Correlation ID generator

When there is a need to follow the business logic route to collect all activities, a correlation id could be used as a key to bind all related log entries.

import java.net.InetAddress; import java.net.UnknownHostException; import java.util.Random; public class CorrelationHolder {  private final static Random RANDOM = new Random();  private final static int RANDOM_UPPER_LIMIT = 10000;  private final static String DEFAULT = "DEFAULT";  private final static ThreadLocal<String> CORRELATION_ID = new ThreadLocal<String>();  private CorrelationHolder() {   // The class is only supposed to be accessed in static  }  public static String getCorrelationId() {   final String identifier = (String) CorrelationHolder.CORRELATION_ID.get();   if (null == identifier) {    try {     CorrelationHolder.setCorrelationId(CorrelationHolder.createCorrelationId());    } catch (Exception e) {     CorrelationHolder.setCorrelationId(DEFAULT);    }   }   return CorrelationHolder.CORRELATION_ID.get();  }  private static void setCorrelationId(final String identifier) {   CorrelationHolder.CORRELATION_ID.set(identifier);  }  private static String createCorrelationId() throws Exception {   String identifier = "";   try {    identifier = convert(InetAddress.getLocalHost().getHostName(), 12, false)      + convert(String.valueOf(System.nanoTime()), 11, true)      + convert(String.valueOf(RANDOM.nextInt(RANDOM_UPPER_LIMIT)), 6, true);   } catch (UnknownHostException uhe) {    throw new Exception("Error Creating CorrelationId" + uhe);   }   return identifier;  }  private static String convert(final String original, final int outputLength, final boolean isLeft) {   if (original != null) {    int len = original.length();    if (len > outputLength) {     if (isLeft) {      return original.substring(0, outputLength);     } else {      return original.substring(len - outputLength);     }    } else if (len < outputLength) {     final StringBuilder sBuilder = new StringBuilder();     if (isLeft) {      for (int i = 0; i < (outputLength - len); i++) {       sBuilder.append("0");      }      sBuilder.append(original);      return sBuilder.toString();     } else {      sBuilder.append(original);      for (int i = 0; i < (outputLength - len); i++) {       sBuilder.append("0");      }      return sBuilder.toString();     }    } else {     return original;    }   }   final StringBuilder sbuffer = new StringBuilder();   for (int i = 0; i < outputLength; i++) {    sbuffer.append("0");   }   return sbuffer.toString();  }  public static void main(String[] args) {   System.out.println(CorrelationHolder.getCorrelationId());  } }