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Java CSS 2 and CSS 3 parser and builder. This version supersedes phloc-css.The Maven plugin to compress CSS files at build time is located in sub-project ph-csscompress-maven-plugin and described further down.

ph-css has no logic for applying CSS onto HTML elements. This page shows some basic code examples that can be used to use the library. All snippets are free for any use.

ph-css and ph-csscompress-maven-plugin are both licensed under theApache 2.0 license.

ph-css is used as a part ofApache JMeter 3 :)

Add the following to your pom.xml to use this artifact, replacingx.y.z with the latest version:

<dependency>  <groupId>com.helger</groupId>  <artifactId>ph-css</artifactId>  <version>x.y.z</version></dependency>

To build ph-css from source, Maven 3.0.4 is required. Any Maven version below doesNOT work!

As ph-css is mainly concerned about the grammatical structure of CSS, the main classes are for reading and writing CSS. Additionally it offers the possibility to traverse the elements in a CSS and make modifications on them.

Please look at my personalCoding Styleguide for the naming conventions used in this project.

A complete stylesheet is represented as an instance ofcom.helger.css.decl.CascadingStyleSheet. There is no difference between CSS 2.1 and CSS 3.0 instances. The classcom.helger.css.decl.CascadingStyleSheet contains all top-level rules that may be present in a CSS:

• Import rules (@import) -com.helger.css.decl.CSSImportRule
• Namespace rules (@namespace) -com.helger.css.decl.CSSNamespaceRule
• Style rules (e.g.div{color:red;}) -com.helger.css.decl.CSSStyleRule
• Page rules (@page) -com.helger.css.decl.CSSPageRule
• Media rules (@media) -com.helger.css.decl.CSSMediaRule
• Font face rules (@font-face) -com.helger.css.decl.CSSFontFaceRule
• Keyframes rules (@keyframes) -com.helger.css.decl.CSSKeyframesRule
• Viewport rules (@viewport) -com.helger.css.decl.CSSViewportRule
• Supports rules (@supports) -com.helger.css.decl.CSSSupportsRule
• Any other unknown rules (@foo) -com.helger.css.decl.CSSUnknownRule

ph-css contains two different possibilities to read CSS data:

• Reading a complete CSS file can be achieved usingcom.helger.css.reader.CSSReader. The result in this case will be an instance ofcom.helger.css.decl.CascadingStyleSheet.
• Reading only a list of style information (as e.g. present in an HTMLstyle element) can be achieved usingcom.helger.css.reader.CSSReaderDeclarationList. The result in this case will be an instance ofcom.helger.css.decl.CSSDeclarationList.

Both reading classes support the reading from either ajava.io.File, ajava.io.Reader, acom.helger.commons.io.IInputStreamProvider or aString. The reason whyjava.io.InputStream is not supported directly is because internally the stream is passed twice - first to determine a potentially available charset and second to read the content with the correctly determined charset. That's why anIInputStreamProvider must be used, that creates 2 unique input streams!

Note: reading from aString is possible in two different ways: one that requires a charset and one that doesn't. The version with the charset treats theString as if it was created from a byte array and tries to determine the charset like any other byte array based version. The version without a charset assumes that theString was already created with the correct charset, and any@charset rule contained in the CSS is ignored.

Since v3.8.2 the classcom.helger.css.reader.CSSReaderSettings is present and encapsulates the CSS version, the fallback charset, the recoverable error handler (see below) and the unrecoverable error handler (also see below) in one settings object. This settings object can be used for multiple invocations ofCSSReader andCSSReaderDeclarationList.

ph-css differentiates between recoverable errors and unrecoverable errors. An example for a recoverable error is e.g. an@import rule in the wrong place or a missing closing bracket within a style declaration. For recoverable errors a special handler interfacecom.helger.css.reader.errorhandler.ICSSParseErrorHandler is present. You can pass an implementation of this error handler to the CSS reader (see above). The following implementations are present by default (all residing in packagecom.helger.css.reader.errorhandler):

• DoNothingCSSParseErrorHandler - silently ignoring all recoverable errors
• LoggingCSSParseErrorHandler - logging all recoverable errors to an SLF4J logger
• ThrowingCSSParseErrorHandler - throws acom.helger.css.parser.ParseException in case of a recoverable error which is afterwards handled by the unrecoverable error handler (see below). This can be used to enforce handling only 100% valid CSS files. This is the default setting, if no error handler is specified during reading.
• CollectingCSSParseErrorHandler - collects all recoverable errors into a list ofcom.helger.css.reader.errorhandler.CSSParseError instances for later evaluation.

