Issue googleapis#1329

Allow extended classes to access the LogEntry building, so that
additional information may be encoded in each log entry (eg traceid).

Use addLabel rather than setLabels as it avoids the creation and copy
of a HashMap per log entry.

Signed-off-by: Greg Wilkins <[email protected]>

Author: gregw

google-cloud-logging/src/main/java/com/google/cloud/logging/LoggingHandler.java

@@ -293,7 +293,7 @@ public synchronized void publish(LogRecord record) {
     }
   }
 
-  private LogEntry entryFor(LogRecord record) {
+  protected LogEntry entryFor(LogRecord record) {
     String payload;
     try {
       payload = getFormatter().format(record);
@@ -303,15 +303,17 @@ private LogEntry entryFor(LogRecord record) {
       return null;
     }
     Level level = record.getLevel();
-    Map<String, String> labels = ImmutableMap.of(
-        "levelName", level.getName(),
-        "levelValue", String.valueOf(level.intValue()));
-    return LogEntry.newBuilder(Payload.StringPayload.of(payload))
-        .setLabels(labels)
-        .setSeverity(severityFor(level))
-        .build();
+    LogEntry.Builder builder = LogEntry.newBuilder(Payload.StringPayload.of(payload))
+        .addLabel("levelName", level.getName())
+        .addLabel("levelValue", String.valueOf(level.intValue()))
+        .setSeverity(severityFor(level));
+    return buildEntryFor(record, builder);
   }
 
+  protected LogEntry buildEntryFor(LogRecord record, LogEntry.Builder builder) {
+    return builder.build();
+  }
+  
   private static Severity severityFor(Level level) {
     if (level instanceof LoggingLevel) {
       return ((LoggingLevel) level).getSeverity();