src/main/org/apache/tools/ant/ProjectHelper.java - ant - Git at Google

 /*
  * The Apache Software License, Version 1.1
  *
  * Copyright (c) 2000-2002 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 acknowlegement:
  *       "This product includes software developed by the
  *        Apache Software Foundation (http://www.apache.org/)."
  *    Alternately, this acknowlegement may appear in the software itself,
  *    if and wherever such third-party acknowlegements normally appear.
  *
  * 4. The names "The Jakarta Project", "Ant", and "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 apache@apache.org.
  *
  * 5. Products derived from this software may not be called "Apache"
  *    nor may "Apache" appear in their names without prior written
  *    permission of the Apache Group.
  *
  * 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.  For more
  * information on the Apache Software Foundation, please see
  * <http://www.apache.org/>.
  */

 package org.apache.tools.ant;

 import java.io.File;
 import java.io.InputStream;
 import java.io.BufferedReader;
 import java.io.InputStreamReader;
 import java.util.Hashtable;
 import java.util.Vector;
 import java.util.Enumeration;
 import java.util.Locale;

 import org.xml.sax.AttributeList;
 import org.apache.tools.ant.helper.ProjectHelperImpl;
 import org.apache.tools.ant.util.LoaderUtils;

 /**
  * Configures a Project (complete with Targets and Tasks) based on
  * a XML build file. It'll rely on a plugin to do the actual processing
  * of the xml file.
  *
  * This class also provide static wrappers for common introspection.
  *
  * All helper plugins must provide backward compatiblity with the
  * original ant patterns, unless a different behavior is explicitely
  * specified. For example, if namespace is used on the &lt;project&gt; tag
  * the helper can expect the entire build file to be namespace-enabled.
  * Namespaces or helper-specific tags can provide meta-information to
  * the helper, allowing it to use new ( or different policies ).
  *
  * However, if no namespace is used the behavior should be exactly
  * identical with the default helper.
  *
  * @author duncan@x180.com
  */
 public class ProjectHelper {
     /**
      * Name of JVM system property which provides the name of the
      * ProjectHelper class to use.
      */
     public static final String HELPER_PROPERTY =
         "org.apache.tools.ant.ProjectHelper";

     /**
      * The service identifier in jars which provide Project Helper
      * implementations.
      */
     public static final String SERVICE_ID =
         "META-INF/services/org.apache.tools.ant.ProjectHelper";

     /**
      * Configures the project with the contents of the specified XML file.
      *
      * @param project The project to configure. Must not be <code>null</code>.
      * @param buildFile An XML file giving the project's configuration.
      *                  Must not be <code>null</code>.
      *
      * @exception BuildException if the configuration is invalid or cannot
      *                           be read
      */
     public static void configureProject(Project project, File buildFile)
         throws BuildException {
         ProjectHelper helper = ProjectHelper.getProjectHelper();
         helper.parse(project, buildFile);
     }

     /** Default constructor */
     public ProjectHelper() {
     }

     /**
      * Parses the project file, configuring the project as it goes.
      *
      * @param project The project for the resulting ProjectHelper to configure.
      *                Must not be <code>null</code>.
      * @param source The source for XML configuration. A helper must support
      *               at least File, for backward compatibility. Helpers may
      *               support URL, InputStream, etc or specialized types.
      *
      * @since Ant1.5
      * @exception BuildException if the configuration is invalid or cannot
      *                           be read
      */
     public void parse(Project project, Object source) throws BuildException {
         throw new BuildException("ProjectHelper.parse() must be implemented "
             + "in a helper plugin " + this.getClass().getName());
     }


     /**
      * Discovers a project helper instance. Uses the same patterns
      * as JAXP, commons-logging, etc: a system property, a JDK1.3
      * service discovery, default.
      *
      * @return a ProjectHelper, either a custom implementation
      * if one is available and configured, or the default implementation
      * otherwise.
      *
      * @exception BuildException if a specified helper class cannot
      * be loaded/instantiated.
      */
     public static ProjectHelper getProjectHelper()
         throws BuildException {
         // Identify the class loader we will be using. Ant may be
         // in a webapp or embeded in a different app
         ProjectHelper helper = null;

         // First, try the system property
         String helperClass = System.getProperty(HELPER_PROPERTY);
         try {
             if (helperClass != null) {
                 helper = newHelper(helperClass);
             }
         } catch (SecurityException e) {
             System.out.println("Unable to load ProjectHelper class \""
                 + helperClass + " specified in system property "
                 + HELPER_PROPERTY);
         }

