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The question is similar to one stated under - How to configure log4j to log different log levels to different files for the same logger. The existing questions that I could find here are mostly dealing with logback and log4j configuration. Looking something specifically in Dropwizard configuration for a solution to this problem.

Have tried to look around over the internet and seem like a LevelMatchFilter might be appropriate to use, but couldn't figure out the Dropwizard's documentation around it.

What I have currently is

logging:
  level: INFO
  appenders:
    - type: file
      threshold: INFO
      logFormat: '%date{dd-MM-yyyy HH:mm:ss.SSS} %X{X-Request-Id} [%thread] %-5level %logger{36} - %msg%n'
      currentLogFilename: .../info.log
      archivedLogFilenamePattern: .../info-%i.log.gz
      archivedFileCount: 2
      timeZone: IST
      maxFileSize: 100MB

    - type: file
      threshold: WARN
      currentLogFilename: .../warn.log
      archivedLogFilenamePattern: .../warn-%i.log.gz
      ... other attributes

    - type: file
      threshold: ERROR
      ...similar attributes for error logs

But this results in a log.error being part of three files and what I would intend to perform is to ensure its just part of the error.log file and relevant for others.

Naman
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1 Answers1

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Dropwizard has its own logging configuration, and it supports adding filters by writing FilterFactory classes.

For example, here is a FilterFactory that filters out everything but ERROR level log events:

@JsonTypeName("error-only")
public class ErrorLogFilter implements FilterFactory<ILoggingEvent> {

    @Override
    public Filter<ILoggingEvent> build() {
        return new Filter<ILoggingEvent>() {
            @Override
            public FilterReply decide(ILoggingEvent event) {
                if (event.getLevel().equals(Level.ERROR)) {
                    return FilterReply.NEUTRAL;
                } else {
                    return FilterReply.DENY;
                }
            }
        };

    }
}

To register a factory, its fully qualified classname must be listed in META-INF/services/io.dropwizard.logging.filter.FilterFactory file.

And the configuration to get one of the file appenders to use it, would be like this:

  - type: file
    threshold: ERROR
    logFormat: '%date{dd-MM-yyyy HH:mm:ss.SSS} %X{X-Request-Id} [%thread] %-5level %logger{36} - %msg%n'
    currentLogFilename: .../error.log
    archivedLogFilenamePattern: .../error-%i.log.gz
    archivedFileCount: 2
    timeZone: IST
    maxFileSize: 100MB
    filterFactories:
      - type: error-only
Jenneth
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  • Thank you for answering, this looks promising. I could further relate it to the findings that I had with [#filterfactories](https://www.dropwizard.io/en/latest/manual/configuration.html#filterfactories) as well. But I still cannot apprehend the importance of registering it via `META-INF`, mind elaborating that part? Additionally, there is no way to actually translate [#levelFilter](http://logback.qos.ch/manual/filters.html#levelFilter) in dropwizard without factory registration? – Naman Oct 01 '20 at 13:24
  • Here is the source of the [FilterFactory](https://github.com/dropwizard/dropwizard/blob/master/dropwizard-logging/src/main/java/io/dropwizard/logging/filter/FilterFactory.java) which uses the [Discoverable](https://github.com/dropwizard/dropwizard/blob/master/dropwizard-jackson/src/main/java/io/dropwizard/jackson/DiscoverableSubtypeResolver.java) to discover subtypes. So that is just the built-in Dropwizard way of registering subtypes. If you look at the code in dropwizard-logging, this is the simplest way to add a logging filter. – Jenneth Oct 02 '20 at 07:55
  • Also the answers to this question https://stackoverflow.com/questions/27483442/dropwizard-doesnt-log-custom-loggers-to-file/ may be of interest to you. Extending FileAppenderFactory is an option and so is implementing a separate logger. – Jenneth Oct 02 '20 at 08:20