Logback configuration to have exceptions on a single line?

Question

My logs are extracted, piped and consolidated into elasticsearch. Multiline events are hard to track and diagnose.

Instead of playing with collectors and regular expressions to group exception lines in a single record, is there a way with logback configuration to have Exception stacktrace on a single line ?

Answer 1

You can declare a conversion rule in your logback.xml for the %ex symbolic like so:

<?xml version="1.0" encoding="UTF-8" ?>
<configuration>
    <conversionRule conversionWord="ex" converterClass="com.foo.CompressedStackTraceConverter" /> 

    ...

</configuration>

Then declare CompressedStackTraceConverter like so:

import ch.qos.logback.classic.pattern.ThrowableProxyConverter;
import ch.qos.logback.classic.spi.IThrowableProxy;

public class CompressedStackTraceConverter extends ThrowableProxyConverter {
    @Override
    protected String throwableProxyToString(IThrowableProxy tp) {
        String original = super.throwableProxyToString(tp);

        // replace the new line characters with something, 
        // use your own replacement value here
        return original.replaceAll("\n", " ~~ ");
    }
}

This custom conversion specifier will work as long as your logging pattern contains the %ex symbolic. For example, a pattern like this:

<encoder class="ch.qos.logback.classic.encoder.PatternLayoutEncoder">
    <pattern>%d{yyyy-MM-dd HH:mm:ss}|%-5level|%logger{36}|%msg %ex %n</pattern>
</encoder>

If your pattern does not include the %ex symbolic then the stacktrace is part of the %msg in which case you would declare the conversion rule like this ...

<conversionRule conversionWord="msg" converterClass="com.foo.CompressedStackTraceConverter" /> 

... though this would have the effect of applying the CompressedStackTraceConverter to your entire log message, not just to the stack trace portion of it.