Event Handler: Exceptions

import java.io.StringWriter;
import java.io.Writer;

import org.apache.velocity.Template;
import org.apache.velocity.VelocityContext;
import org.apache.velocity.app.Velocity;
import org.apache.velocity.app.event.EventCartridge;
import org.apache.velocity.app.event.MethodExceptionEventHandler;
import org.apache.velocity.app.event.NullSetEventHandler;
import org.apache.velocity.app.event.ReferenceInsertionEventHandler;
import org.apache.velocity.context.Context;

public class EventHandler implements ReferenceInsertionEventHandler,
    NullSetEventHandler, MethodExceptionEventHandler {

  public EventHandler(Context ctx) {
    EventCartridge ec = new EventCartridge();
    ec.addEventHandler(this);
    ec.attachToContext(ctx);
  }

  public Object referenceInsert(String reference, Object data) {
    System.out.println("referenceInsert: " + reference + " data: " + data);

    return data;
  }

  public boolean shouldLogOnNullSet(String lhs, String rhs) {
    System.out.println("shouldLogOnNullSet");
    System.out.println("lhs:" + lhs + " rhs:" + rhs);

      return true;
  }

  public Object methodException(Class cls, String method, Exception e)
      throws Exception {
    return "An " + e.getClass().getName() + " was thrown by the " + method
        + " method of the " + cls.getName() + " class [" + e.getMessage() + "]";
  }

  public static void main(String[] args) throws Exception {
    Velocity.init();

    Template t = Velocity.getTemplate("./src/eventHandler.vm");

    Context ctx = new VelocityContext();
    ctx.put("person", "Joe");
    ctx.put("exception", new ExceptionGenerator());

    EventHandler hdl = new EventHandler(ctx);

    Writer writer = new StringWriter();
    t.merge(ctx, writer);

    System.out.println(writer);
  }

}


import java.util.Random;

public class ExceptionGenerator {

  public String generate() throws Exception {
    Random rnd = new Random();

    int x = rnd.nextInt(5);

    if (x == 2) {
      throw new Exception("Unlucky!");
    } else {
      return "No Exception";
    }
  }
}
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#set($myNull1 = $validNull)
#set($myNull2 = $invalidNull)

This is $person 

$exception.generate()
$exception.generate()
$exception.generate()
$exception.generate()

velocity-Processing-Exception-Handling.zip( 2,195 k)

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