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Posted to j-dev@xerces.apache.org by bu...@apache.org on 2001/07/30 12:06:23 UTC
[Bug 2882] New: - [PERFORMANCE] Why SAX parser needs DOM classes?
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http://nagoya.apache.org/bugzilla/show_bug.cgi?id=2882
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+ +============================================================================+
+ | [PERFORMANCE] Why SAX parser needs DOM classes? |
+ +----------------------------------------------------------------------------+
+ | Bug #: 2882 Product: Xerces-J |
+ | Status: NEW Version: 1.3.0 |
+ | Resolution: Platform: Other |
+ | Severity: Normal OS/Version: Other |
+ | Priority: Other Component: Core |
+ +----------------------------------------------------------------------------+
+ | Assigned To: xerces-j-dev@xml.apache.org |
+ | Reported By: pkuzel@sun.com |
+ | CC list: Cc: |
+ +----------------------------------------------------------------------------+
+ | URL: |
+ +============================================================================+
+ | DESCRIPTION |
+ Petr Kuzel wrote:
+
+ >
+ > Sandeep Randhawa wrote:
+ >
+
+ > > You don't have to be parser dependent.
+ > >
+ > > Set the feature by calling
+ > > XMLReader.setFeature("http://apache.org/xml/features/nonvalidating/load-exte
+ > > rnal-dtd", false);
+
+ >
+ > Other implementations may throw an Exception as they does not support the
+ > feature by its name. It can be catched and hidden.
+ >
+ > Anyway I dislike the idea of turning off validation. Xerces should come with
+ > cached grammars with near future eliminating reparsing known DTDs.
+
+
+ What the hell you'd like to use validation for, when you're reading a
+ file
+ from inside a distribution jar that never changes again and again?
+
+ And even chached grammars won't help Xerces read the little documents
+ faster,
+ because it still needs to prepare the instance of the grammar and then
+ check
+ the elements against the grammar.
+
+ Try to tell Dafe to use validation for his window management stuff,
+ where he is using files with about two elements in them and even
+ the DOCTYPE declaration is bigger that the content.
+
+ The problem with the Xerces is that it uses a part of DOM (even in SAX
+ parsing),
+ whenever in ecounters DOCTYPE declaration. I understand that it needs
+ it in the case the document will have internal DTD, but how many
+ of our XMLs uses this feature? I think that it could wait with creating
+ the Document till it finds '[' inside the DOCTYPE, otherwise it is
+ overkill
+ for lightweight SAX parsing.
+
+ I just looked what the Xerces loads when it encouters DOCTYPE,
+ I'm not saying that the loads are bad (the clacces will be loaded
+ a bit later anyway), but it signs that there is something wrong
+ with it to me:
+ [Loaded org.openide.filesystems.StreamPool]
+ [Loaded org.openide.filesystems.StreamPool$NotifyInputStream]
+ [Loaded org.xml.sax.InputSource]
+ [Loaded org.openide.filesystems.FileURL]
+ [Loaded org.openide.filesystems.FileURL$1]
+ [Loaded org.netbeans.core.modules.ModuleList$1]
+ [Loaded org.apache.xerces.readers.DefaultEntityHandler$ReaderState]
+ [Loaded org.apache.xerces.readers.XMLEntityHandler$EntityReader]
+ [Loaded org.apache.xerces.readers.DefaultEntityHandler$NullReader]
+ [Loaded org.apache.xerces.utils.URI]
+ [Loaded sun.io.ByteToCharUTF8 from /pn/Jdks/jdk1.3.1-fcs/jre/lib/rt.jar]
+ [Loaded org.apache.xerces.readers.XMLEntityReader]
+ [Loaded org.apache.xerces.readers.AbstractCharReader]
+ [Loaded org.apache.xerces.readers.CharReader]
+ [Loaded org.apache.xerces.utils.XMLCharacterProperties]
