Integrating Servlets and JSP: The Model View ... - UniNa STiDuE

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© 2010 Marty Hall
Integrating Servlets and JSP:
The Model View Controller
(MVC) Architecture
(MVC)

Architecture
Originals of Slides and Source Code for Examples:
http://courses.coreservlets.com/Course-Materials/csajsp2.html
Customized Java EE Training: http://courses.coreservlets.com/
Servlets, JSP, JSF 2.0, Struts, Ajax, GWT 2.0, Spring, Hibernate, SOAP & RESTful Web Services, Java 6.
Developed and taught by well-known author and developer. At public venues or onsite at your location.
3
© 2010 Marty Hall
For live Java EE training, please see training courses
at http://courses.coreservlets.com/.
at http://courses.coreservlets.com/.
Servlets, JSP, Struts, JSF 1.x, JSF 2.0, Ajax (with jQuery, Dojo,
Prototype, Ext-JS, Google Closure, etc.), GWT 2.0 (with GXT),
Java 5, Java 6, SOAP-based and RESTful Web Services, Sprin
g
,
g
Hibernate/JPA, and customized combinations of topics.
Taught by the author of Core Servlets and JSP, More
Servlets and JSP
and this tutorial Available at public
Customized Java EE Training: http://courses.coreservlets.com/
Servlets, JSP, JSF 2.0, Struts, Ajax, GWT 2.0, Spring, Hibernate, SOAP & RESTful Web Services, Java 6.
Developed and taught by well-known author and developer. At public venues or onsite at your location.
Servlets and JSP
,
and this tutorial
.
Available at public
venues, or customized versions can be held on-site at your
organization. Contact hall@coreservlets.com for details.
Agenda
• Understanding the benefits of MVC
• Using RequestDispatcher to implement MVC
• Forwarding requests from servlets to JSP
pages
• Handling relative URLs
• Choosing among different display options
• Comparing data-sharing strategies
5
© 2010 Marty Hall
MVC Motivation
Customized Java EE Training: http://courses.coreservlets.com/
Servlets, JSP, JSF 2.0, Struts, Ajax, GWT 2.0, Spring, Hibernate, SOAP & RESTful Web Services, Java 6.
Developed and taught by well-known author and developer. At public venues or onsite at your location.
6
Uses of JSP Constructs

Scripting elements calling servlet
Sim
p
le
Scripting

elements

calling

servlet

code directly
• Scriptin
g
elements callin
g
servlet
p
Application
g g
code indirectly (by means of utility
classes)
B

B
eans
• Servlet/JSP combo (MVC)
MVC ith JSP i l

MVC
w
ith

JSP
express
i
on
l
anguage
• Custom tags
MVC ith b t t d
Complex
Application

MVC
w
ith

b
eans, cus
t
om
t
ags, an
d

a framework like Struts or JSF
7
Why Combine Servlets & JSP?
• Typical picture: use JSP to make it easier to
d l d i i h HTM
d
eve
l
op an
d
ma
i
nta
i
n t
h
e
HTM
L content
– For simple dynamic code, call servlet code from
scripting elements
scripting

elements
– For slightly more complex applications, use custom
classes called from scripting elements
– For moderately complex applications,
use beans and custom tags

But that

s not enough

But
,
that s

not

enough
– For complex processing, starting with JSP is awkward
– Des
p
ite the ease of se
p
aratin
g
the real code into se
p
arate
p p g p
classes, beans, and custom tags, the assumption behind
JSP is that a single page gives a single basic look
8
Possibilities for Handling a
Single Request
Single

Request
• Servlet only. Works well when:
O i bi E i

O
utput
i
s a
bi
nar
y
t
y
pe.
E
.
g
.: an
i
ma
g
e
– There is no output. E.g.: you are doing forwarding or redirection as
in Search Engine example.

Format/la
y
out of pa
g
e is hi
g
hl
y
variable. E.
g
.: portal.
• JSP only. Works well when:

Out
p
ut is mostl
y
character data. E.
g
.: HTML
p y g
– Format/layout mostly fixed.
• Combination (MVC architecture). Needed when:
A i l t ill lt i lti l b t ti ll diff t

A
s
i
n
gl
e reques
t
w
ill
resu
lt

i
n mu
lti
p
l
e su
b
s
t
an
ti
a
lly

diff
eren
t
-
looking results.
– You have a large development team with different team members
doing the Web development and the business logic
doing

the

Web

development

and

the

business

logic
.
– You perform complicated data processing, but have a relatively
fixed layout.
9
MVC Misconceptions
• An elaborate framework is necessary
– Frameworks are often useful
• JSF (JavaServer Faces)

You should
strongly
consider JSF2.0for medium/large projects!
You

should

strongly
consider

JSF

2.0

for

medium/large

projects!
•Struts
– They are not required!
Implementing MVC with the builtin RequestDispatcher

Implementing

MVC

with

the

builtin

RequestDispatcher

works very well for most simple and even moderately
complex applications
MVC t t ll h
t
d i

