On Wed, Dec 25, 2019, at 01:38, Ralph Goers wrote:
>
>
> > On Dec 24, 2019, at 2:06 PM, Volkan Yazıcı <volkan.yaz...@gmail.com> wrote:
> >
> > Indeed ColumnMapping is an alternative approach. I believe due to its
> > origin, i.e., RDBMSes, it facilitates a 1-to-1 mapping particularly
> > targeted at table column names, e.g.,
> >
> > timestamp -> instant
> > message -> summary
> >
> > One can borrow the idea and extend it a little bit to support the
> > structured form of a JSON:
> >
> > timestamp.millis -> instant
> > throwable -> error.message
> >
> > That said, I believe current JSON-based templating in LogstashLayout
> > communicates the intent more concisely (the template is WYSIWYG) and
> > allows extra (JSON-specific) flexibility, e.g.,
> >
> > "user": ["${json:mdc:user}", "${json:mdc:fallbackUser}”]
> >
>
> Looking at
> https://github.com/vy/log4j2-logstash-layout/blob/master/layout/src/main/resources/LogstashJsonEventLayoutV1.json
>
> <https://github.com/vy/log4j2-logstash-layout/blob/master/layout/src/main/resources/LogstashJsonEventLayoutV1.json>
> makes me think that you could accomplish the same thing with a few
> enhancements to the PatternLayout. In fact, all the expressions with
> ${json:…} look like they could be a LogEvent Lookup where you want the output
> to be formatted as JSON. I am not sure why you didn’t implement it that way.
>
> I could also see creating a new pattern converter to cause formatting to be
> in JSON so when any pattern converter is called it knows to output JSON. So
> %d would result in “timestamp”: “2019-12-25 01:02:03,123” etc. So a pattern
> of “%json{%d, %p, %c, %C, %M, %L, %m}” would generate “{“timestamp”:
> “2019-12-25 01:02:03,123”, “level”: “debug”, “logger”: “com.mycorp.MyClass”,
> “class”: “com.mycorp.MyClass”, “method”: “doSomething”: “lineNumber”: 123,
> “message”: “Hello, world!”}
>
> FWIW, I am not necessarily proposing we implement that. I am trying to point
> out that your templating approach doesn’t really seem to be tied to JSON, so
> calling it JsonLogstashLayout seems a bit misleading. I could just as easily
> imagine an XML template with xml resolvers.
>
> Also, I must admit I probably would have implemented the resolvers
> differently. It seems to me that each “entity" is going to return either a
> String, a number, a Map, or an array. So I would have just had the resolver
> return its key and its data and left calling the jsonGenerator to the class
> that calls all the resolvers. Then you could have reused the same resolvers
> to generate XML. At least, that is the path I would have tried to go down.
> Obviously I have only glanced at your code so it could be more challenging
> than it appears.
>
> Anyway, those are just my first random thoughts after looking at what the
> layout does.
>
> Ralph
>
I've had a lot of success using pattern layout with the
EncodingPatternConverter to escape json strings. The layout definition can be
difficult to read, but it's incredibly powerful. For example:
{"timestamp":"%d", "level":"%p", "origin":"%encode{%c}{JSON}",
"thread":"%encode{%t}{JSON}", "message":%encode{m}{JSON}}%n
There are a few pattern converters that don't map particularly well to this
method, for example the MdcPatternConverter with multiple keys doesn't
currently have a JSON formatting option. It would be great if we could make
this functionality easier for users, likely through some combination of
documentation and features. I've found it helpful that we don't require jackson
for this approach to work.
-ck
