Hi Andy,
A couple of thoughts. Firstly, if the only way to choose your
configuration depends on a META-INF/services entry, then how would an
application create different parsers for diffirent situations? e.g., how
would a webserver that knows certain documents need schema validation
create a parser for that, while creating a DTD-only parser for docs it
knows need no schema support?
It seems to me that using a system property would be a more flexible--and
no more difficult--solution. I guess your approach doesn't preclude that,
but I think the system property approach is the one we'd want to emphasize.
I would agree with you that it seems to make sense to adapt the xml-commons
JAXP code to use the more generic solution you propose. I'm sure the
commons folks could figure out some appropriate packaging solution that
would work for us as well.
Finally, have you thought about how this will impact the SAX
XMLReaderFactory and ParserFactory? Looks to me like they'll be
unaffected, but just thought I'd make sure.
Cheers,
Neil
Neil Graham
XML Parser Development
IBM Toronto Lab
Phone: 905-413-3519, T/L 969-3519
E-mail: [EMAIL PROTECTED]
Andy Clark <[EMAIL PROTECTED]> on 01/11/2002 04:50:20 AM
Please respond to [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
cc:
Subject: [Xerces2] Parser Configuration Selection
I'm working on writing some custom parser configurations and
I am running into the same problem again and again: how to take
advantage of the JAXP implementation to automatically create
DOM and SAX parsers that use *my* configuration instead of the
standard Xerces configuration WITHOUT rewriting or copying (and
modifying) any JAXP code.
So I made the attached changes to my local copy of Xerces2 to
implement a similar mechanism to what our JAXP implementation
does. I copied (and renamed) our javax.xml.parsers.FactoryFinder
class to org.apache.xerces.util.ObjectFactory so that we have a
generic tool for dynamically instantiating classes. (Remember
that this code works the "correct" way for both Java 1.1 and
Java 2.)
Then I changed the parser code to use this factory to create
JAXP factories *and* for the Xerces parsers in creating the
default parser configuration that they use. I do this by adding
a new file in the META-INF/services directory. In this way, if
you write a new custom configuration you can override the
default Xerces configuration simply by changing the parser
configuration specified in this file.
I've used it for my own parser configurations and it works
like a champ! But I would like someone to review my changes
before I commit them to the CVS repository.
--
Andy Clark * [EMAIL PROTECTED]?
src/org/apache/xerces/parsers/org.apache.xerces.xni.parser.XMLParserConfiguration
? src/org/apache/xerces/util/ObjectFactory.java
Index: build.xml
===================================================================
RCS file: /home/cvs/xml-xerces/java/build.xml,v
retrieving revision 1.69
diff -r1.69 build.xml
142a143,145
> <copy file="
${src.dir}/org/apache/xerces/parsers/org.apache.xerces.xni.parser.XMLParserConfiguration"
> tofile="
${build.dest}/META-INF/services/org.apache.xerces.xni.parser.XMLParserConfiguration"/>
>
Index: src/javax/xml/parsers/DocumentBuilderFactory.java
===================================================================
RCS file:
/home/cvs/xml-xerces/java/src/javax/xml/parsers/DocumentBuilderFactory.java,v
retrieving revision 1.9
diff -r1.9 DocumentBuilderFactory.java
5c5
< * Copyright (c) 2001 The Apache Software Foundation. All rights
---
> * Copyright (c) 2001-2002 The Apache Software Foundation. All rights
66a67,68
> import org.apache.xerces.util.ObjectFactory;
>
70c72
< *
---
> * <p>
81c83
< * @version 1.0
---
> * @version $Id$
139c141
< return (DocumentBuilderFactory) FactoryFinder.find(
---
> return (DocumentBuilderFactory) ObjectFactory.createObject(
141a144,145
> // the properties file in $java.hom/lib
