JSP and web applications

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 EJB Container application EJB EJB Database Web Container
JMS JavaIDL RMI JNDI XML servlet servlet browser JSP JDBC JTA/JTS Client Tier Middle Tier EIS Tier

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 common/lib src conf
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 work webapps HTML documentation about Tomcat
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

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
<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 holds a single table Teams containing match data
football.jsp highly graphic interactive results page football.html Database handles the request, submits SQL and processes result FootballSearchBean represents football game data contained in a DB table FootballGame static page to request results helper class to create the DB connection DBInfo tomcat

football.html call JSP with a search parameter
<html><head><title>Football Search</title></head> <body bgcolor = “white”> <h1>Search the football league table</h1> <ul><li> <a href = “ List all games </a> </li><li> <a href = List drawn matches </a> </li></ul> </body></html> call JSP with a search parameter call JSP with a search parameter

FootballGame class to handle results of data query
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 handle DB queries to use Java Iterator class
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 queries to use Java Iterator class searchType query parameter from football.html ends up here set up SQL query strings

FootballSearchBean contains results from the DB query
private Vector results; public Iterator games () { if (results != null) return results.iterator (); else return null; } public int numGames () { return results.size (); return 0; contains results from the DB query for manipulating retrieved data counts the number of results

FootballSearchBean connect to the database
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 database create 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 add the FootballGame to the results Vector

football.jsp util package for the Iterator class
page import = “java.util.*” %> page import = “football.*” %> <html><head><title>League Results</title></head><body>  <h1>Results</h1> <jsp:useBean id = “theLeague” class = “football.FootballSearchBean” /> <jsp:setProperty name = “theLeague” property = “*”/> util package for the Iterator class football package with its classes searchType property from football.html passed to Bean here Bean created and given an Id

football.jsp <% theLeague.doSearch (); %> <% if (theLeague.numGames () == 0) { %> <p> No games played yet </p> <% } else { %>  <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 option determines the size of the result set and acts accordingly

football.jsp creates an Iterator containing FootballGame objects
<% 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 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
Match Report.jsp No Result.jsp football.html Database FootballSearchBean web.xml preprcessing servelet FootballGame hyperlinks now go to a pre-processing servelet DBInfo tomcat

web.xml <web-app> <servelet>
<servelet-name>FootballServelet</servelet-name> <servelet-class>PreprocessServelet</servelet-class> </servelet> <servelet-mapping> <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”; drawstr = “there have been no drawn games”; homestr = “there have been no home wins”; 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
 <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>

revised architecture much improved iterator code still exposed
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” /> ...  </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

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