写MR Job的时候遇到一个坑爹的异常：
LongWritable cannot be cast to org.apache.hadoop.io.IntWritable
当写Map的时候，key的默认输入就是LongWritable。
因为LongWritable指代Block中的数据偏移量。
所以把它强行转换成Text当然就Error了。。
- public static class TempMapper extends Mapper<LongWritable, Text, IntWritable, FloatWritable>{
- @Override
- protected void map(<span style="background-color: #ffff00;">LongWritable key</span>, Text value, Context context)
- throws IOException, InterruptedException {
- //code for getting date and temperature
- String temp = columns.get(3);
- context.write(new IntWritable(year), new FloatWritable(Float.valueOf(temp)));
- }
- }
坑啊。。