Java 生成唯一的ID

/**
 * Generator for Globally unique Strings.
 */
public class IdGenerator {

    private static final Logger LOG = LoggerFactory.getLogger(IdGenerator.class);
    
    private static final String UNIQUE_STUB;
    
    private static int instanceCount;
    
    private static String hostName;
    
    private String seed;
    
    private final AtomicLong sequence = new AtomicLong(1);
    
    private int length;
    
   

    static {
    	
        String stub = "";
        
        boolean canAccessSystemProps = true;
        
        try {
        	
            SecurityManager sm = System.getSecurityManager();
            
            if (sm != null) {
            	
                sm.checkPropertiesAccess();
                
            }
            
        } catch (SecurityException se) {
        	
            canAccessSystemProps = false;
            
        }

        if (canAccessSystemProps) {
        	
            int idGeneratorPort = 0;
            
            ServerSocket ss = null;
            
            try {

                
                
                LOG.trace("Using port {}", idGeneratorPort);

                hostName = InetAddressUtil.getLocalHostName();
                
                ss = new ServerSocket(idGeneratorPort);
                // -54842-1451457944520-
                stub = "-" + ss.getLocalPort() + "-" + System.currentTimeMillis() + "-";
                
                Thread.sleep(100);
                
            } catch (Exception e) {
            	
                if (LOG.isTraceEnabled()) {
                    LOG.trace("could not generate unique stub by using DNS and binding to local port", e);
                } else {
                    LOG.warn("could not generate unique stub by using DNS and binding to local port: {} {}", e.getClass().getCanonicalName(), e.getMessage());
                }

                // Restore interrupted state so higher level code can deal with it.
                if (e instanceof InterruptedException) {
                    Thread.currentThread().interrupt();
                }
            } finally {
                if (ss != null) {
                    try {
                        // TODO: replace the following line with IOHelper.close(ss) when Java 6 support is dropped
                        ss.close();
                    } catch (IOException ioe) {
                        if (LOG.isTraceEnabled()) {
                            LOG.trace("Closing the server socket failed", ioe);
                        } else {
                            LOG.warn("Closing the server socket failed" + " due " + ioe.getMessage());
                        }
                    }
                }
            }
        }
        // fallback
        if (hostName == null) {
            hostName = "localhost";
        }
        hostName = sanitizeHostName(hostName);

        if (stub.length() == 0) {
            stub = "-1-" + System.currentTimeMillis() + "-";
        }
        UNIQUE_STUB = stub;
    }

    /**
     * Construct an IdGenerator
     */
    public IdGenerator(String prefix) {
        synchronized (UNIQUE_STUB) {
            this.seed = prefix + UNIQUE_STUB + (instanceCount++) + ":";
            this.length = this.seed.length() + ("" + Long.MAX_VALUE).length();
        }
    }

    public IdGenerator() {
        this("ID:" + hostName);
    }

    /**
     * As we have to find the hostname as a side-affect of generating a unique
     * stub, we allow it's easy retrieval here
     *
     * @return the local host name
     */
    public static String getHostName() {
        return hostName;
    }

    /**
     * Generate a unique id
     *
     * @return a unique id
     */
    public synchronized String generateId() {
        StringBuilder sb = new StringBuilder(length);
        sb.append(seed);
        sb.append(sequence.getAndIncrement());
        return sb.toString();
    }

    public static String sanitizeHostName(String hostName) {
        boolean changed = false;

        StringBuilder sb = new StringBuilder();
        for (char ch : hostName.toCharArray()) {
            // only include ASCII chars
            if (ch < 127) {
                sb.append(ch);
            } else {
                changed = true;
            }
        }

        if (changed) {
            String newHost = sb.toString();
            LOG.info("Sanitized hostname from: {} to: {}", hostName, newHost);
            return newHost;
        } else {
            return hostName;
        }
    }

   

   

   

    
//    public static void main(String[] args) {
//    	IdGenerator generator = new IdGenerator();
//    	System.out.println(generator.generateId());
//	}
}