[logback-user] Split long data on multiple rows

Ceki Gulcu ceki at qos.ch
Tue Sep 22 11:38:28 CEST 2009

Hello Anders,

Logback-core? Nice.

If only the field 'foo' needs to be split, then just override the converter for 
the field foo to do the splitting, and you are done. However, you requirements 
differ as you also require the repetition of other fields.

The approach which seems the most logical to me, would be to derive a sub-class 
from PatternLayoutBase overriding the writeLoopOnConverters method so that when 
the foo field needs splitting, you would loop over the converter chain as many 
times as necessary.

Here is a possible implementation:

class MyPatternLayout extends PatternLayoutBase<MyEvent> {


   protected String writeLoopOnConverters(MyEvent event) {
     Foo foo = event.getFoo();
     StringBuilder sb = new StringBuilder();	
     String[] fooParts = split(foo);
     for(String s: fooParts) {
       // construct a new event from 'event' so that foo has only one part
       MyEvent splitEvent = new MyEvent(event, s);
       String line = super.writeLoopOnConverters(splitEvent);
     return sb.toString();


Anders Hammar wrote:
> Hi,
> I have a framework that utilizes logback-core for logging. Due to 
> limitations in the software reading the log files, a new requirement is 
> that long data should be split on multiple rows. I'm trying to figure 
> out if there a simple way of doing this?
> More info: What I have is an extension of the PatternLayoutBase which 
> adds the converters for my event class. I'm using the standard 
> RollingFileAppender. So, let's say I have a FooConverter, which gets the 
> foo info from the event. But, when logging to the file, the foo info 
> part must never be longer than x chars. If it is, it should be split on 
> multiple rows. Other data (generated by other converters) should then be 
> repeated.
> Any suggestions on how to do this in a clean logback way is appreciated! 
> What I'm currently thinking is to loop on the converters (calling 
> PatternLayoutBase.writeLoopOnConverters multiple times), but I need to 
> know when that's required... Anyone done something similar?
> /Anders

Ceki Gülcü
Logback: The reliable, generic, fast and flexible logging framework for Java.

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