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Posted to user@velocity.apache.org by Matthew Twomey <mt...@beakstar.com> on 2007/05/10 07:23:38 UTC
Question on using RenderTool in Java
Greetings,
I'm new to Velocity and I fear I may be misinterpreting the intent of this
the "tools" package. What I'd like to do is use the RenderTool.eval function
to process strings with template information in them. As a simple test of
this (which isn't working) I am trying the following:
// relevant imports
import org.apache.velocity.VelocityContext;
import org.apache.velocity.context.Context;
import org.apache.velocity.tools.generic.RenderTool;
.
.
.
// relevant code
Context ctx = new VelocityContext();
RenderTool rtool = new RenderTool();
ctx.put("cat", "Beakman");
String s99 = rtool.eval(ctx, "Hello $cat");
//
What I'm hoping for here is a result where s99 contains "Hello Beakman".
What happens is rtool.eval returns null.
I realize this type of simple text replacement is easy to do without
Velocity - this is just my "hello world" test. Ultimately I am aiming to
build complex router configurations that will require looping through many
lines of access-lists applying various variables and so forth.
I'd just like to be able to evaluate strings from within Java using the
templating language (e.g. this isn't web or Tomcat related at all).
Can anyone tell me what I'm doing wrong here, or if I'm going about it
completely wrong - what I should be looking at?
Thanks,
-Matt
Re: Question on using RenderTool in Java
Posted by Nathan Bubna <nb...@gmail.com>.
Great! Thanks for letting us know how it's going!
On 5/10/07, Matthew Twomey <mt...@beakstar.com> wrote:
> Nathan,
>
> Thank you very much - that was just what I needed to get going. I am now up
> and running (at least with some rudimentary test templates).
>
> I was initially using the velocity-tools package and including
> "velocity-tools-1.3.jar" as well as "velocity-1.4.jar" in my classpath. I
> had some trouble getting the resourceloader and logging going and I've since
> switched to the full velocity 1.5 system. I'm including "velocity-1.5.jar"
> as well as everything in the lib subdirectory.
>
> This appears to be working perfectly at this point, so I'm on to building my
> template. Thanks again for your help!
>
> -Matt
>
> -----Original Message-----
> From: Nathan Bubna [mailto:nbubna@gmail.com]
> Sent: Thursday, May 10, 2007 1:05 AM
> To: Velocity Users List
> Subject: Re: Question on using RenderTool in Java
>
> On 5/9/07, Matthew Twomey <mt...@beakstar.com> wrote:
> > Greetings,
>
> hi!
> >
> > I'm new to Velocity and I fear I may be misinterpreting the intent of this
> > the "tools" package. What I'd like to do is use the RenderTool.eval
> function
> > to process strings with template information in them.
>
> The RenderTool is primarily for doing eval() stuff *within templates*
> as opposed to within java. This where most tools are designed to be
> used, though they can be used elsewhere, of course.
>
> > As a simple test of
> > this (which isn't working) I am trying the following:
> >
> >
> >
> > // relevant imports
> >
> > import org.apache.velocity.VelocityContext;
> >
> > import org.apache.velocity.context.Context;
> >
> > import org.apache.velocity.tools.generic.RenderTool;
> >
> > .
> >
> > .
> >
> > .
> >
> > // relevant code
> >
> > Context ctx = new VelocityContext();
> >
> > RenderTool rtool = new RenderTool();
> >
> > ctx.put("cat", "Beakman");
> >
> > String s99 = rtool.eval(ctx, "Hello $cat");
> >
> > //
> >
> >
> >
> > What I'm hoping for here is a result where s99 contains "Hello Beakman".
> > What happens is rtool.eval returns null.
>
> this almost certainly means that the Velocity singleton failed to
> initialize. here is where using the RenderTool is probably not ideal
> for your application. We don't like tools to throw exceptions when
> used in the middle of processing a template, so we catch them, log
> them (when possible) and return null. Within Java, you usually want
> the exceptions rather than the gentle failure. So, i'd recommend you
> do something like this instead:
>
> VelocityEngine engine = new VelocityEngine();
> engine.init(); //configuration could optionally be done before this
> VelocityContext ctx = new VelocityContext();
> ctx.put("cat", "Beakman");
> StringWriter out = new StringWriter();
> engine.evaluate(ctx, out, "test template", "Hello $cat");
> String s99 = out.toString();
>
> it's a wee bit more code, but it won't swallow exceptions!
