Log4j2 Google Stackdriver appender (using github.com/GoogleCloudPlatform/google-cloud-java)

CloudAppender.java

@Plugin(name = "CloudAppender", category = "Core", printObject = false)
public class CloudAppender extends AbstractAppender {
    private final LoggingOptions loggingOptions;
    private final List<LoggingEnhancer> enhancers;
    private volatile Logging logging;

    protected CloudAppender(String name,
                            Filter filter,
                            Layout<? extends Serializable> layout,
                            LoggingOptions options) {
        super(name, filter, layout);
        loggingOptions = options != null ? options : LoggingOptions.getDefaultInstance();
        final List<LoggingEnhancer> enhancers = MonitoredResourceUtil.getResourceEnhancers();
        this.enhancers = new LinkedList<>();
        this.enhancers.addAll(enhancers);

    }

    protected CloudAppender(String name,
                            Filter filter,
                            Layout<? extends Serializable> layout,
                            boolean ignoreExceptions,
                            LoggingOptions options) {
        super(name, filter, layout, ignoreExceptions);
        loggingOptions = options != null ? options : LoggingOptions.getDefaultInstance();
        final List<LoggingEnhancer> enhancers = MonitoredResourceUtil.getResourceEnhancers();
        this.enhancers = new LinkedList<>();
        this.enhancers.addAll(enhancers);
    }

    private static Severity severityFor(Level level) {
        if (level.intLevel() == DEBUG.intLevel()) {
            return Severity.DEBUG;
        } else if (level.intLevel() == INFO.intLevel()) {
            return Severity.INFO;
        } else if (level.intLevel() == WARN.intLevel()) {
            return Severity.WARNING;
        } else if (level.intLevel() == ERROR.intLevel()) {
            return Severity.ERROR;
        } else {
            return Severity.DEFAULT;
        }
    }

    @PluginFactory
    public static CloudAppender createAppender(
            @PluginAttribute("name") String name,
            @PluginElement("Layout") Layout<? extends Serializable> layout,
            @PluginElement("Filter") final Filter filter,
            @PluginAttribute("otherAttribute") String otherAttribute) {
        if (name == null) {
            LOGGER.error("No name provided for CloudAppender");
            return null;
        }
        if (layout == null) {
            layout = PatternLayout.createDefaultLayout();
        }
        return new CloudAppender(name, filter, layout, false, null);
    }

    @Override
    public void append(LogEvent event) {
        final LogEntry logEntry = logEntryFor(event);
        getLogging().write(ImmutableList.of(logEntry));

    }

    private LogEntry logEntryFor(LogEvent event) {
        final String payload = event.getMessage().getFormattedMessage();
        final Level level = event.getLevel();
        LogEntry.Builder builder =
                LogEntry.newBuilder(Payload.StringPayload.of(payload))
                        .setTimestamp(event.getTimeMillis())
                        .setResource(MonitoredResource.newBuilder("global")
                                .addLabel("project_id", loggingOptions.getProjectId())
                                .build())
                        .setSeverity(severityFor(level))
                        .setLogName("blenge-vision")
                        .addLabel("levelName", level.name())
                        .addLabel("levelValue", String.valueOf(level.intLevel()));
        for (LoggingEnhancer enhancer : enhancers) {
            enhancer.enhanceLogEntry(builder);
        }
        return builder.build();
    }

    /**
     * Returns an instance of the logging service.
     */
    private Logging getLogging() {
        if (logging == null) {
            synchronized (this) {
                if (logging == null) {
                    logging = loggingOptions.getService();
                }
            }
        }
        return logging;
    }