Package javax.xml.transform
Source
and
Result
interfaces.
To provide concrete classes for the user, the API defines specializations
of the interfaces found at the root level. These interfaces are found in
javax.xml.transform.sax
, javax.xml.transform.dom
,
javax.xml.transform.stax
, and javax.xml.transform.stream
.
Creating Objects
The API allows a concrete TransformerFactory
object to be created from the static function
TransformerFactory.newInstance()
.
Specification of Inputs and Outputs
This API defines two interface objects called Source
and Result
. In order to pass Source and Result
objects to the interfaces, concrete classes must be used. The following concrete
representations are defined for each of these objects:
StreamSource
and
StreamResult
,
StAXSource
and
StAXResult
, and
SAXSource
and
SAXResult
, and
DOMSource
and
DOMResult
. Each of these objects defines a
FEATURE string (which is in the form of a URL), which can be passed into
TransformerFactory.getFeature(java.lang.String)
to see if the given
type of Source or Result object is supported. For instance, to test if a
DOMSource and a StreamResult is supported, you can apply the following test.
TransformerFactory tfactory = TransformerFactory.newInstance();
if (tfactory.getFeature(DOMSource.FEATURE) &&
tfactory.getFeature(StreamResult.FEATURE)) {
...
}
Qualified Name Representation
Namespaces present something of a problem area when dealing with XML objects. Qualified Names appear in XML markup as prefixed names. But the prefixes themselves do not hold identity. Rather, it is the URIs that they contextually map to that hold the identity. Therefore, when passing a Qualified Name like "xyz:foo" among Java programs, one must provide a means to map "xyz" to a namespace.
One solution has been to create a "QName" object that holds the namespace URI, as well as the prefix and local name, but this is not always an optimal solution, as when, for example, you want to use unique strings as keys in a dictionary object. Not having a string representation also makes it difficult to specify a namespaced identity outside the context of an XML document.
In order to pass namespaced values to transformations, for instance when setting
a property or a parameter on a Transformer
object,
this specification defines that a String "qname" object parameter be passed as
two-part string, the namespace URI enclosed in curly braces ({}), followed by
the local name. If the qname has a null URI, then the String object only
contains the local name. An application can safely check for a non-null URI by
testing to see if the first character of the name is a '{' character.
For example, if a URI and local name were obtained from an element defined with <xyz:foo xmlns:xyz="http://xyz.foo.com/yada/baz.html"/>, then the Qualified Name would be "{http://xyz.foo.com/yada/baz.html}foo". Note that the prefix is lost.
Result Tree Serialization
Serialization of the result tree to a stream can be controlled with the
Transformer.setOutputProperties(java.util.Properties)
and the
Transformer.setOutputProperty(java.lang.String, java.lang.String)
methods.
These properties only apply to stream results, they have no effect when
the result is a DOM tree or SAX event stream.
Strings that match the XSLT
specification for xsl:output attributes can be referenced from the
OutputKeys
class. Other strings can be
specified as well.
If the transformer does not recognize an output key, a
IllegalArgumentException
is thrown, unless the key name
is namespace qualified. Output key names
that are namespace qualified are always allowed, although they may be
ignored by some implementations.
If all that is desired is the simple identity transformation of a
source to a result, then TransformerFactory
provides a
TransformerFactory.newTransformer()
method
with no arguments. This method creates a Transformer that effectively copies
the source to the result. This method may be used to create a DOM from SAX
events or to create an XML or HTML stream from a DOM or SAX events.
Exceptions and Error Reporting
The transformation API throw three types of specialized exceptions. A
TransformerFactoryConfigurationError
is parallel to
the FactoryConfigurationError
, and is thrown
when a configuration problem with the TransformerFactory exists. This error
will typically be thrown when the transformation factory class specified with
the "javax.xml.transform.TransformerFactory" system property cannot be found or
instantiated.
A TransformerConfigurationException
may be thrown if for any reason a Transformer can not be created. A
TransformerConfigurationException may be thrown if there is a syntax error in
the transformation instructions, for example when
TransformerFactory.newTransformer(javax.xml.transform.Source)
is
called.
TransformerException
is a general
exception that occurs during the course of a transformation. A transformer
exception may wrap another exception, and if any of the
TransformerException.printStackTrace()
methods are called on it, it will produce a list of stack dumps, starting from
the most recent. The transformer exception also provides a
SourceLocator
object which indicates where
in the source tree or transformation instructions the error occurred.
TransformerException.getMessageAndLocation()
may be called to get an error message with location info, and
TransformerException.getLocationAsString()
may be called to get just the location string.
Transformation warnings and errors are sent to an
ErrorListener
, at which point the application may
decide to report the error or warning, and may decide to throw an
Exception
for a non-fatal error. The ErrorListener
may be set via TransformerFactory.setErrorListener(javax.xml.transform.ErrorListener)
for reporting errors that have to do with syntax errors in the transformation
instructions, or via Transformer.setErrorListener(javax.xml.transform.ErrorListener)
to report errors that occur during the transformation. The ErrorListener
on both objects will always be valid and non-null
, whether set by
the application or a default implementation provided by the processor.
Resolution of URIs within a transformation
The API provides a way for URIs referenced from within the stylesheet
instructions or within the transformation to be resolved by the calling
application. This can be done by creating a class that implements the
URIResolver
interface, with its one method,
URIResolver.resolve(java.lang.String, java.lang.String)
, and use this class to
set the URI resolution for the transformation instructions or transformation
with TransformerFactory.setURIResolver(javax.xml.transform.URIResolver)
or
Transformer.setURIResolver(javax.xml.transform.URIResolver)
. The
URIResolver.resolve
method takes two String arguments, the URI
found in the stylesheet instructions or built as part of the transformation
process, and the base URI against which the first argument will be made absolute
if the absolute URI is required.
The returned Source
object must be usable by
the transformer, as specified in its implemented features.
- Since:
- 1.5
-
ClassDescriptionThe listener interface used by a
TransformerFactory
orTransformer
to notify callers of error messages that occur during a transformation process.Provides string constants that can be used to set output properties for a Transformer, or to retrieve output properties from a Transformer or Templates object.An object that implements this interface contains the information needed to build a transformation result tree.An object that implements this interface contains the information needed to act as source input (XML source or transformation instructions).This interface is primarily for the purposes of reporting where an error occurred in the XML source or transformation instructions.An object that implements this interface is the runtime representation of processed transformation instructions.An instance of this abstract class can transform a source tree into a result tree.Indicates a serious configuration error.This class specifies an exceptional condition that occurred during the transformation process.A TransformerFactory instance can be used to createTransformer
andTemplates
objects.Thrown when a problem with configuration with the Transformer Factories exists.An object that implements this interface that can be called by the processor to turn a URI used in document(), xsl:import, or xsl:include into a Source object.