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How to Write MVC
Webapps
Core Servlets & JSP book: www.coreservlets.com
More Servlets & JSP book: www.moreservlets.com
Servlet and JSP Training Courses: courses.coreservlets.com
1
Slides © Marty Hall, http://www.coreservlets.com, book © Sun Microsystems Press
Agenda
g
•
•
•
•
2
How to design a webapp using MVC
Development and Deployment Strategies
Understand how a webapp works
Learn how to write a webapp using MVC
Form Data
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The Design
g Phase
• Generate the User View
– Decide how it is to appear and what it does
– Write it (mostly) in HTML
– Decide what the overall response will be
• Design the Architecture: here MVC
– Label the components
p
appropriately
pp p
y
– Show interactions between components
3
Form Data
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WineApp
pp Architecture
Container
2
Servlet
3
1
4
5
Model
6
request
form.html
4
result.jsp
jp
1. Container retrieves form.html
4. Result into request
2. Container calls action
q
to JSP
5. Forward request
3. Servlet calls model
6. JSP obtains result from
request
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Form Data
Set up Development
Environment
• Make a root directory, call it, e.g. wine
• Make the following subdirectories
– etc: For your web.xml
– lib:
lib For
F thi
thirdd party
t JAR files
fil
– src: Remember packaging strategies! Also separate
model and controller code!
– classes: Ditto
– web: For your HTML’s and JSP’s
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Form Data
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Set up Deployment
Environment
• Make a new subdirectory under webapps,
h i
having
same name as your app, i.e.
i wine
– Put your HTML’s and JSP’s in here
– This is Tomcat
Tomcat’ss “context
context root
root” for resolving URL
URL’ss
• Mirror your development classes directory
structure,
st
uctu e, sepa
separating
at g controllers
co t o e s and
a d
models
– Note the extra subdirectory model for POJ
– Note the
h extra subdirectory
bdi
web for
f servlets
l
– Be sure to maintain your package structure
6
Form Data
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The Implementation
p
Phase
•
•
7
Start with the initial HTML Form page
Develope incrementally
1. Write the form.html
2 Do
2.
D th
the web.xml
b
l thing
thi
3. Test
4. Write the servlet action code
5. Compile & Test
6. Write the model in POJ (and modify the servlet)
7 Compile
7.
C
il & Test
T t
8. Modify the servlet to call the model
9. Co
Compile
p e & Test
est
10. Add on the JSP (and modify the servlet)
11. Compile & Test
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Form Data
Write the form.html
<html><body>
<h1 align="center">Wine
align= center >Wine Selection Page</h1>
<form method="POST"
action="SelectWine.do">
Select
Se
ect Wine
e C
Characteristics<p>
a acte st cs p
Color:
<select name="color" size="1">
<option value="red"> red </option>
<option value="white"> white </option>
<option value="rose"> </option>
</select>
<br><br>
<center>
<input type="SUBMIT">
</center>
</form></body></html><
8
Form Data
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Comments
• Note we are using POST
• The action routine is the servlet
WineSelect.do
– Note
N t the
th .do
d suffix.
ffi This
Thi is
i a convention
ti
• We are using the input type select to
choose one value from a scrolled list
• This is only one possibility, depending on
your app.
y
pp Your choice may
y be different
9
Form Data
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Write the web.xml
• You already know how
• Pay attention to the name in the action
routine
10
Form Data
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Test
• There is no action routine yet
• Just want to see if the initial HTML page is
correct and appears as desired
• Start
St t it from
f
your browser
b
• Will be demonstrated in class
11
Form Data
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Write the Action Servlet for
form html
form.html
package com.example.web;
import com
com.example.model.*;
example model *;
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.util.*;
import java.sql.*;
public class WineSelect extends HttpServlet{
public void doPost(HttpServletRequest request
request,
HttpServletResponse response)
throws IOException, ServletException{
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String c = request.getParameter("color");
out.println(”Wine Selection Advice<br>");
out.println("<br>Got
out.println(
<br>Got Wine color " + c);
}}
12
Form Data
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Compile
p and Test
• Remember to shutdown and startup Tomcat
each
h time
i
you run a webapp
b
• When “Submit” is clicked the output of the
servlet should be something like
Wine Selection Advice
Got wine color white
13
Form Data
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Write the Model
package com.example.model;
import java
java.util.
