Java library for parsing and rendering Markdown text according to the CommonMark specification (and some extensions).
Provides classes for parsing input to an abstract syntax tree (AST), visiting and manipulating nodes, and rendering to HTML or back to Markdown. It started out as a port of commonmark.js, but has since evolved into an extensible library with the following features:
- Small (core has no dependencies, extensions in separate artifacts)
- Fast (10-20 times faster than pegdown which used to be a popular Markdown library, see benchmarks in repo)
- Flexible (manipulate the AST after parsing, customize HTML rendering)
- Extensible (tables, strikethrough, autolinking and more, see below)
The library is supported on Java 11 and later. It works on Android too, but that is on a best-effort basis, please report problems. For Android the minimum API level is 19, see the commonmark-android-test directory.
Coordinates for core library (see all on Maven Central):
<dependency>
<groupId>org.commonmark</groupId>
<artifactId>commonmark</artifactId>
<version>0.21.0</version>
</dependency>The module names to use in Java 9 are org.commonmark,
org.commonmark.ext.autolink, etc, corresponding to package names.
Note that for 0.x releases of this library, the API is not considered stable
yet and may break between minor releases. After 1.0, Semantic Versioning will
be followed. A package containing beta means it's not subject to stable API
guarantees yet; but for normal usage it should not be necessary to use.
See the spec.txt
file if you're wondering which version of the spec is currently
implemented. Also check out the CommonMark dingus for getting familiar
with the syntax or trying out edge cases. If you clone the repository,
you can also use the DingusApp class to try out things interactively.
import org.commonmark.node.*;
import org.commonmark.parser.Parser;
import org.commonmark.renderer.html.HtmlRenderer;
Parser parser = Parser.builder().build();
Node document = parser.parse("This is *Markdown*");
HtmlRenderer renderer = HtmlRenderer.builder().build();
renderer.render(document); // "<p>This is <em>Markdown</em></p>\n"This uses the parser and renderer with default options. Both builders have methods for configuring their behavior:
escapeHtml(true)onHtmlRendererwill escape raw HTML tags and blocks.sanitizeUrls(true)onHtmlRendererwill strip potentially unsafe URLs from<a>and<img>tags- For all available options, see methods on the builders.
Note that this library doesn't try to sanitize the resulting HTML with regards to which tags are allowed, etc. That is the responsibility of the caller, and if you expose the resulting HTML, you probably want to run a sanitizer on it after this.
import org.commonmark.node.*;
import org.commonmark.renderer.markdown.MarkdownRenderer;
MarkdownRenderer renderer = MarkdownRenderer.builder().build();
Node document = new Document();
Heading heading = new Heading();
heading.setLevel(2);
heading.appendChild(new Text("My title"));
document.appendChild(heading);
renderer.render(document); // "## My title\n"For rendering to plain text with minimal markup, there's also TextContentRenderer.
After the source text has been parsed, the result is a tree of nodes. That tree can be modified before rendering, or just inspected without rendering:
Node node = parser.parse("Example\n=======\n\nSome more text");
WordCountVisitor visitor = new WordCountVisitor();
node.accept(visitor);
visitor.wordCount; // 4
class WordCountVisitor extends AbstractVisitor {
int wordCount = 0;
@Override
public void visit(Text text) {
// This is called for all Text nodes. Override other visit methods for other node types.
// Count words (this is just an example, don't actually do it this way for various reasons).
wordCount += text.getLiteral().split("\\W+").length;
// Descend into children (could be omitted in this case because Text nodes don't have children).
visitChildren(text);
}
}Sometimes you might want to customize how HTML is rendered. If all you want to do is add or change attributes on some elements, there's a simple way to do that.
In this example, we register a factory for an AttributeProvider on the
renderer to set a class="border" attribute on img elements.
Parser parser = Parser.builder().build();
HtmlRenderer renderer = HtmlRenderer.builder()
.attributeProviderFactory(new AttributeProviderFactory() {
public AttributeProvider create(AttributeProviderContext context) {
return new ImageAttributeProvider();
}
})
.build();
Node document = parser.parse("");
renderer.render(document);
// "<p><img src=\"/url.png\" alt=\"text\" class=\"border\" /></p>\n"
class ImageAttributeProvider implements AttributeProvider {
@Override
public void setAttributes(Node node, String tagName, Map<String, String> attributes) {
if (node instanceof Image) {
attributes.put("class", "border");
}
}
}If you want to do more than just change attributes, there's also a way to take complete control over how HTML is rendered.
In this example, we're changing the rendering of indented code blocks to
only wrap them in pre instead of pre and code:
Parser parser = Parser.builder().build();
HtmlRenderer renderer = HtmlRenderer.builder()
.nodeRendererFactory(new HtmlNodeRendererFactory() {
public NodeRenderer create(HtmlNodeRendererContext context) {
return new IndentedCodeBlockNodeRenderer(context);
}
})
.build();
Node document = parser.parse("Example:\n\n code");
renderer.render(document);
// "<p>Example:</p>\n<pre>code\n</pre>\n"
class IndentedCodeBlockNodeRenderer implements NodeRenderer {
private final HtmlWriter html;
IndentedCodeBlockNodeRenderer(HtmlNodeRendererContext context) {
this.html = context.getWriter();
}
@Override
public Set<Class<? extends Node>> getNodeTypes() {
// Return the node types we want to use this renderer for.
return Set.of(IndentedCodeBlock.class);
}
@Override
public void render(Node node) {
// We only handle one type as per getNodeTypes, so we can just cast it here.
