[logback-dev] Layout setter/getter methods in AppenderBase

Maarten Bosteels mbosteels.dns at gmail.com
Fri Feb 13 16:23:33 CET 2009

On Fri, Feb 13, 2009 at 3:25 PM, Ceki Gulcu <ceki at qos.ch> wrote:

> Hi Maarteen,
> I really like the idea of pluggable encoders.


> Putting UnsyncronizedAppenderBase aside for a second, I could imagine the
> following class hierarchy:
> interface LayoutAware extends Appender;
> interface EncoderAware extends Appender;

I don't understand.
In my opinion LayoutAware and EncoderAware should be standalone interface
with just a getter and a setter, and not extend Appender.

All appenders that need a layout should implement LayoutAware.
They can implement the interface themselves or - when its practical -
inherit from LayoutAwareAppenderBase

Why would you tie LayoutAware to the Appender interface.

Imagine this Encoder implementation:  it implements layoutAware but it's not
an Appender

public class LayoutBasedEncoder implements Encoder, LayoutAware {
  private Layout layout;
  public Layout getLayout() {...}
  public void setLayout(...) {...}

  public ByteBuffer encode(LoggingEvent event) {
    String str = layout.format(event);
    byte[] bytes = getUtf8Bytes(str);
    ByteBuffer buffer = ByteBuffer.allocate(bytes.length + 4);
    return buffer;


PS:  Not yet sure whether the encode method should return a byte[] or a
java.nio.ByteBuffer, I think the latter is easier to use.


> abstract class AppenderBase implements Appender;
> abstract class LayoutAwareAppenderBase ext. AppenderBase implements
> LayoutAware;
> abstract class EncodrAwareAppenderBase ext. AppenderBase implements
> LayoutAware;
> class WriterAppender extends LayoutAwareAppenderBase;
> class FileAppender extends WriterAppender;
> ...
> class SocketAppender extends EncoderAwareAppenderBase;
> Appenders such as DBAppender and SMTPAppender, where LoggingEvent to byte[]
> encoding nor layouts make sense, could extend AppenderBase directly.
> We should pursue this....
> Maarten Bosteels wrote:
>> Hello,
>> I agree with Joern, it would be cleaner to have a LayoutAware interface,
>> and only appenders that use a Layout should implement it.
>> The way it is now, people can set a layout on the SocketAppender, they
>> don't get an exception, but the layout would never be used.
>> I can understand the "historical" reasons, but IMO things like this can be
>> changed as long as logback doesn't reach 1.0Maarten
>> Related idea/proposal:  an Encoder interface similar to Layout but
>> returning a byte array instead of a String:
>> public interface Encoder {
>>  byte[] encode(LoggingEvent event)
>> }
>> I recently worked on an AsyncSocketAppender (extending
>> UnsyncronizedAppenderBase) and with this interface the wire-format would be
>> pluggable.
>> Some wire-formats I am thinking about:  Apache Thrift, Google protobuf and
>> of course Java serialization.
>> I still have to implement these encoders and compare their perfomance.  I
>> will let you know when I get there.
>> It would be really cool if we could define a wire-format based on Protobuf
>> and/or Thrift that could also be used for encoding log4j events.
>> But I guess it would be better to do this in a separate project ...
>> regards,
>> Maarten
> --
> Ceki Gülcü
> Logback: The reliable, generic, fast and flexible logging framework for
> Java.
> http://logback.qos.ch
> _______________________________________________
> logback-dev mailing list
> logback-dev at qos.ch
> http://qos.ch/mailman/listinfo/logback-dev
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