gnu.xml.pipeline

Class TeeConsumer

Implemented Interfaces:
ContentHandler, DeclHandler, DTDHandler, EventConsumer, LexicalHandler

public final class TeeConsumer
extends java.lang.Object
implements EventConsumer, ContentHandler, DTDHandler, LexicalHandler, DeclHandler

Fans its events out to two other consumers, a "tee" filter stage in an event pipeline. Networks can be assembled with multiple output points.

Error handling should be simple if you remember that exceptions you throw will cancel later stages in that callback's pipeline, and generally the producer will stop if it sees such an exception. You may want to protect your pipeline against such backflows, making a kind of reverse filter (or valve?) so that certain exceptions thrown by your pipeline will caught and handled before the producer sees them. Just use a "try/catch" block, rememebering that really important cleanup tasks should be in "finally" clauses.

That issue isn't unique to "tee" consumers, but tee consumers have the additional twist that exceptions thrown by the first consumer will cause the second consumer not to see the callback (except for the endDocument callback, which signals state cleanup).

Constructor Summary

TeeConsumer(EventConsumer car, EventConsumer cdr)
Constructs a consumer which sends all its events to the first consumer, and then the second one.

Method Summary

void
attributeDecl(String eName, String aName, String type, String mode, String value)
Report an attribute type declaration.
void
characters(ch[] , int start, int length)
Receive notification of character data.
void
comment(ch[] , int start, int length)
void
elementDecl(String name, String model)
Report an element type declaration.
void
endCDATA()
void
endDTD()
void
endDocument()
Receive notification of the end of a document.
void
endElement(String uri, String localName, String qName)
Receive notification of the end of an element.
void
endEntity(String name)
void
endPrefixMapping(String prefix)
End the scope of a prefix-URI mapping.
void
externalEntityDecl(String name, String publicId, String systemId)
Report a parsed external entity declaration.
ContentHandler
getContentHandler()
Returns the content handler being used.
DTDHandler
getDTDHandler()
Returns the dtd handler being used.
EventConsumer
getFirst()
Returns the first pipeline to get event calls.
Object
getProperty(String id)
Returns the declaration or lexical handler being used.
EventConsumer
getRest()
Returns the second pipeline to get event calls.
void
ignorableWhitespace(ch[] , int start, int length)
Receive notification of ignorable whitespace in element content.
void
internalEntityDecl(String name, String value)
Report an internal entity declaration.
void
notationDecl(String name, String publicId, String systemId)
Receive notification of a notation declaration event.
void
processingInstruction(String target, String data)
Receive notification of a processing instruction.
void
setDocumentLocator(Locator locator)
Receive an object for locating the origin of SAX document events.
void
setErrorHandler(ErrorHandler handler)
Provides the error handler to both subsequent nodes of this filter stage.
void
skippedEntity(String name)
Receive notification of a skipped entity.
void
startCDATA()
void
startDTD(String name, String publicId, String systemId)
void
startDocument()
Receive notification of the beginning of a document.
void
startElement(String uri, String localName, String qName, Attributes atts)
Receive notification of the beginning of an element.
void
startEntity(String name)
void
startPrefixMapping(String prefix, String uri)
Begin the scope of a prefix-URI Namespace mapping.
void
unparsedEntityDecl(String name, String publicId, String systemId, String notationName)
Receive notification of an unparsed entity declaration event.

Constructor Details

TeeConsumer

public TeeConsumer(EventConsumer car,
                   EventConsumer cdr)
Constructs a consumer which sends all its events to the first consumer, and then the second one. If the first consumer throws an exception, the second one will not see the event which caused that exception to be reported.
Parameters:
car - The first consumer to get the events
cdr - The second consumer to get the events

Method Details

attributeDecl

public void attributeDecl(String eName,
                          String aName,
                          String type,
                          String mode,
                          String value)
            throws SAXException
Report an attribute type declaration.

Only the effective (first) declaration for an attribute will be reported. The type will be one of the strings "CDATA", "ID", "IDREF", "IDREFS", "NMTOKEN", "NMTOKENS", "ENTITY", "ENTITIES", a parenthesized token group with the separator "|" and all whitespace removed, or the word "NOTATION" followed by a space followed by a parenthesized token group with all whitespace removed.

The value will be the value as reported to applications, appropriately normalized and with entity and character references expanded.

Specified by:
attributeDecl in interface DeclHandler
Parameters:
eName - The name of the associated element.
aName - The name of the attribute.
type - A string representing the attribute type.
mode - A string representing the attribute defaulting mode ("#IMPLIED", "#REQUIRED", or "#FIXED") or null if none of these applies.
value - A string representing the attribute's default value, or null if there is none.
Throws:
SAXException - The application may raise an exception.

characters

public void characters(ch[] ,
                       int start,
                       int length)
            throws SAXException
Receive notification of character data.

