id.java

来自「JXTA&#8482 is a set of open, generalize」· Java 代码 · 共 326 行

/*
 * Copyright (c) 2001-2007 Sun Microsystems, Inc.  All rights reserved.
 *  
 *  The Sun Project JXTA(TM) Software License
 *  
 *  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 Sun Microsystems, Inc. for JXTA(TM) technology." 
 *     Alternately, this acknowledgment may appear in the software itself, if 
 *     and wherever such third-party acknowledgments normally appear.
 *  
 *  4. The names "Sun", "Sun Microsystems, Inc.", "JXTA" and "Project JXTA" must 
 *     not be used to endorse or promote products derived from this software 
 *     without prior written permission. For written permission, please contact 
 *     Project JXTA at http://www.jxta.org.
 *  
 *  5. Products derived from this software may not be called "JXTA", nor may 
 *     "JXTA" appear in their name, without prior written permission of Sun.
 *  
 *  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 SUN 
 *  MICROSYSTEMS 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.
 *  
 *  JXTA is a registered trademark of Sun Microsystems, Inc. in the United 
 *  States and other countries.
 *  
 *  Please see the license information page at :
 *  <http://www.jxta.org/project/www/license.html> for instructions on use of 
 *  the license in source files.
 *  
 *  ====================================================================
 *  
 *  This software consists of voluntary contributions made by many individuals 
 *  on behalf of Project JXTA. For more information on Project JXTA, please see 
 *  http://www.jxta.org.
 *  
 *  This license is based on the BSD license adopted by the Apache Foundation. 
 */

package net.jxta.id;


import java.io.ObjectStreamException;
import java.lang.ref.Reference;
import java.lang.ref.WeakReference;
import java.net.URI;
import java.net.URL;
import java.util.Map;
import java.util.WeakHashMap;

import java.net.MalformedURLException;
import java.net.URISyntaxException;


/**
 *  IDs are used to uniquely identify peers, peer groups, pipes and other
 *  types of objects manipulated by the JXTA APIs.
 *
 *  @see net.jxta.id.IDFactory
 *  @see net.jxta.codat.CodatID
 *  @see net.jxta.peer.PeerID
 *  @see net.jxta.peergroup.PeerGroupID
 *  @see net.jxta.pipe.PipeID
 *  @see net.jxta.platform.ModuleClassID
 *  @see net.jxta.platform.ModuleSpecID
 *  @see <a href="http://spec.jxta.org/nonav/v1.0/docbook/JXTAProtocols.html#ids" target='_blank'>JXTA Protocols Specification : IDs</a>
 */
public abstract class ID implements java.io.Serializable {
    
    /**
     * Collection of interned IDs. All IDs visible within in the VM are
     * contained within this table.
     */
    private static final Map<ID, WeakReference<ID>> interned = new WeakHashMap<ID, WeakReference<ID>>(1000);
    
    /**
     * This defines the URI scheme that we will be using to present JXTA IDs.
     * JXTA IDs are encoded for presentation into URIs (see
     * {@link <a href="http://www.ietf.org/rfc/rfc2396.txt">IETF RFC 2396 Uniform Resource Identifiers (URI) : Generic Syntax</a>}
     * ) as URNs (see
     * {@link <a href="http://www.ietf.org/rfc/rfc2141.txt">IETF RFC 2141 Uniform Resource Names (URN) Syntax</a>}
     * ).
     */
    public static final String URIEncodingName = "urn";
    
    /**
     *  This defines the URN Namespace that we will be using to present JXTA IDs.
     *  The namespace allows URN resolvers to determine which sub-resolver to use
     *  to resolve URN references. All JXTA IDs are presented in this namespace.
     */
    public static final String URNNamespace = "jxta";
    
    /**
     *	The null ID. The NullID is often used as a placeholder in fields which
     *  are uninitialized.
     *
     *  <p/>This is a singleton within the scope of a VM.
     */
    public static final ID nullID = (new NullID()).intern();
    
    /**
     *
     * Creates an ID by parsing the given URI.
     *
     * <p>This convenience factory method works as if by invoking the
     * {@link IDFactory#fromURI(URI)} method; any {@link URISyntaxException}
     * thrown is caught and wrapped in a new {@link IllegalArgumentException}
     * object, which is then thrown.  
     *
     * <p> This method is provided for use in situations where it is known that
     * the given string is a legal ID, for example for ID constants declared
     * within in a program, and so it would be considered a programming error
     * for the URI not to parse as such.  The {@link IDFactory}, which throws
     * {@link URISyntaxException} directly, should be used situations where a
     * ID is being constructed from user input or from some other source that
     * may be prone to errors. 
     *
     * @param  fromURI   The URI to be parsed into an ID
     * @return The new ID
     *
     * @throws  NullPointerException
     *          If <tt>fromURI</tt> is <tt>null</tt>
     *
     * @throws  IllegalArgumentException
     *          If the given URI is not a valid ID.
     */
    public static ID create(URI fromURI) {
        try {
            return IDFactory.fromURI(fromURI);
        } catch (URISyntaxException badid) {
            IllegalArgumentException failure = new IllegalArgumentException();

            failure.initCause(badid);
            throw failure;
        }
    }
    
    /**
     *  Constructor for IDs. IDs are constructed using the {@link IDFactory} or
     *  {@link #create(URI)}.
     *
     */
    protected ID() {}
    