MVC

t
o
t
a
ll
y c
h
anges your sys
t
em
d
es
i
gn
– You can use MVC for individual requests
Think of it as the MVC
approach
not the

Think

of

it

as

the

MVC

approach
,
not

the

MVC architecture
• Also called the Model 2 approach
10
© 2010 Marty Hall
Beans
Customized Java EE Training: http://courses.coreservlets.com/
Servlets, JSP, JSF 2.0, Struts, Ajax, GWT 2.0, Spring, Hibernate, SOAP & RESTful Web Services, Java 6.
Developed and taught by well-known author and developer. At public venues or onsite at your location.
11
Review: Beans
• Java classes that follow certain conventions
– (Must have a zero-argument (empty) constructor)
• You can satisfy this requirement either by explicitly
definin
g
such a constructor or b
y
omittin
g
all constructors
g y g
• In this version of MVC, it is not
required to have zero arg
constructor if you only instantiate from Java code

Should have no public instance variables (fields)
Should

have

no

public

instance

variables

(fields)
• I hope you already follow this practice and use accessor
methods instead of allowing direct access to fields
Persistent values should be accessed through methods

Persistent

values

should

be

accessed

through

methods

called getXxx and setXxx
• If class has method getTitle that returns a String, class
i id t h St i
t
d
i l
i
s sa
id

t
o
h
ave a
St
r
i
ng
p
roper
ty
name
d
t
i
t
l
e
• Boolean properties can use isXxx instead of getXxx
12
Bean Properties: Examples
Method Names Property Name Example JSP Usage
getFirstName
setFirstName
firstName <jsp:getProperty … property="firstName"/>
<jsp:setProperty … property="firstName"/>
${customer.firstName}
isExecutive
setExecutive
(boolean property)
executive <jsp:getProperty … property="executive"/>
<jsp:setProperty … property="executive"/>
${customer.executive}
getExecutive
setExecutive
(boolean property)
executive <jsp:getProperty … property="executive"/>
<jsp:setProperty … property="executive"/>
${customer.executive}
getZIP
setZIP
ZIP <jsp:getProperty … property="ZIP"/>
<jsp:setProperty … property="ZIP"/>
${address.ZIP}
13
Note 1: property name does not exist anywhere in your code. It is just a shortcut for the method name.
Note 2: property name is derived only from method name. Instance variable name is irrelevant.
Example: StringBean
package coreservlets;
public class StringBean {
private String message = "No message specified";
public String getMessage() {
return(message);
}
public void setMessage(String message) {
hi
t
hi
s.message = message;
}
}
• Beans installed in normal Java directory
– Eclipse: src/folderMatchingPackage
l d
/
/l/
f ld h k
– Dep
l
oye
d
:…
/
WEB-INF
/
c
l
asses
/
f
o
ld
erMatc
h
ingPac
k
age
• Beans (and utility classes) must always be in packages!
14
© 2010 Marty Hall
Basic MVC Design
Customized Java EE Training: http://courses.coreservlets.com/
Servlets, JSP, JSF 2.0, Struts, Ajax, GWT 2.0, Spring, Hibernate, SOAP & RESTful Web Services, Java 6.
Developed and taught by well-known author and developer. At public venues or onsite at your location.
15
MVC Flow of Control
Java Code
HTML or JSP
Java Code
(Business Logic)
Results
(beans)
Arguments
based on
Form
Servlet
submit form
(Form action matches URL of servlet,
which is either from @WebServlet or
from url-pattern in web.xml)
(beans)
(Store beans in request,
session, or application scope)
form data
JSP
JSP
1
JSP
2
JSP
3
(Extract data from beans
and
p
ut in out
p
ut
)
16
p p )
MVC Flow of Control
(Annotated)
(Annotated)
Java Code
Customer currentCustomer =
lookupService.findCustomer(customerId);
HTML or JSP
Java Code
(Business Logic)
Results
(beans)
Pass
customer
ID to
lookup
i
Get back
current
customer
Arguments
based on
Form
Servlet
submit form
(Form action matches
URL of servlet.)
(beans)
(Store beans in request,
session, or application scope)
request setAttribute("customer"
Send customer ID
serv
i
ce
that has
the ID
form data
JSP
request
.
setAttribute("customer"
,

currentCustomer);
JSP
1
JSP
2
JSP
3
(Extract data from beans
and
p
ut in out
p
ut
)
17
p p )
${customer.firstName}
${customer.balance}
Parts in blue are examples for a banking application.
Implementing MVC with
RequestDispatcher
RequestDispatcher
1.Define beans to represent result data
– Ordinary Java classes with at least one getBlah metho
d
2.Use a servlet to handle requests
S l d h k f i i

S
erv
l
et rea
d
s request parameters, c
h
ec
k
s
f
or m
i
ss
i
ng
and malformed data, calls business logic, etc.
3.
Obtain bean instances
3.
Obtain

bean

instances
– The servlet invokes business logic (application-specific
code) or data-access code to obtain the results.
4.Store the bean in the request, session, or
servlet context
Th l t ll
tAtt ib t
th t i

