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java.lang.Objectgnu.xml.pipeline.EventFilter
gnu.xml.pipeline.ValidationConsumer
This class checks SAX2 events to report validity errors; it works as both a filter and a terminus on an event pipeline. It relies on the producer of SAX events to:
xmlns*
attributes (rather than omitting either or both). At this writing, the major SAX2 parsers (such as Ælfred2, Crimson, and Xerces) meet these requirements, and this validation module is used by the optional Ælfred2 validation support.
Note that because this is a layered validator, it has to duplicate some work that the parser is doing; there are also other cost to layering. However, because of layering it doesn't need a parser in order to work! You can use it with anything that generates SAX events, such as an application component that wants to detect invalid content in a changed area without validating an entire document, or which wants to ensure that it doesn't write invalid data to a communications partner.
Also, note that because this is a layered validator, the line numbers reported for some errors may seem strange. For example, if an element does not permit character content, the validator will use the locator provided to it. That might reflect the last character of a characters event callback, rather than the first non-whitespace character.
Current limitations of the validation performed are in roughly three categories.
The first category represents constraints which demand violations of software layering: exposing lexical details, one of the first things that application programming interfaces (APIs) hide. These invariably relate to XML entity handling, and to historical oddities of the XML validation semantics. Curiously, recent (Autumn 1999) conformance testing showed that these constraints are among those handled worst by existing XML validating parsers. Arguments have been made that each of these VCs should be turned into WFCs (most of them) or discarded (popular for the standalone declaration); in short, that these are bugs in the XML specification (not all via SGML):
The second category of limitations on this validation represent constraints associated with information that is not guaranteed to be available (or in one case, is guaranteed not to be available, through the SAX2 API:
A third category relates to ease of implementation. (Think of this as "bugs".) The most notable issue here is character handling. Rather than attempting to implement the voluminous character tables in the XML specification (Appendix B), Unicode rules are used directly from the java.lang.Character class. Recent JVMs have begun to diverge from the original specification for that class (Unicode 2.0), meaning that different JVMs may handle that aspect of conformance differently.
Note that for some of the validity errors that SAX2 does not expose, a nonvalidating parser is permitted (by the XML specification) to report validity errors. When used with a parser that does so for the validity constraints mentioned above (or any other SAX2 event stream producer that does the same thing), overall conformance is substantially improved.
SAXDriver
,
XmlReader
Field Summary |
Fields inherited from class gnu.xml.pipeline.EventFilter |
DECL_HANDLER, FEATURE_URI, LEXICAL_HANDLER, PROPERTY_URI |
Constructor Summary | |
ValidationConsumer()
Creates a pipeline terminus which consumes all events passed to it; this will report validity errors as if they were fatal errors, unless an error handler is assigned. |
|
ValidationConsumer(EventConsumer next)
Creates a pipeline filter which reports validity errors and then passes events on to the next consumer if they were not fatal. |
|
ValidationConsumer(String rootName,
String publicId,
String systemId,
String internalSubset,
EntityResolver resolver,
String minimalDocument)
Creates a validation consumer which is preloaded with the DTD provided. |
Method Summary | |
void |
attributeDecl(String eName,
String aName,
String type,
String mode,
String value)
DecllHandler Records attribute declaration for later use in validating document content, and checks validity constraints that are applicable to attribute declarations. |
void |
characters(char[] ch,
int start,
int length)
ContentHandler Reports a validity error if the element's content model does not permit character data. |
void |
elementDecl(String name,
String model)
DecllHandler Records the element declaration for later use when checking document content, and checks validity constraints that apply to element declarations. |
void |
endDocument()
ContentHandler Checks whether all ID values that were referenced have been declared, and releases all resources. |
void |
endDTD()
LexicalHandler Verifies that all referenced notations and unparsed entities have been declared. |
void |
endElement(String uri,
String localName,
String qName)
ContentHandler Reports a validity error if the element's content model does not permit end-of-element yet, or a well formedness error if there was no matching startElement call. |
void |
externalEntityDecl(String name,
String publicId,
String systemId)
DecllHandler passed to the next consumer, unless this one was preloaded with a particular DTD |
void |
internalEntityDecl(String name,
String value)
DecllHandler passed to the next consumer, unless this one was preloaded with a particular DTD |
void |
notationDecl(String name,
String publicId,
String systemId)
