Java E-Commerce Martin Cooke,

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1 Java E-Commerce Martin Cooke, Plan The web tier: servlets life cycle Session-management TOMCAT & ANT Applet- communication The servlet life-cycle Notes based largely on Hunter & Crawford (2001) 13/02/2004 Java E-Commerce Martin Cooke, life cycle: creation life cycle: handle request life cycle: handle request Init() called lookup initialisation parameters open shared re - base connections - price lists, 13/02/2004 Java E-Commerce Martin Cooke, doget() or dopost() called 13/02/2004 Java E-Commerce Martin Cooke, doget() or dopost() called 13/02/2004 Java E-Commerce Martin Cooke,

2 Java E-Commerce Martin Cooke, concurrent requests life cycle: shutdown Concurrency: a counter public class Counter extends Http { Each request handled in separate thread destroy() called free up valuable connections save state? public void doget(httprequest req, HttpResponse res) throws Exception, IOException { out.println( Accessed +count+ 13/02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke, Concurrency: a counter Option 1: synchronise entire method Option 2: synchronise refs to count public class Counter extends Http { public void doget(httprequest req, HttpResponse res) throws Exception, IOException { out.println( Accessed +count+ Information stored in variables has potential for corruption: // thread 1 // thread 2 out.println. // thread 1 out.println. // thread 2 13/02/2004 Java E-Commerce Martin Cooke, public class Counter extends Http { public synchronised void doget (HttpRequest req, HttpResponse res) throws Exception, IOException { out.println( Accessed +count+ Safe but slow: one-at-a-time method invocation 13/02/2004 Java E-Commerce Martin Cooke, public class Counter extends Http { public synchronised void doget Faster: servlet can (HttpRequest req, execute multiple HttpResponse res) dogets; throws Exception, IOException { Thread obtains a lock on synchronized(this) { synchronised out.println println( Accessed +count+ code, waiting if another thread has it 13/02/2004 Java E-Commerce Martin Cooke,

3 Java E-Commerce Martin Cooke, Option 3: use local variable Option 4: live with it! A persistent counter public class Counter extends Http { public synchronised void doget (HttpRequest req, HttpResponse res) throws Exception, IOException { Faster still: only one line to be locked public class Counter extends Http { public synchronised void doget (HttpRequest req, HttpResponse res) throws Exception, IOException { Does it really matter? public void init(config config) throws Exception { super.init(config); try { // load the initial count from saved state catch { // various possible exceptions int local_count; synchronized(this) { local_count = ++count; out.println println( Accessed +count+ 13/02/2004 Java E-Commerce Martin Cooke, out.println println( Accessed +count+ 13/02/2004 Java E-Commerce Martin Cooke, public void destroy() { try { // save state etc 13/02/2004 Java E-Commerce Martin Cooke, SingleThreadModel: instead of this SingleThreadModel Each request handled in separate thread Each request handled in separate servlet Better to create pool of needed re and synchronize code sections + Thread-safe: no need to synchronise access to variables - Consumes more re - Doesn t guarantee thread-safety for access to re outside servlet (though JDBC Connections are thread-safe) Session management Overcoming a stateless protocol 13/02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke,

4 Java E-Commerce Martin Cooke, Traditional ways to track requests method what s involved pros cons User Tell to protect a authorisation set of pages, then call getremoteuser() for each request Hidden form fields URL rewriting Persistent cookies <INPUT TYPE=hidden NAME= martin VALUE= cooke > Simple & robust Works even if user exits and restarts Anonymous (can just send an ID) /My?sessionid=123 Works for all dynamic /My/123 docs Send info to for later re-reading Easy & supported in API Requires user registration Works only for forms Involves programming Tedious to program Parameter name clashes Browser ie user may not accept them; cookie attached to, not user Java Session Tracking API Avoids the need to implement session-tracking ourselves Uses one of the techniques listed (usually cookies, but we don t have to know which, though we can find out) Simple and elegant Sessions A session is a continuous connection from the same over a period of time Expires after a set time of inactivity (30 mins is usual) OR when manually invalidated by servlet 13/02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke, Session example public void doget( ){ res.setcontenttype("text/html"); HttpSession session = req.getsession(true); Integer count = (Integer) session.getvalue( counter ); if (count == null) count = new Integer(1); else count = new Integer(count.intValue()+1); session.putvalue( counter,count); out.println("<html><body>"); out.println( you ve visited + count+ times ); out.println("</body></html>"); 13/02/2004 Java E-Commerce Martin Cooke, Session example public void doget( ){ res.setcontenttype("text/html"); HttpSession session = req.getsession(true); Integer count = (Integer) session.getvalue( counter ); if (count == null) count = new Integer(1); else count = new Integer(count.intValue()+1); session.putvalue( counter,count); out.println("<html><body>"); out.println( you ve visited + count+ times ); out.println("</body></html>"); getsession(true) Returns a new session if one doesn t exist 13/02/2004 Java E-Commerce Martin Cooke, Session example public void doget( ){ res.setcontenttype("text/html"); HttpSession session = req.getsession(true); Integer count = (Integer) session.getvalue( counter ); if (count == null) count = new Integer(1); else count = new Integer(count.intValue()+1); session.putvalue( counter,count); out.println("<html><body>"); out.println( you ve visited + count+ times ); out.println("</body></html>"); Can store any nonprimitive object in the session 13/02/2004 Java E-Commerce Martin Cooke,