         // A JDK1.3 'service' ( like in JAXP ). That will plug a helper
         // automatically if in CLASSPATH, with the right META-INF/services.
         if (helper == null) {
             try {
                 ClassLoader classLoader = getContextClassLoader();
                 InputStream is = null;
                 if (classLoader != null) {
                     is = classLoader.getResourceAsStream(SERVICE_ID);
                 }
                 if (is == null) {
                     is = ClassLoader.getSystemResourceAsStream(SERVICE_ID);
                 }

                 if (is != null) {
                     // This code is needed by EBCDIC and other strange systems.
                     // It's a fix for bugs reported in xerces
                     InputStreamReader isr;
                     try {
                         isr = new InputStreamReader(is, "UTF-8");
                     } catch (java.io.UnsupportedEncodingException e) {
                         isr = new InputStreamReader(is);
                     }
                     BufferedReader rd = new BufferedReader(isr);

                     String helperClassName = rd.readLine();
                     rd.close();

                     if (helperClassName != null &&
                         !"".equals(helperClassName)) {

                         helper = newHelper(helperClassName);
                     }
                 }
             } catch (Exception ex) {
                 System.out.println("Unable to load ProjectHelper "
                     + "from service \"" + SERVICE_ID);
             }
         }

         if (helper != null) {
             return helper;
         } else {
             try {
                 // Default
                 return new ProjectHelperImpl();
             } catch (Throwable e) {
                 String message = "Unable to load default ProjectHelper due to "
                     + e.getClass().getName() + ": " + e.getMessage();
                 throw new BuildException(message, e);
             }
         }
     }

     /**
      * Creates a new helper instance from the name of the class.
      * It'll first try the thread class loader, then Class.forName()
      * will load from the same loader that loaded this class.
      *
      * @param helperClass The name of the class to create an instance
      *                    of. Must not be <code>null</code>.
      *
      * @return a new instance of the specified class.
      *
      * @exception BuildException if the class cannot be found or
      * cannot be appropriate instantiated.
      */
     private static ProjectHelper newHelper(String helperClass)
         throws BuildException {
         ClassLoader classLoader = getContextClassLoader();
         try {
             Class clazz = null;
             if (classLoader != null) {
                 try {
                     clazz = classLoader.loadClass(helperClass);
                 } catch (ClassNotFoundException ex) {
                     // try next method
                 }
             }
             if (clazz == null) {
                 clazz = Class.forName(helperClass);
             }
             return ((ProjectHelper) clazz.newInstance());
         } catch (Exception e) {
             throw new BuildException(e);
         }
     }

     /**
      * JDK1.1 compatible access to the context class loader.
      * Cut&paste from JAXP.
      *
      * @return the current context class loader, or <code>null</code>
      * if the context class loader is unavailable.
      */
     public static ClassLoader getContextClassLoader() {
         if (!LoaderUtils.isContextLoaderAvailable()) {
             return null;
         }

         return LoaderUtils.getContextClassLoader();
     }

     // -------------------- Static utils, used by most helpers ----------------

     /**
      * Configures an object using an introspection handler.
      *
      * @param target The target object to be configured.
      *               Must not be <code>null</code>.
      * @param attrs  A list of attributes to configure within the target.
      *               Must not be <code>null</code>.
      * @param project The project containing the target.
      *                Must not be <code>null</code>.
      *
      * @exception BuildException if any of the attributes can't be handled by
      *                           the target
      */
     public static void configure(Object target, AttributeList attrs,
                                  Project project) throws BuildException {
         if (target instanceof TaskAdapter) {
             target = ((TaskAdapter) target).getProxy();
         }

         IntrospectionHelper ih =
             IntrospectionHelper.getHelper(target.getClass());

         project.addBuildListener(ih);

         for (int i = 0; i < attrs.getLength(); i++) {
             // reflect these into the target
             String value = replaceProperties(project, attrs.getValue(i),
                                            project.getProperties());
             try {
                 ih.setAttribute(project, target,
                                 attrs.getName(i).toLowerCase(Locale.US), value);

             } catch (BuildException be) {
                 // id attribute must be set externally
                 if (!attrs.getName(i).equals("id")) {
                     throw be;
                 }
             }
         }
     }