The Parser will call this method to report each chunk of character data. SAX parsers may return all contiguous character data in a single chunk, or they may split it into several chunks; however, all of the characters in any single event must come from the same external entity so that the Locator provides useful information.

The application must not attempt to read from the array outside of the specified range.

Individual characters may consist of more than one Java char value. There are two important cases where this happens, because characters can't be represented in just sixteen bits. In one case, characters are represented in a Surrogate Pair, using two special Unicode values. Such characters are in the so-called "Astral Planes", with a code point above U+FFFF. A second case involves composite characters, such as a base character combining with one or more accent characters.

Your code should not assume that algorithms using char-at-a-time idioms will be working in character units; in some cases they will split characters. This is relevant wherever XML permits arbitrary characters, such as attribute values, processing instruction data, and comments as well as in data reported from this method. It's also generally relevant whenever Java code manipulates internationalized text; the issue isn't unique to XML.

Note that some parsers will report whitespace in element content using the ignorableWhitespace method rather than this one (validating parsers must do so).

Specified by:
characters in interface ContentHandler
Parameters:
start - the start position in the array
length - the number of characters to read from the array
Throws:
SAXException - any SAX exception, possibly wrapping another exception

comment

public void comment(ch[] ,
                    int start,
                    int length)
            throws SAXException
Specified by:
comment in interface LexicalHandler

elementDecl

public void elementDecl(String name,
                        String model)
            throws SAXException
Report an element type declaration.

The content model will consist of the string "EMPTY", the string "ANY", or a parenthesised group, optionally followed by an occurrence indicator. The model will be normalized so that all parameter entities are fully resolved and all whitespace is removed,and will include the enclosing parentheses. Other normalization (such as removing redundant parentheses or simplifying occurrence indicators) is at the discretion of the parser.

Specified by:
elementDecl in interface DeclHandler
Parameters:
name - The element type name.
model - The content model as a normalized string.
Throws:
SAXException - The application may raise an exception.

endCDATA

public void endCDATA()
            throws SAXException
Specified by:
endCDATA in interface LexicalHandler

endDTD

public void endDTD()
            throws SAXException
Specified by:
endDTD in interface LexicalHandler

endDocument

public void endDocument()
            throws SAXException
Receive notification of the end of a document.

There is an apparent contradiction between the documentation for this method and the documentation for ErrorHandler.fatalError(SAXParseException). Until this ambiguity is resolved in a future major release, clients should make no assumptions about whether endDocument() will or will not be invoked when the parser has reported a fatalError() or thrown an exception.

The SAX parser will invoke this method only once, and it will be the last method invoked during the parse. The parser shall not invoke this method until it has either abandoned parsing (because of an unrecoverable error) or reached the end of input.

Specified by:
endDocument in interface ContentHandler
Throws:
SAXException - any SAX exception, possibly wrapping another exception

endElement

public void endElement(String uri,
                       String localName,
                       String qName)
            throws SAXException
Receive notification of the end of an element.

The SAX parser will invoke this method at the end of every element in the XML document; there will be a corresponding startElement event for every endElement event (even when the element is empty).

For information on the names, see startElement.

Specified by:
endElement in interface ContentHandler
Parameters:
uri - the Namespace URI, or the empty string if the element has no Namespace URI or if Namespace processing is not being performed
localName - the local name (without prefix), or the empty string if Namespace processing is not being performed
qName - the qualified XML name (with prefix), or the empty string if qualified names are not available
Throws:
SAXException - any SAX exception, possibly wrapping another exception

endEntity

public void endEntity(String name)
            throws SAXException
Specified by:
endEntity in interface LexicalHandler

endPrefixMapping

public void endPrefixMapping(String prefix)
            throws SAXException
End the scope of a prefix-URI mapping.

See startPrefixMapping for details. These events will always occur immediately after the corresponding endElement event, but the order of endPrefixMapping events is not otherwise guaranteed.

Specified by:
endPrefixMapping in interface ContentHandler
Parameters:
prefix - the prefix that was being mapped. This is the empty string when a default mapping scope ends.
Throws:
SAXException - the client may throw an exception during processing

externalEntityDecl

public void externalEntityDecl(String name,
                               String publicId,
                               String systemId)
            throws SAXException
Report a parsed external entity declaration.

Only the effective (first) declaration for each entity will be reported.

If the system identifier is a URL, the parser must resolve it fully before passing it to the application.

