transformservice.java

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/*
 * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
 */
/*
 * $Id: TransformService.java,v 1.6.4.1 2005/09/15 12:42:11 mullan Exp $
 */
package javax.xml.crypto.dsig;

import java.security.InvalidAlgorithmParameterException;
import java.security.NoSuchAlgorithmException;
import java.security.NoSuchProviderException;
import java.security.Provider;
import java.security.Provider.Service;
import java.security.Security;
import java.util.*;
import javax.xml.crypto.MarshalException;
import javax.xml.crypto.XMLStructure;
import javax.xml.crypto.XMLCryptoContext;
import javax.xml.crypto.dsig.spec.TransformParameterSpec;

import sun.security.jca.*;
import sun.security.jca.GetInstance.Instance;

/**
 * A Service Provider Interface for transform and canonicalization algorithms.
 *
 * <p>Each instance of <code>TransformService</code> supports a specific 
 * transform or canonicalization algorithm and XML mechanism type. To create a 
 * <code>TransformService</code>, call one of the static 
 * {@link #getInstance getInstance} methods, passing in the algorithm URI and 
 * XML mechanism type desired, for example:
 *
 * <blockquote><code>
 * TransformService ts = TransformService.getInstance(Transform.XPATH2, "DOM");
 * </code></blockquote>
 *
 * <p><code>TransformService</code> implementations are registered and loaded 
 * using the {@link java.security.Provider} mechanism.  Each 
 * <code>TransformService</code> service provider implementation should include 
 * a <code>MechanismType</code> service attribute that identifies the XML 
 * mechanism type that it supports. If the attribute is not specified,
 * "DOM" is assumed. For example, a service provider that supports the
 * XPath Filter 2 Transform and DOM mechanism would be specified in the 
 * <code>Provider</code> subclass as:
 * <pre>
 *     put("TransformService." + Transform.XPATH2,
 *         "org.example.XPath2TransformService");
 *     put("TransformService." + Transform.XPATH2 + " MechanismType", "DOM");
 * </pre>
 * <code>TransformService</code> implementations that support the DOM
 * mechanism type must abide by the DOM interoperability requirements defined 
 * in the 
 * <a href="../../../../../technotes/guides/security/xmldsig/overview.html#DOM Mechanism Requirements">
 * DOM Mechanism Requirements</a> section of the API overview. See the
 * <a href="../../../../../technotes/guides/security/xmldsig/overview.html#Service Provider">
 * Service Providers</a> section of the API overview for a list of standard 
 * mechanism types.
 * <p>
 * Once a <code>TransformService</code> has been created, it can be used
 * to process <code>Transform</code> or <code>CanonicalizationMethod</code>
 * objects. If the <code>Transform</code> or <code>CanonicalizationMethod</code>
 * exists in XML form (for example, when validating an existing 
 * <code>XMLSignature</code>), the {@link #init(XMLStructure, XMLCryptoContext)}
 * method must be first called to initialize the transform and provide document
 * context (even if there are no parameters). Alternatively, if the 
 * <code>Transform</code> or <code>CanonicalizationMethod</code> is being
 * created from scratch, the {@link #init(TransformParameterSpec)} method
 * is called to initialize the transform with parameters and the 
 * {@link #marshalParams marshalParams} method is called to marshal the 
 * parameters to XML and provide the transform with document context. Finally, 
 * the {@link #transform transform} method is called to perform the 
 * transformation.
 * <p>
 * <b>Concurrent Access</b>
 * <p>The static methods of this class are guaranteed to be thread-safe.
 * Multiple threads may concurrently invoke the static methods defined in this
 * class with no ill effects.
 *
 * <p>However, this is not true for the non-static methods defined by this
 * class. Unless otherwise documented by a specific provider, threads that
 * need to access a single <code>TransformService</code> instance
 * concurrently should synchronize amongst themselves and provide the
 * necessary locking. Multiple threads each manipulating a different
 * <code>TransformService</code> instance need not synchronize.
 *
 * @author Sean Mullan
 * @author JSR 105 Expert Group
 * @since 1.6
 */
public abstract class TransformService implements Transform {

    private String algorithm;
    private String mechanism;
    private Provider provider;

