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Writing A Velocity Pluglet
- About This Document
- Step 1: Find The VelocityPluglet Directory
- Step 2: Look at an Example
- Step 3: Use Advanced Velocity Features
- Step 4: Get More Information From Pavlov
- Step 5: Publish
About This Document
One of the big improvements in Pavlov 1.1 is the leveraging of the Apache Jakarta Project's Velocity Template Engine to create templated Pluglets and Skins. This document describes how to write a Velocity Feedback Pluglet for Pavlov.
Step 1: Find The VelocityPluglet Directory
Let's assume you already have Pavlov 1.1B1 or later installed. Find the directory it was installed in. Now, there will be a subdirectory called pluglets and its subdirectory of pluglets/velocity. In the 1.1BX release, there are two subdirectories here called aliengrades and navylife. Every subdirectory of pluglets/velocity is scanned at startup for a file named index.vm. Those with a valid index.vm are accepted and added to the Feedback Menu in Pavlov. So, for example, on my machine, I have
/home/haus/pup/pluglets/velocity/aliengrades/index.vm
/home/haus/pup/pluglets/velocity/navylife/index.vm
let's take a look at one of these.
Step 2: Look at an Example
We open up the file pluglets/velocity/aliengrades/index.vm and see something like this:
01 <HTML>
02 <HEAD></HEAD>
03 <BODY BGCOLOR="black">
04
05 <TABLE HEIGHT="223" WIDTH="304">
06 <TR>
07 <TD HEIGHT="223" WIDTH="304">
08 #set ( $right = $ANSWER_EVENT.getNumberOfCorrectAnswers() )
09 #set ( $tot= $ANSWER_EVENT.getNumberOfAnswers() )
10 #set ( $perc = 100 * $right/$tot )
11
12 #if ( !$perc )
13 #set ($img ="logo.jpg")
14 #elseif ( $perc < 59 )
15 #set ($img ="f.jpg")
...stuff deleted...
16 #else
17 #set ($img ="aplus.jpg")
18 #end
19 <IMG SRC ="$BASE_URL$img">
20 </TD>
21 </TR>
22 </TABLE>
23
24 </BODY>
25 </HTML>
Let's make a few observations:
- This is a well formed HTML document (Java doesn't like bad HTML)
- It has some funny stuff with pound "#" signs (this is Velocity for "do something")
- It has some funny stuff with dollar "$" signs (this is Velocity for "value of something")
- $ANSWER_EVENT shows up a lot (Pavlov sends an ANSWER_EVENT to the VelocityModel every time the user answers a question. ANSWER_EVENT has a lot of fun information in it, see http://pavlov.sourceforge.net/api-docs/net/sourceforge/pavlov/event/AnswerEvent.html for all the goodies.
- On lines 8 and 9 we get the number of correct answers and number of total answers in the current quiz
- In line 10, we get perc, which is a percentage from 0 to 100 representing the score in the current quiz
- In line 12, we see if $perc exists. If it does not exist there have been no answers in this quiz, and we set $img to a default value
- In lines 14-18 we choose an image to display based on the value of $perc
- In line 19 we display the image.
- Note the $BASE_URL variable in line 19. This lets you use resources in the same directory as index.vm.
- The rest of the code just closes the table and document.
- Since we know about how big this HTML page is going to be, we set the table height and width. This makes life a little easier on Java. If we do not know the size, the Java components can figure it out on their own.
Step 3: Use Advanced Velocity Features
The best source for information on advanced Velocity features is at Apache Jakarta Project's Velocity Site. There are some neat tricks on display there.
Step 4: Get More Information From Pavlov
Pavlov passes a great deal of information to your template using the AnswerEvent class. You can get information from the AnswerEvent by using it's methods. A few examples:
| $ANSWER_EVENT.getQuestionData().getPercentage() | Percentage of correct answers over whole user history |
| $ANSWER_EVENT.getUser().getName() | User's login name. |
| $ANSWER_EVENT.getBookData().getTitle() | Title of book in use |
| $ANSWER_EVENT.getChapterData().getStrategy().getName() | Name of the question selection strategy in use |
| $ANSWER_EVENT.getChapterData().getQuizCollectionData().numQuizzes | Number of quizzes this user has taken on this chapter |
| $ANSWER_EVENT.getChapterData().getQuizCollectionData().totalAsked | Number of questions this user has answered over all quizzes on this chapter |
The point here is not to list all the possible types of information you can glean from the system, but to illustrate that there is a lot to choose from.
Step 5: Publish
When you get a feedback pluglet that you like, send it to the Pavlov project. We'll need copyright information and have to filter out obscenities, but other than that, we'll be happy to make your pluglet available. That way, others can not only use your pluglet, but learn from it as well!
