Log4j2: How to Mask Logs Personal/Confidential/SPI Information

You can configure Log4j2 LogEventConverter plugin for masking personal/ confidential/ SPI data. For example here we are masking credit card number, SSN and CVV of log statements.

Below Log4j2 dependencies you need to add with your application.


Log4j2 Dependency

pom.xml entry


Log4j2.xml Configuration File

Below is basic console based configuration for masking where packages used for where loggers need to apply and masking plugin annotation as in below program. In PatternLayout used key as spi which is map with plugin which will mask log text and print as message.

<?xml version="1.0" encoding="UTF-8"?>
<configuration xmlns="http://logging.apache.org/log4j/2.0/config"
       status="OFF" packages="com.mask.logs">
    <Console name="STDOUT" target="SYSTEM_OUT">
     <PatternLayout pattern="%d{yyyyMMdd HH:mm:ss.SSS} [%t] %-5level %logger{36} - %spi%n"/>
              <Logger name="org.apache.log4j.xml" level="all" />
              <root level="all">
                     <appender-ref ref="STDOUT" level="TRACE" />

Log4j2 Java Logging Example Tutorial – XML Configuration, Severity Levels, Formatting and Appenders

Log4j2 Plugin Code for Masking

Created this LogMakingConverter Plug in for masking logs statement
Here masking for Credit card number, CVV and SSN . You can also implement for password and rest depend on your application needs. Here we have used Java regular expression Mater and Pattern apis for maskin and also different character as +++ for CVV,********* for SSN and **************** for credit card by matching number of digits in log lines.

package com.mask.logs;
 * Created this LogMakingConverter Plug in for masking logs statement
 * Here masking for Credit card number, CVV and SSN .
 * You can also implement for password and rest depend on your application needs.
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import org.apache.logging.log4j.core.LogEvent;
import org.apache.logging.log4j.core.config.plugins.Plugin;
import org.apache.logging.log4j.core.pattern.ConverterKeys;
import org.apache.logging.log4j.core.pattern.LogEventPatternConverter;

@Plugin(name="LogMaskingConverter", category = "Converter")
public class LogMaskingConverter extends LogEventPatternConverter{
	private static final String CREDIT_CARD_REGEX = "([0-9]{16})";;
	private static final Pattern CREDIT_CARD_PATTERN = Pattern.compile(CREDIT_CARD_REGEX);

	private static final String CVV_REGEX = "([0-9]{3})";
	private static final Pattern CVV_PATTERN = Pattern.compile(CVV_REGEX);
	private static final String CVV_REPLACEMENT_REGEX = "+++";

	private static final String SSN_REGEX = "([0-9]{9})";
	private static final Pattern SSN_PATTERN = Pattern.compile(SSN_REGEX);
	private static final String SSN_REPLACEMENT_REGEX = "*********";

    protected LogMaskingConverter(String name, String style) {
        super(name, style);

    public static LogMaskingConverter newInstance(String[] options) {
        return new LogMaskingConverter("spi",Thread.currentThread().getName());

    public void format(LogEvent event, StringBuilder outputMessage) {
    	String message = event.getMessage().getFormattedMessage();
		String maskedMessage = message;
		try {
			maskedMessage = mask(message);
		} catch (Exception e) {
			System.out.println("Failed While Masking");
			maskedMessage = message;


    private String mask(String message) {
    	Matcher matcher =null;
		StringBuffer buffer = new StringBuffer();

		matcher = CREDIT_CARD_PATTERN.matcher(message);
		maskMatcher(matcher, buffer,CAREDIT_CARD_REPLACEMENT_REGEX);

		matcher = SSN_PATTERN.matcher(message);
		maskMatcher(matcher, buffer,SSN_REPLACEMENT_REGEX);

		matcher = CVV_PATTERN.matcher(message);
		maskMatcher(matcher, buffer,CVV_REPLACEMENT_REGEX);

		return buffer.toString();

    private StringBuffer maskMatcher(Matcher matcher, StringBuffer buffer, String maskStr)
    	while (matcher.find()) {
    	return buffer;


Masking Test Program

Below is test program to print some log statements which are converting by Log4j2.

package com.mask.logs;

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;

public class MaskingTest {
	  private static final Logger logger = LogManager.getLogger(MaskingTest.class);
      public static void myTest(){
             logger.info("this is my info message");
             logger.debug("This is debug message");
             logger.debug("Passed to server::0084USER:17603,IP:0:0:0:0:0:0:0:1,3425,Credit Card 1:1000002367844224,3425,Credit Card2:1000002367844224 , CVV:234,SSN:123456789");

      public static void main(String[] args) {


Below is mask logs by log4j2 for confidential/personal/spi data.

20180607 11:20:43.558 [main] INFO  com.mask.logs.MaskingTest - this is my info message
20180607 11:20:43.559 [main] DEBUG com.mask.logs.MaskingTest - This is debug message
20180607 11:20:43.560 [main] DEBUG com.mask.logs.MaskingTest - Passed to server::+++4USER:+++03,IP:0:0:0:0:0:0:0:1,+++5,Credit Card 1:XXXXXXXXXXXXXXXX,+++5,Credit Card2:XXXXXXXXXXXXXXXX , CVV:+++,SSN:


  • Step by step program for masking sensitive information in logs.
  • Log4j2 XML Configuration for loggers and appenders for masking.
  • LogMaskingConverter Log4j2 plugin for masking log statements.
  • Regular expression for Creditcard, SSN and CVV.
  • Test program to write logs  by java logging api to write in logs file.

See More 

Below are some more masking ways for different type of data like XML, JSON and printing objects before logging , sending to page or transferring over network.

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