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

Logback doesn't do anything unusual with JSON. It's just a string that gets logged as normal. The escaping is probably happening on your end, unless you're talking about some kind of JSON Appender that's writing it out in that format. I'm pretty sure Logback itself doesn't have anything like that, so you'd want to look at wherever you got the Appender from instead if that's your problem. An SSCCE would help with further troubleshooting.