Specified by:
externalEntityDecl in interface DeclHandler
Parameters:
name - The name of the entity. If it is a parameter entity, the name will begin with '%'.
publicId - The entity's public identifier, or null if none was given.
systemId - The entity's system identifier.
Throws:
SAXException - The application may raise an exception.

getContentHandler

public final ContentHandler getContentHandler()
Returns the content handler being used.
Specified by:
getContentHandler in interface EventConsumer

getDTDHandler

public final DTDHandler getDTDHandler()
Returns the dtd handler being used.
Specified by:
getDTDHandler in interface EventConsumer

getFirst

public EventConsumer getFirst()
Returns the first pipeline to get event calls.

getProperty

public final Object getProperty(String id)
            throws SAXNotRecognizedException
Returns the declaration or lexical handler being used.
Specified by:
getProperty in interface EventConsumer

getRest

public EventConsumer getRest()
Returns the second pipeline to get event calls.

ignorableWhitespace

public void ignorableWhitespace(ch[] ,
                                int start,
                                int length)
            throws SAXException
Receive notification of ignorable whitespace in element content.

Validating Parsers must use this method to report each chunk of whitespace in element content (see the W3C XML 1.0 recommendation, section 2.10): non-validating parsers may also use this method if they are capable of parsing and using content models.

SAX parsers may return all contiguous whitespace in a single chunk, or they may split it into several chunks; however, all of the characters in any single event must come from the same external entity, so that the Locator provides useful information.

The application must not attempt to read from the array outside of the specified range.

Specified by:
ignorableWhitespace in interface ContentHandler
Parameters:
start - the start position in the array
length - the number of characters to read from the array
Throws:
SAXException - any SAX exception, possibly wrapping another exception

internalEntityDecl

public void internalEntityDecl(String name,
                               String value)
            throws SAXException
Report an internal entity declaration.

Only the effective (first) declaration for each entity will be reported. All parameter entities in the value will be expanded, but general entities will not.

Specified by:
internalEntityDecl in interface DeclHandler
Parameters:
name - The name of the entity. If it is a parameter entity, the name will begin with '%'.
value - The replacement text of the entity.
Throws:
SAXException - The application may raise an exception.

notationDecl

public void notationDecl(String name,
                         String publicId,
                         String systemId)
            throws SAXException
Receive notification of a notation declaration event.

It is up to the application to record the notation for later reference, if necessary; notations may appear as attribute values and in unparsed entity declarations, and are sometime used with processing instruction target names.

At least one of publicId and systemId must be non-null. If a system identifier is present, and it is a URL, the SAX parser must resolve it fully before passing it to the application through this event.

There is no guarantee that the notation declaration will be reported before any unparsed entities that use it.

Specified by:
notationDecl in interface DTDHandler
Parameters:
name - The notation name.
publicId - The notation's public identifier, or null if none was given.
systemId - The notation's system identifier, or null if none was given.
Throws:
SAXException - Any SAX exception, possibly wrapping another exception.

processingInstruction

public void processingInstruction(String target,
                                  String data)
            throws SAXException
Receive notification of a processing instruction.

The Parser will invoke this method once for each processing instruction found: note that processing instructions may occur before or after the main document element.

A SAX parser must never report an XML declaration (XML 1.0, section 2.8) or a text declaration (XML 1.0, section 4.3.1) using this method.

Like characters(), processing instruction data may have characters that need more than one char value.

Specified by:
processingInstruction in interface ContentHandler
Parameters:
target - the processing instruction target
data - the processing instruction data, or null if none was supplied. The data does not include any whitespace separating it from the target
Throws:
SAXException - any SAX exception, possibly wrapping another exception

setDocumentLocator

public void setDocumentLocator(Locator locator)
Receive an object for locating the origin of SAX document events.

SAX parsers are strongly encouraged (though not absolutely required) to supply a locator: if it does so, it must supply the locator to the application by invoking this method before invoking any of the other methods in the ContentHandler interface.

The locator allows the application to determine the end position of any document-related event, even if the parser is not reporting an error. Typically, the application will use this information for reporting its own errors (such as character content that does not match an application's business rules). The information returned by the locator is probably not sufficient for use with a search engine.

Note that the locator will return correct information only during the invocation SAX event callbacks after startDocument returns and before endDocument is called. The application should not attempt to use it at any other time.

Specified by:
setDocumentLocator in interface ContentHandler
Parameters:
locator - an object that can return the location of any SAX document event
See Also:
Locator

setErrorHandler

public void setErrorHandler(ErrorHandler handler)
Provides the error handler to both subsequent nodes of this filter stage.
Specified by:
setErrorHandler in interface EventConsumer

skippedEntity

public void skippedEntity(String name)
            throws SAXException
Receive notification of a skipped entity. This is not called for entity references within markup constructs such as element start tags or markup declarations. (The XML recommendation requires reporting skipped external entities. SAX also reports internal entity expansion/non-expansion, except within markup constructs.)

The Parser will invoke this method each time the entity is skipped. Non-validating processors may skip entities if they have not seen the declarations (because, for example, the entity was declared in an external DTD subset). All processors may skip external entities, depending on the values of the http://xml.org/sax/features/external-general-entities and the http://xml.org/sax/features/external-parameter-entities properties.

