The java library SimpleDateFormat (java.text.SimpleDateFormat) cannot be considered thread safe and the programmer should avoid the usage in a multi thread environment.
The problem is based on the way it’s implemented
To fix the problem there are 3 main ways:
- To create a new instance of
SimpleDateFormatfor each usage (slow) - Sync it properly
- use
FastDateFormat (org.apache.commons.lang3.time.FastDateFormat)that by documentation says : “FastDateFormat is a fast and thread-safe version of java.text.SimpleDateFormat”
Here a main in which is demostrated the issue and the resolution using FastDateFormat
package utils;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.TimeZone;
import org.apache.commons.lang3.time.FastDateFormat;
public class JustMain {
private static SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSSXXX");
/* timezone is optional */
private static final FastDateFormat fastFormat = FastDateFormat.getInstance("yyyy-MM-dd'T'HH:mm:ss.SSSXXX",
TimeZone.getTimeZone("GMT"));
/* problem */
public static void main(String[] args) {
List<Thread> threads = new ArrayList<Thread>();
for (int ii = 0; ii < 1000; ii++) {
threads.add(new Thread(() -> {
try {
Thread.sleep(10L);
System.out.println(sdf.parse("2022-08-05T16:03:11.759Z"));
System.out.println(sdf.format(new Date()));
} catch (Exception e) {
e.printStackTrace();
}
}));
}
for (Thread thread : threads) {
thread.start();
}
}
public static void mainFastFormat(String[] args) {
List<Thread> threads = new ArrayList<Thread>();
for (int ii = 0; ii < 1000; ii++) {
threads.add(new Thread(() -> {
try {
Thread.sleep(10L);
System.out.println(fastFormat.parse("2022-08-05T16:03:11.759Z"));
System.out.println(fastFormat.format(new Date()));
} catch (Exception e) {
e.printStackTrace();
}
}));
}
for (Thread thread : threads) {
thread.start();
}
}
}happy coding
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