Transformer

AI-generated Key Takeaways

• The Transformer class in Java transforms XML data from a source to a result.

• It allows setting parameters, output properties, and error handling for the transformation process.

• Transformer objects are not thread-safe for concurrent use but can be reused multiple times.

• Developers can obtain a Transformer instance using the TransformerFactory.

• The transform method executes the transformation, taking a Source and a Result as input.

public abstract class Transformer extends Object

An instance of this abstract class can transform a source tree into a result tree.

An instance of this class can be obtained with the TransformerFactory.newTransformer method. This instance may then be used to process XML from a variety of sources and write the transformation output to a variety of sinks.

An object of this class may not be used in multiple threads running concurrently. Different Transformers may be used concurrently by different threads.

A Transformer may be used multiple times. Parameters and output properties are preserved across transformations.

Protected Constructor Summary

Transformer() Default constructor is protected on purpose.

Public Method Summary

abstract void	clearParameters() Clear all parameters set with setParameter.
abstract ErrorListener	getErrorListener() Get the error event handler in effect for the transformation.
abstract Properties	getOutputProperties() Get a copy of the output properties for the transformation.
abstract String	getOutputProperty(String name) Get an output property that is in effect for the transformer.
abstract Object	getParameter(String name) Get a parameter that was explicitly set with setParameter.
abstract URIResolver	getURIResolver() Get an object that will be used to resolve URIs used in document().
void	reset() Reset this Transformer to its original configuration.
abstract void	setErrorListener(ErrorListener listener) Set the error event listener in effect for the transformation.
abstract void	setOutputProperties(Properties oformat) Set the output properties for the transformation.
abstract void	setOutputProperty(String name, String value) Set an output property that will be in effect for the transformation.
abstract void	setParameter(String name, Object value) Add a parameter for the transformation.
abstract void	setURIResolver(URIResolver resolver) Set an object that will be used to resolve URIs used in document().
abstract void	transform(Source xmlSource, Result outputTarget) Transform the XML Source to a Result.

Inherited Method Summary

From class java.lang.Object

Object	clone() Creates and returns a copy of this Object.
boolean	equals(Object obj) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of Class that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait(long timeout, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait(long timeout) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object.

Protected Constructors

protected Transformer ()

Default constructor is protected on purpose.

Public Methods

public abstract void clearParameters ()

Clear all parameters set with setParameter.

public abstract ErrorListener getErrorListener ()

Get the error event handler in effect for the transformation. Implementations must provide a default error listener.

Returns

• The current error handler, which should never be null.

public abstract Properties getOutputProperties ()

Get a copy of the output properties for the transformation.

The properties returned should contain properties set by the user, and properties set by the stylesheet, and these properties are "defaulted" by default properties specified by section 16 of the XSL Transformations (XSLT) W3C Recommendation. The properties that were specifically set by the user or the stylesheet should be in the base Properties list, while the XSLT default properties that were not specifically set should be the default Properties list. Thus, getOutputProperties().getProperty(String key) will obtain any property in that was set by setOutputProperty(String, String), setOutputProperties(Properties), in the stylesheet, or the default properties, while getOutputProperties().get(String key) will only retrieve properties that were explicitly set by setOutputProperty(String, String), setOutputProperties(Properties), or in the stylesheet.

Note that mutation of the Properties object returned will not effect the properties that the transformer contains.

If any of the argument keys are not recognized and are not namespace qualified, the property will be ignored and not returned. In other words the behavior is not orthogonal with setOutputProperties.

Returns

• A copy of the set of output properties in effect for the next transformation.

See Also

• OutputKeys
• Properties
• XSL Transformations (XSLT) Version 1.0

public abstract String getOutputProperty (String name)

Get an output property that is in effect for the transformer. The property specified may be a property that was set with setOutputProperty, or it may be a property specified in the stylesheet.

Parameters

name	A non-null String that specifies an output property name, which may be namespace qualified.

Returns

• The string value of the output property, or null if no property was found.

Throws

IllegalArgumentException	If the property is not supported.

See Also

• OutputKeys

public abstract Object getParameter (String name)

Get a parameter that was explicitly set with setParameter.

This method does not return a default parameter value, which cannot be determined until the node context is evaluated during the transformation process.

Parameters

name	of Object to get

Returns

• A parameter that has been set with setParameter.

public abstract URIResolver getURIResolver ()

Get an object that will be used to resolve URIs used in document().

Returns

• An object that implements the URIResolver interface, or null.

public void reset ()

Reset this Transformer to its original configuration.

Transformer is reset to the same state as when it was created with TransformerFactory.newTransformer(), TransformerFactory.newTransformer(Source) or Templates.newTransformer(). reset() is designed to allow the reuse of existing Transformers thus saving resources associated with the creation of new Transformers.

The reset Transformer is not guaranteed to have the same URIResolver or ErrorListener Objects, e.g. Object.equals(Object). It is guaranteed to have a functionally equal URIResolver and ErrorListener.

public abstract void setErrorListener (ErrorListener listener)

Set the error event listener in effect for the transformation.

Parameters

listener	The new error listener.

Throws

IllegalArgumentException	if listener is null.

public abstract void setOutputProperties (Properties oformat)

Set the output properties for the transformation. These properties will override properties set in the Templates with xsl:output.

If argument to this function is null, any properties previously set are removed, and the value will revert to the value defined in the templates object.

Pass a qualified property key name as a two-part string, the namespace URI enclosed in curly braces ({}), followed by the local name. If the name has a null URL, the String only contain 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 no prefix is used.

An IllegalArgumentException is thrown if any of the argument keys are not recognized and are not namespace qualified.

Parameters

oformat	A set of output properties that will be used to override any of the same properties in affect for the transformation.

See Also

• OutputKeys
• Properties

public abstract void setOutputProperty (String name, String value)

Set an output property that will be in effect for the transformation.

Pass a qualified property name as a two-part string, the namespace URI enclosed in curly braces ({}), followed by the local name. If the name has a null URL, the String only contain 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 no prefix is used.

The Properties object that was passed to setOutputProperties(Properties) won't be effected by calling this method.

Parameters

name	A non-null String that specifies an output property name, which may be namespace qualified.
value	The non-null string value of the output property.

Throws

IllegalArgumentException	If the property is not supported, and is not qualified with a namespace.

See Also

• OutputKeys

public abstract void setParameter (String name, Object value)

Add a parameter for the transformation.

Pass a qualified name as a two-part string, the namespace URI enclosed in curly braces ({}), followed by the local name. If the name has a null URL, the String only contain 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 no prefix is used.

Parameters

name	The name of the parameter, which may begin with a namespace URI in curly braces ({}).
value	The value object. This can be any valid Java object. It is up to the processor to provide the proper object coercion or to simply pass the object on for use in an extension.

Throws

NullPointerException	If value is null.

public abstract void setURIResolver (URIResolver resolver)

Set an object that will be used to resolve URIs used in document().

If the resolver argument is null, the URIResolver value will be cleared and the transformer will no longer have a resolver.

Parameters

resolver	An object that implements the URIResolver interface, or null.

public abstract void transform (Source xmlSource, Result outputTarget)

Transform the XML Source to a Result. Specific transformation behavior is determined by the settings of the TransformerFactory in effect when the Transformer was instantiated and any modifications made to the Transformer instance.

An empty Source is represented as an empty document as constructed by DocumentBuilder.newDocument(). The result of transforming an empty Source depends on the transformation behavior; it is not always an empty Result.

Parameters

xmlSource	The XML input to transform.
outputTarget	The Result of transforming the xmlSource.

Throws

TransformerException	If an unrecoverable error occurs during the course of the transformation.