code: public ConverterServerBuilder workerPool(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit) {
          assertNumericArgument(corePoolSize, true);
          assertNumericArgument(maximumPoolSize, true);
          assertNumericArgument(corePoolSize + maximumPoolSize, false);
          assertNumericArgument(keepAliveTime, true);
          this.corePoolSize = corePoolSize;
          this.maximumPoolSize = maximumPoolSize;
          this.keepAliveTime = unit.toMillis(keepAliveTime);
          return this;
      }
docs: Configures a worker pool for the converter.
  
  @param corePoolSize    The core pool size of the worker pool.
  @param maximumPoolSize The maximum pool size of the worker pool.
  @param keepAliveTime   The keep alive time of the worker pool.
  @param unit            The time unit of the specified keep alive time.
  @return This builder instance.