5 Java E-Commerce Martin Cooke, Session example Session binding events public void doget( ){ res.setcontenttype("text/html"); HttpSession session = req.getsession(true); Integer count = (Integer) session.getvalue( counter ); if (count == null) count = new Integer(1); else count = new Integer(count.intValue()+1); session.putvalue( counter,count); out.println("<html><body>"); out.println( you ve visited + count+ times ); out.println("</body></html>"); Other useful methods: getvaluenames() returns String[] invalidate() removes session and all objects contained getcreationtime() getlastaccessedtime() 13/02/2004 Java E-Commerce Martin Cooke, Provides a mechanism to allow servlets to listen for the creation and destruction (binding and unbinding) of sessions Useful for e.g. allocating and closing base connections Need class which implements HttpSessionBindingListener interface, with methods: public void valuebound(httpsessionbindingevent event) public void valueunbound(httpsessionbindingevent event) 13/02/2004 Java E-Commerce Martin Cooke, How-to Tomcat & Ant Tomcat Installation & running app configuration (web.xml) Tomcat is a free servlet (and JSP) container Sun s reference implementation, developed by Apache Versions for Win, Linux, etc Obtain from jakarta.apache.org/tomcat Easy to install Available in the dept: see Dept web guide Some alternatives (eg Jetty - small footprint) 13/02/2004 Java E-Commerce Martin Cooke, Extract Ensure JAVA_HOME points to directory where JDK is installed Ensure CATALINA_HOME points to directory where Tomcat was extracted Execute the startup file in bin\startup.bat (or startup.sh) Check Ensure you have nothing else listening on port If you do, change the Tomcat port in conf\.xml 13/02/2004 Java E-Commerce Martin Cooke, <servlet> <servlet-name>controller</servlet-name> <servlet-class>shef.wtt.controller</servlet-class> <init-param> <param-name>dbdriver</param-name> <param-value>org.gjt.mm.mysql.driver</param-value> </init-param> </servlet> <servlet-mapping> <servlet-name>controller</servlet-name> <url-pattern>/controller</url-pattern> </servlet-mapping> <session-config> <session-timeout>120</session-timeout> </session-config> 13/02/2004 Java E-Commerce Martin Cooke,

6 Java E-Commerce Martin Cooke, Using Tomcat Ant Example build.xml Lots of beginners pitfalls! Leave time to sort them out classpath issues visibility issues application organisation Check log files Use logging Typical (smallish) webapp has 100 s of files Screen definitions Event handlers Static pages Ant is a Java-based build tool cf UNIX make Uses XML Will save you hours! <!-- ============ Compile Target ================== --> <target name="compile" depends="prepare,xmlc" description="compile Java "> <!-- Compile Java classes as necessary --> <javac srcdir="src" destdir="${build.home/web-inf/classes" debug="${compile.debug" deprecation="${compile.deprecation" optimize="${compile.optimize"> <classpath refid="compile.classpath"/> </javac> </target> 13/02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke, homework Install Tomcat 4 Install Ant Develop your first servlet using both Applet-servlet communication Applets are sometimes useful (if time) 13/02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke,

7 Java E-Commerce Martin Cooke, The applet problem A solution How-to: send from applet Persistent storage Applet can only talk to its host. But what if the base is located elsewhere? Persistent storage Use one of many techniques for appletservlet communication - simplest is HTTP URLConnection con = con.setdoinput(true); con.setdooutput(true); // further incantations ObjectOutputStream oos = new ObjectOutputStream( con.getoutputstream()); oos.writeobject(obj); out.flush(); out.close(); 13/02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke, How-to: receiving at the servlet Filters ObjectInputStream ois = new ObjectInputStream (req.getinputstream()); Object obj = ois.readobject(); Filters A filter is an object that can transform a request or modify a response Not servlets: don t actually create a response Pre- or post-processors of servlets Can be configured to act on a servlet or a group of servlets Zero or more filters can filter one or more servlets 13/02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke,

8 Java E-Commerce Martin Cooke, Some applications Example filter: logging General model Record duration of all requests Track user requests and request sequences (AKA clickstreams) Compress the response Authentication Logging/auditing Image conversion Encryption XSLT transforming XML public class LogFilter implements Filter { public void dofilter(request req, Response res, FilterChain chain) { Context context = getfilterconfig().getcontext(); long bef = System.currentTimeMillis(); chain.dofilter(req,res); long aft = System.currentTimeMillis(); context.log( Request: +req.getrequesturi()+ : +(aft-bef)); public void dofilter(request req, Response res, FilterChain chain) { // do something with req // e.g. check headers to see if gzip accepted chain.dofilter(req,res); // do something with res // e.g. compress 13/02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke, Sending things other than HTML Serving WAP devices Encode application using WML Set content type to text/vnd.wap.wml or add line like this to web.xml: <mime-mapping> <extension>wml</extension> <mime-type>text/vnd.wap.wml</mime-type> </mime-mapping> Test using a simulator 13/02/2004 Java E-Commerce Martin Cooke, Sending images set content type to image/gif or image/jpeg, send image on OutputStream: OutputStream out = res.getoutputstream(); can generate image dynamically: Create Image object (eg use Java2D or AWT or ) GifEncoder encoder = new GifEncoder(image,out); encoder.encode(); Can use free GIF encoder from import Acme.JPM.Encoders.GifEncoder; often worth compressing: res.setheader( Content-Encoding, gzip ); Use ZipOutputStream from java.util.zip 13/02/2004 Java E-Commerce Martin Cooke,