Th
e serv
l
e
t
ca
ll
s se
tAtt
r
ib
u
t
e on
th
e reques
t
, sess
i
on, or
servlet context objects to store a reference to the beans
that represent the results of the request.
18
Implementing MVC with
RequestDispatcher (Continued)
RequestDispatcher

(Continued)
5.Forward the request to a JSP page.
– The servlet determines which JSP page is appropriate to
the situation and uses the forward method of
RequestDispatcher
to transfer control to that page.
RequestDispatcher
to

transfer

control

to

that

page.
6.Extract the data from the beans.
– JSP 1.2
(
Old!
)
( )
• The JSP page accesses beans with jsp:useBean and a
scope matching the location of step 4. The page then
uses jsp:getProperty to output the bean properties.
– JSP 2.0
(Preferred!)
• The JSP page uses ${nameFromServlet.property} to
output bean properties
output

bean

properties
– Either way, JSP page does not create or modify bean; it
merely extracts and displays data that servlet created.
19
Request Forwarding Example
public void doGet(HttpServletRequest request,
Htt
p
ServletRes
p
onse res
p
onse
)
p p p )
t h r o w s S e r v l e t E x c e p t i o n, I O E x c e p t i o n {
... // D o b u s i n e s s l o g i c a n d g e t d a t a
S t r i n g o p e r a t i o n = r e q u e s t.g e t P a r a m e t e r ("o p e r a t i o n");
i f ( o p e r a t i o n = = n u l l ) {
i f

(operation

==

null)

{
operation = "unknown";
}
String address;
if (operation.equals("order")) {
address = "/WEB-INF/Order.jsp";
} else if (operation.equals("cancel")) {
address =
"
/WEB
-
INF/Cancel jsp
"
;
address

=

/WEB
INF/Cancel
.
jsp;
} else {
address = "/WEB-INF/UnknownOperation.jsp";
}
RequestDispatcher dispatcher =
request.getRequestDispatcher(address);
dispatcher.forward(request, response);
}
20
jsp:useBean in MVC vs.
in Standalone JSP Pages
in

Standalone

JSP

Pages
• The JSP page should not create the objects
– The servlet, not the JSP page, should create all the data
objects. So, to guarantee that the JSP page will not create
bj t h ld
o
bj
ec
t
s, you s
h
ou
ld
use
<jsp:useBean... type="package.Class"/>
instead of
instead

of

<jsp:useBean... class="package.Class" />
Th JSP h ld dif
h
bj

Th
e
JSP
page s
h
ou
ld
not mo
dif
y t
h
e o
bj
ects
– So, you should use jsp:getProperty but not
jsp:setProperty
jsp:setProperty
.
21
© 2010 Marty Hall
Scopes:
request, session, and
application (ServletContext)
application

(ServletContext)
Customized Java EE Training: http://courses.coreservlets.com/
Servlets, JSP, JSF 2.0, Struts, Ajax, GWT 2.0, Spring, Hibernate, SOAP & RESTful Web Services, Java 6.
Developed and taught by well-known author and developer. At public venues or onsite at your location.
22
Reminder: jsp:useBean
Scope Alternatives
(JSP 1 2 Only!)
Scope

Alternatives

(JSP

1
.
2

Only!)
• request
– <jsp:useBean id="..." type="..." scope="request"/>
• session
j B id""""
"i"
/
– <
j
sp:use
B
ean
id
=
"
...
"
type=
"
...
"
scope=
"
sess
i
on
"
/
>
• application
<jsp:useBean id=
""
type=
""
scope=
"
application
"
/>

<jsp:useBean

id=
...
type=
...
scope= application
/>
• page

<jsp:useBean id
=""
type
=""
scope
="
page
"
/>
<jsp:useBean

id
...
type
...
scope page
/>

or just
<jsp:useBean id="..." type="..." />
Thi i t d i MVC (M d l 2) hit t

Thi
s scope
i
s no
t
use
d

i
n
MVC

(M
o
d
e
l

2)
arc
hit
ec
t
ure
23
Request-Based Data Sharing
• Servlet
ValueObject value = LookupService.findResult(...);
request.setAttribute("key", value);
RequestDispatcher dispatcher =
request.getRequestDispatcher
("/WEB-INF/SomePage.jsp");
dispatcher.forward(request, response);
• JSP 1.2
<
jsp:useBean
id
="
key
"
type
="
somePackage.ValueObject
"
<
jsp:useBean
id
key

type
somePackage.ValueObject
scope="request"/>
<jsp:getProperty name="key" property="someProperty" />
JSP 2 0
Name chosen by the
servlet

JSP

2
.
0
${key.someProperty}
24
Name chosen by the
servlet
.
Name of accessor method, minus the
word "get", with next letter changed
to lower case.
Request-Based Data Sharing:
Simplified Example
Simplified