> "jaxp.properties",
144c148
< } catch (FactoryFinder.ConfigurationError e) {
---
> } catch (ObjectFactory.ConfigurationError e) {
Index: src/javax/xml/parsers/SAXParserFactory.java
===================================================================
RCS file:
/home/cvs/xml-xerces/java/src/javax/xml/parsers/SAXParserFactory.java,v
retrieving revision 1.7
diff -r1.7 SAXParserFactory.java
5c5
< * Copyright (c) 2001 The Apache Software Foundation. All rights
---
> * Copyright (c) 2001-2002 The Apache Software Foundation. All rights
62a63,64
> import org.apache.xerces.util.ObjectFactory;
>
80c82
< * @version 1.0
---
> * @version $Id$
135c137
< return (SAXParserFactory) FactoryFinder.find(
---
> return (SAXParserFactory) ObjectFactory.createObject(
137a140,141
> // the properties file in $java.home/lib
> "jaxp.properties",
140c144
< } catch (FactoryFinder.ConfigurationError e) {
---
> } catch (ObjectFactory.ConfigurationError e) {
Index: src/org/apache/xerces/parsers/DOMParser.java
===================================================================
RCS file:
/home/cvs/xml-xerces/java/src/org/apache/xerces/parsers/DOMParser.java,v
retrieving revision 1.55
diff -r1.55 DOMParser.java
5c5
< * Copyright (c) 2000,2001 The Apache Software Foundation. All rights
---
> * Copyright (c) 2000-2002 The Apache Software Foundation. All rights
66a67
> import org.apache.xerces.util.ObjectFactory;
106,107c107,111
< super(new StandardParserConfiguration());
< } // <init>
---
> super((XMLParserConfiguration)ObjectFactory.createObject(
> "org.apache.xerces.xni.parser.XMLParserConfiguration",
> "org.apache.xerces.parsers.StandardParserConfiguration"
> ));
> } // <init>()
Index: src/org/apache/xerces/parsers/SAXParser.java
===================================================================
RCS file:
/home/cvs/xml-xerces/java/src/org/apache/xerces/parsers/SAXParser.java,v
retrieving revision 1.26
diff -r1.26 SAXParser.java
5c5
< * Copyright (c) 2000,2001 The Apache Software Foundation. All rights
---
> * Copyright (c) 2000-2002 The Apache Software Foundation. All rights
60a61
> import org.apache.xerces.util.ObjectFactory;
85c86,89
< super(new StandardParserConfiguration());
---
> super((XMLParserConfiguration)ObjectFactory.createObject(
> "org.apache.xerces.xni.parser.XMLParserConfiguration",
> "org.apache.xerces.parsers.StandardParserConfiguration"
> ));
Index: src/org/apache/xerces/parsers/XMLDocumentParser.java
===================================================================
RCS file:
/home/cvs/xml-xerces/java/src/org/apache/xerces/parsers/XMLDocumentParser.java,v
retrieving revision 1.2
diff -r1.2 XMLDocumentParser.java
5c5
< * Copyright (c) 2001 The Apache Software Foundation. All rights
---
> * Copyright (c) 2001-2002 The Apache Software Foundation. All rights
60a61
> import org.apache.xerces.util.ObjectFactory;
73c74,75
< * @version $Id: XMLDocumentParser.java,v 1.2 2001/08/23 00:35:31 lehors
Exp $ */
---
> * @version $Id: XMLDocumentParser.java,v 1.2 2001/08/23 00:35:31 lehors
Exp $
> */
86,87c88,92
< super(new StandardParserConfiguration());
< } // <init>
---
> super((XMLParserConfiguration)ObjectFactory.createObject(
> "org.apache.xerces.xni.parser.XMLParserConfiguration",
> "org.apache.xerces.parsers.StandardParserConfiguration"
> ));
> } // <init>()
org.apache.xerces.parsers.StandardParserConfiguration
/*
* The Apache Software License, Version 1.1
*
*
* Copyright (c) 2001-2002 The Apache Software Foundation. All rights
* reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* 3. The end-user documentation included with the redistribution,
* if any, must include the following acknowledgment:
* "This product includes software developed by the
* Apache Software Foundation (http://www.apache.org/)."
* Alternately, this acknowledgment may appear in the software itself,
* if and wherever such third-party acknowledgments normally appear.
