Allow DateTimeFormatter constants to be used for the date pattern.

src/main/java/org/jboss/logmanager/formatters/Formatters.java

@@ -477,8 +477,7 @@ public static FormatStep dateFormatStep(final TimeZone timeZone, final String fo
             final int minimumWidth,
             final boolean truncateBeginning, final int maximumWidth) {
         return new JustifyingFormatStep(leftJustify, minimumWidth, truncateBeginning, maximumWidth) {
-            final DateTimeFormatter dtf = DateTimeFormatter
-                    .ofPattern(formatString == null ? "yyyy-MM-DD HH:mm:ss,SSS" : formatString);
+            final DateTimeFormatter dtf = StandardDateFormat.resolve(formatString);
 
             public ItemType getItemType() {
                 return ItemType.DATE;

src/main/java/org/jboss/logmanager/formatters/StandardDateFormat.java

@@ -0,0 +1,77 @@
+/*
+ * JBoss, Home of Professional Open Source.
+ *
+ * Copyright 2023 Red Hat, Inc., and individual contributors
+ * as indicated by the @author tags.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.jboss.logmanager.formatters;
+
+import java.time.format.DateTimeFormatter;
+import java.util.Locale;
+
+/**
+ * Standard date formats.
+ *
+ * @author <a href="mailto:jperkins@redhat.com">James R. Perkins</a>
+ */
+enum StandardDateFormat {
+    /**
+     * Format: {@code HH:mm:ss,SSS}
+     */
+    ABSOLUTE("HH:mm:ss,SSS"),
+    /**
+     * Format: {@code yyyyMMddHHmmssSSS}
+     */
+    COMPACT("yyyyMMddHHmmssSSS"),
+    /**
+     * Format: {@code yyyy-MM-dd HH:mm:ss,SSS}
+     */
+    DEFAULT("yyyy-MM-dd HH:mm:ss,SSS"),
+    /**
+     * Format: {@code yyyy-MM-dd'T'HH:mm:ss,SSS}
+     */
+    ISO8601("yyyy-MM-dd'T'HH:mm:ss,SSS"),
+    ;
+
+    private final DateTimeFormatter formatter;
+    private final String pattern;
+
+    StandardDateFormat(final String pattern) {
+        this.formatter = DateTimeFormatter.ofPattern(pattern);
+        this.pattern = pattern;
+    }
+
+    /**
+     * Resolves the requested date format based on the pattern. If the pattern is {@code null}, then the {@link #DEFAULT}
+     * pattern is used. If the pattern matches one of the constants, that format will be returned. Otherwise, the
+     * pattern is assumed to be a valid {@link DateTimeFormatter#ofPattern(String)} format pattern}.
+     *
+     * @param pattern the pattern to return the formatter for
+     *
+     * @return the formatter used to format timestamps
+     */
+    static DateTimeFormatter resolve(final String pattern) {
+        if (pattern == null) {
+            return DEFAULT.formatter;
+        }
+        for (StandardDateFormat constant : values()) {
+            if (pattern.toUpperCase(Locale.ROOT).equals(constant.name()) || pattern.equals(constant.pattern)) {
+                return constant.formatter;
+            }
+        }
+        return DateTimeFormatter.ofPattern(pattern);
+    }
+}

src/test/java/org/jboss/logmanager/formatters/PatternFormatterTests.java

@@ -19,6 +19,10 @@
 
 package org.jboss.logmanager.formatters;
 
+import java.time.Instant;
+import java.time.ZoneId;
+import java.time.format.DateTimeFormatter;
+
 import org.jboss.logmanager.ExtLogRecord;
 import org.jboss.logmanager.MDC;
 import org.jboss.logmanager.NDC;
@@ -269,6 +273,28 @@ public void unqualifiedHost() {
         Assert.assertEquals("manager", formatter.format(record));
     }
 
+    @Test
+    public void dateFormat() {
+        final var now = Instant.now();
+        final var record = createLogRecord("test", now);
+        var formatter = new PatternFormatter("%d{ISO8601}");
+        Assert.assertEquals(DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ss,SSS").format(now.atZone(ZoneId.systemDefault())),
+                formatter.format(record));
+
+        formatter = new PatternFormatter("%d");
+        Assert.assertEquals(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss,SSS").format(now.atZone(ZoneId.systemDefault())),
+                formatter.format(record));
+
+        formatter = new PatternFormatter("%d{ABSOLUTE}");
+        Assert.assertEquals(DateTimeFormatter.ofPattern("HH:mm:ss,SSS").format(now.atZone(ZoneId.systemDefault())),
+                formatter.format(record));
+
+        formatter = new PatternFormatter("%d{compact}");
+        Assert.assertEquals(DateTimeFormatter.ofPattern("yyyyMMddHHmmssSSS").format(now.atZone(ZoneId.systemDefault())),
+                formatter.format(record));
+
+    }
+
     @Test
     public void qualifiedHost() {
         final String hostName = "logmanager.jboss.org";
@@ -330,8 +356,13 @@ private void systemProperties(final String propertyPrefix) throws Exception {
     }
 
     protected static ExtLogRecord createLogRecord(final String msg) {
+        return createLogRecord(msg, Instant.now());
+    }
+
+    protected static ExtLogRecord createLogRecord(final String msg, final Instant instant) {
         final ExtLogRecord result = new ExtLogRecord(org.jboss.logmanager.Level.INFO, msg,
                 PatternFormatterTests.class.getName());
+        result.setInstant(instant);
         result.setSourceClassName(PatternFormatterTests.class.getName());
         result.setLoggerName(CATEGORY);
         return result;