Question

我是Hadoop和Java的新手。我的mapper输出文本和Arraywritable。我无法读取ArrayWritable值。取消将.get（）值转换为整数。附加了映射器和缩减器代码。有人可以帮我纠正我的reducer代码以读取ArrayWritable值吗？

public static class Temp2Mapper extends Mapper<LongWritable, Text, Text, ArrayWritable>{
    private static final int MISSING=9999;

    @Override public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException{
        String line = value.toString();
        String date = line.substring(07,14);
        int maxTemp,minTemp,avgTemp;

        IntArrayWritable carrier = new IntArrayWritable();
        IntWritable innercarrier[] = new IntWritable[3];
        maxTemp=Integer.parseInt(line.substring(39,45));
        minTemp=Integer.parseInt(line.substring(47,53));
        avgTemp=Integer.parseInt(line.substring(63,69));
        if (maxTemp!= MISSING)
        innercarrier[0]=new IntWritable(maxTemp); // maximum Temperature
        if (minTemp!= MISSING)
        innercarrier[1]=new IntWritable(minTemp); //minimum temperature
        if (avgTemp!= MISSING)
        innercarrier[2]=new IntWritable(avgTemp); // average temperature of 24 hours

        carrier.set(innercarrier);
        context.write(new Text(date), carrier); // Output Text and ArrayWritable
        }
}

public static class Temp2Reducer
extends Reducer<Text, ArrayWritable, Text, IntWritable>{
@Override public void reduce(Text key, Iterable<ArrayWritable> values, Context context ) 
            throws IOException, InterruptedException {

          int max = Integer.MIN_VALUE;
          int[] arr= new int[3];

          for (ArrayWritable val : values) {
              arr = (Int) val.get(); // Error: cannot cast Writable to int
              max = Math.max(max, arr[0]);
          }

          context.write( key, new IntWritable(max) );
        }

}

Answer 1

ArrayWritable#get方法返回Writable的数组。

您无法将Writable的数组转换为int。你能做的是：

遍历此数组
将数组的每个项目（类型为Writable）投射到IntWritable
使用IntWritable#get方法获取int值。

for (ArrayWritable val: values) {
  for (Writable writable: val.get()) {                 // iterate
     IntWritable intWritable = (IntWritable)writable;  // cast
     int value = intWritable.get();                    // get
     // do your thing with int value
  }
}

读取Hadoop ArrayWritable中包含的值

1 个答案: