Truncate individual log messages above a certain character count with Spring logback

Question

I would like to reduce the size of certain logs using logback (I attempted to use Pattern layout with with a pattern of %.100000msg to limit the max size to one hundred thousand but had no luck), the large(over 1 million characters caused by a few REST GET calls) logs are causing Elastic to slow down when searching for certain information.

What would be the best practice to overcome this?

<include resource="org/springframework/boot/logging/logback/base.xml"/>
    <appender name="Console"
              class="ch.qos.logback.core.ConsoleAppender">
        <layout class="ch.qos.logback.classic.PatternLayout">
            <Pattern>
                %.30msg
            </Pattern>
        </layout>
    </appender>
    <logger name="" level="INFO"/>

Answer 1

I solved this by refering to this documentation to create a custom converter. The property was an extra, it was implemented to allow for configuration within the xml file.

<property scope="context" name="max-message-length" value="100000"/>

<conversionRule conversionWord="boundedMsg"
                    converterClass="za.co.ksdc.qadee.config.TruncationCustomLogConverter" />

The following java class was implemented to truncate the log message:

public class TruncationCustomLogConverter extends ClassicConverter {

    @Override
    public String convert(ILoggingEvent event) {
        int maxMessageLength = Integer.parseInt(getContext().getProperty("max- 
     message-length"));
        String formattedMessage = event.getFormattedMessage();
        if (formattedMessage == null ||
                formattedMessage.length() < maxMessageLength) {
            return formattedMessage;
        }
        return new StringBuilder(maxMessageLength)
                .append(formattedMessage, 0, maxMessageLength)
                .toString();
    }
}