     /**
      * Adds the content of #PCDATA sections to an element.
      *
      * @param project The project containing the target.
      *                Must not be <code>null</code>.
      * @param target  The target object to be configured.
      *                Must not be <code>null</code>.
      * @param buf A character array of the text within the element.
      *            Will not be <code>null</code>.
      * @param start The start element in the array.
      * @param count The number of characters to read from the array.
      *
      * @exception BuildException if the target object doesn't accept text
      */
     public static void addText(Project project, Object target, char[] buf,
         int start, int count) throws BuildException {
         addText(project, target, new String(buf, start, count));
     }

     /**
      * Adds the content of #PCDATA sections to an element.
      *
      * @param project The project containing the target.
      *                Must not be <code>null</code>.
      * @param target  The target object to be configured.
      *                Must not be <code>null</code>.
      * @param text    Text to add to the target.
      *                May be <code>null</code>, in which case this
      *                method call is a no-op.
      *
      * @exception BuildException if the target object doesn't accept text
      */
     public static void addText(Project project, Object target, String text)
         throws BuildException {

         if (text == null) {
             return;
         }

         if (target instanceof TaskAdapter) {
             target = ((TaskAdapter) target).getProxy();
         }

         IntrospectionHelper.getHelper(target.getClass()).addText(project,
             target, text);
     }

     /**
      * Stores a configured child element within its parent object.
      *
      * @param project Project containing the objects.
      *                May be <code>null</code>.
      * @param parent  Parent object to add child to.
      *                Must not be <code>null</code>.
      * @param child   Child object to store in parent.
      *                Should not be <code>null</code>.
      * @param tag     Name of element which generated the child.
      *                May be <code>null</code>, in which case
      *                the child is not stored.
      */
     public static void storeChild(Project project, Object parent,
          Object child, String tag) {
         IntrospectionHelper ih
             = IntrospectionHelper.getHelper(parent.getClass());
         ih.storeElement(project, parent, child, tag);
     }

     /**
      * Replaces <code>${xxx}</code> style constructions in the given value with
      * the string value of the corresponding properties.
      *
      * @param project The project containing the properties to replace.
      *                Must not be <code>null</code>.
      *
      * @param value The string to be scanned for property references.
      *              May be <code>null</code>.
      *
      * @exception BuildException if the string contains an opening
      *                           <code>${</code> without a closing
      *                           <code>}</code>
      * @return the original string with the properties replaced, or
      *         <code>null</code> if the original string is <code>null</code>.
      *
      * @since 1.5
      */
      public static String replaceProperties(Project project, String value)
             throws BuildException {
          return project.replaceProperties(value);
      }

     /**
      * Replaces <code>${xxx}</code> style constructions in the given value
      * with the string value of the corresponding data types.
      *
      * @param project The container project. This is used solely for
      *                logging purposes. Must not be <code>null</code>.
      * @param value The string to be scanned for property references.
      *              May be <code>null</code>, in which case this
      *              method returns immediately with no effect.
      * @param keys  Mapping (String to String) of property names to their
      *              values. Must not be <code>null</code>.
      *
      * @exception BuildException if the string contains an opening
      *                           <code>${</code> without a closing
      *                           <code>}</code>
      * @return the original string with the properties replaced, or
      *         <code>null</code> if the original string is <code>null</code>.
      */
      public static String replaceProperties(Project project, String value,
          Hashtable keys) throws BuildException {
         if (value == null) {
             return null;
         }

         Vector fragments = new Vector();
         Vector propertyRefs = new Vector();
         parsePropertyString(value, fragments, propertyRefs);

         StringBuffer sb = new StringBuffer();
         Enumeration i = fragments.elements();
         Enumeration j = propertyRefs.elements();
         while (i.hasMoreElements()) {
             String fragment = (String) i.nextElement();
             if (fragment == null) {
                 String propertyName = (String) j.nextElement();
                 if (!keys.containsKey(propertyName)) {
                     project.log("Property ${" + propertyName
                         + "} has not been set", Project.MSG_VERBOSE);
                 }
                 fragment = (keys.containsKey(propertyName))
                     ? (String) keys.get(propertyName)
                     : "${" + propertyName + "}";
             }
             sb.append(fragment);
         }

