From Scala to JavaLooking for the best markdown parser and markedj

@takezoenBizReach, Inc

10 Oct. 2015 #shibuya_java 13th

Prelude

● We are developing GitBucket which is a Scala based GitHub clone

● It should support markdown for many purpose● We are looking for better markdown processor on JVM

A lot of markdown processors in Java

● pegdown○ https://github.com/sirthias/pegdown

● markdown4j○ https://code.google.com/p/markdown4j/

● MarkdownJ○ https://github.com/myabc/markdownj

● MarkdownPapers○ http://markdown.tautua.org/

● Txtmark○ https://github.com/rjeschke/txtmark

From: http://www.w3.org/community/markdown/wiki/MarkdownImplementations

Problems about GFM support

1. Run following code in REPL:...

2. Result is: ...

Plugin version | GitBucket version:--------------|:-----------------3.6.x | 3.6.x3.5.x | 3.5.x

Table:

Block in list:

```$ mvn clean$ mvn package```

Fence:

Status

Library Table Fence Block in List

Remarks

pegdown ○ ○ × Previously GitBucket were using this.

markdown4j × ○ ○ Plugin systemUML support using YUML

MarkdownJ × × ○

MarkdownPapers × △ ○

Txtmark × △ ○ Highly buggy?

In other languages

● redcarpet (Ruby)○ https://github.com/vmg/redcarpet

● marked.js (JavaScript)○ https://github.com/chjj/marked

Road to markedj

● At first, I started porting marked.js into Scala

Regular expressions!!

Jamie Zawinski said:

Some people, when confronted with a problem, think

"I know, I'll use regular expressions."

Now they have two problems.

Side-effect! Mutable!! Not functional!!!

Reassign!!

Break!!

Mutable stack!!

Road to markedj

● Many regular expressions and mutables, Why Scala?● Porting to Java may be useful for many people on JVM

○ No Scala runtime library○ Available for Java and any other JVM langs

● I decided to port from Scala to Java!

markedj is JVM port of marked.js

● GitHub Flavored Markdown support● Simple and extensible API● GitBucket switches to markedj in the next version (3.7)!

import io.github.gitbucket.markedj.Marked;

String markdown = ...

String html = Marked.marked(markdown);

markedj is a graceful markdown processor on JVM. Try it!!

https://github.com/gitbucket/markedj