    /**
     *  Returns a string representation of the ID. This representation should be
     *  used primarily for debugging purposes. For most other situations IDs
     *  should be externalized as Java URI Objects via {@link #toURI()}.
     *
     *  <p/>The default implementation is the <code>toString()</code> of the ID
     *  represented as a URI.
     *
     *  @return	String containing the URI
     *
     */
    @Override
    public String toString() {
        return toURI().toString();
    }
    
    /**
     *  Return the interned form of the ID.
     */
    private Object readResolve() throws ObjectStreamException {
        return intern();
    }

    /**
     *  Returns a string identifier which indicates which ID format is
     *  used by this ID instance.
     *
     *  @return	a string identifier which indicates which ID format is
     *  used by this ID instance.
     */
    public abstract String getIDFormat();
    
    /**
     *  Returns an object containing the unique value of the ID. This object
     *  must provide implementations of toString(), equals() and hashCode() that
     *  are canonical and consistent from run-to-run given the same input values.
     *  Beyond this nothing should be assumed about the nature of this object.
     *  For some implementations the object returned may be <code>this</code>.
     *
     *  @return	Object which can provide canonical representations of the ID.
     */
    public abstract Object getUniqueValue();
    
    /**
     *  Returns a URL representation of the ID. The
     *  {@link net.jxta.id.IDFactory JXTA ID Factory} can be used to construct
     *  ID Objects from URLs containing JXTA IDs.
     *
     *  @deprecated URIs are now the preferred way of manipulating IDs
     *
     *  @see net.jxta.id.IDFactory#fromURL( java.net.URL )
     *
     *  @return	URL Object containing the URI
     */
    @Deprecated
    public URL getURL() {
        try {
            return IDFactory.jxtaURL(URIEncodingName, "", URNNamespace + ":" + getUniqueValue());
        } catch (MalformedURLException caught) {
            IllegalStateException failure = new IllegalStateException("Environment incorrectly intialized.");

            failure.initCause(caught);
            throw failure;
        }
    }
    
    /**
     * Returns a canonical representation for the ID object.
     *
     * <p/>A pool of IDs, is maintained privately by the class.
     *
     * <p/>When the intern() method is invoked, if the pool already contains a
     * ID equal to this ID object as determined by the
     * equals(Object) method, then the ID from the pool is returned.
     * Otherwise, this ID object is added to the pool and a reference
     * to this ID object is returned.
     *
     * <p/>It follows that for any two ID <tt>s</tt> and <tt>t</tt>,
     * <tt>s.intern() == t.intern()</tt> is true if and only if <tt>s.equals(t)</tt>
     * is true.
     *
     * @return a ID that has the same value as this type, but is guaranteed to
     * be from a pool of unique types.
     */
    protected ID intern() {
        synchronized (ID.class) {
            Reference<ID> common = interned.get(this);
            
            ID result = null;
            
            if (null != common) {
                result = common.get();
            }
            
            if (null == result) {
                interned.put(this, new WeakReference<ID>(this));
                result = this;
            }
            
            return result;
        }
    }
    
    /**
     *  Returns a URI representation of the ID. {@link java.net.URI URIs} are
     *  the preferred way of externalizing and presenting JXTA IDs. The
     *  {@link net.jxta.id.IDFactory JXTA ID Factory} can be used to construct
     *  ID Objects from URIs containing JXTA IDs.
     *
     *  @see net.jxta.id.IDFactory#fromURI( java.net.URI )
     *
     *  @return	URI Object containing the URI
     */
    public URI toURI() {
        return URI.create(URIEncodingName + ":" + URNNamespace + ":" + getUniqueValue());
    }
}


/**
 * The NullID is often used as a placeholder in fields which are uninitialized.
 */
final class NullID extends ID {
    final static String JXTAFormat = "jxta";
    
    final static String UNIQUEVALUE = "Null";
    
    /**
     *  NullID is not intended to be constructed. You should use the
     *  {@link #nullID} constant instead.
     */
    NullID() {}
    
    /**
     *  {@inheritDoc}
     */
    @Override
    public boolean equals(Object target) {
        return (this == target); // null is only itself.
    }
    
    /**
     * deserialization has to point back to the singleton in this VM.
     */
    private Object readResolve() {
        return ID.nullID;
    }
    
    /**
     *  {@inheritDoc}
     */
    @Override
    public String getIDFormat() {
        return JXTAFormat;
    }
    
    /**
     *  {@inheritDoc}
     */
    @Override
    public Object getUniqueValue() {
        return getIDFormat() + "-" + UNIQUEVALUE;
    }
}