code: public Integer getAbsoluteSourcePort() {
          if (this.getSourcePort() == null) {
              return null;
          }
          if (this.fixedSourcePort) {
              return this.sourcePort;
          }
          final int portOffset = this.socketBindingManager.getPortOffset();
          return this.sourcePort + portOffset;
      }
docs: Returns the absolute source port for this outbound socket binding. The absolute source port is the same as {@link #getSourcePort()}
  if the outbound socket binding is marked for "fixed source port". Else, it is the sum of {@link #getSourcePort()}
  and the port offset configured on the {@link SocketBindingManager}.
  
  @return the absolute source port accounting for port offset/fixation; {@code null} if an ephemeral port should be used