Fix NPE in PatternProcessor for the UNIX pattern

log4j-core-test/src/test/java/org/apache/logging/log4j/core/appender/rolling/PatternProcessorTest.java

@@ -16,6 +16,7 @@
  */
 package org.apache.logging.log4j.core.appender.rolling;
 
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
 import java.time.Instant;
@@ -29,6 +30,8 @@
 import org.junit.jupiter.api.parallel.ResourceAccessMode;
 import org.junit.jupiter.api.parallel.ResourceLock;
 import org.junit.jupiter.api.parallel.Resources;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
 
 /**
  * Tests the PatternProcessor class.
@@ -394,4 +397,10 @@ public void testGetNextTimeDailyReturnsFirstHourOfNextDayInGmtIfZoneIsInvalid()
  TimeZone.setDefault(old);
  }
  }
+
+ @ParameterizedTest
+ @ValueSource(strings = {"%d{UNIX}", "%d{UNIX_MILLIS}"})
+ void does_not_throw_with_unix_pattern(final String pattern) {
+ assertDoesNotThrow(() -> new PatternProcessor(pattern));
+ }
 }

log4j-core/src/main/java/org/apache/logging/log4j/core/appender/rolling/PatternProcessor.java

@@ -325,6 +325,10 @@ protected final void formatFileName(final StringBuilder buf, final Object... obj
  }
 
  private RolloverFrequency calculateFrequency(final String pattern) {
+ // The UNIX and UNIX_MILLIS converters do not have a pattern
+ if (pattern == null) {
+ return null;
+ }
  if (patternContains(pattern, MILLIS_CHAR)) {
  return RolloverFrequency.EVERY_MILLISECOND;
  }

log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java

@@ -359,7 +359,7 @@ public void format(final StringBuilder toAppendTo, final Object... objects) {
  /**
  * Gets the pattern string describing this date format.
  *
- * @return the pattern string describing this date format.
+ * @return the pattern string describing this date format or {@code null} if the format does not have a pattern.
  */
  public String getPattern() {
  return formatter.toPattern();

src/changelog/.2.x.x/2346_unix_millis_data_pattern.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<entry xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+ xmlns="http://logging.apache.org/log4j/changelog"
+ xsi:schemaLocation="http://logging.apache.org/log4j/changelog https://logging.apache.org/log4j/changelog-0.1.3.xsd"
+ type="changed">
+ <issue id="2346" link="https:/apache/logging-log4j2/pull/2346"/>
+ <description format="asciidoc">Fix `NullPointerException` in `PatternProcessor` for a `UNIX_MILLIS` pattern.</description>
+</entry>