Some error handlers can be nested so that a combination of a logging handler and a collecting handler can easily be achieved like:

newCollectingCSSParseErrorHandler (newLoggingCSSParseErrorHandler ())

DoNothingCSSParseErrorHandler andThrowingCSSParseErrorHandler cannot be nested because it makes no sense.

BothCSSReader andCSSReaderDeclarationList have the possibility to define a default recoverable error handler using the methodsetDefaultParseErrorHandler(ICSSParseErrorHandler). If a reading method is invoked without an explicitICSSParseErrorHandler than this default error handler is used.

In case of an unrecoverable error, the underlying parser engine of JavaCC throws acom.helger.css.parser.ParseException. This exception contains all the necessary information on where the error occurred. In case of such an unrecoverable error, the result of the reading will always benull and the exception is not automatically propagated to the caller. To explicitly get notified when such a parse error occurs, the handler interfacecom.helger.css.handler.ICSSParseExceptionCallback is available. The available implementations are (all residing in packagecom.helger.css.handler):

• DoNothingCSSParseExceptionHandler - silently ignore all unrecoverable errors
• LoggingCSSParseExceptionHandler - log all unrecoverable errors to an SLF4J logger

As there is at most one unrecoverable error per parse there is no collecting implementation of anICSSParseExceptionCallback available. If it is desired to propagate the Exception to the caller you need to implement your ownICSSParseExceptionCallback subclass that throws an unchecked exception (one derived fromRuntimeException). Example:

finalICSSParseExceptionCallbackaThrowingExceptionHandler =newICSSParseExceptionCallback () {publicvoidonException (finalParseExceptionex) {thrownewIllegalStateException ("Failed to parse CSS",ex);    }  };

BothCSSReader andCSSReaderDeclarationList have the possibility to define a default unrecoverable error handler using the methodsetDefaultParseExceptionHandler(ICSSParseExceptionCallback). If a reading method is invoked without an explicitICSSParseExceptionCallback than this default exception handler is used.

Once a CSS file was successfully read, it can easily be iterated using the classcom.helger.css.decl.visit.CSSVisitor. It requires a valid instance ofcom.helger.css.decl.CascadingStyleSheet as well as an implementation ofcom.helger.css.decl.visit.ICSSVisitor. TheCascadingStyleSheet can be acquired either by reading from a file/stream or by creating a new one from scratch. For theICSSVisitor it is recommended to use the classcom.helger.css.decl.visit.DefaultCSSVisitor as the base class - this class contains empty implementations of all methods defined in theICSSVisitor interface. To visit all declarations (e.g.color:red;) it is sufficient to simply override the methodpublic void onDeclaration (@Nonnull final CSSDeclaration aDeclaration). For details please have a look at the JavaDocs ofICSSVisitor. To start the visiting callCSSVisitor.visitCSS (CascadingStyleSheet, ICSSVisitor).

A special visitor is present for URLs. URLs can occur on several places in CSS files, especially in the@import rules and within declarations (like inbackground-image: url(../images/bg.gif)). Therefore a special interfacecom.helger.css.decl.visit.ICSSUrlVisitor together with the empty default implementationcom.helger.css.decl.visit.DefaultCSSUrlVisitor is provided. So to visit all URLs within a CSS callCSSVisitor.visitCSSUrl(CascadingStyleSheet, ICSSUrlVisitor).Since v6.2.3 the URL visitor recursively descends into expression members (seeissue #59).

For modifying URLs (e.g. to adopt paths to a different environment) a special base classcom.helger.css.decl.visit.AbstractModifyingCSSUrlVisitor is available. It offers the abstract methodprotected abstract String getModifiedURI (@Nonnull String sURI) to modify a URL and write the result back into the originalCascadingStyleSheet. An example of how this can be used, can be found in the test methodcom.helger.css.decl.visit.CSSVisitorDeclarationListTest.testModifyingCSSUrlVisitor ().

