org.apache.pig.piggybank.storage

Class CSVLoader

java.lang.Object

org.apache.pig.LoadFunc

org.apache.pig.FileInputLoadFunc

org.apache.pig.piggybank.storage.CSVLoader

All Implemented Interfaces:

LoadPushDown, OrderedLoadFunc

public class CSVLoader
extends FileInputLoadFunc
implements LoadPushDown

A load function based on PigStorage that implements part of the CSV "standard" This loader properly supports double-quoted fields that contain commas and other double-quotes escaped with backslashes. The following fields are all parsed as one tuple, per each line "the man, he said ""hello""" "one,two,three" This version supports pig 0.7+

Nested Class Summary

Nested classes/interfaces inherited from interface org.apache.pig.LoadPushDown

LoadPushDown.OperatorSet, LoadPushDown.RequiredField, LoadPushDown.RequiredFieldList, LoadPushDown.RequiredFieldResponse

Field Summary

Fields

Modifier and Type	Field and Description
protected org.apache.hadoop.mapreduce.RecordReader	in
protected static org.apache.commons.logging.Log	LOG

Constructor Summary

Constructors

Constructor and Description
CSVLoader()

Method Summary

Modifier and Type	Method and Description
List<LoadPushDown.OperatorSet>	getFeatures() Determine the operators that can be pushed to the loader.
org.apache.hadoop.mapreduce.InputFormat	getInputFormat() This will be called during planning on the front end.
Tuple	getNext() Retrieves the next tuple to be processed.
void	prepareToRead(org.apache.hadoop.mapreduce.RecordReader reader, PigSplit split) Initializes LoadFunc for reading data.
LoadPushDown.RequiredFieldResponse	pushProjection(LoadPushDown.RequiredFieldList requiredFieldList) Indicate to the loader fields that will be needed.
void	setLocation(String location, org.apache.hadoop.mapreduce.Job job) Communicate to the loader the location of the object(s) being loaded.
void	setUDFContextSignature(String signature) This method will be called by Pig both in the front end and back end to pass a unique signature to the LoadFunc.

Methods inherited from class org.apache.pig.FileInputLoadFunc

getSplitComparable

Methods inherited from class org.apache.pig.LoadFunc

getAbsolutePath, getCacheFiles, getLoadCaster, getPathStrings, getShipFiles, join, relativeToAbsolutePath, warn

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

in

protected org.apache.hadoop.mapreduce.RecordReader in

LOG

protected static final org.apache.commons.logging.Log LOG

Constructor Detail

CSVLoader

public CSVLoader()

Method Detail

getNext

public Tuple getNext()
              throws IOException

Description copied from class: LoadFunc

Retrieves the next tuple to be processed. Implementations should NOT reuse tuple objects (or inner member objects) they return across calls and should return a different tuple object in each call.

Specified by:

getNext in class LoadFunc

Returns:

the next tuple to be processed or null if there are no more tuples to be processed.

Throws:

IOException - if there is an exception while retrieving the next tuple

setLocation

public void setLocation(String location,
                        org.apache.hadoop.mapreduce.Job job)
                 throws IOException

Description copied from class: LoadFunc

Communicate to the loader the location of the object(s) being loaded. The location string passed to the LoadFunc here is the return value of LoadFunc.relativeToAbsolutePath(String, Path). Implementations should use this method to communicate the location (and any other information) to its underlying InputFormat through the Job object. This method will be called in the frontend and backend multiple times. Implementations should bear in mind that this method is called multiple times and should ensure there are no inconsistent side effects due to the multiple calls.

Specified by:

setLocation in class LoadFunc

Parameters:

location - Location as returned by LoadFunc.relativeToAbsolutePath(String, Path)

job - the Job object store or retrieve earlier stored information from the UDFContext

Throws:

IOException - if the location is not valid.

getInputFormat

public org.apache.hadoop.mapreduce.InputFormat getInputFormat()
                                                       throws IOException

Description copied from class: LoadFunc

This will be called during planning on the front end. This is the instance of InputFormat (rather than the class name) because the load function may need to instantiate the InputFormat in order to control how it is constructed.

Specified by:

getInputFormat in class LoadFunc

Returns:

the InputFormat associated with this loader.

Throws:

IOException - if there is an exception during InputFormat construction

prepareToRead

public void prepareToRead(org.apache.hadoop.mapreduce.RecordReader reader,
                          PigSplit split)
                   throws IOException

Description copied from class: LoadFunc

Initializes LoadFunc for reading data. This will be called during execution before any calls to getNext. The RecordReader needs to be passed here because it has been instantiated for a particular InputSplit.

Specified by:

prepareToRead in class LoadFunc

Parameters:

reader - RecordReader to be used by this instance of the LoadFunc

split - The input PigSplit to process

Throws:

IOException - if there is an exception during initialization

pushProjection

public LoadPushDown.RequiredFieldResponse pushProjection(LoadPushDown.RequiredFieldList requiredFieldList)
                                                  throws FrontendException

Description copied from interface: LoadPushDown

Indicate to the loader fields that will be needed. This can be useful for loaders that access data that is stored in a columnar format where indicating columns to be accessed a head of time will save scans. This method will not be invoked by the Pig runtime if all fields are required. So implementations should assume that if this method is not invoked, then all fields from the input are required. If the loader function cannot make use of this information, it is free to ignore it by returning an appropriate Response

Specified by:

pushProjection in interface LoadPushDown

Parameters:

requiredFieldList - RequiredFieldList indicating which columns will be needed. This structure is read only. User cannot make change to it inside pushProjection.

Returns:

Indicates which fields will be returned

Throws:

FrontendException

setUDFContextSignature

public void setUDFContextSignature(String signature)

Description copied from class: LoadFunc

This method will be called by Pig both in the front end and back end to pass a unique signature to the LoadFunc. The signature can be used to store into the UDFContext any information which the LoadFunc needs to store between various method invocations in the front end and back end. A use case is to store LoadPushDown.RequiredFieldList passed to it in LoadPushDown.pushProjection(RequiredFieldList) for use in the back end before returning tuples in LoadFunc.getNext(). This method will be call before other methods in LoadFunc

Overrides:

setUDFContextSignature in class LoadFunc

Parameters:

signature - a unique signature to identify this LoadFunc

getFeatures

public List<LoadPushDown.OperatorSet> getFeatures()

Description copied from interface: LoadPushDown

Determine the operators that can be pushed to the loader. Note that by indicating a loader can accept a certain operator (such as selection) the loader is not promising that it can handle all selections. When it is passed the actual operators to push down it will still have a chance to reject them.

Specified by:

getFeatures in interface LoadPushDown

Returns:

list of all features that the loader can support