JSP and Servelets
How does JSP work? NOT a Java scripting language NOT like php JSP are NOT parsed on request Java code must involve classes, creation of objects, etc… JSP is a designer-friendly way of writing servlets
Clock example
2 clock.jsp read 1 translation client 3 4 6 request processing 5 GET clock.jsp 1 Server with Tomcat Web Container client Servelet clock.java generate 3 http response 6 clock.class compile and deploy 4 execute 5 request processing
public class clock implements Servlet { public void service (ServletRequest r, ServletResponse s) throws ServletException, IOException { s.setContentType (“text/html”); PrintWriter out = s.getWriter (); out.println (“<HTML>”); out.println (“<HEAD>”); out.println (“<TITLE>JSP… </TITLE>”); out.println (“</HEAD>”); out.println (“<BODY>”);
out.println (“<H1>Date and Time</H1>”); (new java.util.Date.toString()); out.println (“</BODY>”); out.println (“</HTML>”); }
JSP directive elements applied when the JSP is compiled into a servelet Only executed once (on compilation) Do not affect the response Used to set up resources such as Java classes inclusions
JSP directive elements specify page information (static) <%@ page … > scripting language, error page <%@ include … > includes a file, e.g. an applet <%@ taglib … > declare a tag library (custom actions)
JSP and http
JSP and http A JSP is a servelet Permanently resident in server memory Multi-threaded Request and response objects Sessions and cookies
Accessing request information Methods of the request object provide all request information object is called “request” public String getParameter (String name) public String getMethod () public String getHeader (String name) public Cookie [] getCookies ()
javax.servelet.http.Cookie class getName () the name of the cookie getValue(), setValue (String value) gets/sets the value of a cookie getDomain(), setDomain(String dName) get/set the cookie domain name getPath(), String setPath(String path) get/set the request path the cookie is associated with getMaxAge(), setMaxAge (int expiry) get/set maximum age for the cookie
javax.servelet.http.HttpSession provides standard functionality for handling sessions handles cookies as standard but must be extended to handle URL rewriting holds client state info resident in memory automatically times out abandoned sessions created/returned by HttpServeletRequest class getSession method
JSP and Java Beans
Java Beans ordinary Java classes with the following properties: introspection customization events properties persistence
Java Beans introspection properties persistence an analyser can inspect how the Bean works properties naming conventions for getter and setter methods persistence implement the Serializable interface Bean state can be stored
Example Java bean public class ExampleBean implements java.io.Serializable { private String name = null; private int score = 0; public ExampleBean() {} // Empty constructor /* Getter and Setter Methods */ public String getName() { return name; } public void setName(String s) { name = s;
Example Java bean public int getScore() { return score; } public void setScore(int i) { score = i; /* No method required to implement Serializable */
JSP action elements action elements <jsp:useBean> perform an action when page is requested <jsp:useBean> uses a JavaBean component <jsp:getProperty> property from JavaBean used in the page <jsp:setProperty> sets a JavaBean property (possibly using request information)
</jsp:useBean> id="userInfo" class="com.ora.jsp.beans.userInfo.UserInfoBean“ > <jsp:setProperty name = “userInfo” property = “userName” value = “Gandalf” /> </jsp:useBean>
The following information was saved: <ul> <li>User Name: <jsp:getProperty name="userInfo" property="userName"/></li> <li>Email Address: property="emailAddr"/></li> </ul></body></html>
Other JSP action elements <jsp:include> responses from other jsp pages or servelets <jsp:forward> forwards processing to other jsp or servelet <jsp:param> passes a parameter with include or forward <jsp:plugin> generates the HTML to embed an applet
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
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 <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 = “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 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> <!-- 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 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 { %> <!-- 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 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 <!-- 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 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” /> ... <!-- HTML and JSP actions to write other cells --> </logic:iterate>
Timetable change From w/c 23/11/09 No Monday Lecture Two lectures moved into one slot: Wednesday 11-1 B39 Labs will still be Thursday, 9-11