IndentedCodeBlock codeBlock = (IndentedCodeBlock) node;
html.line();
html.tag("pre");
html.text(codeBlock.getLiteral());
html.tag("/pre");
html.line();
}
}In case you want to store additional data in the document or have custom
elements in the resulting HTML, you can create your own subclass of
CustomNode and add instances as child nodes to existing nodes.
To define the HTML rendering for them, you can use a NodeRenderer as
explained above.
There are a few ways to extend parsing or even override built-in parsing,
all of them via methods on Parser.Builder
(see Blocks and inlines in the spec for an overview of blocks/inlines):
- Parsing of specific block types (e.g. headings, code blocks, etc) can be
enabled/disabled with
enabledBlockTypes - Parsing of blocks can be extended/overridden with
customBlockParserFactory - Parsing of inline content can be extended/overridden with
customInlineContentParserFactory - Parsing of delimiters in inline content can be
extended with
customDelimiterProcessor
Both the Parser and HtmlRenderer are designed so that you can
configure them once using the builders and then use them multiple
times/from multiple threads. This is done by separating the state for
parsing/rendering from the configuration.
Having said that, there might be bugs of course. If you find one, please report an issue.
Javadocs are available online on javadoc.io.
Extensions need to extend the parser, or the HTML renderer, or both. To use an extension, the builder objects can be configured with a list of extensions. Because extensions are optional, they live in separate artifacts, so additional dependencies need to be added as well.
Let's look at how to enable tables from GitHub Flavored Markdown. First, add an additional dependency (see Maven Central for others):
<dependency>
<groupId>org.commonmark</groupId>
<artifactId>commonmark-ext-gfm-tables</artifactId>
<version>0.21.0</version>
</dependency>Then, configure the extension on the builders:
import org.commonmark.ext.gfm.tables.TablesExtension;
List<Extension> extensions = List.of(TablesExtension.create());
Parser parser = Parser.builder()
.extensions(extensions)
.build();
HtmlRenderer renderer = HtmlRenderer.builder()
.extensions(extensions)
.build();To configure another extension in the above example, just add it to the list.
The following extensions are developed with this library, each in their own artifact.
Turns plain links such as URLs and email addresses into links (based on autolink-java).
Use class AutolinkExtension from artifact commonmark-ext-autolink.
Enables strikethrough of text by enclosing it in ~~. For example, in
hey ~~you~~, you will be rendered as strikethrough text.
Use class StrikethroughExtension in artifact commonmark-ext-gfm-strikethrough.
Enables tables using pipes as in GitHub Flavored Markdown.
Use class TablesExtension in artifact commonmark-ext-gfm-tables.
Enables adding auto generated "id" attributes to heading tags. The "id" is based on the text of the heading.
# Heading will be rendered as:
<h1 id="heading">Heading</h1>
Use class HeadingAnchorExtension in artifact commonmark-ext-heading-anchor.
In case you want custom rendering of the heading instead, you can use
the IdGenerator class directly together with a
HtmlNodeRendererFactory (see example above).
Enables underlining of text by enclosing it in ++. For example, in
hey ++you++, you will be rendered as underline text. Uses the <ins> tag.
Use class InsExtension in artifact commonmark-ext-ins.
Adds support for metadata through a YAML front matter block. This extension only supports a subset of YAML syntax. Here's an example of what's supported:
---
key: value
list:
- value 1
- value 2
literal: |
this is literal value.
literal values 2
---
document start here
Use class YamlFrontMatterExtension in artifact commonmark-ext-yaml-front-matter. To fetch metadata, use YamlFrontMatterVisitor.
Adds support for specifying attributes (specifically height and width) for images.
The attribute elements are given as key=value pairs inside curly braces { } after the image node to which they apply,
for example:
{width=640 height=480}
will be rendered as:
<img src="/url.png" alt="text" width="640" height="480" />
Use class ImageAttributesExtension in artifact commonmark-ext-image-attributes.
Note: since this extension uses curly braces { } as its delimiters (in StylesDelimiterProcessor), this means that
other delimiter processors cannot use curly braces for delimiting.
Adds support for tasks as list items.
A task can be represented as a list item where the first non-whitespace character is a left bracket [, then a single
whitespace character or the letter x in lowercase or uppercase, then a right bracket ] followed by at least one
whitespace before any other content.
For example:
- [ ] task #1
- [x] task #2
will be rendered as:
<ul>
<li><input type="checkbox" disabled=""> task #1</li>
<li><input type="checkbox" disabled="" checked=""> task #2</li>
</ul>
Use class TaskListItemsExtension in artifact commonmark-ext-task-list-items.
You can also find other extensions in the wild:
- commonmark-ext-notifications: this extension allows to easily create notifications/admonitions paragraphs like
INFO,SUCCESS,WARNINGorERROR
- Markwon: Android library for rendering markdown as system-native Spannables
- flexmark-java: Fork that added support for a lot more syntax and flexibility
See CONTRIBUTING.md file.
Copyright (c) Atlassian and others.
BSD (2-clause) licensed, see LICENSE.txt file.
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