Filter Tutorial

Introduction

SnipSnap uses Macros and Filters to render the text markup to XHTML. Macros are commands and filters usually replace markup with XHTML, for example the BoldFilter replaces __bold__ with <b>bold</b>. You shoud understand the SnipSnap architecture and have read the Macro Tutorial. You should also be familiar with regular expressions.

Filter Interface

The basis for all filters is the Filter interface. All classes that want to act as filters have to implement it.

public interface Filter {
  public String filter(String input, FilterContext context);
  public String[] before();
}

Example Filter

To write your own filter and implement Filter there are some support classes. The most basic is FilterSupport which does not much, but implement the before() method so you do not have to care. Most of the time though you want to use regular expressions (regex) to filter your content. For this there are two classes you can inherit from

• RegexReplaceFilter
• RegexTokenFilter

We want to write a smily replace filter as an example. Suppose we want to replace every Frowny :-( with a smiley :-)

The only thing you have to do is supply the regular expressions:

import org.radeox.filter.regex.RegexReplaceFilter;
public class SmileyFilter extends RegexReplaceFilter {
  public SmileyFilter() {
    super(":-\(", ":-)");
  }
}

The \ is for quoting the ( in the regular expression.

Caching

Radeox supports caching. To tell the engine that the output from your filter is cachable (= produces the same output for the same input which is usually the case with static filters) add the marker interface CacheFilter:

public class SmileyFilter extends RegexReplaceFilter implements CacheFilter {
...

Deployment

To make this filter work you have to create a jar file with

META-INF/services/org.radeox.filter.Filter
example/SmileyFilter.class

META-INF/services/org.radeox.filter.Filter should contain lines with the class names of your filters, for example

example.SmileyFilter

Put this jar into applications/<AppName>/WEB-INF/lib for example if your application is named MyBlog then applications/MyBlog/WEB-INF/lib. Restart the server and the filter should work.

For advanced filters take a look at Advanced Filter Tutorial.