    /**
     * Default constructor, for invocation by subclasses.
     */
    protected TransformService() {}

    /**
     * Returns a <code>TransformService</code> that supports the specified 
     * algorithm URI (ex: {@link Transform#XPATH2}) and mechanism type 
     * (ex: DOM).
     *
     * <p>This method uses the standard JCA provider lookup mechanism to
     * locate and instantiate a <code>TransformService</code> implementation
     * of the desired algorithm and <code>MechanismType</code> service 
     * attribute. It traverses the list of registered security 
     * <code>Provider</code>s, starting with the most preferred 
     * <code>Provider</code>. A new <code>TransformService</code> object
     * from the first <code>Provider</code> that supports the specified 
     * algorithm and mechanism type is returned. 
     * 
     * <p> Note that the list of registered providers may be retrieved via 
     * the {@link Security#getProviders() Security.getProviders()} method. 
     *
     * @param algorithm the URI of the algorithm
     * @param mechanismType the type of the XML processing mechanism and 
     *   representation
     * @return a new <code>TransformService</code>
     * @throws NullPointerException if <code>algorithm</code> or 
     *   <code>mechanismType</code> is  <code>null</code>
     * @throws NoSuchAlgorithmException if no <code>Provider</code> supports a
     *   <code>TransformService</code> implementation for the specified 
     *   algorithm and mechanism type
     * @see Provider
     */
    public static TransformService getInstance
	(String algorithm, String mechanismType) 
	throws NoSuchAlgorithmException {
	if (mechanismType == null || algorithm == null) {
	    throw new NullPointerException();
	}
	boolean dom = false;
	if (mechanismType.equals("DOM")) {
	    dom = true;
	}
        List services = GetInstance.getServices("TransformService", algorithm);
        for (Iterator t = services.iterator(); t.hasNext(); ) {
            Service s = (Service)t.next();
	    String value = s.getAttribute("MechanismType");
	    if ((value == null && dom) || 
		(value != null && value.equals(mechanismType))) {
                Instance instance = GetInstance.getInstance(s, null);
        	TransformService ts = (TransformService) instance.impl;
        	ts.algorithm = algorithm;
        	ts.mechanism = mechanismType;
        	ts.provider = instance.provider;
        	return ts;
	    }
        }
        throw new NoSuchAlgorithmException
            (algorithm + " algorithm and " + mechanismType 
		 + " mechanism not available");
    }

    /**
     * Returns a <code>TransformService</code> that supports the specified 
     * algorithm URI (ex: {@link Transform#XPATH2}) and mechanism type 
     * (ex: DOM) as supplied by the specified provider. Note that the specified 
     * <code>Provider</code> object does not have to be registered in the 
     * provider list. 
     *
     * @param algorithm the URI of the algorithm
     * @param mechanismType the type of the XML processing mechanism and 
     *   representation
     * @param provider the <code>Provider</code> object
     * @return a new <code>TransformService</code>
     * @throws NullPointerException if <code>provider</code>, 
     *   <code>algorithm</code>, or <code>mechanismType</code> is 
     *   <code>null</code>
     * @throws NoSuchAlgorithmException if a <code>TransformService</code> 
     *   implementation for the specified algorithm and mechanism type is not 
     *   available from the specified <code>Provider</code> object
     * @see Provider
     */
    public static TransformService getInstance
	(String algorithm, String mechanismType, Provider provider) 
	throws NoSuchAlgorithmException {
	if (mechanismType == null || algorithm == null || provider == null) {
	    throw new NullPointerException();
	}

	boolean dom = false;
	if (mechanismType.equals("DOM")) {
	    dom = true;