Is the Java MessageFormat Class thread safe? (as opposed to SimpleDateFormat)
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16-09-2020 - |
Question
I know that SimpleDateFormat and NumberFormat are NOT thread safe.
http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4101500
But what about the other Format classes like MessageFormat?
Fortify 360 is flagging the use of "MessageFormat.format(String, Object...)" static method as a "Race Condition - Format Flaw" issue, but when I analyze the the source code of MessageFormat, I saw that in that method, it creates a new local instance of MessageFormat itself.
Is the Java MessageFormat Class thread safe?
Solution
The javadoc for MessageFormat
says:
Message formats are not synchronized. It is recommended to create separate format instances for each thread. If multiple threads access a format concurrently, it must be synchronized externally.
So officially, no - it's not thread-safe.
The docs for SimpleDateFormat
say much the same thing.
Now, the docs may just be being conservative, and in practice it'll work just fine in multiple threads, but it's not worth the risk.
OTHER TIPS
If you are referrring to the method
public static String format(String pattern, Object... arguments)
this is thread-safe since as described in the javadoc it creates a new MessageFormat to do the formatting.
BTW, thats a funny typo in your title 'SimpleThreadFormat' :)
Per the javadoc, MessageFormat
objects are not thread-safe. You can use a ThreadLocal
to create a separate object for each thread that needs one.
ThreadLocal<MessageFormat> threadLocalMessageFormat =
new ThreadLocal<MessageFormat>() {
@Override
protected MessageFormat initialValue() {
return new MessageFormat(pattern);
}
};
You can then use threadLocalMessageFormat.get()
to obtain a MessageFormat
for the current thread.