Example
• Servlet
C t
C t
Assume that the funCust method
handles missing/malformed data.
C
us
t
omer my
C
us
t
omer =
Lookup.findCust(request.getParameter("customerID"));
request.setAttribute("customer", myCustomer);
RequestDispatcher
dispatcher
=
RequestDispatcher
dispatcher

request.getRequestDispatcher
("/WEB-INF/SomePage.jsp");
dispatcher.forward(request, response);
• JSP 1.2
<
j
s
p
:useBean id="customer" t
yp
e="somePacka
g
e.Customer"
j p
y p
g
scope="request"/>
<jsp:getProperty name="customer" property="firstName"/>

JSP 2 0

JSP

2
.
0
${customer.firstName}
25
Note: the Customer class must
have a method called “getFirstName”.
Session-Based Data Sharing
• Servlet
ValueObject value = LookupService.findResult(...);
HttpSession session = request.getSession();
session.setAttribute("key", value);
RequestDispatcher
dispatcher =
RequestDispatcher
dispatcher

=

request.getRequestDispatcher
("/WEB-INF/SomePage.jsp");
dis
p
atcher.forward
(
re
q
uest
,
res
p
onse
);
p
( q,p );
• JSP 1.2
<
jsp:useBean id="key" type="somePackage.ValueObject"
scope="session"/>
<jsp:getProperty name="key" property="someProperty" />
• JSP 2.0
${key.someProperty}
26
Session-Based Data Sharing:
Variation
Variation
• Redirect to page instead of forwarding to it
U dR di i d f R Di h f d

U
se response.sen
dR
e
di
rect
i
nstea
d
o
f

R
equest
Di
spatc
h
er.
f
orwar
d
• Distinctions: with sendRedirect:

User sees JSP URL
(
user sees onl
y
servlet URL with
( y
RequestDispatcher.forward)
– Two round trips to client (only one with forward)

Advantage of sendRedirect
Advantage

of

sendRedirect
– User can visit JSP page separately
• User can bookmark JSP page
Disadvantages of sendRedirect

Disadvantages

of

sendRedirect
– Two round trips to server is more expensive
– Since user can visit JSP page without going through servlet first,
b d i h b il bl
b
ean
d
ata m
igh
t not
b
e ava
il
a
bl
e
• So, JSP page needs code to detect this situation
27
ServletContext-Based Data
Sharing (Rare)
Sharing

(Rare)
• Servlet
synchronized(this) {
ValueObject value = SomeLookup.findResult(...);
getServletContext().setAttribute("key", value);
Req estDispatcher
dispatcher
Req
u
estDispatcher
dispatcher
=
request.getRequestDispatcher
("/WEB-INF/SomePage.jsp");
dispatcher forward
(request response);
dispatcher
.
forward
(request
,
response);
}
• JSP 1.2
<
j B
id"
k
"t"
P k V l Obj t
"
<
j
sp:use
B
ean
id
=
"
k
ey
"

t
ype=
"
some
P
ac
k
age.
V
a
l
ue
Obj
ec
t
"
scope="application"/>
<jsp:getProperty name="key" property="someProperty" />
• JSP 2.0
${key.someProperty}
28
Relative URLs in JSP Pages
• Issue:
– Forwarding with a request dispatcher is transparent to the
client. Original URL (i.e., the form action URL) is only
URL browser knows about.
URL

browser

knows

about.
• Why does this matter?
– What will browser do with ta
g
s like the followin
g
?
g g
<img src="foo.gif"…>
<
link rel
="
stylesheet
"
link

rel stylesheet
href="my-styles.css"
type="text/css">
<a
href=
"
bar jsp
"
> </a>
<a

href= bar
.
jsp
>

</a>
– Browser treats addresses as relative to servlet URL
29
© 2010 Marty Hall
Example:
Example:
Bank Balance Looku
p
p
Customized Java EE Training: http://courses.coreservlets.com/
Servlets, JSP, JSF 2.0, Struts, Ajax, GWT 2.0, Spring, Hibernate, SOAP & RESTful Web Services, Java 6.
Developed and taught by well-known author and developer. At public venues or onsite at your location.
30
Applying MVC:
Bank Account Balances
Bank

Account

Balances
• Bean
B kC t

B
an
kC
us
t
omer
• Business Logic
– BankCustomerLookup
• Servlet that populates bean and forwards to
appropriate JSP page

Reads customer ID calls
BankCustomerLookup

s
Reads

customer

ID
,
calls

BankCustomerLookup s
data-access code to obtain BankCustomer
– Uses current balance to decide on appropriate result page

JSP pages to display results

JSP

pages

to

display

results
– Negative balance: warning page
– Regular balance: standard page
Hi h b l ith d ti t dd d

Hi
g
h

b
a
l
ance: page w
ith
a
d
ver
ti
semen
t
s a
dd
e
d
– Unknown customer ID: error page
31
Bank Account Balances:
Servlet Code
Servlet

