geirm 01/05/17 06:00:05 Added: examples/event_example EventExample.java README.txt Log: Example which demonstrates some uses of the event handling features of Velocity. Revision Changes Path 1.1 jakarta-velocity/examples/event_example/EventExample.java Index: EventExample.java =================================================================== /* * The Apache Software License, Version 1.1 * * Copyright (c) 2001 The Apache Software Foundation. All rights * reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in * the documentation and/or other materials provided with the * distribution. * * 3. The end-user documentation included with the redistribution, if * any, must include the following acknowlegement: * "This product includes software developed by the * Apache Software Foundation (http://www.apache.org/)." * Alternately, this acknowlegement may appear in the software itself, * if and wherever such third-party acknowlegements normally appear. * * 4. The names "The Jakarta Project", "Velocity", and "Apache Software * Foundation" must not be used to endorse or promote products derived * from this software without prior written permission. For written * permission, please contact [EMAIL PROTECTED] * * 5. Products derived from this software may not be called "Apache" * nor may "Apache" appear in their names without prior written * permission of the Apache Group. * * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE * DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. * ==================================================================== * * This software consists of voluntary contributions made by many * individuals on behalf of the Apache Software Foundation. For more * information on the Apache Software Foundation, please see * <http://www.apache.org/>. */ import java.io.StringWriter; import java.util.Properties; import org.apache.velocity.app.Velocity; import org.apache.velocity.VelocityContext; import org.apache.velocity.exception.ParseErrorException; import org.apache.velocity.exception.MethodInvocationException; import org.apache.velocity.runtime.log.LogSystem; import org.apache.velocity.context.EventCartridge; import org.apache.velocity.context.ReferenceInsertionEventHandler; import org.apache.velocity.context.MethodExceptionEventHandler; import org.apache.velocity.context.NullSetEventHandler; import org.apache.velocity.context.Context; /** * This class is a simple demonstration of how the event handling * features of the Velocity Servlet Engine are used. It uses a * custom logger as well to check the log message stream * when testing the NullSetEventHandler * * @author <a href="mailto:[EMAIL PROTECTED]";>Geir Magnusson Jr.</a> * @version $Id: EventExample.java,v 1.1 2001/05/17 13:00:03 geirm Exp $ */ public class EventExample implements ReferenceInsertionEventHandler, NullSetEventHandler, MethodExceptionEventHandler, LogSystem { private boolean logOutput = false; private boolean exceptionSwitch = false; public static void main( String args[] ) { EventExample ee = new EventExample(); } public EventExample() { try { /* * this class implements the LogSystem interface, so we * can use it as a logger for Velocity */ Velocity.setProperty(Velocity.RUNTIME_LOG_LOGSYSTEM, this ); Velocity.init(); } catch(Exception e) { System.out.println("Problem initializing Velocity : " + e ); return; } /* * lets make a Context and add some data */ VelocityContext context = new VelocityContext(); context.put("name", "Velocity"); /* * Now make an event cartridge, register all the * event handlers (at once) and attach it to the * Context */ EventCartridge ec = new EventCartridge(); ec.addEventHandler(this); ec.attachToContext( context ); try { /* * lets test each type of event handler individually * using 'dynamic' templates * * First, the reference insertion handler */ System.out.println(""); System.out.println("Velocity Event Handling Demo"); System.out.println("============================"); System.out.println(""); String s = "The word 'Velocity' should be bounded by emoticons : $name."; StringWriter w = new StringWriter(); Velocity.evaluate( context, w, "mystring", s ); System.out.println("Reference Insertion Test : "); System.out.println(" " + w.toString()); System.out.println(""); /* * using the same handler, we can deal with * null references as well */ s = "There is no reference $floobie, $nullvalue or anything in the brackets : >$!silentnull<"; w = new StringWriter(); Velocity.evaluate( context, w, "mystring", s ); System.out.println("Reference Insertion Test with null references : "); System.out.println(" " + w.toString()); System.out.println(""); /* * now lets test setting a null value - this test * should result in *no* log output. * Turn on the logger output. */ logOutput = true; s = "#set($settest = $NotAReference)"; w = new StringWriter(); System.out.println("NullSetEventHandler test : " ); System.out.print(" There should be nothing between >"); Velocity.evaluate( context, w, "mystring", s ); System.out.println("< the brackets."); System.out.println(""); /* * now lets test setting a null value - this test * should result in log output. */ s = "#set($logthis = $NotAReference)"; w = new StringWriter(); System.out.println("NullSetEventHandler test : " ); System.out.print(" There should be a log message between >"); Velocity.evaluate( context, w, "mystring", s ); System.out.println("< the brackets."); System.out.println(""); logOutput = false; /* * finally, we test a method exception event - we do this * by putting this class in the context, and calling * a method that does nothing but throw an exception. * we use a little switch to turn the event handling * on and off * * Note also how the reference insertion process * happens as well */ exceptionSwitch = true; context.put("this", this ); s = " $this.throwException()"; w = new StringWriter(); System.out.println("MethodExceptionEventHandler test : " ); System.out.print(" This exception will be controlled and converted into a string : "); Velocity.evaluate( context, w, "mystring", s ); System.out.println(" " + w.toString()); System.out.println(""); /* * now, we turn the switch off, and we can see that the * exception will propgate all the way up here, and * wil be caught by the catch() block below */ exceptionSwitch = false; s = " $this.throwException()"; w = new StringWriter(); System.out.println("MethodExceptionEventHandler test : " ); System.out.println(" This exception will NOT be controlled. " + " The next thing you should see is the catch() output "); Velocity.evaluate( context, w, "mystring", s ); System.out.println("If you see this, it didn't work!"); } catch( ParseErrorException pee ) { /* * thrown if something is wrong with the * syntax of our template string */ System.out.println("ParseErrorException : " + pee ); } catch( MethodInvocationException mee ) { /* * thrown if a method of a reference * called by the template * throws an exception. That won't happen here * as we aren't calling any methods in this * example, but we have to catch them anyway */ System.out.println(" Catch Block : MethodInvocationException : " + mee ); } catch( Exception e ) { System.out.println("Exception : " + e ); } } /** * silly method to throw an exception to demonstrate * the method invocation exception event handling */ public void throwException() throws Exception { throw new Exception("Hello from throwException()"); } /** * Event handler for when a reference is inserted into the output stream. */ public Object referenceInsert( String reference, Object value ) { /* * if we have a value * lets decorate the reference with emoticons */ String s = null; if( value != null ) { s = " ;) " + value.toString() + " :-)"; } else { /* * we only want to deal with $floobie - anything * else we let go */ if ( reference.equals("floobie") ) { s = "<no floobie value>"; } } return s; } /** * Event handler for when the right hand side of * a #set() directive is null, which results in * a log message. This method gives the application * a chance to 'vote' on msg generation */ public boolean nullSetLogMessage( String reference ) { if (reference.equals("$settest")) return false; return true; } public Object methodException( Class claz, String method, Exception e ) throws Exception { /* * only do processing if the switch is on */ if( exceptionSwitch && method.equals("throwException")) { return "Hello from the methodException() event handler method."; } throw e; } /** * This is the key method needed to implement a logging interface * for Velocity. */ public void logVelocityMessage(int level, String message) { if (logOutput) { System.out.print("Velocity Log : level : " + level + " msg : " + message); } } } 1.1 jakarta-velocity/examples/event_example/README.txt Index: README.txt =================================================================== Welcome to Velocity! As always, the if you have any questions : 1) Make sure you followed any directions :) (did you build everything?) 2) Review documentation included in this package, or online at http://jakarta.apache.org/velocity/ 3) Ask on the velocity-user list. This is a great source of support information. To join, read http://jakarta.apache.org/site/mail.html and then follow the link at the bottom to join the lists. event_example ------------ This simple example demonstrates the event handling features of the Velocity Template Engine. Note that this is considered a more advanced topic - you don't need to know this to use 99% of the features of Velocity, so if this seems like too much at first - ignore it! This is a standalone program. It is compiled by the 'examples' build target. To run, and assuming you have the Velocity jar in your CLASSPATH, simply do : java EventExample if it's not in your classpath, do : java -cp ../../bin/velocity-1.1.jar:. EventExample (make sure that the jarname is correct - this document might get out of synch with the release version number.)
