Is Xerces DOM implementation thread-safe?
No. DOM does not require implementations to be thread safe. If you need to access the DOM from multiple threads, you are required to add the appropriate locks to your application code.
How do I create a DOM parser?
You can create a DOM parser by using the Java APIs for XML Processing (JAXP) or using the DOM Level 3 Load and Save.
The following source code shows how to create the parser with JAXP:
The following source code shows how to create the parser using
How do I serialize DOM to an output stream?
You can serialize a DOM tree by using the DOM Level 3 Load and Save.
LSSerializer performs automatic namespace fixup to make your document namespace
well-formed.
You can also serialize a DOM tree by using the JAXP Transformer API.
It is also possible to serialize a DOM tree by using the Xerces org.apache.xml.XMLSerializer serialization code directly.
This non-standard way of serializing a DOM has been deprecated since Xerces-J 2.9.0 and should be avoided if possible.
Does Xerces DOM implement java.io.Serializable?
Yes. Xerces DOM can be serialized using Java object serialization. It is recommended that a DOM be serialized as XML where possible instead of using object serialization.
By choosing object serialization you sacrifice interoperability between parsers and we do not guarantee interoperability between versions of Xerces. It should be used with caution.
Some rough measurements have shown that XML serialization performs better than Java object serialization and that XML instance documents require less storage space than object serialized DOMs.
How do I supply my own implementation of the DOM?
Use the
http://apache.org/xml/properties/dom/document-class-name property
to register your own implementation of the
org.w3c.dom.Document interface.
Xerces provides the following implementations of the
org.w3c.dom.Document interface:
org.apache.xerces.dom.CoreDocumentImpl --
supports DOM Level 3 Core Recommendation.org.apache.xerces.dom.DocumentImpl --
supports DOM Level 3 Core, Mutation Events, Traversal and Ranges.org.apache.xerces.dom.PSVIDocumentImpl --
provides access to the post schema validation infoset via DOM.How do I access the DOM Level 3 functionality?
The DOM Level 3 functionality is now exposed by default since Xerces-J 2.7.0.
The experimental interfaces which were once present in the org.apache.xerces.dom3
package no longer exist. This package existed primarily so that the DOM Level 2
and DOM Level 3 implementations in Xerces-J 2.6.2 and prior could co-exist. Code which
depended on the org.apache.xerces.dom3 package must be modified to use the
official DOM Level 3 API located in the org.w3c.dom.* packages.
For more information, refer to the DOM Level 3 Implementation page.
How do I run DOM Level 3 applications under JDK 1.4 and higher?
Use the
How do I retrieve PSVI from the DOM?
By default Xerces does not store the PSVI information in the DOM tree.
The following source shows you how to parse an XML document (using JAXP) and how to retrieve PSVI (using the dbf is JAXP DocumentBuilderFactory
// all of the following features must be set:
dbf.setNamespaceAware(true);
dbf.setValidating(true);
dbf.setAttribute("http://apache.org/xml/features/validation/schema",
Boolean.TRUE);
// you also must specify Xerces PSVI DOM implementation
// "org.apache.xerces.dom.PSVIDocumentImpl"
dbf.setAttribute("http://apache.org/xml/properties/dom/document-class-name",
"org.apache.xerces.dom.PSVIDocumentImpl");
...
Document doc = db.parse(args[0]);
if (doc.getDocumentElement().isSupported("psvi", "1.0")){
ElementPSVI psviElem = (ElementPSVI)doc.getDocumentElement();
XSElementDeclaration decl = psviElem.getElementDeclaration();
...
}
If you want to build the DOM tree in memory and be able to access the PSVI information you need to start by instantiating org.apache.xerces.dom.PSVIDocumentImpl or you need to use the DOM Level 3 API as shown in the following example:
You can find more information about how to use the XML Schema API
How can I make sure that my DOM document in memory conforms to a schema?
DOM revalidation is supported via W3C DOM Level 3 Core Document.normalizeDocument().
To revalidate the document you need:
DOMConfiguration from the Document,
and set validate feature to true.
documentElement, or
by setting schema-location parameter on the
DOMConfiguration.
LSResourceResolver and set it
via resource-resolver on the DOMConfiguration.
Note: if a document contains any DOM Level 1 nodes (the nodes created using createElement,
createAttribute, etc.) a fatal error will occur as described in the
DOM Level 1 methods are namespace ignorant. Therefore, while it is safe to use these methods when not dealing with namespaces, using them and the new ones at the same time should be avoided. DOM Level 1 methods solely identify attribute nodes by their nodeName. On the contrary, the DOM Level 2 methods related to namespaces, identify attribute nodes by their namespaceURI and localName. Because of this fundamental difference, mixing both sets of methods can lead to unpredictable results.
For more information, please refer to the DOM Level 3 Implementation page.
How do I handle errors?
You should register an error handler with the parser by supplying
a class which implements the org.xml.sax.ErrorHandler
interface. This is true regardless of whether your parser is a
DOM based or SAX based parser.
You can register an error handler on a DocumentBuilder
created using JAXP like this:
If you are using LSParser by supplying
a class which implements the org.w3c.dom.DOMErrorHandler
interface. Note: all exceptions during parsing or saving XML data
are reported via DOMErrorHandler.
How can I control the way that entities are represented in the DOM?
The Xerces http://apache.org/xml/features/dom/create-entity-ref-nodes
feature
(or corresponding DOM Level 3 LSParser entities feature)
controls how entities appear in the DOM tree. When one of those features
is set to true (the default), an occurrence of an entity reference
in the XML document will be represented by a subtree with an
EntityReference node at the root whose children represent the
entity expansion.
If the feature is false, an entity reference in the XML document is represented by only the nodes that represent the entity expansion.
In either case, the entity expansion will be a DOM tree representing the structure of the entity expansion, not a text node containing the entity expansion as text.
How do I associate my own data with a node in the DOM tree?
The class org.apache.xerces.dom.NodeImpl provides the
setUserData(Object o) and the Object
getUserData() methods that you can use to attach any object
to a node in the DOM tree.
Beware that you should try and remove references to your data on
nodes you no longer use (by calling setUserData(null),
or these nodes will not be garbage collected until the entire
document is garbage collected.
If you are using Xerces with the DOM Level 3 support
you can use org.w3c.dom.Node.setUserData() and register your own
UserDataHandler.
Why does getElementById not work for documents validated against XML Schemas?
Make sure the validation feature and the schema feature are turned on before you parse a document.
How do I specify an ID attribute in the DOM?
You can use the DOM level 3 setIdAttribute, setIdAttributeNS, and setIdAttributeNode methods
to specify ID attribute in the DOM. See
How do I access type information in the DOM?
validate or
validate-if-schema feature must be turned on).
If you need to access the full PSVI in the DOM please refer to Using XML Schemas.