Json logging: exception in message

[agreedSkiing]

Is there a way to get the exception stack into the top level message field? Like a normal non json log stacktrace print?

[cescoffier]

@xstefank do you know? You have been looking into JSON logging not so long ago.

[xstefank]

Hi @agreedSkiing, this will be possible in Quarkus 3.36.0 with the JsonProvider SPI - https://github.com/xstefank/quarkus-reproducers/blob/main/json-log-error-message/src/main/java/io/xstefank/ErrorJsonProvider.java.

But we cannot override the already supplied JSON keys because Generator directly writes to the stream. So, you need to exclude the existing "message" and provided a different name of your new key. Hopefully, this works for you.

[agreedSkiing]

Seems like it would be time to write a inhouse depency, that combindes the original message with a normal java stacktrace

[xstefank]

Sorry, I don't understand then what you are after? You would like to override the "message" key? Any kind of this mutation will be slowing down logging which in case of big logging load would dramatically slow down the Quarkus app.

[agreedSkiing]

No. I would add a new dynamic tag that combines the result of message with if exists a exception stacktrace

[MILLERMARRU]

To add a ready-to-use implementation of the JsonProvider SPI that @xstefank mentioned (Quarkus 3.36+):

Implement JsonProvider to merge the stacktrace into the message field:

import io.quarkus.logging.json.runtime.JsonProvider;
import jakarta.json.stream.JsonGenerator;
import org.jboss.logmanager.ExtLogRecord;
import java.io.PrintWriter;
import java.io.StringWriter;

public class StackTraceInMessageProvider implements JsonProvider {

    @Override
    public void writeTo(JsonGenerator generator, ExtLogRecord record) {
        String message = record.getFormattedMessage();
        Throwable thrown = record.getThrown();

        if (thrown != null) {
            StringWriter sw = new StringWriter();
            thrown.printStackTrace(new PrintWriter(sw));
            message = message + "
" + sw;
        }

        generator.write("message", message);
    }

    @Override
    public boolean isDefault() {
        return true; // replaces the default "message" field
    }
}

Register via ServiceLoader — create the file:
src/main/resources/META-INF/services/io.quarkus.logging.json.runtime.JsonProvider

With the content:

com.example.StackTraceInMessageProvider

This merges the full stacktrace into the message field as a single string, matching the format of non-JSON log output.

[agreedSkiing]

@MILLERMARRU Thank you :) That works for me, just needed to do some changes with quarkus 3.37 like using .add("log", message) instead of write(log", message) and to avoid the deprecation warning of getFormattedMessage() use getMessage() (after a while i noticed that the getMessage() still needed to be formatted, so copied the jboss implementation to my class https://github.com/agreedSkiing/quarkus-json-logging-testing)

[MILLERMARRU]

Glad it worked! Thanks for sharing the adjustments for 3.37 — replacing write() with .add() and switching to getMessage() are good catches. That kind of deprecation drift is easy to miss when writing against a moving API. The repo link is a nice reference for anyone hitting this same issue going forward.