import org.apache.pig.LoadPushDown; //导入依赖的package包/类
@Override
public List<OperatorSet> getFeatures() {
    return Arrays.asList(LoadPushDown.OperatorSet.PROJECTION);
}
 

import org.apache.pig.LoadPushDown; //导入依赖的package包/类
@Override
public List<OperatorSet> getFeatures() {
    return Lists.newArrayList(LoadPushDown.OperatorSet.PROJECTION);
}
 

import org.apache.pig.LoadPushDown; //导入依赖的package包/类
@Override
public List<OperatorSet> getFeatures() {
    List<OperatorSet> features = new ArrayList<OperatorSet>(1);
    features.add( LoadPushDown.OperatorSet.PROJECTION );
    return features;
}
 

import org.apache.pig.LoadPushDown; //导入依赖的package包/类
@Override
public void prepareToRead(
        @SuppressWarnings("rawtypes") RecordReader reader, PigSplit split)
        throws IOException {

    AllReader allReader = (AllReader) reader;

    if (currentPath == null || !(currentPath.equals(allReader.path))) {
        currentPathPartitionKeyMap = (partitionColumns == null) ? null
                : pathPartitionerHelper
                        .getPathPartitionKeyValues(allReader.path
                                .toString());
        currentPath = allReader.path;
    }

    childLoadFunc = allReader.prepareLoadFuncForReading(split);

    String projectProperty = getUDFContext().getProperty(PROJECTION_ID);

    if (projectProperty != null) {

        // load the required field list from the current UDF context
        ByteArrayInputStream input = new ByteArrayInputStream(
                Base64.decodeBase64(projectProperty.getBytes("UTF-8")));

        ObjectInputStream objInput = new ObjectInputStream(input);

        try {
            requiredFieldList = (RequiredFieldList) objInput.readObject();
        } catch (ClassNotFoundException e) {
            throw new FrontendException(e.toString(), e);
        } finally {
            IOUtils.closeStream(objInput);
        }

        if (childLoadFunc.getClass().isAssignableFrom(LoadPushDown.class)) {
            supportPushDownProjection = true;
            ((LoadPushDown) childLoadFunc)
                    .pushProjection(requiredFieldList);
        } else {
            if (requiredFieldList != null) {
                requiredFieldHashSet = new TreeSet<Integer>();
                for (RequiredField requiredField : requiredFieldList
                        .getFields()) {
                    requiredFieldHashSet.add(requiredField.getIndex());
                }
            }
        }

    }

}
 

import org.apache.pig.LoadPushDown; //导入依赖的package包/类
@Override
   public List<OperatorSet> getFeatures() {
return Arrays.asList(LoadPushDown.OperatorSet.PROJECTION);
   }
 

import org.apache.pig.LoadPushDown; //导入依赖的package包/类
@Override
public List<OperatorSet> getFeatures() {
  return asList(LoadPushDown.OperatorSet.PROJECTION);
}
 

import org.apache.pig.LoadPushDown; //导入依赖的package包/类
@Override
public List<OperatorSet> getFeatures() {
    return ((LoadPushDown)super.loadFunc()).getFeatures();
}
 

import org.apache.pig.LoadPushDown; //导入依赖的package包/类
@Override
public RequiredFieldResponse pushProjection(RequiredFieldList requiredFieldList)
        throws FrontendException {
    return ((LoadPushDown)super.loadFunc()).pushProjection(requiredFieldList);
}
 

import org.apache.pig.LoadPushDown; //导入依赖的package包/类
@Override
public List<OperatorSet> getFeatures() {
	return Arrays.asList(LoadPushDown.OperatorSet.PROJECTION);
}