When the NekoHTML project was re-launched on SourceForge, the version was changed from 0.9.5 to 1.9.6. The new version marks a fresh start for NekoHTML and indicates that the project is mature and stable.
The HTML DOM specification explicitly states that element and attribute names follow the semantics, including case-sensitivity, specified in the HTML 4 specification. In addition, section 1.2.1 of the HTML 4.01 specification states:
Element names are written in uppercase letters (e.g., BODY). Attribute names are written in lowercase letters (e.g., lang, onsubmit).
The Xerces HTML DOM implementation (used by default in the
NekoHTML DOMParser class) follows this convention.
Therefore, even if the
"http://cyberneko.org/html/properties/names/elems" property is
set to "lower", the DOM will still uppercase the element names.
To get around this problem, instantiate a Xerces2 DOMParser
object using the NekoHTML parser configuration. By default, the
Xerces DOM parser class creates a standard XML DOM tree, not
an HTML DOM tree. Therefore, the element and attribute names
will follow the settings for the
"http://cyberneko.org/html/properties/names/elems" and
"http://cyberneko.org/html/properties/names/attrs" properties.
However, realize that the application will not be able to cast
the document nodes to the HTML DOM interfaces for accessing the
document's information.
The following sample code shows how to instantiate a DOM parser using the NekoHTML parser configuration:
// import org.apache.xerces.parsers.DOMParser; // import org.cyberneko.html.HTMLConfiguration; DOMParser parser = new DOMParser(new HTMLConfiguration());
Using the NekoHTML DOM parser to parse HTML documents with namespace information can result in a hierarchy request error to be thrown. For example:
org.w3c.dom.DOMException: HIERARCHY_REQUEST_ERR: An attempt was made to insert a node where it is not permitted.
The Xerces HTML DOM implementation does not support namespaces
and cannot represent XHTML documents with namespace information.
Therefore, in order to use the default HTML DOM implementation
with NekoHTML's DOMParser to parse XHTML documents,
you must turn off namespace processing. For example:
// import org.cyberneko.html.parsers.DOMParser; DOMParser parser = new DOMParser(); parser.setFeature("http://xml.org/sax/features/namespaces", false);
If your application requires namespace processing to be turned
on and uses the DOM API, another option is to add a
custom filter to the parsing pipeline to remove namespace
information before the DOMParser constructs the
document. For example:
// import org.cyberneko.html.filters.DefaultFilter; // import org.cyberneko.html.parsers.DOMParser; // import org.apache.xerces.xni.*; // import org.apache.xerces.xni.parser.XMLDocumentFilter; DOMParser parser = new DOMParser(); parser.setProperty("http://cyberneko.org/html/properties/filters", new XMLDocumentFilter[] { new DefaultFilter() { public void startElement(QName element, XMLAttributes attrs, Augmentations augs) throws XNIException { element.uri = null; super.startElement(element, attrs, augs); } // ...etc... } });
The NekoHTML parser has a property that allows you to append custom filter components at the end of the parser pipeline as detailed in the Pipeline Filters documentation. But this means that processing occurs after the tag-balancer does its job. However, the same property can also be used to insert custom components before the tag-balancer as well.
The secret is to disable the tag-balancing feature and
then add another instance of the HTMLTagBalancer
component at the end of your custom filter pipeline. The following
example shows how to add a custom filter before the tag-balancer
in the DOM parser. (This also works on all other types of parsers
that use the HTMLConfiguration.)
// import org.cyberneko.html.HTMLConfiguration; // import org.cyberneko.html.parsers.DOMParser; // import org.apache.xerces.xni.parser.XMLDocumentFilter; DOMParser parser = new DOMParser(); parser.setFeature("http://cyberneko.org/html/features/balance-tags", false); XMLDocumentFilter[] filters = { new MyFilter(), new HTMLTagBalancer() }; parser.setProperty("http://cyberneko.org/html/properties/filters", filters);
Frequently, HTML is used within applications and online forms to allow users to enter rich-text. In these situations, it is useful to be able to parse the entered text as a document fragment. In other words, the entered text represents content within the HTML <body> element — it is not a full HTML document.
Starting with version 0.7.0, NekoHTML has added a feature that
allows the application to parse HTML document fragments. Setting
the "http://cyberneko.org/html/features/balance-tags/document-fragment"
feature to true instructs the tag-balancer to
balance only tags found within the HTML <body> element.
The surrounding <body> and <html> elements are not
inserted.
Note:
The document-fragment feature should not be
used on the DOMParser class since it relies on
balanced elements in order to correctly construct the DOM
tree. However, a new parser class has been added to NekoHTML
to allow you parser DOM document fragments. Please refer to
the Usage Instructions
for more information.
