Logging utility for java

Log.java

import java.io.PrintWriter;
import java.io.StringWriter;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * Created by bloodybadboycreation on 17/9/17.
 */
public class Log {
    private static final int TAG_CALL_STACK_INDEX = 4;
    private static final Pattern ANONYMOUS_CLASS = Pattern.compile("(\\$\\d+)+$");
    private static final Log INSTANCE = new Log();

    private Log() {

    }

    public static void log(String message, Object... args) {
        INSTANCE.prepareLog(null, false, message, args);
    }

    public static void log(Throwable t, String message, Object... args) {
        INSTANCE.prepareLog(t, false, message, args);
    }

    public static void err(String message, Object... args) {
        INSTANCE.prepareLog(null, true, message, args);
    }

    public static void err(Throwable t, String message, Object... args) {
        INSTANCE.prepareLog(t, true, message, args);
    }

    private static String getStackTraceString(Throwable t) {
        StringWriter sw = new StringWriter(256);
        PrintWriter pw = new PrintWriter(sw, false);
        t.printStackTrace(pw);
        pw.flush();
        return sw.toString();
    }

    private void prepareLog(Throwable t, boolean error, String message, Object... args) {
        String tag = getTag();

        if (message != null && message.length() == 0) {
            message = null;
        }
        if (message == null) {
            if (t == null) {
                return; // Swallow message if it's null and there's no throwable.
            }
            message = getStackTraceString(t);
        } else {
            if (args != null && args.length > 0) {
                message = String.format(message, args);
            }
            if (t != null) {
                message += "\n" + getStackTraceString(t);
            }
        }
        printLog(tag, message, error);
    }

    private void printLog(String tag, String message, boolean error) {
        String log;
        try {
            log = new SimpleDateFormat("MM-dd HH:mm:ss.SSS").format(new Date(System.currentTimeMillis())) + " - " + tag + "." + Thread.currentThread().getStackTrace()[4].getMethodName() + " : " + message;
        } catch (Exception e) {
            log = new SimpleDateFormat("MM-dd HH:mm:ss.SSS").format(new Date(System.currentTimeMillis())) + " - " + tag + " : " + message;
        }
        if (error) {
            System.err.println(log);
        } else {
            System.out.println(log);
        }
    }

    private String getTag() {
        StackTraceElement[] stackTrace = Thread.currentThread().getStackTrace();
        if (stackTrace.length <= TAG_CALL_STACK_INDEX) {
            throw new IllegalStateException("Synthetic stacktrace didn't have enough elements");
        }
        String tag = stackTrace[TAG_CALL_STACK_INDEX].getClassName();
        Matcher m = ANONYMOUS_CLASS.matcher(tag);
        if (m.find()) {
            tag = m.replaceAll("");
        }
        tag = tag.substring(tag.lastIndexOf('.') + 1);
        return tag;
    }
}