Code
@WebServlet("/show-balance")
p
ublic class ShowBalance extends Htt
p
Servlet
{
p
p {
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
(
)
String customerId = request.getParameter
(
"customerId"
)
;
CustomerLookupService service = new CustomerSimpleMap();
Customer customer = service.findCustomer(customerId);
request.setAttribute(
"
customer
"
,customer);
request.setAttribute( customer,

customer);
String address;
if (customer == null) {
request.setAttribute("badId", customerId);
address = "/WEB-INF/results/unknown-customer.jsp";
} else if (customer.getBalance() < 0) {
address = "/WEB-INF/results/negative-balance.jsp";
}
/
*
normal
-
balance and high
-
balance cases
*
/}
}

/

normal
balance

and

high
balance

cases/

}
RequestDispatcher dispatcher =
request.getRequestDispatcher(address);
dispatcher.forward(request, response);
32
Bank Account Balances:
Bean
Bean
public class Customer {
p
rivate final Strin
g
id
,
firstName
,
lastName
;
p g,
,
;
private final double balance;
public Customer(String id,
String
firstName
Since the constructor is called from Java only
(never from JSP), the requirement for a zero-arg
constructor is eliminated. Also, since bean state
is set only with constructor, rather than with
jsp:setProperty, we can eliminate setter
methods and make the class immutable.
String

firstName
,
String lastName,
double balance) {
this.id = id;
this.firstName = firstName;
this.lastName = lastName;
this.balance = balance;
}
}
// getId, getFirstName, getLastName, getBalance. No setters.
public double getBalanceNoSign() {
return(Math.abs(balance));
}
}
33
Bank Account Balances:
Business
Logic Interface
Business

Logic

Interface
public interface CustomerLookupService {
public Customer
findCustomer
(String id);
public

Customer

findCustomer
(String

id);
}
34
Bank Account Balances:
Business
Logic Implementation
Business

Logic

Implementation
public class CustomerSimpleMap
implements
CustomerLookupService
{
implements

CustomerLookupService
{
private Map<String,Customer> customers;
p
ublic CustomerSim
p
leMa
p
()

{
p
p p
()
{
// Populate Map with some sample customers
}
public Customer findCustomer(String id) {
if (id!=null) {
return(customers.get(id.toLowerCase()));
} l {
}
e
l
se
{
return(null);
}
}
}

}
35
Bank Account Balances:
Input Form
Input

Form

<fieldset>
<fieldset>
<legend>Bank Account Balance</legend>
<form action="show-balance">
Customer ID
(
id001
,
id002
,
id003
)
:
(,,)
<input type="text" name="customerId"/><br/>
<input type="submit" value="Show Balance"/>
</form>
The address http://host/appName/show-balance comes from the @WebServlet annotation in this case,
but could also be set in older servers using the url
pattern entry in web xml
<
/fieldset
>

but could also be set in older servers using the url
-
pattern entry in web
.
xml
.
36
Bank Account Balances:
Negative Balance (JSP 2 0)
Negative

Balance

(JSP

2
.
0)

<body>
<div align="center">
<table border="5">
<table

border="5">
<tr><th class="title">
We Know Where You Live!
</th></t >
</th></t
r
>
</table>
<p/>
///
<
img src=".
/
images
/
club.gif" align="left"
/>
<h2>Watch out, ${customer.firstName},
we know where you live. </h2>
<
h2>Pay us the $${customer.balanceNoSign}
you owe us before it is too late!</h2>
</div></body></html>
37
Bank Account Balances:
Negative Balance (JSP 1 2)
Negative

Balance

(JSP

1
.
2)
…<body>
<div align
="
center
"
>
<div

align center >
<table border="5">
<tr><th class="title">We Know Where You Live!</th></tr>
</table>
<p/
>
<img src="./images/club.gif" align="left"/>
<jsp:useBean id="customer"
type=
"
coreservlets Customer
"
type=
coreservlets
.
Customer
scope="request"/>
<h2>Watch out,
<jsp:getProperty name="customer"
property="firstName"/>,
we know where you live. </h2>
<h2>Pay us the
$<
j tP t
"t"
$<
j
sp:ge
tP
roper
t
y name=
"
cus
t
omer
"

property="balanceNoSign"/>
you owe us before it is too late!</h2>
</div></body></html>
38
Bank Account Balances:
Normal Balance
Normal

Balance
…<body>
<table border=
"
5
"
align=
"
center
"
>
<table

border= 5

align= center >
<tr><th class="title">Your Balance</th></tr>
</table>
<p/>
<p/>
<img src="./images/money.gif" align="left" hspace="20"/>
<ul>
<li>First name:
${
customer.firstName
}
</li>
<li>First

name:

${
customer.firstName
}
</li>
<li>Last name: ${customer.lastName}</li>
<li>ID: ${customer.id}</li>
<
li>Balance:
$
${
customer.balance
}
</
li
>
$
${
}
/
</ul>
</body></html>
39
Bank Account Balances:
High Balance
High

