java程序员的大数据之路（15）：Pig Latin用户自定义函数

过滤函数

所有的过滤函数都要继承FilterFunc类，并且实现抽象方法exec()，该方法的返回类型为Boolean。
示例代码如下：

package com.udf.filter;

import org.apache.pig.FilterFunc;
import org.apache.pig.backend.executionengine.ExecException;
import org.apache.pig.data.Tuple;

import java.io.IOException;

public class IsGoodQuantity extends FilterFunc {

    @Override
    public Boolean exec(Tuple tuple) throws IOException {
        if (tuple == null || tuple.size() == 0) {
            return false;
        }
        try {
            Object object = tuple.get(0);
            if (object == null) {
                return false;
            }
            int i = (Integer)object;
            return i == 0 || i == 1 || i == 4 || i == 5 || i == 9;
        } catch (ExecException e) {
            throw new IOException(e);
        }
    }
}

编写好代码之后，首先将它打成一个jar包。然后通过REGISTER操作指定文件的路径。

grunt> records = LOAD '/home/jackeyzhe/hadoop-book/input/ncdc/micro-tab/sample.txt'
>> AS (year:chararray, temperature:int, quality:int);
DUMP records;
(1950,0,1)
(1950,22,1)
(1950,-11,1)
(1949,111,1)
(1949,78,1)
(1994,24,2)
REGISTER pigFilterUdf.jar

grunt> filtered_records = FILTER records BY temperature != 9999 AND 
>> com.udf.filter.IsGoodQuantity(quality);
DUMP filtered_records;
(1950,0,1)
(1950,22,1)
(1950,-11,1)
(1949,111,1)
(1949,78,1)

结果如上所示，quality为2的数据被过滤掉了。

计算函数

自定义的计算函数要继承EvalFunc类，需要注意的是，写计算函数需要参数化返回类型。该类型为String。
示例代码如下：

public class Trim extends EvalFunc<String> {
    @Override
    public String exec(Tuple tuple) throws IOException {
        if (tuple == null || tuple.size() == 0) {
            return null;
        }
        try {
            Object object = tuple.get(0);
            if (object == null) {
                return null;
            }
            return ((String) object).trim();
        } catch (ExecException e) {
            throw new IOException(e);
        }
    }

    @Override
    public List getArgToFuncMapping() throws FrontendException {
        List funcList = new ArrayList();
        funcList.add(new FuncSpec(this.getClass().getName(), new Schema(new Schema.FieldSchema(null, DataType.CHARARRAY))));
        return funcList;
    }
}

加载函数

加载函数需要继承LoadFunc，并实现相应的抽象方法。
具体代码示例如下：
CutLoadFunc.java

public class CutLoadFunc extends LoadFunc {

    private static final Log LOG = LogFactory.getLog(CutLoadFunc.class);

    private final List ranges;
    private final TupleFactory tupleFactory = TupleFactory.getInstance();
    private RecordReader reader;

    public CutLoadFunc(String cutPattern) {
        ranges = Range.parse(cutPattern);
    }

    @Override
    public void setLocation(String location, Job job) throws IOException {
        FileInputFormat.setInputPaths(job, location);
    }

    @Override
    public InputFormat getInputFormat() throws IOException {
        return new TextInputFormat();
    }

    @Override
    public void prepareToRead(RecordReader recordReader, PigSplit pigSplit) throws IOException {
        this.reader = recordReader;
    }

    @Override
    public Tuple getNext() throws IOException {
        try {
            if (!reader.nextKeyValue()) {
                return null;
            }
            Text value = (Text) reader.getCurrentValue();
            String line = value.toString();
            Tuple tuple = tupleFactory.newTuple(ranges.size());
            for (int i=0;i < ranges.size();i++) {
                Range range = ranges.get(i);
                if (range.getEnd() > line.length()) {
                    LOG.warn(String.format(" Range end (%s) is longer than line length (%s)",range.getEnd(), line.length()));
                    continue;
                }
                tuple.set(i, new DataByteArray(range.getSubstring(line)));
            }
            return tuple;
        } catch (InterruptedException e) {
            throw new ExecException(e);
        }
    }
}

Range.java

public class Range {
  private final int start;
  private final int end;

  public Range(int start, int end) {
    this.start = start;
    this.end = end;
  }

  public int getStart() {
    return start;
  }

  public int getEnd() {
    return end;
  }

  public String getSubstring(String line) {
    return line.substring(start - 1, end);
  }

  @Override
  public int hashCode() {
    return start * 37 + end;
  }

  @Override
  public boolean equals(Object obj) {
    if (!(obj instanceof Range)) {
      return false;
    }
    Range other = (Range) obj;
    return this.start == other.start && this.end == other.end;
  }

  public static List parse(String rangeSpec)
      throws IllegalArgumentException {
    if (rangeSpec.length() == 0) {
      return Collections.emptyList();
    }
    List ranges = new ArrayList();
    String[] specs = rangeSpec.split(",");
    for (String spec : specs) {
      String[] split = spec.split("-");
      try {
        ranges.add(new Range(Integer.parseInt(split[0]), Integer
            .parseInt(split[1])));
      } catch (NumberFormatException e) {
        throw new IllegalArgumentException(e.getMessage());
      }
    }
    return ranges;
  }

}

加载结果：

grunt> records = LOAD '/home/jackeyzhe/hadoop-book/input/ncdc/micro/sample.txt'
>> USING com.udf.load.CutLoadFunc('16-19,88-92,93-93')
>> AS (year:int, temperature:int, quality:int);
grunt> DUMP records;

(1950,0,1)
(1950,22,1)
(1950,-11,1)
(1949,111,1)
(1949,78,1)