fix: unsafe usage of SimpleDateFormat object in different threads

SVN: 6293

bds/source/java/ch/systemsx/cisd/bds/Constants.java

@@ -18,7 +18,6 @@ package ch.systemsx.cisd.bds;
 
 import java.text.DateFormat;
 import java.text.SimpleDateFormat;
-import java.util.concurrent.atomic.AtomicReference;
 
 /**
  * Some constants used inside the <i>BDS</i> library
@@ -35,8 +34,16 @@ public final class Constants
     public final static char PATH_SEPARATOR = '/';
 
     /** The uniformly date format used. */
-    public static final AtomicReference<DateFormat> DATE_FORMAT =
-            new AtomicReference<DateFormat>(new SimpleDateFormat(DATE_FORMAT_PATTERN));
+    // Note that DateFormats objects are not thread-safe.
+    public static final ThreadLocal<DateFormat> DATE_FORMAT =
+            new ThreadLocal<DateFormat>()
+            {
+                @Override
+                protected DateFormat initialValue()
+                {
+                    return new SimpleDateFormat(DATE_FORMAT_PATTERN);
+                }
+            };
 
     private Constants()
     {