         return sb.toString();
     }

     /**
      * Parses a string containing <code>${xxx}</code> style property
      * references into two lists. The first list is a collection
      * of text fragments, while the other is a set of string property names.
      * <code>null</code> entries in the first list indicate a property
      * reference from the second list.
      *
      * @param value     Text to parse. Must not be <code>null</code>.
      * @param fragments List to add text fragments to.
      *                  Must not be <code>null</code>.
      * @param propertyRefs List to add property names to.
      *                     Must not be <code>null</code>.
      *
      * @exception BuildException if the string contains an opening
      *                           <code>${</code> without a closing
      *                           <code>}</code>
      */
     public static void parsePropertyString(String value, Vector fragments,
                                            Vector propertyRefs)
         throws BuildException {
         int prev = 0;
         int pos;
         //search for the next instance of $ from the 'prev' position
         while ((pos = value.indexOf("$", prev)) >= 0) {

             //if there was any text before this, add it as a fragment
             //TODO, this check could be modified to go if pos>prev;
             //seems like this current version could stick empty strings
             //into the list
             if (pos > 0) {
                 fragments.addElement(value.substring(prev, pos));
             }
             //if we are at the end of the string, we tack on a $
             //then move past it
             if (pos == (value.length() - 1)) {
                 fragments.addElement("$");
                 prev = pos + 1;
             } else if (value.charAt(pos + 1) != '{') {
                 //peek ahead to see if the next char is a property or not
                 //not a property: insert the char as a literal
                 /*
                 fragments.addElement(value.substring(pos + 1, pos + 2));
                 prev = pos + 2;
                 */
                 if (value.charAt(pos + 1) == '$') {
                     //backwards compatibility two $ map to one mode
                     fragments.addElement("$");
                     prev = pos + 2;
                 } else {
                     //new behaviour: $X maps to $X for all values of X!='$'
                     fragments.addElement(value.substring(pos, pos + 2));
                     prev = pos + 2;
                 }

             } else {
                 //property found, extract its name or bail on a typo
                 int endName = value.indexOf('}', pos);
                 if (endName < 0) {
                     throw new BuildException("Syntax error in property: "
                                                  + value);
                 }
                 String propertyName = value.substring(pos + 2, endName);
                 fragments.addElement(null);
                 propertyRefs.addElement(propertyName);
                 prev = endName + 1;
             }
         }
         //no more $ signs found
         //if there is any tail to the file, append it
         if (prev < value.length()) {
             fragments.addElement(value.substring(prev));
         }
     }
 //end class
 }
	/*
	* The Apache Software License, Version 1.1
	*
	* Copyright (c) 2000-2002 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 acknowlegement:
	* "This product includes software developed by the
	* Apache Software Foundation (http://www.apache.org/)."
	* Alternately, this acknowlegement may appear in the software itself,
	* if and wherever such third-party acknowlegements normally appear.
	*
	* 4. The names "The Jakarta Project", "Ant", and "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 apache@apache.org.
	*
	* 5. Products derived from this software may not be called "Apache"
	* nor may "Apache" appear in their names without prior written
	* permission of the Apache Group.
	*
	* 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. For more
	* information on the Apache Software Foundation, please see
	* <http://www.apache.org/>.
	*/

	package org.apache.tools.ant;

	import java.io.File;
	import java.io.InputStream;
	import java.io.BufferedReader;
	import java.io.InputStreamReader;
	import java.util.Hashtable;
	import java.util.Vector;
	import java.util.Enumeration;
	import java.util.Locale;

	import org.xml.sax.AttributeList;
	import org.apache.tools.ant.helper.ProjectHelperImpl;
	import org.apache.tools.ant.util.LoaderUtils;

	/**
	* Configures a Project (complete with Targets and Tasks) based on
	* a XML build file. It'll rely on a plugin to do the actual processing
	* of the xml file.
	*
	* This class also provide static wrappers for common introspection.
	*
	* All helper plugins must provide backward compatiblity with the
	* original ant patterns, unless a different behavior is explicitely
	* specified. For example, if namespace is used on the <project> tag
	* the helper can expect the entire build file to be namespace-enabled.
	* Namespaces or helper-specific tags can provide meta-information to
	* the helper, allowing it to use new ( or different policies ).
	*
	* However, if no namespace is used the behavior should be exactly
	* identical with the default helper.
	*
	* @author duncan@x180.com
	*/
	public class ProjectHelper {
	/**
	* Name of JVM system property which provides the name of the
	* ProjectHelper class to use.
	*/
	public static final String HELPER_PROPERTY =
	"org.apache.tools.ant.ProjectHelper";

