HBase 利用Coprocessor实现聚合函数

aggregationClient.avg(Bytes. toBytes("TableName"), ci, scan);

/**
* Double类型的列解释器实现
*
 * @author OneCoder
*/
public class DoubleColumnInterpreter implements
           ColumnInterpreter<Double, Double> {

     @Override
     public void write(DataOutput out) throws IOException {


     }

     @Override
     public void readFields(DataInput in) throws IOException {


     }

     @Override
     public Double getValue( byte[] colFamily, byte[] colQualifier, KeyValue kv)
                 throws IOException {
            if (kv == null)
                 return null;
            // 临时解决方案，如果采用Bytes.toDouble(kv.getValue())会报错，偏移量大于总长度。
            // toDouble(getBuffer(), getValueOffset)，偏移量也不对。
            return Double. valueOf(new String(kv.getValue()));
     }


     @Override
     public Double add(Double l1, Double l2) {
            if (l1 == null ^ l2 == null) {
                 return l1 == null ? l2 : l1;
           } else if (l1 == null) {
                 return null;
           }
            return l1 + l2;
     }

     @Override
     public Double getMaxValue() {
            // TODO Auto-generated method stub
            return null;
     }


     @Override
     public Double getMinValue() {
            // TODO Auto-generated method stub
            return null;
     }

     @Override
     public Double multiply(Double o1, Double o2) {
            if (o1 == null ^ o2 == null) {
                 return o1 == null ? o2 : o1;
           } else if (o1 == null) {
                 return null;
           }
            return o1 * o2;
     }


     @Override
     public Double increment(Double o) {
            // TODO Auto-generated method stub
            return null;
     }

     @Override
     public Double castToReturnType(Double o) {
            return o.doubleValue();
     }


     @Override
     public int compare(Double l1, Double l2) {
            if (l1 == null ^ l2 == null) {
                 return l1 == null ? -1 : 1; // either of one is null.
           } else if (l1 == null)
                 return 0; // both are null
            return l1.compareTo(l2); // natural ordering.
     }


     @Override
     public double divideForAvg(Double o, Long l) {
            return (o == null || l == null) ? Double. NaN : (o.doubleValue() / l
                     .doubleValue());
     }
}

<property>
            <name >hbase.coprocessor.region.classes </name >
           <value >org.apache.hadoop.hbase.coprocessor.AggregateImplementation </value >
 </property >