jStyleParser

jStyleParser is a Java library for parsing CSS style sheets and assigning styles to the HTML or XML document elements according to the CSS 3 specifications. It allows parsing the individual CSS files as well as computing the efficient style of the DOM elements.

See the project page for more information: http://cssbox.sourceforge.net/jstyleparser

Installation

With Maven, use the following dependency:

<dependency>
    <groupId>net.sf.cssbox</groupId>
    <artifactId>jstyleparser</artifactId>
    <version>4.0.1</version>
</dependency>

Parsing CSS

The basic CSSFactory interface provides functions parsing CSS strings, files or URLs. The parsed style sheet is represented by the corresponding data structures that allow accessing all parts of the style sheet in a type-safe way.

String css = "div { background-color: red; width: 12px; }";

//parse the style sheet
StyleSheet sheet = CSSFactory.parseString(css, new URL("http://base.url"));

//access the rules and declarations
RuleSet rule = (RuleSet) sheet.get(0);       //get the first rule
CombinedSelector selector = rule.getSelectors()[0]; //read the 'div' selector
Declaration bgDecl = rule.get(0);            //read the 'background-color' declaration
String bgProperty = bgDecl.getProperty();    //read the property name
TermColor color = (TermColor) bgDecl.get(0); //read the color

//print the results
System.out.println(selector);   //prints 'div'
System.out.println(bgProperty); //prints 'background-color'
System.out.println(color);      //prints '#ff0000'

//or even print the entire style sheet (formatted)
System.out.println(sheet);

See the details in the documentation.

Computing style for DOM elements

jStyleParser allows to map the style rules to the individual elements in a DOM tree based on their selectors. This allows obtaining the exact style for any HTML element.

org.w3c.dom.Document doc = ... //source DOM

MediaSpec media = new MediaSpecAll(); //use styles for all media

//create the style map
StyleMap map = CSSFactory.assignDOM(doc, "UTF-8", new URL("https://base.url/"), media, true);

//get the style of a single element
Element div = doc.getElementById("searchelement"); //choose a DOM element
NodeData style = map.get(div); //get the style map for the element
//get the type of the assigned value
CSSProperty.Margin mm = style.getProperty("margin-top");
System.out.println("margin-top=" + mm);
//if a length is specified, obtain the exact value
if (mm == Margin.length) {
    TermLength mtop = style.getValue(TermLength.class, "margin-top");
    System.out.println("value=" + mtop);
}

Multi-value properties

Some properties (e.g. background) allow multiple values. In that case, the NodeData interface includes the getListSize() method for getting the number of values specified and the getProperty() and getValue() functions with an index argument:

//get the style of a single element
Element div = doc.getElementById("searchelement"); //choose a DOM element
NodeData style = map.get(div); //get the style map for the element

//get the number of background images specified for the element
int bgcnt = style.getListSize("background-image", true);

//read all images
for (int index = 0; index < bgcnt; index++>) {
    CSSProperty.BackgroundImage image = style.getProperty("background-image", index);
    if (image == CSSProperty.BackgroundImage.uri) { //if the image is specified by its url
        TermURI urlstring = style.getValue(TermURI.class, "background-image", index);
        //... do something with the image url
    }
}

See the details in the documentation.

Gradle and Jitpack support

This project now supports Gradle and Jitpack. After making a change, create a new release using the x.x.x format (See: https://docs.github.com/en/repositories/releasing-projects-on-github/managing-releases-in-a-repository)

If using in conjunction with CSSBox, you will then also need to update CSSBox's build.gradle.kts file and increment the version of jStyleParser with the new version number.

ANTLR4 File generation

jStyleParser uses pre-generated ANTLR4 files. If any changes are made to any .g4 files, these files will need to be re-generated.

To do so, use ANTRL4 version 4.13.2 for compatibility. Inside of any folder containing CSSLexer.g4 and CSSParser.g4 (these files can be found in src/main/antlr4/cz/vutbr/web/csskit/antlr4/) and the antlr-4.13.2-complete.jar file, use the following commands in this order:

Java -jar antlr-4.13.2-complete.jar CSSLexer.g4
Java -jar antlr-4.13.2-complete.jar CSSParser.g4 -visitor

This should generate 8 files. Place these files in src/main/java/cz/vutbr/web/csskit/antlr4/ At the top of each of the generated .java files, write the following package information if not already present:

package cz.vutbr.web.csskit.antlr4;

License

All the source code of jStyleParser itself is licensed under the GNU Lesser General Public License (LGPL), version 3. A copy of the LGPL can be found in the LICENSE file.