Java: How to log raw JSON as JSON and avoid escaping during logging with logback / slf4j

Question

I'm using SLF4J with Logback in a JAX-RS application... I want to log to JSON in such a way that my message is not encoded again but printed raw into the logfile:

At the moment it looks like this:

{"@timestamp":1363834123012,"@message":"{\"text\":\"From MLK to Barack 
Ob...\n\"}"

But I want to have this:

  {"@timestamp":1363834123012,"@message": { "text ": "From MLK to Barack 
Ob...\n\}

The reason is I want to parse the JSON again and want to avoid the unescaping of the data.

I've written a custom logback encoder but I found no way to avoid the escaping. Can I pass a object to logback and change the settings based on the type of the object?

Edit: I've found a way - not exactly elegant - as requested a SSCE:

In my Application

// SLF4J Logger
private static Logger logger = LoggerFactory.getLogger(MyClass.class);
// A logback? Marker
private Marker foo = MarkerFactory.getMarker("foo");
// Jackson ObjectMapper()
ObjectMapper mapper = new ObjectMapper();

// Log something... 
logger.info(foo, mapper.writeValueAsString(json));

I've used a variation of the Logstash-Encoder found here: https://github.com/logstash/logstash-logback-encoder

package my.package;

import static org.apache.commons.io.IOUtils.*;

import java.io.IOException;
import java.util.Map;
import java.util.Map.Entry;

import org.codehaus.jackson.JsonGenerator.Feature;
import org.codehaus.jackson.JsonNode;
import org.codehaus.jackson.map.ObjectMapper;
import org.codehaus.jackson.node.ObjectNode;
import org.slf4j.Marker;

import ch.qos.logback.classic.spi.ILoggingEvent;
import ch.qos.logback.classic.spi.IThrowableProxy;
import ch.qos.logback.classic.spi.ThrowableProxyUtil;
import ch.qos.logback.core.CoreConstants;
import ch.qos.logback.core.encoder.EncoderBase;

public class JsonEncoder extends EncoderBase<ILoggingEvent> {

    private static final ObjectMapper MAPPER = new ObjectMapper().configure(
        Feature.ESCAPE_NON_ASCII, true);
    private static Marker M;

    private boolean immediateFlush = true;

@Override
public void doEncode(ILoggingEvent event) throws IOException {

    M = event.getMarker();

    ObjectNode eventNode = MAPPER.createObjectNode();

    eventNode.put("@timestamp", event.getTimeStamp());
    //
    if (M != null) {
        if (M.getName().equals("foo")) {
            JsonNode j = MAPPER.readTree(event.getFormattedMessage());
            eventNode.put("@foo", j);
        }
    } else {
        eventNode.put("@message", event.getFormattedMessage());
    }
    eventNode.put("@fields", createFields(event));

    write(MAPPER.writeValueAsBytes(eventNode), outputStream);
    write(CoreConstants.LINE_SEPARATOR, outputStream);

    if (immediateFlush) {
        outputStream.flush();
    }

}

private ObjectNode createFields(ILoggingEvent event) {
         // not important here
    return fieldsNode;

}

@Override
public void close() throws IOException {
    write(LINE_SEPARATOR, outputStream);
}

public boolean isImmediateFlush() {
    return immediateFlush;
}

public void setImmediateFlush(boolean immediateFlush) {
    this.immediateFlush = immediateFlush;
}
}

It's works now! Yeah! But I guess it's not the best way to do it (serialize, deserialize the JSON...)

Answer 1

If you have a Json formatted messages, the upper solutions work, but are not so nice, since you don´t want to call a logstash specific code, each time you use your logger in the code.

Just adding a

net.logstash.logback.encoder.LogstashEncoder

is not enough, since the message itsself stays escaped. To solve this, try the following in your logback.xml:

<encoder class="net.logstash.logback.encoder.LoggingEventCompositeJsonEncoder">
     <providers>
        <timestamp/>
        <version/>
        <loggerName/>
        <pattern>
            <pattern>
                {
                "jsonMessage": "#asJson{%message}"
                }
            </pattern>
        </pattern>
    </providers>
</encoder>

The #asJson pattern will unescape your message.

Answer 2

Use the RawJsonAppendingMarker:

log.trace(net.logstash.logback.marker.Markers.appendRaw("jsonMessage", jsonString), null);