Specified by:
skippedEntity in interface ContentHandler
Parameters:
name - the name of the skipped entity. If it is a parameter entity, the name will begin with '%', and if it is the external DTD subset, it will be the string "[dtd]"
Throws:
SAXException - any SAX exception, possibly wrapping another exception

startCDATA

public void startCDATA()
            throws SAXException
Specified by:
startCDATA in interface LexicalHandler

startDTD

public void startDTD(String name,
                     String publicId,
                     String systemId)
            throws SAXException
Specified by:
startDTD in interface LexicalHandler

startDocument

public void startDocument()
            throws SAXException
Receive notification of the beginning of a document.

The SAX parser will invoke this method only once, before any other event callbacks (except for setDocumentLocator).

Specified by:
startDocument in interface ContentHandler
Throws:
SAXException - any SAX exception, possibly wrapping another exception

startElement

public void startElement(String uri,
                         String localName,
                         String qName,
                         Attributes atts)
            throws SAXException
Receive notification of the beginning of an element.

The Parser will invoke this method at the beginning of every element in the XML document; there will be a corresponding endElement event for every startElement event (even when the element is empty). All of the element's content will be reported, in order, before the corresponding endElement event.

This event allows up to three name components for each element:

  1. the Namespace URI;
  2. the local name; and
  3. the qualified (prefixed) name.

Any or all of these may be provided, depending on the values of the http://xml.org/sax/features/namespaces and the http://xml.org/sax/features/namespace-prefixes properties:

  • the Namespace URI and local name are required when the namespaces property is true (the default), and are optional when the namespaces property is false (if one is specified, both must be);
  • the qualified name is required when the namespace-prefixes property is true, and is optional when the namespace-prefixes property is false (the default).

Note that the attribute list provided will contain only attributes with explicit values (specified or defaulted): #IMPLIED attributes will be omitted. The attribute list will contain attributes used for Namespace declarations (xmlns* attributes) only if the http://xml.org/sax/features/namespace-prefixes property is true (it is false by default, and support for a true value is optional).

Like characters(), attribute values may have characters that need more than one char value.

Specified by:
startElement in interface ContentHandler
Parameters:
uri - the Namespace URI, or the empty string if the element has no Namespace URI or if Namespace processing is not being performed
localName - the local name (without prefix), or the empty string if Namespace processing is not being performed
qName - the qualified name (with prefix), or the empty string if qualified names are not available
atts - the attributes attached to the element. If there are no attributes, it shall be an empty Attributes object. The value of this object after startElement returns is undefined
Throws:
SAXException - any SAX exception, possibly wrapping another exception

startEntity

public void startEntity(String name)
            throws SAXException
Specified by:
startEntity in interface LexicalHandler

startPrefixMapping

public void startPrefixMapping(String prefix,
                               String uri)
            throws SAXException
Begin the scope of a prefix-URI Namespace mapping.

The information from this event is not necessary for normal Namespace processing: the SAX XML reader will automatically replace prefixes for element and attribute names when the http://xml.org/sax/features/namespaces feature is true (the default).

There are cases, however, when applications need to use prefixes in character data or in attribute values, where they cannot safely be expanded automatically; the start/endPrefixMapping event supplies the information to the application to expand prefixes in those contexts itself, if necessary.

Note that start/endPrefixMapping events are not guaranteed to be properly nested relative to each other: all startPrefixMapping events will occur immediately before the corresponding startElement event, and all endPrefixMapping events will occur immediately after the corresponding endElement event, but their order is not otherwise guaranteed.

There should never be start/endPrefixMapping events for the "xml" prefix, since it is predeclared and immutable.

Specified by:
startPrefixMapping in interface ContentHandler
Parameters:
prefix - the Namespace prefix being declared. An empty string is used for the default element namespace, which has no prefix.
uri - the Namespace URI the prefix is mapped to
Throws:
SAXException - the client may throw an exception during processing

unparsedEntityDecl

public void unparsedEntityDecl(String name,
                               String publicId,
                               String systemId,
                               String notationName)
            throws SAXException
Receive notification of an unparsed entity declaration event.

Note that the notation name corresponds to a notation reported by the notationDecl event. It is up to the application to record the entity for later reference, if necessary; unparsed entities may appear as attribute values.

If the system identifier is a URL, the parser must resolve it fully before passing it to the application.

Specified by:
unparsedEntityDecl in interface DTDHandler
Parameters:
name - The unparsed entity's name.
publicId - The entity's public identifier, or null if none was given.
systemId - The entity's system identifier.
notationName - The name of the associated notation.
Throws:
SAXException - Any SAX exception, possibly wrapping another exception.