Balance

<body>
<
div align="center">

<img src="./images/sailing.gif"/><br clear="all"/>
<h2>It is an honor to serve you
<h2>It

is

an

honor

to

serve

you
,
${customer.firstName} ${customer.lastName}!
</h2>
<h2>
Since you are one of our most valued customers, we would like
to offer you the opportunity to spend a mere fraction of your
$${customer.balance} on a boat worthy of your status.
Please visit <a href="http://overpricedyachts com">
Please

visit

<a

href="http://overpricedyachts
.
com">
our boat store</a> for more information.
</h2>
<
/div></body></html>
40
Bank Account Balances:
Unknown Customer
Unknown

Customer

<body>
<body>
<div align="center">
<table border="5">
<
tr><th class="title">Unknown Customer<
/
th><
/
tr
>
//
</table>
<p/>
<
h2>No customer found with id "${badI
d
}"</h2
>
<p>Please <a href="index.html">try again</a>.</p>
</div></body></html>
41
Bank Account Balances:
Results
Results
42
© 2010 Marty Hall
Comparing Data
Comparing

Data

Sharin
g
A
pp
roaches
g pp
Customized Java EE Training: http://courses.coreservlets.com/
Servlets, JSP, JSF 2.0, Struts, Ajax, GWT 2.0, Spring, Hibernate, SOAP & RESTful Web Services, Java 6.
Developed and taught by well-known author and developer. At public venues or onsite at your location.
43
Summary
• Request scope
– A new bean instance is made on every HTTP request.
– The most common scope.
Session scope

Session

scope
– A bean instance could be reused if the request is from the
same user in the same browser session.
U
seful for
U
tracking user-specific data.
• See session tracking lecture for details

Remember to make bean Serializable

Remember

to

make

bean

Serializable
• Application (ServletContext) scope
– Once created
,
the same bean instance is used for all
,
requests and all users.
• Must synchronize. Very rare.
44
Comparing Data-Sharing
Approaches:Request
Approaches:

Request
• Goal
– Display a random number to the user
Type of sharing

Type

of

sharing
– Each request should result in a new number, so request-
b
ased sharin
g
is a
pp
ro
p
riate.
g pp p
45
Request-Based Sharing: Bean
public class NumberBean {
private final double num;
private

final

double

num;
public NumberBean(double number) {
this num = number;
this
.
num

=

number;
}
public double
getNumber
() {
public

double

getNumber
()

{
return(num);
}
}
}
The property name in JSP will be “number”. The property name is derived from the method name, not from
the instance variable name. Also note the lack of a corresponding setter.
46
Request-Based Sharing: Servlet
@WebServlet("/random-number")
public class
RandomNumberServlet
extends HttpServlet {
public

class

RandomNumberServlet
extends

HttpServlet

{
@Override
public void doGet(HttpServletRequest request,
HttpServletResponse response)
HttpServletResponse

response)
throws ServletException, IOException {
NumberBean bean =
RanUtils.randomNum
(
re
q
uest.
g
etParameter
(
"ran
g
e"
));
( q g ( g ));
request.setAttribute("randomNum", bean);
String address = "/WEB-INF/results/random-num.jsp";
Re
q
uestDis
p
atcher dis
p
atcher =
q p p
request.getRequestDispatcher(address);
dispatcher.forward(request, response);
}
}
47
Request-Based Sharing:
Business Logic
Business

Logic
public class RanUtils {
public static
NumberBean
randomNum
(String
rangeString
) {
public

static

NumberBean
randomNum
(String

rangeString
)

{
double range;
try {
range
=
Double.parseDouble(
rangeString
);
range

Double.parseDouble(
rangeString
);
} catch(Exception e) {
range = 10.0;
}
}
return(new NumberBean(Math.random() * range));
}
private RanUtils() {} // Uninstantiable class
}
48
Request-Based Sharing:
Input Form
Input

Form
...
<fieldset>
<fieldset>
<legend>Random Number</legend>
<form action="random-number">
Range:<input type"text"
name"range"
><br/>
Range:

<input

type
=
"text"

name
=
"range"
><br/>
<input type="submit" value="Show Number">
</form>
</fi ld t>
</fi
e
ld
se
t>
...
49
Request-Based Sharing:
Results Page
Results

Page
<!DOCTYPE html>
<html>
<html>
<head>
<title>Random Number</title>
<
link rel="stylesheet"
href="./css/styles.css"
type="text/css">
</head>
<body>
<
h2>Random Number:
${
randomNum.number
}
</
h2>
${
}
/
</body></html>
50
Request-Based Sharing:
Results
Results
51
Comparing Data-Sharing
Approaches:Session
Approaches:

Session
• Goal
– Display users’ first and last names.
– If the users fail to tell us their name, we want to use
whatever name they gave us previously
whatever

name

they

gave

us

previously
.
– If the users do not explicitly specify a name and no
previous name is found, a warning should be displayed.
• Type of sharing
D i d f h li i
b d h i i

D
ata
i
s store
d

f
or eac
h
c
li
ent, so sess
i
on-
b
ase
d
s
h
ar
i
ng
i
s
appropriate.
52
Session-Based Sharing: Bean
public class NameBean implements Serializable {
p
rivate Strin
g
firstName = "Missin
g
first name";
p g
g
private String lastName = "Missing last name";
public String getFirstName() {
return(
firstName
);
return(
firstName
);
}
public void setFirstName(String firstName) {
if (!
isMissing
(
firstName
)) {
if