Note: it is safe to modify a CSS while iterating it, but only changes affecting children of the current node may be considered during the same iteration run.

CSS writing is performed with the classcom.helger.css.writer.CSSWriter. The most basic settings can be passed either directly to the constructor or using an instance ofcom.helger.css.writer.CSSWriterSettings which offers a quite find grained control of the output process. To write the content of aCascadingStyleSheet or anyICSSWriteable to an arbitraryjava.io.Writer, the methodwriteCSS is what you need. If you want the CSS serialized to aString the shortcut methodgetCSSAsString is available. For the remaining configuration methods please check the JavaDoc.

By default all CSS code is pretty-printed. To create a minified version of the CSS code callsetOptimizedOutput (true) andsetRemoveUnnecessaryCode (true) on yourCSSWriterSettings object.

Data URLs are URLs that directly contain the content inline. A regular use case is referencing small images directly inside a CSS. During CSS parsing no special handling for data URLs is added. Instead they are stored in aString like any other URL.

To special handle data URLs the classcom.helger.css.utils.CSSDataURLHelper offers the possibility to check if a URL is a data URL viapublic static boolean isDataURL (String). If this method returnstrue the methodpublic static CSSDataURL parseDataURL (String) can be used to extract all the information contained in the data URL. This method returnsnull if the passed URL is not a data URL.

ACSS shorthand property is a property that consists of multiple values. Classical examples aremargin orborder. ph-css contains support for selected shorthand properties. All shorthand related classes can be found in packagecom.helger.css.decl.shorthand. The supported shorthand properties are:

• background
• font
• border
• border-top
• border-right
• border-bottom
• border-left
• border-width
• border-style
• border-color
• margin
• padding
• outline
• list-style

All of these shorthand properties are registered in classCSSShortHandRegistry and you can manually register your own shorthand descriptors. TheCSSShortHandRegistry allows you to split a singleCSSDeclaration likeborder:1px dashed into the corresponding "sub-declarations":

// Parse a dummy declarationfinalCSSDeclarationaDecl =CSSReaderDeclarationList.readFromString ("border:1px dashed",ECSSVersion.CSS30).getDeclarationAtIndex (0);// Get the Shorthand descriptor for "border"finalCSSShortHandDescriptoraSHD =CSSShortHandRegistry.getShortHandDescriptor (ECSSProperty.BORDER);// And now split it into piecesfinalList <CSSDeclaration>aSplittedDecls =aSHD.getSplitIntoPieces (aDecl);

In the above example,aSplittedDecls will contain 3 elements with the following content:

• border-width:1px
• border-style:dashed
• border-color:black

Even though no color value was provided, the default valueblack is returned. For all "sub-declarations", sensible default values are defined.

ph-css contains a multitude of small utility class covering different aspects of CSS

• com.helger.css.utils.CSSColorHelper contains methods to read and write the different types of CSS color values (rgb, rgba, hsl, hsla and hex value)
• com.helger.css.utils.ECSSColor contains the basic CSS colors as an enumeration
• com.helger.css.ECSSUnit contains all the default CSS units (like.px orem)
• com.helger.css.utils.CSSNumberHelper contains methods for handling the combination of numeric values and units.
• com.helger.css.utils.CSSRectHelper contains methods for handling CSSrect values.
• com.helger.css.tools.MediaQueryTools provides shortcut methods for wrapping a completeCascadingStyleSheet in one or more media queries

• Reading a CSS 3.0 file
• Writing a CSS 3.0 file
• Creating a @font-face rule from scratch
• The code creates a CSS @font-face rule that looks like this:

  @font-face {font-family:"Your typeface";src:url("path/basename.eot");src:local("local font name"),url("path/basename.woff")format("woff"),url("path/basename.otf")format("opentype"),url("path/basename.svg#filename")format("svg");}