DTDHandler Records the notation name, for checking NOTATIONS attribute values and declararations of unparsed entities. |
void |
skippedEntity(String name)
ContentHandler Reports a fatal exception. |
void |
startDocument()
ContentHandler Ensures that state from any previous parse has been deleted. |
void |
startDTD(String name,
String publicId,
String systemId)
LexicalHandler Records the declaration of the root element, so it can be verified later. |
void |
startElement(String uri,
String localName,
String qName,
Attributes atts)
ContentHandler Performs validity checks against element (and document) content models, and attribute values. |
void |
unparsedEntityDecl(String name,
String publicId,
String systemId,
String notationName)
DTDHandler Records the entity name, for checking ENTITY and ENTITIES attribute values; records the notation name if it hasn't yet been declared. |
Methods inherited from class gnu.xml.pipeline.EventFilter |
bind, chainTo, comment, endCDATA, endEntity, endPrefixMapping, getContentHandler, getDocumentLocator, getDTDHandler, getErrorHandler, getNext, getProperty, ignorableWhitespace, processingInstruction, setContentHandler, setDocumentLocator, setDTDHandler, setErrorHandler, setProperty, startCDATA, startEntity, startPrefixMapping |
Methods inherited from class java.lang.Object |
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Constructor Detail |
public ValidationConsumer()
EventFilter.setErrorHandler(org.xml.sax.ErrorHandler)
public ValidationConsumer(EventConsumer next)
EventFilter.setErrorHandler(org.xml.sax.ErrorHandler)
public ValidationConsumer(String rootName, String publicId, String systemId, String internalSubset, EntityResolver resolver, String minimalDocument) throws SAXException, IOException
The resulting validation consumer will only validate against the specified DTD, regardless of whether some other DTD is found in a document being parsed.
rootName
- The name of the required root element; if this is
null, any root element name will be accepted.publicId
- If non-null and there is a non-null systemId, this
identifier provides an alternate access identifier for the DTD's
external subset.systemId
- If non-null, this is a URI (normally URL) that
may be used to access the DTD's external subset.internalSubset
- If non-null, holds literal markup declarations
comprising the DTD's internal subset.resolver
- If non-null, this will be provided to the parser for
use when resolving parameter entities (including any external subset).
SAXNotSupportedException
- If the default SAX parser does
not support the standard lexical or declaration handlers.
SAXParseException
- If the specified DTD has either
well-formedness or validity errors
IOException
- If the specified DTD can't be read for
some reason
SAXException
Method Detail |
public void startDTD(String name, String publicId, String systemId) throws SAXException
startDTD
in interface LexicalHandler
startDTD
in class EventFilter
SAXException
public void endDTD() throws SAXException
endDTD
in interface LexicalHandler
endDTD
in class EventFilter
SAXException
public void attributeDecl(String eName, String aName, String type, String mode, String value) throws SAXException
attributeDecl
in interface DeclHandler
attributeDecl
in class EventFilter
SAXException
public void elementDecl(String name, String model) throws SAXException
elementDecl
in interface DeclHandler
elementDecl
in class EventFilter
SAXException
public void internalEntityDecl(String name, String value) throws SAXException
internalEntityDecl
in interface DeclHandler
internalEntityDecl
in class EventFilter
SAXException
public void externalEntityDecl(String name, String publicId, String systemId) throws SAXException
externalEntityDecl
in interface DeclHandler
externalEntityDecl
in class EventFilter
SAXException
public void notationDecl(String name, String publicId, String systemId) throws SAXException
notationDecl
in interface DTDHandler
notationDecl
in class EventFilter
SAXException
public void unparsedEntityDecl(String name, String publicId, String systemId, String notationName) throws SAXException
unparsedEntityDecl
in interface DTDHandler
unparsedEntityDecl
in class EventFilter
SAXException
public void startDocument() throws SAXException
startDocument
in interface ContentHandler
startDocument
in class EventFilter
SAXException
public void skippedEntity(String name) throws SAXException
skippedEntity
in interface ContentHandler
skippedEntity
in class EventFilter
SAXException
public void startElement(String uri, String localName, String qName, Attributes atts) throws SAXException
startElement
in interface ContentHandler
startElement
in class EventFilter
SAXException
public void characters(char[] ch, int start, int length) throws SAXException
characters
in interface ContentHandler
characters
in class EventFilter
SAXException
public void endElement(String uri, String localName, String qName) throws SAXException
endElement
in interface ContentHandler
endElement
in class EventFilter
SAXException
public void endDocument() throws SAXException
endDocument
in interface ContentHandler
endDocument
in class EventFilter
SAXException
EventFilter.setDocumentLocator(org.xml.sax.Locator)
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Source code is under GPL (with library exception) in the JAXP project at http://www.gnu.org/software/classpathx/jaxp
This documentation was derived from that source code on 2004-08-21.