package org.w3c.rdf.implementation.model;import java.security.*;import java.util.*;import org.w3c.rdf.model.*;import org.w3c.rdf.digest.*;import org.w3c.rdf.vocabulary.rdf_syntax_19990222.RDF;public class NodeFactoryImpl implements NodeFactory {  static final int RANDOM_SEED_LEN = 8; // bytes  private static Random rnd;  private static Object rndLock = new String();  private static final int MAX_ORD = 30; // maximal number of cached ordinals  private static Resource[] ords;  static {    ords = new Resource[MAX_ORD + 1]; // 0 is wasted    for(int i=1; i <= MAX_ORD; i++)      ords[i] = new ResourceImpl(RDF._Namespace, "_" + i);    // run a new thread to initialize secure random    Thread th = new Thread() {	public void run() {	  //	  System.err.println("STARTED GENERATING RANDOM");	  // hope 8 bytes for seed are enough...	  rnd = new SecureRandom(SecureRandom.getSeed(RANDOM_SEED_LEN));	  //	  System.err.println("FINISHED GENERATING RANDOM");	  synchronized(rndLock) {	    rndLock.notify();	  }	}      };    th.setPriority(Thread.MIN_PRIORITY);    th.start();  }  /**   * Creates a resource from a URI   */  public Resource createResource(String str) {    return str != null ? new ResourceImpl(str) : null;  }  /**   * Creates a resource from namespace and local name   */  public Resource createResource(String namespace, String localName) {    return localName != null ? new ResourceImpl(namespace, localName) : null;  }  /**   * Creates a literal out of a string   */  public Literal createLiteral(String str) {    return str != null ? new LiteralImpl(str) : null;  }  /**   * Creates a triple   */  public Statement createStatement(Resource subject, Resource predicate, RDFNode object) {		    return (subject != null && predicate != null && object != null) ?			new StatementImpl(subject, predicate, object) : null;  }	/**	 * Creates a resource with a unique ID	 */  public Resource createUniqueResource() {    if(rnd == null) {      // wait for the generator thread to complete      try {	synchronized(rndLock) {	  rndLock.wait();	}      } catch (InterruptedException any) {}      // rnd must be done by now      //      rnd = new SecureRandom(SecureRandom.getSeed(RANDOM_SEED_LEN));    }    byte[] b = new byte[16];    rnd.nextBytes(b);    return new ResourceImpl("urn:rdf:" + DigestUtil.toHexString(b));  }  /**   * Creates an ordinal property (rdf:li, rdf:_N)   */  public Resource createOrdinal(int i) {        if(i < 1)      throw new IllegalArgumentException("Attempt to construct invalid ordinal resource");    if(i <= MAX_ORD)      return ords[i];    else      return new ResourceImpl(RDF._Namespace + "_" + i);  }  /**   * Creates a literal from a boolean   */  public Literal createLiteral(boolean b) throws ModelException {    return createLiteral(String.valueOf(b));  }  /**   * Creates a literal from a byte   */  public Literal createLiteral(byte b) throws ModelException {    return createLiteral(String.valueOf(b));  }  /**   * Creates a literal from a char   */  public Literal createLiteral(char b) throws ModelException {    return createLiteral(String.valueOf(b));  }  /**   * Creates a literal from a short   */  public Literal createLiteral(short b) throws ModelException {    return createLiteral(String.valueOf(b));  }  /**   * Creates a literal from an int   */  public Literal createLiteral(int b) throws ModelException {    return createLiteral(String.valueOf(b));  }  /**   * Creates a literal from a long   */  public Literal createLiteral(long b) throws ModelException{    return createLiteral(String.valueOf(b));  }  /**   * Creates a literal from a float   */  public Literal createLiteral(float b) throws ModelException{    return createLiteral(String.valueOf(b));  }  /**   * Creates a literal from a double   */  public Literal createLiteral(double b) throws ModelException{    return createLiteral(String.valueOf(b));  }}