如何在deeplearning4j中嵌入多个字段？
例如，如果我想嵌入 user_id 以及 ad_id 作为两个字段：

val conf = new NeuralNetConfiguration.Builder()
  .seed(12345)
  .optimizationAlgo(OptimizationAlgorithm.STOCHASTIC_GRADIENT_DESCENT).iterations(1)
  .activation(Activation.LEAKYRELU)
  .weightInit(WeightInit.XAVIER)
  .learningRate(0.01)
  .updater(Updater.NESTEROVS).momentum(0.9)
  .regularization(true).l2(1e-4)
  .list
  .layer(0, new EmbeddingLayer.Builder().nIn(FEATURE_DIMS).nOut(512).activation(Activation.IDENTITY).build())
  .layer(1, new DenseLayer.Builder().nIn(512).nOut(10).build)
  .layer(2, new OutputLayer.Builder(LossFunctions.LossFunction.NEGATIVELOGLIKELIHOOD)
    .activation(Activation.SOFTMAX)
    .nIn(10).nOut(1).build)
  .pretrain(false)
  .backprop(true)
  .build

此代码只在deeplearning4j中嵌入一个字段。如何一次嵌入多个？