• Read the CSS content of a HTML style attribute
  • Reads the CSS content ofsStyle as CSS 3.0 and creates aCSSDeclarationList from it
• Visiting all declarations contained in an HTML style attribute
  • Similar to the above example, but visiting all declarations and printing them on stdout. Two different approaches are shown: first all declarations are retrieved via the native API, and second a custom visitor is used to determine all declarations. The result of this method looks like this:

  color: red (not important)background: fixed (important)

• Visit all URLs contained in a CSS
  • Read a CSS from a String and than extracts all contained URLs. The output looks like this:

  Import: foobar.css - source location reaches from [1/1] up to [1/21]background - references: a.gif - source location reaches from [2/22] up to [2/31]background-image - references: /my/folder/b.gif - source location reaches from [3/25] up to [3/47]

• Visit all URLs (incl.data URLs) contained in a CSS
  • Read a CSS from a String and than extracts all contained URLs with special focus on data URLs. The output looks like this:

  Import: /folder/foobar.cssbackground - references data URL with 158 bytes of contentbackground-image - references regular URL: /my/folder/b.gif

The following list gives an overview of known shortcomings in ph-css

• Escaped characters (like \26) are not interpreted correctly.

A Maven plugin to compress CSS files at build time using ph-css.

It requires Java 11 and Maven 3 to run.

Replacex.y.z with the version you want to use.

      <plugin>        <groupId>com.helger.maven</groupId>        <artifactId>ph-csscompress-maven-plugin</artifactId>        <version>x.y.z</version>        <executions>          <execution>            <goals>              <goal>csscompress</goal>            </goals>          </execution>        </executions>        <configuration>          <forceCompress>false</forceCompress>          <removeUnnecessaryCode>true</removeUnnecessaryCode>          <quoteURLs>true</quoteURLs>          <verbose>true</verbose>          <sourceDirectory>${basedir}/src/main/resources</sourceDirectory>        </configuration>      </plugin>

Configuration items are:

• FilesourceDirectory
  The directory where the source CSS files reside. It must be an existing directory.
  Defaults to${basedir}/src/main/resources
• FiletargetDirectory
  The directory where the taget CSS files reside. If the directory is not existig, it is created.
  Defaults to the source directory
• booleanrecursive
  Should all directories be scanned recursively for CSS files to compress?Defaults totrue
• booleanremoveUnnecessaryCode
  Should unnecessary code be removed (e.g. rules without declarations)?Defaults tofalse
• booleanquoteURLs
  Should URLs always be quoted? If false they are only quoted when absolutely necessary.Defaults tofalse
• booleanwriteNamespaceRules
  Should@namespace rules be written?Defaults totrue
• booleanwriteFontFaceRules
  Should@font-face rules be written?Defaults totrue
• booleanwriteKeyframesRules
  Should@keyframes rules be written?Defaults totrue
• booleanwriteMediaRules
  Should@media rules be written?Defaults totrue
• booleanwritePageRules
  Should@page rules be written?Defaults totrue
• booleanwriteViewportRules
  Should@viewport rules be written?Defaults totrue
• booleanwriteSupportsRules
  Should@supports rules be written?Defaults totrue
• booleanwriteUnknownRules
  Should unknown@ rules be written?Defaults totrue
• booleanforceCompress
  Should the CSS files be compressed, even if the timestamp of the compressed file is newer than the timestamp of the original CSS file?Defaults tofalse
• booleanverbose
  Iftrue some more output is emitted.Defaults tofalse
• booleanbrowserCompliantMode (since 1.4.0)Iftrue the "browser compliant mode" for parsing is selected.Defaults tofalse.
• booleankeepDeprecatedProperties (since 7.0.4)Iftrue, deprecated properties like*zoom are kept when reading. Iffalse they are discarded.Defaults tofalse.
• StringsourceEncoding
  The encoding of the source CSS files to be used for reading the CSS file in case neither a@charset rule nor a BOM is present.Defaults toISO-8859-1 (wasUTF-8 before 7.0.4)
• StringtargetFileExtension
  The filename extension that should be used for the minified/compressed CSS file.Defaults to.min.css
• StringtargetEncoding (since 1.4.0)The encoding of the target CSS files to be used for writing the CSS file.Defaults toUTF-8.

