CSV with Log4j2

EventLoggerTx.java

import org.apache.logging.log4j.EventLogger;
import org.apache.logging.log4j.message.StructuredDataMessage;

import java.util.ArrayList;
import java.util.List;

/**
 * @author Bohdan Mushkevych
 * wraps Class holds List<StructuredDataMessage> and flushes it to the EventLogger
 */
public class EventLoggerTx {
    public static final String MESSAGE_KEY = "m";

    private List<StructuredDataMessage> eventPipe = new ArrayList<StructuredDataMessage>();
    private boolean isTransactionOn = false;

    public EventLoggerTx() {
    }

    /**
     * Method creates an event and flushes it to the filesystem immediately
     * @param body message body
     * @param type message type and thus - name of the log file to record the event
     */
    public void logEventDirectly(String body, String type) {
        StructuredDataMessage msg = new StructuredDataMessage("", "", type);
        msg.put(MESSAGE_KEY, body);
        EventLogger.logEvent(msg);
    }

    /**
     * Method creates an event and keeps it in the pipeline
     * The pipeline will be flushed to the filesystem during CommitTransaction method
     * @param body message body
     * @param type name of the table, and thus - name of the log file to record the event
     */
    public void logEvent(String body, String type) {
        if (!isTransactionOn) {
            logEventDirectly(body, type);
        } else {
            StructuredDataMessage msg = new StructuredDataMessage("", "", type);
            msg.put(MESSAGE_KEY, body);
            eventPipe.add(msg);
        }
    }

    public void startTransaction() {
        if (isTransactionOn) {
            LogHandler.write("On StartTransaction: transaction was already ON.");
        }
        if (!eventPipe.isEmpty()) {
            LogHandler.write("On StartTransaction: pipeline was not empty. Purging " + eventPipe.size() + " elements.");
            eventPipe = new ArrayList<StructuredDataMessage>();
        }
        isTransactionOn = true;
    }

    public void commitTransaction() {
        if (eventPipe.isEmpty()) {
            LogHandler.write("On CommitTransaction: pipeline is empty. Nothing to flush.");
        }
        for (StructuredDataMessage msg: eventPipe) {
            EventLogger.logEvent(msg);
        }

        isTransactionOn = false;
        eventPipe = new ArrayList<StructuredDataMessage>();
    }

    public void rollbackTransaction() {
        if (!isTransactionOn) {
            LogHandler.write("On RollbackTransaction: transaction was already OFF.");
        }
        LogHandler.write("On RollbackTransaction: Purging " + eventPipe.size() + " elements.");
        eventPipe = new ArrayList<StructuredDataMessage>();
        isTransactionOn = false;
    }
}

HeaderContext.java

public class HeaderContext {

    public static final Map<String, TableSchema> TABLE_CONTEXT = new HashMap<String, TableSchema>();
    static {
        // Initialize TABLE_CONTEXT with actual data
    }

    public static outputHeaders() {
        for (String tableName: TABLE_CONTEXT.keySet()) {
            PrintWriter writer = new PrintWriter(tableName + ".header", "UTF-8");
            TableSchema schema = TABLE_CONTEXT.get(tableName);
            writer.println(schema.getFieldNames());
            writer.close();
        }
    }
}

log4j2.xml

<?xml version="1.0" encoding="UTF-8"?>
<!-- status    The level of internal Log4j events that should be logged to the console. -->
<!-- name      The name of the configuration. -->
<!-- packages  A comma separated list of package names to search for plugins. -->
<Configuration status="info" name="RoutingExample" packages="">
    <Properties>
        <Property name="routing_filename">${log.path}/type-$${sd:type}.log</Property>
    </Properties>

    <Appenders>
        <Console name="STDOUT">
            <PatternLayout pattern="%d{yyyyMMddHH}{GMT+0} %m%n"/>
        </Console>

        <Routing name="Routing">
<!-- Here, $${sd:type} inspects message.type field of incoming message for later use in routing and RollingFile setup -->
            <Routes pattern="$${sd:type}">
                <Route>
<!-- ${log.path} is replaced by Maven during the build with absolute path to the folder containing log files -->
                    <RollingFile name="RollingFile-${sd:type}"
                                 fileName="${routing_filename}"
                                 filePattern="${log.path}/%d{yyyyMMdd}{GMT+0}/%d{yyyyMMddHH}{GMT+0}-${sd:type}-${hostName}.%i.log.gz">
                        <PatternLayout>
                            <!-- %K{m} stands for the message passed in StructuredDataMessage map with key "m" -->
                            <!-- %n stands for new line -->
                            <Pattern>%d{yyyyMMddHH}{GMT+0} %K{m}%n</Pattern>
                        </PatternLayout>
                        <Policies>
                            <TimeBasedTriggeringPolicy interval="1"/>
                            <SizeBasedTriggeringPolicy size="64 MB"/>
                        </Policies>
                        <DefaultRolloverStrategy max="999"/>
                    </RollingFile>
                </Route>
            </Routes>
        </Routing>

    </Appenders>
    <Loggers>
        <Logger name="EventLogger" level="info" additivity="false">
            <AppenderRef ref="Routing"/>
        </Logger>

        <Root level="warn">
            <AppenderRef ref="STDOUT"/>
        </Root>
    </Loggers>
</Configuration>