jsp and web applications. java 2 enterprise edition j2ee edition of java architecture specially...
Post on 28-Mar-2015
216 Views
Preview:
TRANSCRIPT
JSP and web applications
Java 2 Enterprise Edition
• J2EE• Edition of Java• Architecture specially designed for server-
based applications– Including web applications
• Highly compatible with M-V-C• Client Tier• Middle Tier• Enterprise Information System Tier
J2EE Overview
Database
servlet
servlet
JSP
EJB
EJB
application
browser
Client Tier Middle Tier EIS Tier
EJB Container
Web Container JMSJavaIDL
RMIJNDIXML
JDBCJTA/JTS
Which J2EE components?
• Pure JSP– Simple applications– Prototyping– Use M-V-C
• Business logic pages (model)• presentation pages (view)• Request processing pages (controller)
– Enhance with JavaBeans components and custom tags
Tomcat web container
Tomcat subdirectories:• bin
– scripts to run Tomcat
• common/lib– jar archives with javax.servlet class files
• src– interface definitions for javax.servlet classes
• conf– configuration files (Tomcat parameters)
Tomcat web container
• docs– HTML documentation about Tomcat
• work– a working directory for temporary files and
generated servlets
• webapps– all web applications run on Tomcat are placed
in subdirectories of this
deploying a web application
• create a subdirectory of webapps, e.g. myDir
• create a WEB-INF subdirectory of myDir
• WEB-INF contains– web.xml file
• specifies deployment parameters for the web application
– lib directory (optional)• contains any special class libraries (.jar files) needed
– .classes directory• class files for servlet and helper classes defined for the
specific application
the web.xml file
• written in XML and contains environment data– descriptions of servlet names and locations– custom tag libraries– security constraints on particular servlets– multiple url aliases for servlets– etc
Creating a web app in NetBeans
Creating a web app in NetBeans
Creating a web app in NetBeans
Creating a web app in NetBeans
Creating a web app in NetBeans
Creating a web app in NetBeans
Creating a web app in NetBeans
Adding a JSP to the Web App
Adding a JSP to the Web App
Adding a JSP to the Web App
Adding a JSP to the Web App
Running the Web App
Browsing the JSP
Adding custom tags to a JSP
custom tags
• used to farm out processing to specialised classes or Beans
• identified by a tag library directive
• basic JSP tag library– e.g. <jsp:useBean … />
• Apache Taglib custom tag library
• JavaServerFaces, struts libraries
• can define your own custom tags
custom tags
• defined as Java classes that extend base classes in javax.servlet.jsp.tagext package
• represented in a JSP using the syntax– <lib:tag att1=“...” att1=“...” att1=“...” />– (can also have element content)
• custom tag in JSP replaced by code in the servelet on translation
custom tag example
package myPack;
import java.util.*;
import java.io.*;
import javax.servelet.jsp.*;
import javax.servelet.jsp.tagext .*;
public class DateStamper extends TagSupport {
protected String comment = null;
public String getComment () {
return comment;
}
public void setComment (String cm) {
comment = cm;
}
public int doEndTag () {
try {
String dateStr = (new Date()).toString ();
pageContext.getOut ().println (
“<hr>This page entitled, “ + comment
+ “, was printed on “ +
dateStr +
“<br>”);
}
catch (Exception e) {//error handling}
return EVAL_PAGE;
}}
<taglib>
<tlibversion>1.0 </tlibversion>
<jspversion>1.1 </jspversion>
<shortname>myTags</shortname>
<tag>
<name>DateStamper</name>
<tagclass>myPack.DateStamper</tagclass>
<bodycontent>empty</bodycontent>
<attribute>
<name>comment</name>
<required>true</required>
</attribute>
</tag>
</taglib>
tag library definition file,
myTags.tld
deployment in a web application
<web-app>
<taglib>
<taglib-uri>
/myTags
</taglib-uri>
<taglib-location>
/WEB-INF/tlds/myTags.tld
</taglib-location
</taglib>
</web-app>
Tag libraries
using the tag in a JSP
<%@ taglib uri=“/myTagLibrary” prefix = “myTags” %>
<html><head><title>Using a custom tag</title></head>
<body bgcolor = “FFFFFF”>