• v7.0.4 - 2025-02-17
  • Added additional media query features. See [#104}(#104) - thx @nhubbard
  • Added new settingCSSReaderSettings.setKeepDeprecatedProperties(boolean) to customize if they should be read or discarded. See#107 - thx @hrozhkov1
  • Added the propertykeepDeprecatedProperties to the Maven plugin
  • Changed the default reading charset of the Maven plugin fromUTF-8 toISO-8859-1 to comply to the API based reading
  • Added thetargetDirectory property to the Maven plugin. See#106 - thx @isochronous
• v7.0.3 - 2024-09-23
  • Added support for the:is,:has and:where pseudo functions, fixing#88 (thx @brbog),#97 (thx @nafg) and#101 (thx @subbudvk)
• v7.0.2 - 2024-03-28
  • Updated to ph-commons 11.1.5
  • Created Java 21 compatibility
• v7.0.1 - 2023-07-31
  • Updated to ph-commons 11.1
• v7.0.0 - 2023-02-01
  • Using Java 11 as the baseline
  • Updated to ph-commons 11
• v6.5.0 - 2022-01-28
  • Re-added explicit support for deprecated property names starting with$ or* but only inside style declarations. Seeissue #84 andPR #85 - thanks @shagkur
  • ThereforeICSSParseErrorHandler.onCSSDeprecatedProperty was added
• v6.4.4 - 2022-01-18
  • Added support for:host-context. Seeissue #80 andPR #81 - thanks @shagkur
  • Improved support for the scientific number parsing. Seeissue #82 andPR #83 - thanks @shagkur
• v6.4.3 - 2022-01-13
  • Extended API ofCSSReaderDeclarationList. Seeissue #78 - thanks @shagkur
  • Added support for the scientific number (as in1e6) support in parsing. Seeissue #79 - thanks @shagkur
• v6.4.2 - 2022-01-12
  • Improved support for:host and::slotted. Seeissue #77 - thanks @shagkur
  • Added a possibility to differentiate between String and Identifier inCSSExpressionMemberTermSimple. Seeissue #75 andPR #76 - thanks @shagkur
• v6.4.1 - 2022-01-10
  • Added support for:host and::slotted. Seeissue #73 andPR #74 - thanks @shagkur
  • Renamed the "math*" rules to "calc*" - that also touched a few internal constants
  • Fixed the emitting of pseudo selector functions without parameters (as in:lang()). Seeissue #72) - thanks @shagkur
  • Updated to latest version of ParserGeneratorCC for a bit more efficient code
• v6.4.0 - 2021-11-22
  • Fixed SonarCloud issues
  • Removed the serialisability of the objects, because it was never done in a consistent way
  • Added support for theflex shorthand property
• v6.3.4 - 2021-06-09
  • Fixed an error with the shorthand expansion ofborder-width. SeePR #68 - thanks @rockwotj
• v6.3.3 - 2021-05-31
  • Allow unknown rules inside@media rules. Seeissue #67 - thanks @yinkwok-ys
• v6.3.2 - 2021-05-25
  • Fixed an error with the negation parameters. Seeissue #66 - thanks @rockwotj
• v6.3.1 - 2021-05-02
  • Added support for@footnote in@page rules. SeePR #64 - thanks @schmidti159
• v6.3.0 - 2021-03-22
  • Updated to ph-commons 10
• v6.2.4 - 2021-02-25
  • Updated to ph-commons 9.4.6, leading to a more resilient DataURL parsing
  • Fixed the ignorance of minimum and maximum parameter count in classCSSPropertyColors
  • Fixed the case-sensitivity of CSS variables declarations. Seeissue #63
• v6.2.3 - 2020-05-14
  • Fixed an issue with the URL visitor not recursively descending into expression members. Seeissue #59
• v6.2.2 - 2020-03-29
  • Updated to ph-commons 9.4.0
• v6.2.1 - 2020-02-29
  • Improved the pattern for colors in hex values. SeePR #55.
  • Fixed a grammar issue that resulted in failedcalc parsing (issue #57). The implications of this change are, that the special IE6 and IE7 hacks with$ and* as identifier prefixes are no longer supported. If you need to parse CSS suitable for these old browsers, stay with v6.2.0.
  • Updated CSS properties of the completed specifications
