A pure-Java Markdown processor based on a parboiled PEG parser supporting a number of extensions
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README.markdown

Introduction

pegdown is a pure Java library for clean and lightweight Markdown processing. It's implementation is based on a parboiled PEG parser and is therefore rather easy to understand and extend.

pegdown is nearly 100% compatible with the original Markdown specification and fully passes the original Markdown test suite. On top of the standard Markdown feature set pegdown implements a number of extensions similar to what other popular Markdown processors offer.
Currently pegdown supports the following extensions over standard Markdown:

  • SMARTS: Beautifies apostrophes, ellipses ("..." and ". . .") and dashes ("--" and "---")
  • QUOTES: Beautifies single quotes, double quotes and double angle quotes (« and »)
  • SMARTYPANTS: Convenience extension enabling both, SMARTS and QUOTES, at once.
  • ABBREVIATIONS: Abbreviations in the way of PHP Markdown Extra.
  • HARDWRAPS: Alternative handling of newlines, see Github-flavoured-Markdown
  • AUTOLINKS: Plain (undelimited) autolinks the way Github-flavoured-Markdown implements them.
  • TABLES: Tables similar to MultiMarkdown (which is in turn like the PHP Markdown Extra tables, but with colspan support).
  • DEFINITION LISTS: Definition lists in the way of PHP Markdown Extra.
  • FENCED CODE BLOCKS: Fenced Code Blocks in the way of PHP Markdown Extra or Github-flavoured-Markdown.
  • HTML BLOCK SUPPRESSION: Suppresses the output of HTML blocks.
  • INLINE HTML SUPPRESSION: Suppresses the output of inline HTML elements.
  • WIKILINKS: Support [[Wiki-style links]] with a customizable URL rendering logic.

Note: pegdown differs from the original Markdown in that it ignores in-word emphasis as in

> my_cool_file.txt
> 2*3*4=5

Currently this "extension" cannot be switched off.

Installation

You have two options:

Usage

Using pegdown is very simple: Just create a new instance of a PegDownProcessor and call one of its markdownToHtml methods to convert the given Markdown source to an HTML string. If you'd like to customize the rendering of HTML links (Auto-Links, Explicit-Links, Mail-Links, Reference-Links and/or Wiki-Links), e.g. for adding rel="nofollow" attributes based on some logic you can supply your own instance of a LinkRenderer with the call to markdownToHtml.

You can also use pegdown only for the actual parsing of the Markdown source and do the serialization to the target format (e.g. XML) yourself. To do this just call the parseMarkdown method of the PegDownProcessor to obtain the root node of the Astract Syntax Tree for the document. With a custom Visitor implementation you can do whatever serialization you want. As an example you might want to take a look at the sources of the ToHtmlSerializer.

Note that the first time you create a PegDownProcessor it can take up to a few hundred milliseconds to prepare the underlying parboiled parser instance. However, once the first processor has been built all further instantiations will be fast. Also, you can reuse an existing PegDownProcessor instance as often as you want, as long as you prevent concurrent accesses, since neither the PegDownProcessor nor the underlying parser is thread-safe.

See http://sirthias.github.com/pegdown/api for the pegdown API documentation.

IDE Support

The excellent idea-markdown plugin for IntelliJ IDEA, RubyMine, PhpStorm, WebStorm, PyCharm and appCode uses pegdown as its underlying parsing engine. The plugin gives you proper syntax-highlighting for markdown source and shows you exactly, how pegdown will parse your texts.

Hacking on pegdown

pegdown uses Apache Buildr for managing the build process. However, if you do not want to install Buildr on your machine, it should be no problem to quickly set up a project structure for the IDE of your choice around the sources, since they are quite compact and the dependencies are few.

In order to provide custom markdown extensions to pegdown you shouldn't even have to get your hands dirty with its sources. A PegDownProcessor can be constructed around a given Parser instance, so you can supply your own. If you want to go that way probably want to subclass the org.pegdown.Parser class and override a limited number of rules to inject your own extensions. Your extensions can create custom Node implementations, which you can process through the general visit(Node) method of a custom Visitor implementation.

Credits

A large part of the underlying PEG grammar was developed by John MacFarlane and made available with his tool peg-markdown.

License

pegdown is licensed under Apache License 2.0.

Patch Policy

Feedback and contributions to the project, no matter what kind, are always very welcome. However, patches can only be accepted from their original author. Along with any patches, please state that the patch is your original work and that you license the work to the pegdown project under the project’s open source license.