<h1>Using a custom tag</h1>
<p>Hello World. My custom tag has the following to say:
<myTags:DateStamper comment=“This is a custom tag” />
</body></html>
JSP, Bean and Servelet example
description
• football league result web application
• users request match results– different requests possible– database search
• html front end– user interaction through web-browser
• servelet/JSP request handling and data processing
system architecture
football.html
football.jsp
FootballSearchBean
FootballGame
DBInfo
Database
tomcat
static page to request results
highly graphic interactive results page
handles the request, submits SQL and processes resultrepresents football game data contained in a DB tablehelper class to create the DB connection
holds a single table Teams containing match data
football.html
<html><head><title>Football Search</title></head>
<body bgcolor = “white”>
<h1>Search the football league table</h1>
<ul><li>
<a href = “http://localhost:8080/jspeg/football.jsp?searchType=all”>
List all games </a>
</li><li>
<a href = http://localhost:8080/jspeg/football.jsp?searchType=drawn>
List drawn matches </a>
</li></ul>
</body></html>
call JSP with a search parameter
call JSP with a search parameter
FootballGame class
package football;
import java.sql;
public class FootballGame {
private String team1,team2
private int score1, score2;
public String getTeam1 () {return team1;}
// similar methods to get team2, score1, score2
public void loadFromResultSet (ResultSet r) throws SQLException {
team1 = r.getString (“TEAM1”); // ditto for team2
score1 = r.getInt (“SCORE1”); // ditto for score2
}
}
to handle results of data query
loads DB query result into the FootballGame object
FootballSearchBean
package football;
import java.sql;
import java.util;
public class FootballSearchbean {
private static final allstr = “select * from TEAMS”;
private static final drawstr =
“select * from TEAMS where SCORE1=SCORE2”;
private String searchType;
public void setSearchType (String type) {
searchType = type;
}
handle DB queriesto use Java Iterator class
set up SQL query strings
searchType query parameter from football.html ends up here
private Vector results;
public Iterator games () {
if (results != null)
return results.iterator ();
else
return null;
}
public int numGames () {
if (results != null)
return results.size ();
else
return 0;
}
contains results from the DB query
for manipulating retrieved data
FootballSearchBean
counts the number of results
public void doSearch () {
results = new Vector ();
try {
Connection db = DBInfo.connectToDatabase ();
Statement stmt = db.createStatement ();
String request = allstr;
if (“drawn”.equals (searchType))
request = drawstr;
// else add code for other search options
connect to the databasecreate a Statement object (SQL
query) to be fired at the DB
FootballSearchBean
ResultSet r = stmt.executeQuery (request);
while (r.next ()) {
FootballGame fg = new FootballGame ();
fg.loadFromResultSet r;
results.addElement (fg);
}
r.close ();
stmt.close ();
db.close ();
} catch (Exception e) {// error-handling code here}
}
}
fire the query at the DB and store the retrieved rows
create a FootballGame object for each retrieved table row
FootballSearchBean
add the FootballGame to the results Vector
<%@ page import = “java.util.*” %>
<%@ page import = “football.*” %>
<html><head><title>League Results</title></head><body>
<!-- cool and flashy DHTML content inserted here by the web designer. Embedded amongst that will be: -->
<h1>Results</h1>
<jsp:useBean
id = “theLeague”
class = “football.FootballSearchBean” />
<jsp:setProperty
name = “theLeague”
property = “*”/>
util package for the Iterator classfootball package with its classes
football.jsp
Bean created and given an Id
searchType property from football.html passed to Bean here
<% theLeague.doSearch (); %>
<% if (theLeague.numGames () == 0) { %>
<p> No games played yet </p>
<% } else { %>
<!-- there are results so set up a table -->
<table> <caption>Results</caption>
<tr>
<th align = “center”>Home Team</th>