	/**
	* The service identifier in jars which provide Project Helper
	* implementations.
	*/
	public static final String SERVICE_ID =
	"META-INF/services/org.apache.tools.ant.ProjectHelper";

	/**
	* Configures the project with the contents of the specified XML file.
	*
	* @param project The project to configure. Must not be <code>null</code>.
	* @param buildFile An XML file giving the project's configuration.
	* Must not be <code>null</code>.
	*
	* @exception BuildException if the configuration is invalid or cannot
	* be read
	*/
	public static void configureProject(Project project, File buildFile)
	throws BuildException {
	ProjectHelper helper = ProjectHelper.getProjectHelper();
	helper.parse(project, buildFile);
	}

	/** Default constructor */
	public ProjectHelper() {
	}

	/**
	* Parses the project file, configuring the project as it goes.
	*
	* @param project The project for the resulting ProjectHelper to configure.
	* Must not be <code>null</code>.
	* @param source The source for XML configuration. A helper must support
	* at least File, for backward compatibility. Helpers may
	* support URL, InputStream, etc or specialized types.
	*
	* @since Ant1.5
	* @exception BuildException if the configuration is invalid or cannot
	* be read
	*/
	public void parse(Project project, Object source) throws BuildException {
	throw new BuildException("ProjectHelper.parse() must be implemented "
	+ "in a helper plugin " + this.getClass().getName());
	}


	/**
	* Discovers a project helper instance. Uses the same patterns
	* as JAXP, commons-logging, etc: a system property, a JDK1.3
	* service discovery, default.
	*
	* @return a ProjectHelper, either a custom implementation
	* if one is available and configured, or the default implementation
	* otherwise.
	*
	* @exception BuildException if a specified helper class cannot
	* be loaded/instantiated.
	*/
	public static ProjectHelper getProjectHelper()
	throws BuildException {
	// Identify the class loader we will be using. Ant may be
	// in a webapp or embeded in a different app
	ProjectHelper helper = null;

	// First, try the system property
	String helperClass = System.getProperty(HELPER_PROPERTY);
	try {
	if (helperClass != null) {
	helper = newHelper(helperClass);
	}
	} catch (SecurityException e) {
	System.out.println("Unable to load ProjectHelper class \""
	+ helperClass + " specified in system property "
	+ HELPER_PROPERTY);
	}

	// A JDK1.3 'service' ( like in JAXP ). That will plug a helper
	// automatically if in CLASSPATH, with the right META-INF/services.
	if (helper == null) {
	try {
	ClassLoader classLoader = getContextClassLoader();
	InputStream is = null;
	if (classLoader != null) {
	is = classLoader.getResourceAsStream(SERVICE_ID);
	}
	if (is == null) {
	is = ClassLoader.getSystemResourceAsStream(SERVICE_ID);
	}

	if (is != null) {
	// This code is needed by EBCDIC and other strange systems.
	// It's a fix for bugs reported in xerces
	InputStreamReader isr;
	try {
	isr = new InputStreamReader(is, "UTF-8");
	} catch (java.io.UnsupportedEncodingException e) {
	isr = new InputStreamReader(is);
	}
	BufferedReader rd = new BufferedReader(isr);

	String helperClassName = rd.readLine();
	rd.close();

	if (helperClassName != null &&
	!"".equals(helperClassName)) {

	helper = newHelper(helperClassName);
	}
	}
	} catch (Exception ex) {
	System.out.println("Unable to load ProjectHelper "
	+ "from service \"" + SERVICE_ID);
	}
	}

	if (helper != null) {
	return helper;
	} else {
	try {
	// Default
	return new ProjectHelperImpl();
	} catch (Throwable e) {
	String message = "Unable to load default ProjectHelper due to "
	+ e.getClass().getName() + ": " + e.getMessage();
	throw new BuildException(message, e);
	}
	}
	}

