205 lines
8.5 KiB
Plaintext
205 lines
8.5 KiB
Plaintext
This file describes the jaxp (xml processing) implementation of GNU Classpath.
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GNU Classpath includes interfaces and implementations for basic XML processing
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in in the java programming language, some general purpose SAX2 utilities, and
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transformation.
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These classes used to be maintained as part of an external project GNU JAXP
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but are now integrated with the rest of the core class library provided by
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GNU Classpath.
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PACKAGES
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. javax.xml.* ... JAXP 1.3 interfaces
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. gnu.xml.aelfred2.* ... SAX2 parser + validator
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. gnu.xml.dom.* ... DOM Level 3 Core, Traversal, XPath implementation
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. gnu.xml.dom.ls.* ... DOM Level 3 Load & Save implementation
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. gnu.xml.xpath.* ... JAXP XPath implementation
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. gnu.xml.transform.* ... JAXP XSL transformer implementation
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. gnu.xml.pipeline.* ... SAX2 event pipeline support
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. gnu.xml.stream.* ... StAX pull parser and SAX-over-StAX driver
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. gnu.xml.util.* ... various XML utility classes
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. gnu.xml.libxmlj.dom.* ... libxmlj DOM Level 3 Core and XPath
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. gnu.xml.libxmlj.sax.* ... libxmlj SAX parser
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. gnu.xml.libxmlj.transform.* ... libxmlj XSL transformer
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. gnu.xml.libxmlj.util.* ... libxmlj utility classes
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In the external directory you can find the following packages.
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They are not maintained as part of GNU Classpath, but are used by the
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classes in the above packages.
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. org.xml.sax.* ... SAX2 interfaces
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. org.w3c.dom.* ... DOM Level 3 interfaces
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. org.relaxng.datatype.* ... RELAX NG pluggable datatypes API
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CONFORMANCE
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The primary test resources are at http://xmlconf.sourceforge.net
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and include:
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SAX2/XML conformance tests
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That the "xml.testing.Driver" addresses the core XML 1.0
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specification requirements, which closely correspond to the
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functionality SAX1 provides. The driver uses SAX2 APIs to
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test that functionality It is used with a bugfixed version of
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the NIST/OASIS XML conformance test cases.
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The AElfred2 parser is highly conformant, though it still takes
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a few implementation shortcuts. See its package documentation
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for information about known XML conformance issues in AElfred2.
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The primary issue is using Unicode character tables, rather than
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those in the XML specification, for determining what names are
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valid. Most applications won't notice the difference, and this
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solution is smaller and faster than the alternative.
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For validation, a secondary issue is that issues relating to
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entity modularity are not validated; they can't all be cleanly
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layered. For example, validity constraints related to standalone
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declarations and PE nesting are not checked.
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The current implementation has also been tested against Elliotte
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Rusty Harold's SAXTest test suite (http://www.cafeconleche.org/SAXTest)
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and achieves approximately 93% conformance to the SAX specification
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according to these tests, higher than any other current Java parser.
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SAX2
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SAX2 API conformance currently has a minimal JUNIT (0.2) test suite,
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which can be accessed at the xmlconf site listed above. It does
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not cover namespaces or LexicalHandler and Declhandler extensions
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anywhere as exhaustively as the SAX1 level functionality is
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tested by the "xml.testing.Driver". However:
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- Applying the DOM unit tests to this implementation gives
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the LexicalHandler (comments, and boundaries of DTDs,
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CDATA sections, and general entities) a workout, and
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does the same for DeclHandler entity declarations.
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- The pipeline package's layered validator demands that
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element and attribute declarations are reported correctly.
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By those metrics, SAX2 conformance for AElfred2 is also strong.
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DOM Level 3 Core Tests
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The DOM implementation has been tested against the W3C DOM Level 3
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Core conformance test suite (http://www.w3.org/DOM/Test/). Current
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conformance according to these tests is 72.3%. Many of the test
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failures are due to the fact that GNU JAXP does not currently
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provide any W3C XML Schema support.
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XSL transformation
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The transformer and XPath implementation have been tested against
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the OASIS XSLT and XPath TC test suite. Conformance against the
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Xalan tests is currently 77%.
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libxmlj
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========================================================================
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libxmlj is an effort to create a 100% JAXP-compatible Java wrapper for
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libxml2 and libxslt. JAXP is the Java API for XML processing, libxml2
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is the XML C library for Gnome, and libxslt is the XSLT C library for
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Gnome.