util *;
;
public class WineExpert{
public
pub
c List
st get
getLabels(String
abe s(St
g co
color){
o ){
List labels = new ArrayList();
if (color.equals("red")){
labels.add("Chateau Fight Club");
labels.add("Dracula Dark");}
else if (color.equals("white")){
labels.add("Gutter Delight");
labels.add("Pale Amoeba");}
else{
labels.add("Hemingway Knockout");
labels add("Vampire Lite")
labels.add("Vampire
Lite");}
}
return (labels);}}
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Form Data
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Remarks
• The model is just a Java program and
k
knows
nothing
hi
about
b
the
h app from
f
which
hi h it
i
will be called
• It communicates with the app by means of a
list of labels
• Of course the servlet will have to be
modified to make this call (next incremental
stage)
g )
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Form Data
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Modify the Servlet to Call the
Model
16
package com.example.web;
import com.example.model.*;
i
import
j
javax.servlet.*;
l
*
import javax.servlet.http.*;
import java.io.*;
import java.util.*;
i
import
t j
java.sql.*;
l *
public class WineSelect extends HttpServlet{
public void doPost(HttpServletRequest request,
HttpServletResponse response)
th
throws
IOE
IOException,
ti
S
ServletException{
l tE
ti {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String c = request.getParameter("color");
Wi E
WineExpert
t we = new WineExpert();
Wi E
t()
List result = we.getLabels(c);
out.println("Wine Selection Advice<br>");
Iteratot iter = result.iterator();
while
hil (it
(iter.hasNext()){
h N t()){
out.print("<br>try: " + iter.next());}
}}
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Form Data
Remarks
• Note the import statement for the model
• We cycled through the arrayList
generated by the model using an iterator
• The
Th list
li t became
b
available
il bl by
b the
th call
ll
mechanism
String c =request.getParameter(“color”);
List result = getLabels(c);
17
Form Data
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Compile
p and Test
• Nothing new, but oh so necessary
18
Form Data
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Add on a JSP for Output
p
<%@ page import="java.util.*" %>
<html>
ht l
<body>
<h1 align="center">Wine Recommendations JSP Style</h1>
<p>
<%
List styles = (List)request.getAttribute(
(List)request.getAttribute("styles");
styles );
Iterator it = styles.iterator();
while (it.hasNext()){
out.print("<br>try: " + it.next());
}
%>
</body>
</html>
19
Form Data
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And Modify the Servlet
Accordingly:
package com.example.web;
i
import
t com.example.model.*;
l
d l *
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.util.*;
import java.sql.*;
public class WineSelect extends HttpServlet{
public void doPost(HttpServletRequest request
request,
HttpServletResponse response)
throws IOException, ServletException{
String c = request.getParameter("color");
WineExpert we = new WineExpert();
List = we.getLabels(c);
request.setAttribute("styles", result);
RequestDispatcher view =
request.getRequestDispatcher("result.jsp");
view.forward(request, response);}}
20
Form Data
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Remarks
• Note the dispatching mechanism for
communication
i i between
b
the
h servlet
l and
d the
h
JSP
– Just copy this for now
– Note that you literally make available the Request and
Response objects to the JSP. These objects are now
within
i hi the
h JSP’s
JSP’ requestt scope.
– Note the getAttribute call in the JSP
21
Form Data
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Compile
p and Test
• You should see a JSP with something like:
Wine Recommendations JSP
Style
try: Chateau Fight Club
try: Dracula Dark
• If you do, open a bottle and celebrate!
22
Form Data
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Questions?
Core Servlets & JSP book: www.coreservlets.com
More Servlets & JSP book: www.moreservlets.com
Servlet and JSP Training Courses: courses.coreservlets.com
23
Slides © Marty Hall, http://www.coreservlets.com, book © Sun Microsystems Press