*
* 4. The name "Apache Software Foundation" must not be used to endorse or
* promote products derived from this software without prior written
* permission. For written permission, please contact [EMAIL PROTECTED]
*
* 5. Products derived from this software may not be called "Apache",
* nor may "Apache" appear in their name, without prior written
* permission of the Apache Software Foundation.
*
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
* ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
* ====================================================================
*
* This software consists of voluntary contributions made by many
* individuals on behalf of the Apache Software Foundation and was
* originally based on software copyright (c) 1999-2001, Sun Microsystems,
* Inc., http://www.sun.com. For more information on the Apache Software
* Foundation, please see <http://www.apache.org/>.
*/
package org.apache.xerces.util;
import java.io.InputStream;
import java.io.IOException;
import java.io.File;
import java.io.FileInputStream;
import java.util.Properties;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.lang.reflect.Method;
import java.lang.reflect.InvocationTargetException;
/**
* This class is duplicated for each JAXP subpackage so keep it in sync.
* It is package private and therefore is not exposed as part of the JAXP
* API.
* <p>
* This code is designed to implement the JAXP 1.1 spec pluggability
* feature and is designed to both compile and run on JDK version 1.1 and
* later. The code also runs both as part of an unbundled jar file and
* when bundled as part of the JDK.
* <p>
* This class was moved from the
<code>javax.xml.parsers.FactoryFinder</code>
* class and modified to be used as a general utility for creating objects
* dynamically.
*
* @version $Id$
*/
public class ObjectFactory {
//
// Constants
//
/** Set to true for debugging */
private static final boolean DEBUG = false;
//
// Public static methods
//
/**
* Finds the implementation Class object in the specified order. The
* specified order is the following:
* <ol>
* <li>query the system property using <code>System.getProperty</code>
* <li>read <code>META-INF/services/<i>factoryId</i></code> file
* <li>use fallback classname
* </ol>
*
* @return Class object of factory, never null
*
* @param factoryId Name of the factory to find, same as
* a property name
* @param fallbackClassName Implementation class name, if nothing
else
* is found. Use null to mean no
fallback.
*
* @exception ObjectFactory.ConfigurationError
*/
public static Object createObject(String factoryId, String
fallbackClassName)
throws ConfigurationError {
return createObject(factoryId, null, fallbackClassName);
} // createObject(String,String):Object
/**
* Finds the implementation Class object in the specified order. The
* specified order is the following:
* <ol>
* <li>query the system property using <code>System.getProperty</code>
* <li>read <code>$java.home/lib/<i>propertiesFilename</i></code> file
* <li>read <code>META-INF/services/<i>factoryId</i></code> file
* <li>use fallback classname
* </ol>
*
* @return Class object of factory, never null
*
* @param factoryId Name of the factory to find, same as
* a property name
* @param propertiesFilename The filename in the $java.home/lib
directory
* of the properties file.
* @param fallbackClassName Implementation class name, if nothing
else
* is found. Use null to mean no
fallback.
*
* @exception ObjectFactory.ConfigurationError
*/
public static Object createObject(String factoryId,
String propertiesFilename,
String fallbackClassName)
throws ConfigurationError
{
debugPrintln("debug is on");
ClassLoader classLoader = findClassLoader();
// Use the system property first
try {
String systemProp =
System.getProperty( factoryId );
if( systemProp!=null) {
debugPrintln("found system property " + systemProp);
return newInstance(systemProp, classLoader);
}
} catch (SecurityException se) {
}
// try to read from $java.home/lib/xml.properties
if (propertiesFilename != null) {
try {
String javah=System.getProperty( "java.home" );
String configFile = javah + File.separator +
"lib" + File.separator + propertiesFilename;
File f=new File( configFile );
if( f.exists()) {
Properties props=new Properties();
props.load( new FileInputStream(f));
String factoryClassName = props.getProperty(factoryId);
debugPrintln("found java.home property " +
factoryClassName);