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libxmlj currently supports most of the DOM Level 3 Core, Traversal, and
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XPath APIs, SAX2, and XSLT transformations. There is no W3C XML Schema
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support yet.
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libxmlj can parse and transform XML documents extremely quickly in
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comparison to Java-based JAXP implementations. DOM manipulations, however,
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involve JNI overhead, so the speed of DOM tree construction and traversal
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can be slower than the Java implementation.
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libxmlj is highly experimental, doesn't always conform to the DOM
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specification correctly, and may leak memory. Production use is not advised.
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The implementation can be found in gnu/xml/libxmlj and native/jni/xmlj.
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See the INSTALL file for the required versions of libxml2 and libxslt.
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configure --enable-xmlj will build it.
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Usage
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------------------------------------------------------------------------
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To enable the various GNU JAXP factories, set the following system properties
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(command-line version shown, but they can equally be set programmatically):
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AElfred2:
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-Djavax.xml.parsers.SAXParserFactory=gnu.xml.aelfred2.JAXPFactory
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GNU DOM (using DOM Level 3 Load & Save):
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-Djavax.xml.parsers.DocumentBuilderFactory=gnu.xml.dom.DomDocumentBuilderFactory
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GNU DOM (using AElfred-only pipeline classes):
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-Djavax.xml.parsers.DocumentBuilderFactory=gnu.xml.dom.JAXPFactory
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GNU XSL transformer:
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-Djavax.xml.transform.TransformerFactory=gnu.xml.transform.TransformerFactoryImpl
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GNU StAX:
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-Djavax.xml.stream.XMLEventFactory=gnu.xml.stream.XMLEventFactoryImpl
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-Djavax.xml.stream.XMLInputFactory=gnu.xml.stream.XMLInputFactoryImpl
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-Djavax.xml.stream.XMLOutputFactory=gnu.xml.stream.XMLOutputFactoryImpl
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GNU SAX-over-StAX:
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-Djavax.xml.parsers.SAXParserFactory=gnu.xml.stream.SAXParserFactory
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libxmlj SAX:
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-Djavax.xml.parsers.SAXParserFactory=gnu.xml.libxmlj.sax.GnomeSAXParserFactory
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libxmlj DOM:
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-Djavax.xml.parsers.DocumentBuilderFactory=gnu.xml.libxmlj.dom.GnomeDocumentBuilderFactory
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libxmlj XSL transformer:
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-Djavax.xml.transform.TransformerFactory=gnu.xml.libxmlj.transform.GnomeTransformerFactory
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When using libxmlj, the libxmlj shared library must be available.
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In general it is picked up by the runtime using GNU Classpath. If not you
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might want to try adding the directory where libxmlj.so is installed
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(by default ${prefix}/lib/classpath/) with ldconfig or specifying in the
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LD_LIBRARY_PATH environment variable. Additionally, you may need to specify
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the location of your shared libraries to the runtime environment using the
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java.library.path system property.
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Missing (libxmlj) Features
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------------------------------------------------------------------------
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See BUGS in native/jni/xmlj for known bugs in the libxmlj native bindings.
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This implementation should be thread-safe, but currently all
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transformation requests are queued via Java synchronization, which
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means that it effectively performs single-threaded. Long story short,
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both libxml2 and libxslt are not fully reentrant.
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Update: it may be possible to make libxmlj thread-safe nonetheless
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using thread context variables.
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Update: thread context variables have been introduced. This is very
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untested though, libxmlj therefore still has the single thread
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bottleneck.
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Validation
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===================================================
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Pluggable datatypes
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---------------------------------------------------
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Validators should use the RELAX NG pluggable datatypes API to retrieve
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datatype (XML Schema simple type) implementations in a schema-neutral
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fashion. The following code demonstrates looking up a W3C XML Schema
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nonNegativeInteger datatype:
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DatatypeLibrary xsd = DatatypeLibraryLoader
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.createDatatypeLibrary(XMLConstants.W3C_XML_SCHEMA_NS_URI);
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Datatype nonNegativeInteger = xsd.createDatatype("nonNegativeInteger");
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It is also possible to create new types by derivation. For instance,
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to create a datatype that will match a US ZIP code:
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DatatypeBuilder b = xsd.createDatatypeBuilder("string");
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b.addParameter("pattern", "(^[0-9]{5}$)|(^[0-9]{5}-[0-9]{4}$)");
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Datatype zipCode = b.createDatatype();
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A datatype library implementation for XML Schema is provided; other
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library implementations may be added.
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