Log4j 2.0 - Padding more conversion specifiers together as one element

Question

I'm wondering if it is possible in Log4j 2.0 library to pad more conversion specifiers concatenated together.

For example, this pattern

%d{HH:mm:ss,SSS} %-5p [%-10t] %-22c - %m%n

produces something like

12.25.34,788 INFO  [SomeThread] my.path.to.Class       - First logged message
12.25.34,789 FATAL [Thread2   ] other.path.SecondClass - Second logged message
12.25.34.790 WARN  [Scheduler ] my.other.path.Class    - Another message

Now imagine I want to pad not only the conversion specifiers, but also whole parts of the pattern. In this case, for example, I want to pad [%-10t] %-22c.

12.25.34,788 INFO  [SomeThread] my.path.to.Class    - First logged message
12.25.34,789 FATAL [Thread2] other.path.SecondClass - Second logged message
12.25.34.790 WARN  [Scheduler] my.other.path.Class  - Another message

The notation could be something like

%d{HH:mm:ss,SSS} %-5p %-32{[%t] %c} - %m%n

(note %-35{...} - I want to pad whole content of this conversion specifier, just as one item)

I found this similar question, but there is no answer how to pad custom parts of the pattern, only answer with sample class extending PatternLayout to generate a string in format Class:method.

---

Additionally, I want to add padding between the two elements, as follows ([%t] is left-justified, %c is right-justified):

12.25.34,788 INFO  [SomeThread]    my.path.to.Class - First logged message
12.25.34,789 FATAL [Thread2] other.path.SecondClass - Second logged message
12.25.34.790 WARN  [Scheduler]  my.other.path.Class - Another message

It seems like the log4j library does not support it. So my question is: How can I achieve it? Possibly you can write a sample code. I believe it will help someone else, too.

Answer 1

I created a custom converter that may work for what you are looking to do. It allows you to group patterns within a pattern, and treat the groups as if they are a single entity. For example, the notation

%d{HH:mm:ss,SSS} %-5p %-32grp{[%t] %c} - %m%n

would produce output similar to your first request:

12.25.34,788 INFO  [SomeThread] my.path.to.Class    - First logged message
12.25.34,789 FATAL [Thread2] other.path.SecondClass - Second logged message
12.25.34.790 WARN  [Scheduler] my.other.path.Class  - Another message

Unfortunately there doesn't seem to be any way for the converter to know how "long" it is supposed to be, so it can't inherently handle your second request for the output to be both left and right justified. However, you can modify your pattern to mimic the behavior with something like:

%d{HH:mm:ss,SSS} %-5p %-16grp{[%t]} %16grp{%c} - %m%n

Here is the converter I wrote:

@Plugin(name="GroupingPatternConverter", category="Converter")
@ConverterKeys({"grp"})
public class GroupingPatternConverter extends LogEventPatternConverter {

    private final String pattern;

    public static GroupingPatternConverter newInstance(String[] options) {
        return new GroupingPatternConverter("grp", "grp", options);
    }

    private GroupingPatternConverter(String name, String style, String[] options) {
        super(name, style);
        if (options != null && options.length > 0) {
            this.pattern = options[0];
        } else {
            this.pattern = null;
        }
    }

    @Override
    public void format(LogEvent event, StringBuilder toAppendTo) {
        if (this.pattern == null) {
            return;
        }

        PatternParser parser = new PatternParser(null, "Converter", LogEventPatternConverter.class);
        List<PatternFormatter> formatters = parser.parse(this.pattern);

        StringBuilder groupBuilder = new StringBuilder();
        for (PatternFormatter formatter : formatters) {
            formatter.format(event, groupBuilder);
        }

        toAppendTo.append(groupBuilder.toString());
    }
}

Answer 2

As of RC2, Log4j2 does not support this. You can raise a feature request on the Log4j2 Jira issue tracker. A patch would be great!

Meanwhile, if you want to align the start of the actual message, you could have a config where the minimum (padding) value is equal to the maximum (truncate) value for both the thread name and the logger name. I realize this is not ideal but this can be achieved with just configuration.