+ [Loaded org.apache.xerces.framework.XMLDocumentScanner$PrologDispatcher]
+ [Loaded org.apache.xerces.framework.XMLDTDScanner]
+ [Loaded org.apache.xerces.framework.XMLContentSpec$Provider]
+ [Loaded org.apache.xerces.validators.common.Grammar]
+ [Loaded org.apache.xerces.framework.XMLDTDScanner$EventHandler]
+ [Loaded org.apache.xerces.validators.dtd.DTDGrammar]
+ [Loaded org.apache.xerces.validators.datatype.DatatypeValidator]
+ [Loaded org.apache.xerces.validators.common.XMLContentModel]
+ [Loaded org.apache.xerces.utils.Hash2intTable]
+ [Loaded org.apache.xerces.framework.XMLContentSpec]
+ [Loaded org.w3c.dom.Node]
+ [Loaded org.w3c.dom.NodeList]
+ [Loaded org.w3c.dom.events.EventTarget]
+ [Loaded org.apache.xerces.dom.NodeImpl]
+ [Loaded org.apache.xerces.dom.ChildNode]
+ [Loaded org.apache.xerces.dom.ParentNode]
+ [Loaded org.w3c.dom.Document]
+ [Loaded org.w3c.dom.traversal.DocumentTraversal]
+ [Loaded org.w3c.dom.events.DocumentEvent]
+ [Loaded org.w3c.dom.ranges.DocumentRange]
+ [Loaded org.apache.xerces.dom.DocumentImpl]
+ [Loaded org.w3c.dom.Element]
+ [Loaded org.apache.xerces.dom.ElementImpl]
+ [Loaded org.w3c.dom.Attr]
+ [Loaded org.apache.xerces.dom.AttrImpl]
+ [Loaded org.w3c.dom.NamedNodeMap]
+ [Loaded org.apache.xerces.dom.NamedNodeMapImpl]
+ [Loaded org.apache.xerces.dom.AttributeMap]
+ [Loaded
+ org.apache.xerces.framework.XMLDocumentScanner$ContentDispatcher]
+ [Loaded org.apache.xerces.utils.StringPool$CharArrayRange]
+ [Loaded
+ org.apache.xerces.framework.XMLDocumentScanner$TrailingMiscDispatcher]
+ [Loaded
+ org.apache.xerces.framework.XMLDocumentScanner$EndOfInputDispatcher]
+ [Loaded org.netbeans.core.modules.ModuleHistory]
+ [Loaded org.netbeans.core.modules.ModuleList$DiskStatus]
+
+ and the file parsed:
+ <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+ <!DOCTYPE module PUBLIC "-//NetBeans//DTD Module Status 1.0//EN"
+
+ "http://www.netbeans.org/dtds/module-status-1_0.dtd">
+ <module name="org.netbeans.modules.apisupport.lite">
+ <param name="autoload">false</param>
+ <param name="enabled">true</param>
+ <param name="jar">apisupport-lite.jar</param>
+ <param name="origin">installation</param>
+ <param name="release">1</param>
+ <param name="reloadable">false</param>
+ <param name="specversion">0.2</param>
+ </module>
+
+ I was parsing using simple SAX parser (not the DOM in your sources of
+ ModuleList)
+ with the above feature set to false and validation also turned off.
+
+ The second thing I don't understand is why I have to switch some
+ proprietary
+ feature to prevent Xercer from asking for DTD when the document itself
+ specifies
+ it is standalone and I'm not validating.
+ Can somebody explain me this behaviour?
+
+ By the way, changing the switch didn't make a difference in its speed,
+ because the additional time was not spent analyzing the DTD (we've
+ already returned empty stream when not validating), but rather
+ creating the instance of the garmmar.
+
+
+
+ > Then we have to setup feature by calling something similar anyway.
+ >
+ > Petr you can try Crimson however expect compatability problems as Xerces
+ > is exposed at IDE classpath and someone may be implementation dependend.
+ > It is real pain to have at IDE classpath implementations that are widely
+ > visible. (We can not remove parser.jar for the same reason.)
+ > Cc.
+ >
+ > --
+ > <address>
+ > <a href="mailto:pkuzel@sun.com">Petr Kuzel</a>, Sun Microsystems
+ > : <a href="http://www.sun.com/forte/ffj/ie/">Forte Tools</a>
+ > : XML and <a href="http://jini.netbeans.org/">Jini</a> modules</address>
+
+
+ -- Petr Nejedly NetBeans/Sun Microsystems http://www.netbeans.org
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