>
> > I realize this type of simple text replacement is easy to do without
> > Velocity - this is just my "hello world" test. Ultimately I am aiming to
> > build complex router configurations that will require looping through many
> > lines of access-lists applying various variables and so forth.
>
> be sure you don't initialize a new VelocityEngine() for each line you
> evaluate. you should be able to create one at the start and use it
> for all of them.
>
> >
> >
> > I'd just like to be able to evaluate strings from within Java using the
> > templating language (e.g. this isn't web or Tomcat related at all).
> >
> >
> >
> > Can anyone tell me what I'm doing wrong here, or if I'm going about it
> > completely wrong - what I should be looking at?
>
> if you really want to get your initial example working, you'll need to
> find out where Velocity sent it's log messages. here's some questions
> that might help clarify that: what versions of Velocity and
> VelocityTools are you using? did you configure the singleton prior to
> using the RenderTool? are you using the velocity-dep jar or the plain
> vanilla velocity jar?
>
> >
> >
> > Thanks,
> >
> >
> >
> > -Matt
> >
> >
> >
> >
>
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> To unsubscribe, e-mail: user-unsubscribe@velocity.apache.org
> For additional commands, e-mail: user-help@velocity.apache.org
>
>
>
> ---------------------------------------------------------------------
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> For additional commands, e-mail: user-help@velocity.apache.org
>
>
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RE: Question on using RenderTool in Java
Posted by Matthew Twomey <mt...@beakstar.com>.
Nathan,
Thank you very much - that was just what I needed to get going. I am now up
and running (at least with some rudimentary test templates).
I was initially using the velocity-tools package and including
"velocity-tools-1.3.jar" as well as "velocity-1.4.jar" in my classpath. I
had some trouble getting the resourceloader and logging going and I've since
switched to the full velocity 1.5 system. I'm including "velocity-1.5.jar"
as well as everything in the lib subdirectory.
This appears to be working perfectly at this point, so I'm on to building my
template. Thanks again for your help!
-Matt
-----Original Message-----
From: Nathan Bubna [mailto:nbubna@gmail.com]
Sent: Thursday, May 10, 2007 1:05 AM
To: Velocity Users List
Subject: Re: Question on using RenderTool in Java
On 5/9/07, Matthew Twomey <mt...@beakstar.com> wrote:
> Greetings,
hi!
>
> I'm new to Velocity and I fear I may be misinterpreting the intent of this
> the "tools" package. What I'd like to do is use the RenderTool.eval
function
> to process strings with template information in them.
The RenderTool is primarily for doing eval() stuff *within templates*
as opposed to within java. This where most tools are designed to be
used, though they can be used elsewhere, of course.
> As a simple test of
> this (which isn't working) I am trying the following:
>
>
>
> // relevant imports
>
> import org.apache.velocity.VelocityContext;
>
> import org.apache.velocity.context.Context;
>
> import org.apache.velocity.tools.generic.RenderTool;
>
> .
>
> .
>
> .
>
> // relevant code
>
> Context ctx = new VelocityContext();
>
> RenderTool rtool = new RenderTool();
>
> ctx.put("cat", "Beakman");
>
> String s99 = rtool.eval(ctx, "Hello $cat");
>
> //
>
>
>
> What I'm hoping for here is a result where s99 contains "Hello Beakman".
> What happens is rtool.eval returns null.
this almost certainly means that the Velocity singleton failed to
initialize. here is where using the RenderTool is probably not ideal
for your application. We don't like tools to throw exceptions when
used in the middle of processing a template, so we catch them, log
them (when possible) and return null. Within Java, you usually want
the exceptions rather than the gentle failure. So, i'd recommend you
do something like this instead:
VelocityEngine engine = new VelocityEngine();
engine.init(); //configuration could optionally be done before this
VelocityContext ctx = new VelocityContext();
ctx.put("cat", "Beakman");
StringWriter out = new StringWriter();
engine.evaluate(ctx, out, "test template", "Hello $cat");
String s99 = out.toString();
it's a wee bit more code, but it won't swallow exceptions!
