Re: Inconsistent and strange NPE when initializing Velocity

We're noticing something now that may or may not be related to our change
to only use a single instance of the Velocity Engine.

Macros that we define in one template seem to be sticking around and being
used when we go to merge or evaluate a different template.

Is this possible related and to be expected when using a single instance of
the VelocityEngine?

On Thu, Jun 7, 2012 at 5:28 PM, Bradley Wagner <
[email protected]> wrote:

> Thanks Will. We'll make sure to just initialize it once.
>
>
> On Thu, Jun 7, 2012 at 3:36 PM, Will Glass-Husain <[email protected]>wrote:
>
>> Hi,
>>
>> You should use either the Velocity static calls or the VelocityEngine but
>> not both-- it's confusing.  They don't technically interfere with each
>> other, but it'll be simpler and less error prone not to mix.
>>
>> It's also a performance hit to continually reinitialize Velocity.  There's
>> no need to do this every time you process a page.  Besides the cost of
>> initialization, it also prevents you from doing any caching.
>>
>> Here's the general pattern
>> * On app start up, initialize a VelocityEngine.  Store it somewhere.
>> * Every time you need to process a template
>>     --> get the template
>>     --> create and populate a context
>>     --> using the velocity engine, merge the template (with the context)
>>
>> WILL
>>
>>
>> On Thu, Jun 7, 2012 at 8:26 AM, Bradley Wagner <
>> [email protected]> wrote:
>>
>> > Thanks Will.
>> >
>> > So looking over the developer documentation about initialization and our
>> > code, it looks like we're using a mix of the Singleton Velocity Engine
>> and
>> > Separate Instances in certain cases. However, in all these cases, we're
>> > using the same set of properties. The documentation suggests that the
>> > Separate Instance method is the newer way to do it, but you're saying
>> that
>> > if we can get away with initializing Velocity one using Velocity.init()
>> we
>> > should do that for better performance, yes? Are both mechanisms for
>> > evaluating templates thread-safe?
>> >
>> > In one place we're doing:
>> >
>> > VelocityContext context = new VelocityContext(contextMap)
>> > Properties props = VelocityProperties.getProperties();
>> > Velocity.init(props);
>> > String templatePath = VelocityTemplates.getTemplatePath(templateName);
>> > Template template = Velocity.getTemplate(templatePath);
>> > StringWriter writer = new StringWriter();
>> > template.merge(context, writer);
>> > return writer.toString();
>> >
>> > and in another we're doing:
>> >
>> > VelocityEngine engine = new VelocityEngine();
>> > Properties velocityProps = VelocityProperties.getProperties();
>> > engine.init(velocityProps);
>> >
>> > // Get a template as stream.
>> > StringWriter writer = new StringWriter();
>> > StringReader reader = new StringReader(template);
>> > // create a temporary template name
>> > String tempTemplateName = "velocityTransform-" +
>> > System.currentTimeMillis();
>> >
>> > // ask Velocity to evaluate it.
>> > boolean result = engine.evaluate(context, writer, tempTemplateName,
>> > reader);
>> >
>> > String strResult = null;
>> > if (result)
>> > {
>> >    strResult = writer.getBuffer().toString();
>> > }
>> > return strResult;
>> >
>> > Thanks a bunch for your help!
>> >
>> > On Wed, Jun 6, 2012 at 6:34 PM, Will Glass-Husain <
>> [email protected]>
>> > wrote:
>> > >
>> > > You only need to initialize Velocity once.  Performance is much better
>> > that
>> > > way.
>> > >
>> > > WILL
>> > >
>> > > On Wed, Jun 6, 2012 at 2:37 PM, Bradley Wagner <
>> > > [email protected]> wrote:
>> > >
>> > > > The odd part about that is that while I could see this being a race
>> > > > condition... once Velocity gets into this state it doesn't matter
>> how
