方法是这样的，

dataset.foreachPartition(new ForeachPartitionFunction<Row>() {
            public void call(Iterator<Row> t) throws Exception {
                while (t.hasNext()){

                    Row row = t.next();
                    System.out.println(row.getString(2));
                }
            }
        });

def foreach(func: ForeachFunction[T]): Unit
 (Java-specific) Runs func on each***element***of this Dataset.

def foreach(f: (T) ⇒ Unit): Unit
 Applies a function f to all***rows***.

def foreachPartition(func: ForeachPartitionFunction[T]): Unit
 (Java-specific) Runs func on each partition of this Dataset.

def foreachPartition(f: (Iterator[T]) ⇒ Unit): Unit
 Applies a function f to each partition of this Dataset.