AWS Log Stream - Java

package au.com.itelasoft.iot;

import com.amazonaws.auth.AWSStaticCredentialsProvider;
import com.amazonaws.auth.BasicAWSCredentials;
import com.amazonaws.services.logs.AWSLogsClient;
import com.amazonaws.services.logs.AWSLogsClientBuilder;
import com.amazonaws.services.logs.model.DescribeLogStreamsRequest;
import com.amazonaws.services.logs.model.DescribeLogStreamsResult;
import com.amazonaws.services.logs.model.InputLogEvent;
import com.amazonaws.services.logs.model.PutLogEventsRequest;
import java.util.ArrayList;
import java.util.List;
import java.util.logging.Level;
import java.util.logging.Logger;

public class AwsCloudWatch implements CloudLogger {

    private static volatile List<InputLogEvent> logEvents = new ArrayList();
    private static AwsCloudWatch instance;
    private static volatile Boolean inflight = false;
    private Thread awsWriteThread;

    private final BasicAWSCredentials awsCreds;
    private final AWSLogsClient cwClient;
    private final String logStreamName = "access-log";
    private final String logStreamGroup = "/test";

    public static AwsCloudWatch getInstance() {
        synchronized (AwsCloudWatch.class) {
            if (!(AwsCloudWatch.instance instanceof AwsCloudWatch)) {
                AwsCloudWatch.instance = new AwsCloudWatch();
            }
        }
        return AwsCloudWatch.instance;
    }

    private AwsCloudWatch() {
        this.awsCreds = new BasicAWSCredentials("xxxxxx", "xxxxxxxxxxxxxxxxxxxxxx");
        this.cwClient = (AWSLogsClient) AWSLogsClientBuilder.standard()
                        .withCredentials(new AWSStaticCredentialsProvider(this.awsCreds))
                        .withRegion("ap-southeast-1").build();
        this.initThread();
    }

    private void initThread(){
        this.awsWriteThread = new Thread(new Runnable() {
            @Override
            public synchronized void run() {
                try {

                    while(true){
                        writeToCloud();
                    }

                } catch (Exception e) {
                    System.err.println("Error logging "+e.toString());
                }
            }
        });
        this.awsWriteThread.setName("AWS Log writer thread");
        this.awsWriteThread.start();
    }

    @Override
    public void write(String message) {
        InputLogEvent logEvent = new InputLogEvent().withMessage(message).withTimestamp(System.currentTimeMillis());
        AwsCloudWatch.logEvents.add(logEvent);
        if(this.awsWriteThread.isAlive()){
            synchronized(this.awsWriteThread){
                this.awsWriteThread.notify();
            }
        }else{
            this.awsWriteThread.start();
        }
    }

    private synchronized void writeToCloud(){
        if(!AwsCloudWatch.logEvents.isEmpty() && AwsCloudWatch.inflight == false){
            AwsCloudWatch.inflight = true;
            PutLogEventsRequest putReq = new PutLogEventsRequest(this.logStreamGroup, this.logStreamName, logEvents)
                .withSequenceToken(this.getUploadSequenceToken());
            AwsCloudWatch.logEvents.removeAll(putReq.getLogEvents());
            this.cwClient.putLogEvents(putReq);
            AwsCloudWatch.inflight = false;
        }else{
            if(AwsCloudWatch.inflight == false){
                try {
                    synchronized(this.awsWriteThread){
                        this.awsWriteThread.wait();
                    }
                } catch (InterruptedException ex) {
                    Logger.getLogger(AwsCloudWatch.class.getName()).log(Level.SEVERE, null, ex);
                }
            }
        }

    }

    private String getUploadSequenceToken() {
        DescribeLogStreamsRequest req = new DescribeLogStreamsRequest().withLogGroupName(logStreamGroup).withLogStreamNamePrefix(logStreamName);
        DescribeLogStreamsResult res = this.cwClient.describeLogStreams(req);
        return res.getLogStreams().get(0).getUploadSequenceToken();
    }
}