code: protected String lookupPattern(String key, String defaultPattern) {
          if (outputPatterns.containsKey(key)) {
              return outputPatterns.getProperty(key);
          }
          return defaultPattern;
      }
docs: Looks up the format pattern for the event output by key, conventionally
  equal to the method name. The pattern is used by the
  {#format(String,String,Object...)} method and by default is formatted
  using the {@link MessageFormat#format(String, Object...)} method. If no
  pattern is found for key or needs to be overridden, the default pattern
  should be returned.
  
  @param key the format pattern key
  @param defaultPattern the default pattern if no pattern is
  @return The format patter for the given key