• v6.2.0 - 2019-06-30
  • Fixed NPE inCSSWriterSettings.DEFAULT_SETTINGS because of wrong initialization order (#53)
  • Added some-o- media expression features
  • Changing browser compliant parsing in a way, so that lessnull is returned in parsing (#41)
  • The default "custom error handler" for parsing was changed fromThrowingCSSParseErrorHandler toLoggingCSSParseErrorHandler for best browser compliant mode handling
  • Improved fault tolerance in parsing when "browser compliant mode" is enabled
• v6.1.3 - 2019-06-12
  • Added some performance tweaks
  • Added possibility to disable the usage of the source location usingCSSReaderSettings (for performance reasons)
• v6.1.2 - 2019-02-17
  • Extended list of known media expression features (e.g. used in Bootstrap 4)
• v6.1.1 - 2018-04-11
  • Allow nestedcalc function (#48)
• v6.1.0 - 2018-03-23
  • Fixed a grammar issue forcalc with spaces (as inwidth: calc( 100% - 2.4em );)
  • Removed dependency uponjava.awt.Color for improved Android compatibility.
• v6.0.0 - 2017-12-20
  • Extracted base classAbstractHasTopLevelRules for type-safe access of top-level rules (#39)
  • Updated to ph-commons 9.0.0
  • Extended API to more easily access the CSS declaration expression string (#43)
  • Data URI scheme is treated case-insensitive (#44)
  • Extended API for easier CSS property comparison (#45)
• v5.0.4 - 2017-04-06
  • Improved special identifier handling in expressions (#38)
  • Added support for css-grid spec with new "line-name" syntax element
  • Added new CSS units:fr,vmax andQ
• v5.0.3 - 2017-01-09
  • Binds to ph-commons 8.6.0
  • Added custom callback for illegal characters
• v5.0.2 - 2016-10-21
  • Made tab size configurable (issue #29)
  • Improved media expressions (issue #30)
  • Allowing to disable consistency checks in classCSSValue
  • Made CSS interpretation warnings customizable with classICSSInterpretErrorHandler (issue #33)
• v5.0.1 - 2016-08-17
  • Using "modern java template" for JavaCC parser - results in quicker execution
  • Enhancement issue #27
  • Integratedph-csscompress-maven-plugin into this repository
  • Bug fix wrong OutputStream (issue #28)
• v5.0.0 - 2016-06-12
  • Using JDK8 as the basis
  • removed explicit grammar for CSS 2.1 (issue #20)
  • Added browser compliant error handler
• v4.2.0 - 2018-03-22
  • Removed dependency uponjava.awt.Color for improved Android compatibility.
• v4.1.6 - 2016-10-21
  • Made CSS interpretation warnings customizable with classICSSInterpretErrorHandler (issue #33)
• v4.1.5 - 2016-09-16
  • Improved media expressions (issue #30)
  • Integrated ph-csscompress-maven-plugin into this project (compatibility to 5.x)
• v4.1.4 - Improved browser compliant parsing (issue #26)
• v4.1.3 - Improved browser compliant parsing (issue #24)
• v4.1.2 - Improved browser compliant parsing (issue #21)
• v4.1.1 - Skipping style rules with invalid selectors in browser compliant mode; allowing "--" identifier prefix; improved unknown rule parsing (issues #17, #18, #19)
• v4.1.0 - Improved calc parsing; extended support for page rules with page margin blocks
• v4.0.1 - Added customizable newline characters
• v4.0.0 - Updated to ph-commons 6.0.0 and added "browser compliant parsing mode"
• v3.9.2 - Updated to ph-commons 5.7.1 and fix for some minor issues
• v3.9.1 - Updated to ph-commons 5.6.0 and fix for some shorthand handling
• v3.9.0 - API improvements and support for vendor specific "-calc" added
• v3.8.2 - small bugfix release
• v3.8.1 - improvements for expression parsing and single line comment handling
• v3.8.0 - initial version in com.helger group and package

My personalCoding Styleguide |It is appreciated if you star the GitHub project if you like it.