> I realize this type of simple text replacement is easy to do without
> Velocity - this is just my "hello world" test. Ultimately I am aiming to
> build complex router configurations that will require looping through many
> lines of access-lists applying various variables and so forth.
be sure you don't initialize a new VelocityEngine() for each line you
evaluate. you should be able to create one at the start and use it
for all of them.
>
>
> I'd just like to be able to evaluate strings from within Java using the
> templating language (e.g. this isn't web or Tomcat related at all).
>
>
>
> Can anyone tell me what I'm doing wrong here, or if I'm going about it
> completely wrong - what I should be looking at?
if you really want to get your initial example working, you'll need to
find out where Velocity sent it's log messages. here's some questions
that might help clarify that: what versions of Velocity and
VelocityTools are you using? did you configure the singleton prior to
using the RenderTool? are you using the velocity-dep jar or the plain
vanilla velocity jar?
>
>
> Thanks,
>
>
>
> -Matt
>
>
>
>
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---------------------------------------------------------------------
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Re: Question on using RenderTool in Java
Posted by Nathan Bubna <nb...@gmail.com>.
On 5/9/07, Matthew Twomey <mt...@beakstar.com> wrote:
> Greetings,
hi!
>
> I'm new to Velocity and I fear I may be misinterpreting the intent of this
> the "tools" package. What I'd like to do is use the RenderTool.eval function
> to process strings with template information in them.
The RenderTool is primarily for doing eval() stuff *within templates*
as opposed to within java. This where most tools are designed to be
used, though they can be used elsewhere, of course.
> As a simple test of
> this (which isn't working) I am trying the following:
>
>
>
> // relevant imports
>
> import org.apache.velocity.VelocityContext;
>
> import org.apache.velocity.context.Context;
>
> import org.apache.velocity.tools.generic.RenderTool;
>
> .
>
> .
>
> .
>
> // relevant code
>
> Context ctx = new VelocityContext();
>
> RenderTool rtool = new RenderTool();
>
> ctx.put("cat", "Beakman");
>
> String s99 = rtool.eval(ctx, "Hello $cat");
>
> //
>
>
>
> What I'm hoping for here is a result where s99 contains "Hello Beakman".
> What happens is rtool.eval returns null.
this almost certainly means that the Velocity singleton failed to
initialize. here is where using the RenderTool is probably not ideal
for your application. We don't like tools to throw exceptions when
used in the middle of processing a template, so we catch them, log
them (when possible) and return null. Within Java, you usually want
the exceptions rather than the gentle failure. So, i'd recommend you
do something like this instead:
VelocityEngine engine = new VelocityEngine();
engine.init(); //configuration could optionally be done before this
VelocityContext ctx = new VelocityContext();
ctx.put("cat", "Beakman");
StringWriter out = new StringWriter();
engine.evaluate(ctx, out, "test template", "Hello $cat");
String s99 = out.toString();
it's a wee bit more code, but it won't swallow exceptions!
> I realize this type of simple text replacement is easy to do without
> Velocity - this is just my "hello world" test. Ultimately I am aiming to
> build complex router configurations that will require looping through many
> lines of access-lists applying various variables and so forth.
be sure you don't initialize a new VelocityEngine() for each line you
evaluate. you should be able to create one at the start and use it
for all of them.
>
>
> I'd just like to be able to evaluate strings from within Java using the
> templating language (e.g. this isn't web or Tomcat related at all).
>
>
>
> Can anyone tell me what I'm doing wrong here, or if I'm going about it
> completely wrong - what I should be looking at?
if you really want to get your initial example working, you'll need to
find out where Velocity sent it's log messages. here's some questions
that might help clarify that: what versions of Velocity and
VelocityTools are you using? did you configure the singleton prior to
using the RenderTool? are you using the velocity-dep jar or the plain
vanilla velocity jar?
>
>
> Thanks,
>
>
>
> -Matt
>
>
>
>
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