Many applications are interested in knowing where elements, attributes, and character data appear within the source document. To aid these applications, NekoHTML has a feature that reports the starting and ending character offsets of each piece of information in the document.
In order to tell NekoHTML to report the character offsets for document information, the augmentations feature needs to be turned on. For example:
// import org.cyberneko.html.parsers.SAXParser; String AUGMENTATIONS = "http://cyberneko.org/html/features/augmentations"; SAXParser parser = new SAXParser(); parser.setFeature(AUGMENTATIONS, true);
Once the feature is enabled, the location information can be
obtained by querying the
HTMLEventInfo
object in the Augmentations parameter passed to
all XNI callbacks. This dependency is required because DOM
and SAX lack the ability to communicate this detailed
information to the application.
The XNI dependence does not restrict applications to only
using the Xerces Native Interface, however. The best way to
use this information is by extending one of the parsers in the
org.cyberneko.html.parsers package and overriding
the methods of interest. The following example extends the
SAXParser class to retrieve the event information
for start elements:
public class MySAXParser extends SAXParser { static final String AUGMENTATIONS = "http://cyberneko.org/html/features/augmentations"; public MySAXParser() { setFeature(AUGMENTATIONS, true); } public void startElement(QName element, XMLAttributes attrs, Augmentations augs) throws XNIException { // get offset information HTMLEventInfo info = (HTMLEventInfo)augs.getItem(AUGMENTATIONS); boolean synthesized = info.isSynthesized(); int beginRow = info.getBeginLineNumber(); int beginCol = info.getBeginColumnNumber(); int endRow = info.getEndLineNumber(); int endCol = info.getEndColumnNumber(); // perform default processing super.startElement(element, attrs, augs); } }
Note: The NekoHTML parser reports character offsets and is unable to report the byte offsets that map to the resulting characters. The parser takes advantage of the character decoders present in the JVM which do not report byte offsets. And because these decoders buffer blocks of bytes internally for performance reasons, it is not possible to write a custom input stream to perform this mapping between byte and character offsets. If you control the source documents and can restrict them to a single character encoding, then writing a custom reader to perform this mapping is more feasible.
Note: Currently, only the start and end row and column information can be queried. In the future, NekoHTML will be able to report character offsets from the beginning of the file. This does not, however, mean that byte offsets will also be supported at a future date.
While NekoHTML is a rather small library, many users complain about the size of the Xerces2 library. However, the full Xerces2 library is not required in order to use the NekoHTML parser. Because the CyberNeko HTML parser is written using the Xerces Native Interface (XNI) framework that forms the foundation of the Xerces2 implementation, only that part is required to write applications using NekoHTML.
For convenience, a small Jar file containing only the necessary
parts of the framework and utility classes from Xerces2 is
distributed with the NekoHTML package. The Jar file, called
xercesMinimal.jar, can be found in the
lib/ directory of the distribution. Simply add
this file to your classpath along with nekohtml.jar.
However, there are a few restrictions if you choose to use
the xercesMinimal.jar file instead of the full
Xerces2 package. First, you cannot use the DOM and SAX parsers
included with NekoHTML because they use the Xerces2 base
classes. Second, because you cannot use the convenience
parser classes, your application must be written using the
XNI framework. However, using the XNI framework is not
difficult for programmers familiar with SAX. [Note: future
versions of NekoHTML may include custom implementations of
the DOM and SAX parsers to avoid this dependence on the
Xerces2 library.]
Most users of the CyberNeko HTML parser will not have a
problem including the full Xerces2 package because the
application is likely to need an XML parser implementation.
However, for those users that are concerned about Jar file
size, then using the xercesMinimal.jar file
may be a useful alternative.
Since version 0.9.3, NekoHTML includes a class that can be
used to query the product version within application code.
The Version class in the
org.cyberneko.html package contains a method,
getVersion that returns the NekoHTML version
as a string. For example:
// import org.cyberneko.html.Version; System.err.println(Version.getVersion());
The Version also includes a main
method that prints the version information to standard output.
The version and product information can also be queried using the Java package API. For example:
Class cls = Class.forName("org.cyberneko.html.HTMLConfiguration"); Package pkg = cls.getPackage(); String name = pkg.getName(); String specTitle = pkg.getSpecificationTitle(); String specVendor = pkg.getSpecificationVendor(); String specVersion = pkg.getSpecificationVersion(); String implTitle = pkg.getImplementationTitle(); String implVendor = pkg.getImplementationVendor(); String implVersion = pkg.getImplementationVersion();