>> > many
>> > > > times we call Velocity.init, it returns the NPE every time. I guess
>> I
>> > > > should have mentioned that in the original post. Basically once it
>> > starts
>> > > > returning NPE our only recourse is to restart Tomcat, which fixes
>> the
>> > > > problem, until  it pops up again.
>> > > >
>> > > > On Wed, Jun 6, 2012 at 5:35 PM, Bradley Wagner <
>> > > > [email protected]> wrote:
>> > > >
>> > > > > Ha, that's a good question. Yes, we're initializing Velocity LOTS
>> of
>> > > > > times. Basically every time we use it to create these messages in
>> our
>> > > > > message util. I'm guessing that's not recommended?
>> > > > >
>> > > > >
>> > > > > On Wed, Jun 6, 2012 at 1:53 PM, Will Glass-Husain <
>> > > > [email protected]>wrote:
>> > > > >
>> > > > >> Hi Bradley,
>> > > > >>
>> > > > >> Are you initializing Velocity multiple times?
>> > > > >>
>> > > > >> Though I haven't heard of this issue before, it sounds like a
>> race
>> > > > >> condition, perhaps if the initialization is called twice at the
>> same
>> > > > time.
>> > > > >>
>> > > > >> WILL
>> > > > >>
>> > > > >> On Wed, Jun 6, 2012 at 8:37 AM, Bradley Wagner <
>> > > > >> [email protected]> wrote:
>> > > > >>
>> > > > >> > Hi,
>> > > > >> >
>> > > > >> > I sent this message before I had subscribed to the list so I
>> > wasn't
>> > > > >> sure if
>> > > > >> > the original made it. My apologies if this is a duplicate.
>> > > > >> >
>> > > > >> > One of our clients running our software is *occasionally*
>> running
>> > into
>> > > > >> the
>> > > > >> > stack trace at the bottom when Velocity is initialized. A
>> restart
>> > > > tends
>> > > > >> to
>> > > > >> > fix this problem. But it pops back up after running the system
>> for
>> > a
>> > > > >> while.
>> > > > >> >
>> > > > >> > They're running:
>> > > > >> >
>> > > > >> >   - Velocity 1.7
>> > > > >> >   - Tomcat 6.0.35
>> > > > >> >   - Using the 3.2 of the Apache Commons Collections library
>> > > > >> >   - Running Java 1.6.0_31 in Mac OS X 10.6.8
>> > > > >> >
>> > > > >> > Unfortunately we don't have the ability to debug this problem
>> > > > remotely,
>> > > > >> so
>> > > > >> > we can't see exactly what's going on, but having looked a bit
>> at
>> > the
>> > > > >> > Extended Properties class, it doesn't seem like it should be
>> > possible
>> > > > to
>> > > > >> > get an NPE at that line, because of the containsKey() check a
>> few
>> > > > lines
>> > > > >> > before.
>> > > > >> >
>> > > > >> > java.lang.NullPointerException
>> > > > >> > at
>> > > > >> >
>> > > > >>
>> > > >
>> >
>> >
>> org.apache.commons.collections.ExtendedProperties.clearProperty(ExtendedProperties.java:797)
>> > > > >> > at
>> > > > >> >
>> > > > >>
>> > > >
>> >
>> >
>> org.apache.commons.collections.ExtendedProperties.setProperty(ExtendedProperties.java:722)
>> > > > >> > at
>> > > > >> >
>> > > > >>
>> > > >
>> >
>> >
>> org.apache.commons.collections.ExtendedProperties.combine(ExtendedProperties.java:783)
>> > > > >> > at
>> > > > >> >
>> > > > >>
>> > > >
>> >
>> >
>> org.apache.velocity.runtime.RuntimeInstance.setProperties(RuntimeInstance.java:657)
>> > > > >> > at
>> > > > >> >
>> > > > >>
>> > > >
>> >
>> org.apache.velocity.runtime.RuntimeInstance.init(RuntimeInstance.java:645)
>> > > > >> > at
>> > > > >> >
>> > > > >>
>> > > >
>> >
>> >
>> org.apache.velocity.runtime.RuntimeSingleton.init(RuntimeSingleton.java:226)
>> > > > >> > at org.apache.velocity.app.Velocity.init(Velocity.java:97)
>> > > > >> > at
>> > > > >> >
>> > > > >>
>> > > >
>> >
>> >
>> com.hannonhill.cascade.velocity.VelocityEngineUtil.generateMessage(VelocityEngineUtil.java:66)
>> > > > >> >
>> > > > >> > Also, here's the code that's calling the Velocity.init:
>> > > > >> >
>> > > > >> >        Properties velocityProps =
