsp

+ Servlet

•
<form action=“
Controller
”>

•
What’s the difference?

Servlet Location

•
Source file could be anywhere

•
.class file must be in subdirectory classes

•
classes directory must already exist in
CLASSPATH

•
Define mapping in web.xml

•
JSP must placed in the folder that is
referenced


Servlet Identity FQN

•
Fully Qualified Name (FQN)

–
is an unambiguous name that specifies which
object, function, or variable a call refers
to (WIKI)

•
The package and the class name are
combined to define the unique name of a
class.

Servlet Identity FQN

•
We can use the FQN to define a short name
for tomcat to be used internally


<servlet>


<servlet
-
name>
Ch2Controller


</servlet
-
name>


<
servlet
-
class>ch2.servletController.Controller


</
servlet
-
class>


</servlet>

Servlet Access

•
Create a short name for servlet in web.xml

–
See previous slide

•
Create a mapping


<servlet
-
mapping>


<servlet
-
name>
Ch2Controller
</servlet
-
name
>


<
url
-
pattern
>
/ch2/
servletController
/Controller
</
url
-
pattern>


</
servlet
-
mapping>

More about Servlet Mapping

1.
If the next JSP is in the same directory
where the controller is mapped

–
address=“
Confirm.jsp
”

2.
If is not in the same directory

–
address=“/ch2/
servletController
/
Confirm.jsp
”

Servlet mapping

WAR Files

•
W
eb
application

AR
chive

(WAR)

•
http
://users.cis.fiu.edu/~
downeyt/webdev/cl
assPage.shtml?CSS

–
If you scroll down to Tomcat Information

•
Deploying a WAR file


Web Servlet Annotation

•
One may skip web.xml mapping

•
It does not work in all cases.

•
If you do the mapping in web.xml

–
Must remove the annotation from the class

Web Servlet Annotation

•
Example

@
WebServlet
(
urlPatterns
={"/ch2/
servletController
/annotated/Controller"})

public class Controller extends
HttpServlet

{

…

}


Servlet Engine for Servlets

•
Developer must re
-
compiled

•
Default behaviors does not update .class

–
Some systems may be configured to
automaticly

update


Servlet in IDEs

•
After you build web project

–
Execute them

•
When WAR file is built

–
Source packages will be copied to classes

•
To export WAR File

–
File


Export


Web


War File


Class Files

•
Avoid using default package

–
Only keep your configuration files

•
If web.xml is not created

–
File
-
>New
-
> Standard Deployment
Desctiptor


Questions

•
Any Questions

•
Review your java!