(!
isMissing
(
firstName
))

{
this.firstName = firstName;
}
}
... // getLastName, setLastName
private boolean isMissing(String value) {
return((value == null) || (value.trim().equals("")));
}
}
53
Session-Based Sharing: Servlet
@WebServlet("/register")
public class RegistrationServlet extends HttpServlet {
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
HttpSession session = request.getSession();
synchronized(session) {
NameBean nameBean =
(NameBean)session.getAttribute("name");
if (nameBean == null) {
()
nameBean = new
N
ameBean
()
;
session.setAttribute("name", nameBean);
}
nameBean.setFirstName(request.getParameter("firstName"));
B tL tN
(
t tP t
("
l tN
"))
name
B
ean.se
tL
as
tN
ame
(
reques
t
.ge
tP
arame
t
er
("
l
as
tN
ame
"))
;
String address = "/WEB-INF/mvc-sharing/ShowName.jsp";
RequestDispatcher dispatcher =
request.getRequestDispatcher(address);
di t h f d
( t )
di
spa
t
c
h
er.
f
orwar
d
(
reques
t
, response
)
;
}
}
}
54
Session-Based Sharing:
Results Page
Results

Page
<!DOCTYPE html>
<html>
<html>
<head><title>Thanks for Registering</title>
<link rel="stylesheet"
href="./css/styles.css"
type="text/css"/>
</head>
<body>
<h1>Thanks for Registering</h1>
<
h2>First Name:
${
name.firstName
}
</
h2>
${
}
/
<h2>Last Name: ${name.lastName}</h2>
</body></html>
55
Session-Based Sharing:
Results
Results
56
Comparing Data-Sharing
Approaches:ServletContext
Approaches:

ServletContext
• Goal
– Display a prime number of a specified length.
– If the user fails to tell us the desired length, we want to
use whatever prime number we most recently computed
use

whatever

prime

number

we

most

recently

computed

for any user.
• Type of sharing
– Data is shared among multiple clients, so application-
based sharing is appropriate
based

sharing

is

appropriate
.
57
ServletContext-Based Sharing:
Bean
Bean
package coreservlets;
im
p
ort
j
ava.math.Bi
g
Inte
g
er
;
p
j g g
;
public class PrimeBean {
private BigInteger prime;
public PrimeBean(String lengthString) {
int length = 150;
t
r
y

{
t y {
length = Integer.parseInt(lengthString);
} catch(NumberFormatException nfe) {}
this.prime = Primes.nextPrime(Primes.random(length));
}
}
public BigInteger getPrime() {
return(prime);
return(prime);
}

}
58
ServletContext-Based Sharing:
Servlet
Servlet
@WebServlet("/find-prime")
public class PrimeServlet extends HttpServlet {
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
Strin
g
len
g
th = re
q
uest.
g
etParameter
(
"
p
rimeLen
g
th"
);
g g q g (
p g
);
ServletContext context = getServletContext();
synchronized(this) {
if ((context.getAttribute("primeBean") == null) ||
(!
isMissing
(length))) {
(!
isMissing
(length)))

{
PrimeBean primeBean = new PrimeBean(length);
context.setAttribute("primeBean", primeBean);
}
String address =
"
/WEB
-
INF/
mvc
-
sharing/ShowPrime jsp
"
;
String

address

=

/WEB
-
INF/
mvc
-
sharing/ShowPrime
.
jsp;
RequestDispatcher dispatcher =
request.getRequestDispatcher(address);
dispatcher.forward(request, response);
}
}
}
… // Definition of isMissing: null or empty string
}
59
ServletContext-Based Sharing:
Results Page
Results

Page
<!DOCTYPE html>
<html>
<html>
<head><title>A Prime Number</title>
<link rel="stylesheet"
href=
"
/css/styles css
"
href=
.
/css/styles
.
css
type="text/css"/>
</head>
<body>
<body>
<h1>A Prime Number</h1>
<h2>${primeBean.prime}</h2>
</body
><
/
h
t
ml>
/body/t
60
ServletContext-Based Sharing:
Results
Results
61
© 2010 Marty Hall
Forwarding and
Forwarding

and

Includin
g
g
Customized Java EE Training: http://courses.coreservlets.com/
Servlets, JSP, JSF 2.0, Struts, Ajax, GWT 2.0, Spring, Hibernate, SOAP & RESTful Web Services, Java 6.
Developed and taught by well-known author and developer. At public venues or onsite at your location.
62
Forwarding from JSP Pages
<% String destination;
if (Math random() > 0 5) {
i f

(Math
.
random()

>

0
.
5)

{
destination = "/examples/page1.jsp";
} else {
destination =
"
/examples/page2 jsp
"
;
destination