	/**
	* Creates a new helper instance from the name of the class.
	* It'll first try the thread class loader, then Class.forName()
	* will load from the same loader that loaded this class.
	*
	* @param helperClass The name of the class to create an instance
	* of. Must not be <code>null</code>.
	*
	* @return a new instance of the specified class.
	*
	* @exception BuildException if the class cannot be found or
	* cannot be appropriate instantiated.
	*/
	private static ProjectHelper newHelper(String helperClass)
	throws BuildException {
	ClassLoader classLoader = getContextClassLoader();
	try {
	Class clazz = null;
	if (classLoader != null) {
	try {
	clazz = classLoader.loadClass(helperClass);
	} catch (ClassNotFoundException ex) {
	// try next method
	}
	}
	if (clazz == null) {
	clazz = Class.forName(helperClass);
	}
	return ((ProjectHelper) clazz.newInstance());
	} catch (Exception e) {
	throw new BuildException(e);
	}
	}

	/**
	* JDK1.1 compatible access to the context class loader.
	* Cut&paste from JAXP.
	*
	* @return the current context class loader, or <code>null</code>
	* if the context class loader is unavailable.
	*/
	public static ClassLoader getContextClassLoader() {
	if (!LoaderUtils.isContextLoaderAvailable()) {
	return null;
	}

	return LoaderUtils.getContextClassLoader();
	}

	// -------------------- Static utils, used by most helpers ----------------

	/**
	* Configures an object using an introspection handler.
	*
	* @param target The target object to be configured.
	* Must not be <code>null</code>.
	* @param attrs A list of attributes to configure within the target.
	* Must not be <code>null</code>.
	* @param project The project containing the target.
	* Must not be <code>null</code>.
	*
	* @exception BuildException if any of the attributes can't be handled by
	* the target
	*/
	public static void configure(Object target, AttributeList attrs,
	Project project) throws BuildException {
	if (target instanceof TaskAdapter) {
	target = ((TaskAdapter) target).getProxy();
	}

	IntrospectionHelper ih =
	IntrospectionHelper.getHelper(target.getClass());

	project.addBuildListener(ih);

	for (int i = 0; i < attrs.getLength(); i++) {
	// reflect these into the target
	String value = replaceProperties(project, attrs.getValue(i),
	project.getProperties());
	try {
	ih.setAttribute(project, target,
	attrs.getName(i).toLowerCase(Locale.US), value);

	} catch (BuildException be) {
	// id attribute must be set externally
	if (!attrs.getName(i).equals("id")) {
	throw be;
	}
	}
	}
	}

	/**
	* Adds the content of #PCDATA sections to an element.
	*
	* @param project The project containing the target.
	* Must not be <code>null</code>.
	* @param target The target object to be configured.
	* Must not be <code>null</code>.
	* @param buf A character array of the text within the element.
	* Will not be <code>null</code>.
	* @param start The start element in the array.
	* @param count The number of characters to read from the array.
	*
	* @exception BuildException if the target object doesn't accept text
	*/
	public static void addText(Project project, Object target, char[] buf,
	int start, int count) throws BuildException {
	addText(project, target, new String(buf, start, count));
	}

	/**
	* Adds the content of #PCDATA sections to an element.
	*
	* @param project The project containing the target.
	* Must not be <code>null</code>.
	* @param target The target object to be configured.
	* Must not be <code>null</code>.
	* @param text Text to add to the target.
	* May be <code>null</code>, in which case this
	* method call is a no-op.
	*
	* @exception BuildException if the target object doesn't accept text
	*/
	public static void addText(Project project, Object target, String text)
	throws BuildException {

	if (text == null) {
	return;
	}

	if (target instanceof TaskAdapter) {
	target = ((TaskAdapter) target).getProxy();
	}

	IntrospectionHelper.getHelper(target.getClass()).addText(project,
	target, text);
	}

	/**
	* Stores a configured child element within its parent object.
	*
	* @param project Project containing the objects.
	* May be <code>null</code>.
	* @param parent Parent object to add child to.
	* Must not be <code>null</code>.
	* @param child Child object to store in parent.
	* Should not be <code>null</code>.
	* @param tag Name of element which generated the child.
	* May be <code>null</code>, in which case
	* the child is not stored.
	*/
	public static void storeChild(Project project, Object parent,
	Object child, String tag) {
	IntrospectionHelper ih
	= IntrospectionHelper.getHelper(parent.getClass());
	ih.storeElement(project, parent, child, tag);
	}

