logback-android/src/main/java/ch/qos/logback/core/rolling/RollingPolicyBase.java
protected void determineCompressionMode() {
    if (fileNamePatternStr.endsWith(".gz")) {
      addInfo("Will use gz compression");
      compressionMode = CompressionMode.GZ;
    } else if (fileNamePatternStr.endsWith(".zip")) {
      addInfo("Will use zip compression");
      compressionMode = CompressionMode.ZIP;
    } else {
      addInfo("No compression will be used");
      compressionMode = CompressionMode.NONE;
    }
  }
protected void determineCompressionMode() {
    if (fileNamePatternStr.endsWith(".gz")) {
      addInfo("Will use gz compression");
      compressionMode = CompressionMode.GZ;
    } else if (fileNamePatternStr.endsWith(".zip")) {
      addInfo("Will use zip compression");
      compressionMode = CompressionMode.ZIP;
    } else {
      addInfo("No compression will be used");
      compressionMode = CompressionMode.NONE;
    }
  }
Given the FileNamePattern string, this method determines the compression
mode depending on last letters of the fileNamePatternStr. Patterns ending
with .gz imply GZIP compression, endings with '.zip' imply ZIP compression.
Otherwise and by default, there is no compression.