return newInstance(factoryClassName, classLoader);
}
} catch(Exception ex ) {
if( DEBUG ) ex.printStackTrace();
}
}
// try to find services in CLASSPATH
String serviceId = "META-INF/services/" + factoryId;
try {
InputStream is=null;
if (classLoader == null) {
is=ClassLoader.getSystemResourceAsStream( serviceId );
} else {
is=classLoader.getResourceAsStream( serviceId );
}
if( is!=null ) {
debugPrintln("found " + serviceId);
// Read the service provider name in UTF-8 as specified in
// the jar spec. Unfortunately this fails in Microsoft
// VJ++, which does not implement the UTF-8
// encoding. Theoretically, we should simply let it fail in
// that case, since the JVM is obviously broken if it
// doesn't support such a basic standard. But since there
// are still some users attempting to use VJ++ for
// development, we have dropped in a fallback which makes a
// second attempt using the platform's default encoding. In
// VJ++ this is apparently ASCII, which is a subset of
// UTF-8... and since the strings we'll be reading here are
// also primarily limited to the 7-bit ASCII range (at
// least, in English versions), this should work well
// enough to keep us on the air until we're ready to
// officially decommit from VJ++. [Edited comment from
// jkesselm]
BufferedReader rd;
try {
rd = new BufferedReader(new InputStreamReader(is,
"UTF-8"));
} catch (java.io.UnsupportedEncodingException e) {
rd = new BufferedReader(new InputStreamReader(is));
}
String factoryClassName = rd.readLine();
rd.close();
if (factoryClassName != null &&
! "".equals(factoryClassName)) {
debugPrintln("loaded from services: " +
factoryClassName);
return newInstance(factoryClassName, classLoader);
}
}
} catch( Exception ex ) {
if( DEBUG ) ex.printStackTrace();
}
if (fallbackClassName == null) {
throw new ConfigurationError(
"Provider for " + factoryId + " cannot be found", null);
}
debugPrintln("loaded from fallback value: " + fallbackClassName);
return newInstance(fallbackClassName, classLoader);
} // createObject(String,String,String):Object
//
// Private static methods
//
/** Prints a message to standard error if debugging is enabled. */
private static void debugPrintln(String msg) {
if (DEBUG) {
System.err.println("JAXP: " + msg);
}
} // debugPrintln(String)
/**
* Figure out which ClassLoader to use. For JDK 1.2 and later use
* the context ClassLoader.
*/
private static ClassLoader findClassLoader()
throws ConfigurationError
{
Method m = null;
try {
m = Thread.class.getMethod("getContextClassLoader", null);
} catch (NoSuchMethodException e) {
// Assume that we are running JDK 1.1, use the current
ClassLoader
debugPrintln("assuming JDK 1.1");
return ObjectFactory.class.getClassLoader();
}
try {
return (ClassLoader) m.invoke(Thread.currentThread(), null);
} catch (IllegalAccessException e) {
// assert(false)
throw new ConfigurationError("Unexpected
IllegalAccessException",
e);
} catch (InvocationTargetException e) {
// assert(e.getTargetException() instanceof SecurityException)
throw new ConfigurationError("Unexpected
InvocationTargetException",
e);
}
} // findClassLoader():ClassLoader
/**
* Create an instance of a class using the specified ClassLoader
*/
private static Object newInstance(String className,
ClassLoader classLoader)
throws ConfigurationError
{
try {
Class spiClass;
if (classLoader == null) {
spiClass = Class.forName(className);
} else {
spiClass = classLoader.loadClass(className);
}
return spiClass.newInstance();
} catch (ClassNotFoundException x) {
throw new ConfigurationError(
"Provider " + className + " not found", x);
} catch (Exception x) {
throw new ConfigurationError(
"Provider " + className + " could not be instantiated: " +
x,
x);
}
} // newInstance(String,ClassLoader):Object
//
// Classes
//
/**
* A configuration error.
*/
public static class ConfigurationError
extends Error {
//
// Data
//
/** Exception. */
private Exception exception;
//
// Constructors
//
/**
* Construct a new instance with the specified detail string and
* exception.
*/
public ConfigurationError(String msg, Exception x) {
super(msg);
this.exception = x;
} // <init>(String,Exception)
//
// Public methods
//
/** Returns the exception associated to this error. */
public Exception getException() {
return exception;
} // getException():Exception
} // class ConfigurationError
} // class ObjectFactory
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