public EventExample()

in velocity-engine-examples/src/main/java/org/apache/velocity/example/EventExample.java [59:230]

• 82 lines of code
• 5 McCabe index (conditional complexity)

    public EventExample()
    {
        try
        {
            /*
             *  this class implements the Logger interface, so we
             *  can use it as a logger for Velocity
             */

            Velocity.setProperty(Velocity.RUNTIME_LOG_INSTANCE, 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("invalidSetMethod 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("invalidSetMethod 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 );
        }
    }