	/**
	* Replaces <code>${xxx}</code> style constructions in the given value with
	* the string value of the corresponding properties.
	*
	* @param project The project containing the properties to replace.
	* Must not be <code>null</code>.
	*
	* @param value The string to be scanned for property references.
	* May be <code>null</code>.
	*
	* @exception BuildException if the string contains an opening
	* <code>${</code> without a closing
	* <code>}</code>
	* @return the original string with the properties replaced, or
	* <code>null</code> if the original string is <code>null</code>.
	*
	* @since 1.5
	*/
	public static String replaceProperties(Project project, String value)
	throws BuildException {
	return project.replaceProperties(value);
	}

	/**
	* Replaces <code>${xxx}</code> style constructions in the given value
	* with the string value of the corresponding data types.
	*
	* @param project The container project. This is used solely for
	* logging purposes. Must not be <code>null</code>.
	* @param value The string to be scanned for property references.
	* May be <code>null</code>, in which case this
	* method returns immediately with no effect.
	* @param keys Mapping (String to String) of property names to their
	* values. Must not be <code>null</code>.
	*
	* @exception BuildException if the string contains an opening
	* <code>${</code> without a closing
	* <code>}</code>
	* @return the original string with the properties replaced, or
	* <code>null</code> if the original string is <code>null</code>.
	*/
	public static String replaceProperties(Project project, String value,
	Hashtable keys) throws BuildException {
	if (value == null) {
	return null;
	}

	Vector fragments = new Vector();
	Vector propertyRefs = new Vector();
	parsePropertyString(value, fragments, propertyRefs);

	StringBuffer sb = new StringBuffer();
	Enumeration i = fragments.elements();
	Enumeration j = propertyRefs.elements();
	while (i.hasMoreElements()) {
	String fragment = (String) i.nextElement();
	if (fragment == null) {
	String propertyName = (String) j.nextElement();
	if (!keys.containsKey(propertyName)) {
	project.log("Property ${" + propertyName
	+ "} has not been set", Project.MSG_VERBOSE);
	}
	fragment = (keys.containsKey(propertyName))
	? (String) keys.get(propertyName)
	: "${" + propertyName + "}";
	}
	sb.append(fragment);
	}

	return sb.toString();
	}

	/**
	* Parses a string containing <code>${xxx}</code> style property
	* references into two lists. The first list is a collection
	* of text fragments, while the other is a set of string property names.
	* <code>null</code> entries in the first list indicate a property
	* reference from the second list.
	*
	* @param value Text to parse. Must not be <code>null</code>.
	* @param fragments List to add text fragments to.
	* Must not be <code>null</code>.
	* @param propertyRefs List to add property names to.
	* Must not be <code>null</code>.
	*
	* @exception BuildException if the string contains an opening
	* <code>${</code> without a closing
	* <code>}</code>
	*/
	public static void parsePropertyString(String value, Vector fragments,
	Vector propertyRefs)
	throws BuildException {
	int prev = 0;
	int pos;
	//search for the next instance of $ from the 'prev' position
	while ((pos = value.indexOf("$", prev)) >= 0) {

	//if there was any text before this, add it as a fragment
	//TODO, this check could be modified to go if pos>prev;
	//seems like this current version could stick empty strings
	//into the list
	if (pos > 0) {
	fragments.addElement(value.substring(prev, pos));
	}
	//if we are at the end of the string, we tack on a $
	//then move past it
	if (pos == (value.length() - 1)) {
	fragments.addElement("$");
	prev = pos + 1;
	} else if (value.charAt(pos + 1) != '{') {
	//peek ahead to see if the next char is a property or not
	//not a property: insert the char as a literal
	/*
	fragments.addElement(value.substring(pos + 1, pos + 2));
	prev = pos + 2;
	*/
	if (value.charAt(pos + 1) == '$') {
	//backwards compatibility two $ map to one mode
	fragments.addElement("$");
	prev = pos + 2;
	} else {
	//new behaviour: $X maps to $X for all values of X!='$'
	fragments.addElement(value.substring(pos, pos + 2));
	prev = pos + 2;
	}

	} else {
	//property found, extract its name or bail on a typo
	int endName = value.indexOf('}', pos);
	if (endName < 0) {
	throw new BuildException("Syntax error in property: "
	+ value);
	}
	String propertyName = value.substring(pos + 2, endName);
	fragments.addElement(null);
	propertyRefs.addElement(propertyName);
	prev = endName + 1;
	}
	}
	//no more $ signs found
	//if there is any tail to the file, append it
	if (prev < value.length()) {
	fragments.addElement(value.substring(prev));
	}
	}
	//end class
	}