>> > VelocityProperties.getProperties();
>> > > > >> >
>> > > > >> >        Velocity.init(velocityProps);
>> > > > >> >
>> > > > >> > Velocity Properties are just loading the following file
>> contents
>> > into
>> > > > a
>> > > > >> > properties object:
>> > > > >> >
>> > > > >> >
>> > > > >> >
>> > > > >>
>> > > >
>> >
>> >
>> #----------------------------------------------------------------------------
>> > > > >> > # This controls if Runtime.error(), info() and warn() messages
>> > include
>> > > > >> the
>> > > > >> > # whole stack trace. The last property controls whether invalid
>> > > > >> references
>> > > > >> > # are logged.
>> > > > >> >
>> > > > >> >
>> > > > >>
>> > > >
>> >
>> >
>> #----------------------------------------------------------------------------
>> > > > >> > runtime.log.error.stacktrace = false
>> > > > >> > runtime.log.warn.stacktrace = false
>> > > > >> > runtime.log.info.stacktrace = false
>> > > > >> > runtime.log.invalid.reference = true
>> > > > >> >
>> > > > >> >
>> > > > >>
>> > > >
>> >
>> >
>> #----------------------------------------------------------------------------
>> > > > >> > # Configuration for the Log4JLogSystem.
>> > > > >> > # You must define the runtime.log.logsystem.class property to
>> be:
>> > > > >> > #   org.apache.velocity.runtime.log.Log4JLogSystem
>> > > > >> > #
>> > > > >> > # You must also include Log4J's .jar files into your classpath.
>> > They
>> > > > are
>> > > > >> > # included with the Velocity distribution in the build/lib
>> > directory.
>> > > > >> > #
>> > > > >> > # There are several different options that you can configure.
>> > > > >> > # Uncomment the ones that you want and also define their
>> settings.
>> > > > >> >
>> > > > >> >
>> > > > >>
>> > > >
>> >
>> >
>> #----------------------------------------------------------------------------
>> > > > >> >
>> > > > >> >
>> > > > >>
>> > > >
>> >
>> >
>> #----------------------------------------------------------------------------
>> > > > >> > # T E M P L A T E  E N C O D I N G
>> > > > >> >
>> > > > >> >
>> > > > >>
>> > > >
>> >
>> >
>> #----------------------------------------------------------------------------
>> > > > >> > input.encoding=UTF-8
>> > > > >> > output.encoding=UTF-8
>> > > > >> >
>> > > > >> >
>> > > > >>
>> > > >
>> >
>> >
>> #----------------------------------------------------------------------------
>> > > > >> > # F O R E A C H  P R O P E R T I E S
>> > > > >> >
>> > > > >> >
>> > > > >>
>> > > >
>> >
>> >
>> #----------------------------------------------------------------------------
>> > > > >> > # These properties control how the counter is accessed in the
>> > #foreach
>> > > > >> > # directive. By default the reference $velocityCount will be
>> > available
>> > > > >> > # in the body of the #foreach directive. The default starting
>> > value
>> > > > >> > # for this reference is 1.
>> > > > >> >
>> > > > >> >
>> > > > >>
>> > > >
>> >
>> >
>> #----------------------------------------------------------------------------
>> > > > >> > directive.foreach.counter.name = velocityCount
>> > > > >> > directive.foreach.counter.initial.value = 1
>> > > > >> >
>> > > > >> >
>> > > > >>
>> > > >
>> >
>> >
>> #----------------------------------------------------------------------------
>> > > > >> > # T E M P L A T E  L O A D E R S
>> > > > >> >
>> > > > >> >
>> > > > >>
>> > > >
>> >
>> >
>> #----------------------------------------------------------------------------
>> > > > >> > resource.loader = class
>> > > > >> > class.resource.loader.description = Velocity Classpath Resource
>> > Loader
>> > > > >> > class.resource.loader.class =
>> > > > >> >
>> > org.apache.velocity.runtime.resource.loader.ClasspathResourceLoader
>> > > > >> >
>> > > > >>
>> > > > >
>> > > > >
>> > > >
>> >
>>
>
>