Filters

There are times when you want to add a field or a condition to all loggers. Although you can wrap individual loggers or create your own wrapper around LoggerFactory, this can be a labor-intensive process that requires lots of code modification, and must be handled for fluent, semantic, async, and regular loggers.

Echopraxia includes filters that wrap around the CoreLogger returned by CoreLoggerFactory that provides the ability to modify the core logger from a single pipeline in the code.

For example, to add a uses_filter field to every Echopraxia logger:

package example;

import com.tersesystems.echopraxia.api.*;

public class ExampleFilter implements CoreLoggerFilter {
  @Override
  public CoreLogger apply(CoreLogger coreLogger) {
    return coreLogger
        .withFields(fb -> fb.bool("uses_filter", true), FieldBuilder.instance());
  }
}

Filters must extend the CoreLoggerFilter interface, and must have a no-args constructor.

Filters must have a fully qualified class name in the /echopraxia.properties file as a resource somewhere in your classpath. The format is filter.N where N is the order in which filters should be loaded.

filter.0=example.ExampleFilter

Filters are particularly helpful when you need to provide "out of context" information for your conditions.

For example, imagine that you have a situation in which the program uses more CPU or memory than normal in production, but works fine in a staging environment. Using OSHI and a filter, you can provide the machine statistics and evaluate with dynamic conditions.

public class SystemInfoFilter implements CoreLoggerFilter {

  private final SystemInfo systemInfo;

  public SystemInfoFilter() {
     systemInfo = new SystemInfo();
  }

  @Override
  public CoreLogger apply(CoreLogger coreLogger) {
    HardwareAbstractionLayer hardware = systemInfo.getHardware();
    GlobalMemory mem = hardware.getMemory();
    CentralProcessor proc = hardware.getProcessor();
    double[] loadAverage = proc.getSystemLoadAverage(3);

    // Now you can add conditions based on these fields, and conditionally
    // enable logging based on your load and memory!
    return coreLogger.withFields(fb -> {
        Field loadField = fb.object("load_average", //
                fb.number("1min", loadAverage[0]), //
                fb.number("5min", loadAverage[1]), //
                fb.number("15min", loadAverage[2]));
        Field memField = fb.object("mem", //
                fb.number("available", mem.getAvailable()), //
                fb.number("total", mem.getTotal()));
        Field sysinfoField = fb.object("sysinfo", loadField, memField);
        return sysinfoField;
      }, FieldBuilder.instance());
  }
}

Please see the system info example for details.