[HUDI-3547] Introduce MaxwellSourcePostProcessor to extract data from Maxwell json string (#4987)

* [HUDI-3547] Introduce MaxwellSourcePostProcessor to extract data from Maxwell json string

* add ut

* Address comment

hudi-common/src/main/java/org/apache/hudi/common/util/DateTimeUtils.java

@@ -21,6 +21,9 @@ package org.apache.hudi.common.util;
 
 import java.time.Duration;
 import java.time.Instant;
+import java.time.LocalDateTime;
+import java.time.ZoneId;
+import java.time.format.DateTimeFormatter;
 import java.time.format.DateTimeParseException;
 import java.time.temporal.ChronoUnit;
 import java.util.Arrays;
@@ -126,6 +129,20 @@ public class DateTimeUtils {
     return labelToUnit;
   }
 
+  /**
+   * Convert UNIX_TIMESTAMP to string in given format.
+   *
+   * @param unixTimestamp UNIX_TIMESTAMP
+   * @param timeFormat string time format
+   */
+  public static String formatUnixTimestamp(long unixTimestamp, String timeFormat) {
+    ValidationUtils.checkArgument(!StringUtils.isNullOrEmpty(timeFormat));
+    DateTimeFormatter dtf = DateTimeFormatter.ofPattern(timeFormat);
+    return LocalDateTime
+        .ofInstant(Instant.ofEpochSecond(unixTimestamp), ZoneId.systemDefault())
+        .format(dtf);
+  }
+
   /**
    * Enum which defines time unit, mostly used to parse value from configuration file.
    */