<th align = “center”>Home Team Score</th>
<th align = “center”>Away Team</th>
<th align = “center”>Away Team Score</th>
</tr>
searches the database with the user selected search optiondetermines the size of the result
set and acts accordingly
football.jsp
<% Iterator it = theLeague.games ();
while (it.hasNext ()) {
FootballGame fg = (FootballGame) it.next (); %>
<tr>
<td><%= fg.getTeam1 () %> </td>
<td><%= fg.getScore1 () %> </td>
<td><%= fg.getTeam2 () %> </td>
<td><%= fg.getScore2 () %> </td>
</tr>
<% } %>
</table>
<% } %>
</body></html>
creates an Iterator containing FootballGame objects
explicit typecast of each object to access the get methods
football.jsp
use expressions to insert names and scores for each game in table
cells
some design issues
• Java code in the JSP fragmented through the HTML
• difficult to trace errors– brackets– parameter declarations– incorrect program logic
• web designer could unwittingly break the code
revised system architecture
football.html
MatchReport.jsp
FootballSearchBean
FootballGame
DBInfo
Database
tomcat
hyperlinks now go to a pre-processing servelet p
reprcessing servelet
No Result.jsp
web.xml
web.xml
<web-app>
<servelet>
<servelet-name>FootballServelet</servelet-name>
<servelet-class>PreprocessServelet</servelet-class>
</servelet>
<servelet-mapping>
<servelet-name>FootballServelet</servelet-name>
<url-pattern>/FootballInfo</url-pattern>
</servelet-mapping>
</web-app>
PreprocessServelet// import all the usual servelet stuff
import football.*;
public class preprocessServelet extends HttpServelet {
private static final String
allstr = “no results available yet”;
private static final String
drawstr = “there have been no drawn games”;
private static final String
homestr = “there have been no home wins”;
private static final String
awaystr = “there have been no away wins”;
private static final String jspFailPage = “NoResult.jsp”;
private static final String jspReportPage = “MatchReport.jsp”;
PreprocessServelet
public void doGet () {HttpServeletRequest req, HttpServeletresponse res) throws ServeletException, IOException {
String search = req.getParameter (“searchType”);
FootballSearchBean fsb = new FootballSearchBean ();
fsb.setSearchType (search);
fsb.doSearch ();
if (fsb.numGames () == 0) {
doSearchFail (search, req, res);
else
doSuccess (fsb, req, res);
}
PreprocessServelet
private void doSearchFail (String search, HttpServeletRequest req, HttpServeletresponse res) throws ServeletException, IOException {
String reason = allstr;
if (“drawn”.equals (search))
reason = drawstr;
// add similar clauses for other possible reasons
req.setAttribute (“Message”, reason);
RequestDispatcher d =
req.getRequestDispatcher (jspFailPage);
d.forward (req, res);
}
PreprocessServelet
private void doSuccess (FootballSearchBean fsb, HttpServeletRequest req, HttpServeletresponse res) throws ServeletException, IOException {
req.setAttribute (“theLeague”, fsb);
RequestDispatcher d =
req.getRequestDispatcher (jspReportPage);
d.forward (req, res);
}
// end of PreprocessServelet
}
revised JSP pages// NoResult.jsp
<!-- contains the following minimal content -->
<jsp:useBean scope=“request” id=“Message” class=“String”>
<%= Message %>
**********************************************************
//MatchReport.jsp
<jsp:useBean scope=“request” id=“theLeague” class=“football.FootballSearchBean”>
...
<% Iterator it = theLeague.games ();
while (it.hasNext ()) {
FootballGame fg = (FootballGame) it.next (); %>
<tr><td><%= fg.getTeam1 () %> </td> <!-- etc. -->
revised architecture• much improved
– separation of most of the code from the web designer
• iterator code still exposed– replace by custom tags from Apache Struts
library
<logic:iterate id=“fg” collection=“<%= theLeague.games() >” >
<td><bean:write name = “fg” property = “team1” />
... <!-- HTML and JSP actions to write other cells -->
</logic:iterate>
Timetable change
• From next week:
• Two lectures moved into one slot:– Wednesday 11-1– B39– (lab with GE being moved)
• Labs will still be Thursday, 9-11
top related