/*
* 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.URISyntaxException;
import java.util.Map;
import java.util.WeakHashMap;
/**
* 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="https://jxta-spec.dev.java.net/nonav/JXTAProtocols.html#ids" target='_blank'>JXTA Protocols Specification : IDs</a>
*/
public abstract class ID implements java.io.Serializable {
/**
* Magic value for this format of serialization version.
*/
protected static final long serialVersionUID = 1L;
/**
* 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 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;
}
}