我找到了一种用自定义项的方法。还有其他方法吗？

HashMap<String, String> options = new HashMap<String, String>();
  options.put("header", "true");
  String input= args[0];

  sqlc.udf().register("toVector", new UDF1<String, Vector>() {
     @Override
     public Vector call(String t1) throws Exception {
        return Vectors.parse(t1);
     }
  }, new VectorUDT());

  StructField[] fields = {new StructField("id",DataTypes.StringType,false, Metadata.empty()) , new StructField("features", DataTypes.StringType, false, Metadata.empty())};
  StructType schema = new StructType(fields);

  DataFrame df = sqlc.read().format("com.databricks.spark.csv").schema(schema).options(options).load(input);

  df = df.withColumn("features", functions.callUDF("toVector", df.col("features")));