Replace some DateTimeFormatter#toString() with #formatTo(StringBuilder) (#2515)

Co-authored-by: Volkan Yazıcı <[email protected]>

Author: michaelbraun

log4j-api/src/main/java/org/apache/logging/log4j/message/ParameterFormatter.java

@@ -459,7 +459,7 @@ private static boolean appendDate(final Object o, final StringBuilder str) {
         if (!(o instanceof Date)) {
             return false;
         }
-        str.append(DATE_FORMATTER.format(((Date) o).toInstant()));
+        DATE_FORMATTER.formatTo(((Date) o).toInstant(), str);
         return true;
     }
 

log4j-api/src/main/java/org/apache/logging/log4j/status/StatusData.java

@@ -38,7 +38,6 @@ public class StatusData implements Serializable {
 
     private final Instant instant;
 
-    @Nullable
     private final DateTimeFormatter instantFormatter;
 
     @Nullable
@@ -79,7 +78,8 @@ public StatusData(
             @Nullable final String threadName,
             @Nullable final DateTimeFormatter instantFormatter,
             final Instant instant) {
-        this.instantFormatter = instantFormatter;
+        // DateTimeFormatter.ISO_INSTANT is the default used in instant.toString()
+        this.instantFormatter = instantFormatter != null ? instantFormatter : DateTimeFormatter.ISO_INSTANT;
         this.instant = instant;
         this.caller = caller;
         this.level = requireNonNull(level, "level");
@@ -167,9 +167,7 @@ public Throwable getThrowable() {
     @SuppressWarnings("DefaultCharset")
     public String getFormattedStatus() {
         final StringBuilder sb = new StringBuilder();
-        final String formattedInstant =
-                instantFormatter != null ? instantFormatter.format(instant) : instant.toString();
-        sb.append(formattedInstant);
+        instantFormatter.formatTo(instant, sb);
         sb.append(SPACE);
         sb.append(getThreadName());
         sb.append(SPACE);

src/changelog/.2.x.x/2515_datetimeformatter_formatto.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<entry xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xmlns="https://logging.apache.org/xml/ns"
+       xsi:schemaLocation="https://logging.apache.org/xml/ns https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
+       type="changed">
+  <issue id="2515" link="https://github.com/apache/logging-log4j2/pull/2515"/>
+  <description format="asciidoc">Replace some usages of `DateTimeFormatter#toString()` with `DateTimeFormatter#formatTo(StringBuilder)` to cut down on allocations</description>
+</entry>