我的输入看起来像：

0RViGi2Rne8,OmnipotentSI,1135,Entertainment,9,490,2.31,26,15
HT_QlOJbDpg,dumbasstheredneck,1095,Comedy,14,1349,2.09,22,13
ShhClb6J-NA,thecrashguy,1136,Entertainment,61,29,0,0,0
g9e1alirMhc,iamdanielisaac,541,Comedy,152,483053,4.65,2689,2932
YZev1imoxX8,threefirstnames,1135,Entertainment,253,63,5,3,2

我希望我的Map器输出是。我基本上希望第4列是我的键，我只希望整数1作为每个键的值：

Entertainment: 1
Comedy: 1
Entertainment: 1
Comedy: 1
Entertainment: 1

我的mapper类如下所示。为此，我得到java.lang.arrayindexoutofboundsexception:3。我不明白为什么，因为在普通java程序上测试时，split函数返回了正确的输出。

public class VidCountByCategory {
    public static class Map extends Mapper<LongWritable,Text,Text,IntWritable>{
        public void map(LongWritable key, Text value,Context context)
                throws IOException,InterruptedException {

            String line = value.toString();
            String category = line.split(",")[3];

                value.set(category);
                context.write(value, new IntWritable(1));
        }

    }

谁能指出我哪里出错了吗？