=

/examples/page2
.
jsp;
}
%>
<
jsp:forward
page
="
<%
=
destination %>
"
/>
<
jsp:forward
page <%

destination

%>

/>

Legal but bad idea

Legal
,
but

bad

idea
– Business and control logic belongs in servlets
– Kee
p
JSP focused on
p
resentation
p p
63
Including Pages Instead of
Forwarding to Them
Forwarding

to

Them
• With the forward method

N
ew page generates all of the output
– Original page or other pages cannot generate any output

With the
i l d
method

With

the

i
nc
l
u
d
e
method
– Output can be generated by multiple pages

Original page
can
generate output before and after the
Original

page

can
generate

output

before

and

after

the

included page
–Original servlet does not see the output of the included
(f hi l i l/JSP fil )
p
age
(f
or t
hi
s, see
l
ater top
i
c on serv
l
et
/JSP

fil
ters
)
–Applications

Portal
-
like applications (see first example)
Portal
like

applications

(see

first

example)
• Setting content type for output (see second example)
64
Using RequestDispatcher.include:
portals
portals
response.setContentType("text/html");
String firstTable, secondTable, thirdTable;
if (someCondition) {
firstTable = "/WEB-INF/results/sports-scores.jsp";
secondTable = "/WEB-INF/results/stock-prices.jsp";
thirdTable = "/WEB-INF/results/weather.jsp";
} else if (...) { ... }
RequestDispatcher dispatcher =
request.getRequestDispatcher("/WEB-INF/results/header.jsp");
dispatcher.include(request, response);
di h
di
spatc
h
er =
request.getRequestDispatcher(firstTable);
dispatcher.include(request, response);
dispatcher =
t tR tDi t h (
dT bl
)
reques
t
.ge
tR
eques
tDi
spa
t
c
h
er
(
secon
dT
a
bl
e
)
;
dispatcher.include(request, response);
dispatcher =
request.getRequestDispatcher(thirdTable);
di t h i l d
( t )
di
spa
t
c
h
er.
i
nc
l
u
d
e
(
reques
t
, response
)
;
dispatcher =
request.getRequestDispatcher("/WEB-INF/results/footer.jsp");
dispatcher.include(request, response);
65
Using RequestDispatcher.include:
Setting Content
-
Type of Output
Setting

Content
Type

of

Output
// From Ajax example
public void
doGet
( ) {
p u b l i c

void

doGet
(
...
)
...
{
...
if ("xml".equals(format)) {
res
p
onse.setContentT
yp
e
(
"text/xml"
)
;
p yp
( )
outputPage = "/WEB-INF/results/cities-xml.jsp";
} else if ("json".equals(format)) {
response.setContentType("application/json");
outputPage = "/WEB-INF/results/cities-json.jsp";
} else {
response.setContentType("text/plain");
t tP
"/WEB
INF/lt/iti
t i j"
ou
t
pu
tP
age =
"/WEB
-
INF/
resu
lt
s
/
c
iti
es-s
t
r
i
ng.
j
sp
"
;
}
RequestDispatcher dispatcher =
request getRequestDispatcher
(
outputPage
);
request
.
getRequestDispatcher
(
outputPage
);
dispatcher.include(request, response);
}
66
cities-xml.jsp
<?xml version="1.0" encoding="UTF-8"?>
<cities>
<cities>
<city>
<name>${cities[0].name}</name>
<time>${cities[0]
shortTime
}</time>
<time>${cities[0]
.
shortTime
}</time>
<population>${cities[0].population}</population>
</city>
...
...
</cities>
• Notes
– Because I use .
j
sp (not .
j
spx) and classic JSP syntax, the
default content-type is text/html

I could use <%@page
contentType
="
text/xml
"
%> here
I

could

use

<%@

page

contentType
text/xml

%>

here
,
but it is more convenient to do it in calling servlet and
keep this page simple and focused on presentation
67
Summary
• Use MVC (Model 2) approach when:
O b i i ill l i h b i l k

O
ne su
b
m
i
ss
i
on w
ill
resu
l
t
i
n more t
h
an one
b
as
i
c
l
oo
k

– Several pages have substantial common processing
– Your a
pp
lication is moderatel
y
com
p
lex
pp y p
• Approach
– A servlet answers the original request
S l t
ll b i l i d
t lt i b

S
erv
l
e
t
ca
ll
s
b
us
i
ness
l
og
i
c an
d
s
t
ores resu
lt
s
i
n
b
eans
• Beans stored in HttpServletRequest, HttpSession, or
ServletContext
– Servlet invokes JSP page via RequestDispatcher.forward
– JSP page reads data from beans

Most modern servers:
${
beanName propertyName
}

Most

modern

servers:

${
beanName
.
propertyName
}
• JSP 1.2 servers: jsp:useBean with appropriate scope
(request, session, or application) plus jsp:getProperty
68
© 2010 Marty Hall
Questions?
Customized Java EE Training: http://courses.coreservlets.com/
Servlets, JSP, JSF 2.0, Struts, Ajax, GWT 2.0, Spring, Hibernate, SOAP & RESTful Web Services, Java 6.
Developed and taught by well-known author and developer. At public venues or onsite at your location.
69